With an extended Su–Schrieffer–Heeger model and Green's function method, the spin–orbit coupling(SOC) effects on spin admixture of electronic states and quantum transport in organic devices are investigated. Th...With an extended Su–Schrieffer–Heeger model and Green's function method, the spin–orbit coupling(SOC) effects on spin admixture of electronic states and quantum transport in organic devices are investigated. The role of lattice distortion induced by the strong electron–lattice interaction in organics is clarified in contrast with a uniform chain. The results demonstrate an enhanced SOC effect on the spin admixture of frontier eigenstates by the lattice distortion at a larger SOC,which is explained by the perturbation theory. The quantum transport under the SOC is calculated for both nonmagnetic and ferromagnetic electrodes. A more notable SOC effect on total transmission and current is observed for ferromagnetic electrodes, where spin filtering induced by spin-flipped transmission and suppression of magnetoresistance are obtained.Unlike the spin admixture, a stronger SOC effect on transmission exists for the uniform chain rather than the organic lattices with distortion. The reason is attributed to the modified spin-polarized conducting states in the electrodes by lattice configuration, and hence the spin-flip transmission, instead of the spin admixture of eigenstates. This work is helpful to understand the SOC effect in organic spin valves in the presence of lattice distortion.展开更多
We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopa...We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation. Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorus- doped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.展开更多
Single and multiple n-channel junctionless nanowire transistors （JNTs） are fabricated and experimentally investigated at variable temperatures. Clear current oscillations caused by the quantum-confinement effect are...Single and multiple n-channel junctionless nanowire transistors （JNTs） are fabricated and experimentally investigated at variable temperatures. Clear current oscillations caused by the quantum-confinement effect are observed in the curve of drain current versus gate voltage acquired at low temperatures （10 K-100 K） and variable drain bias voltages （10 mV- 90 mV）. Transfer characteristics exhibit current oscillation peaks below flat-band voltage （VFB） at temperatures up to 75 K, which is possibly due to Coulomb-blocking from quantum dots, which are randomly formed by ionized dopants in the just opened n-type one-dimensional （1D） channel of silicon nanowires. However, at higher voltages than VFB, regular current steps are observed in single-channel JNTs, which corresponds to the fully populated subbands in the 1D channel. The subband energy spacing extracted from transconductance peaks accords well with theoretical predication. However, in multiple-channel JNT, only tiny oscillation peaks of the drain current are observed due to the combination of the drain current from multiple channels with quantum-confinement effects.展开更多
We use the transfer matrix method and the Green function technique to theoretically study the quantum tunnelling through a DNA-type molecule. Ferromagnetic electrodes are used to produce the spin-polarized transmissio...We use the transfer matrix method and the Green function technique to theoretically study the quantum tunnelling through a DNA-type molecule. Ferromagnetic electrodes are used to produce the spin-polarized transmission probability and therefore the spin current. The distance-dependent crossover comes from the topological variation from the one- dimensional to the two-dimensional model transform as we switch on the interstrand coupling; a new base pair will present N - 1 extrachannels for the charge and spin as N being the total base pairs. This will restrain the decay of the transmission and improve the stability of the quantum transport. The spin and charge transfer through the DNA-type molecule is consistent with the quantum tunneling barrier.展开更多
We investigate the influence of source and drain bias voltages(V_(DS))on the quantum sub-band transport spectrum in the 10-nm width N-typed junctionless nanowire transistor at the low temperature of 6 K.We demonstrate...We investigate the influence of source and drain bias voltages(V_(DS))on the quantum sub-band transport spectrum in the 10-nm width N-typed junctionless nanowire transistor at the low temperature of 6 K.We demonstrate that the transverse electric field introduced from V_(DS) has a minor influence on the threshold voltage of the device.The transverse electric field plays the role of amplifying the gate restriction effect of the channel.The one-dimensional(1D)-band dominated transport is demonstrated to be modulated by V_(DS) in the saturation region and the linear region,with the sub-band energy levels in the channel(E_(channel))intersecting with Fermi levels of the source(E_(fS))and the drain(E_(fD))in turn as V_(g) increases.The turning points from the linear region to the saturation region shift to higher gate voltages with V_(DS) increase because the higher Fermi energy levels of the channel required to meet the situation of E_(fD)=E_(channel).We also find that the bias electric field has the effect to accelerate the thermally activated electrons in the channel,equivalent to the effect of thermal temperature on the increase of electron energy.Our work provides a detailed description of the bias-modulated quantum electronic properties,which will give a more comprehensive understanding of transport behavior in nanoscale devices.展开更多
Besides its fundamental importance, non-reciprocity has also found many potential applications in quantum technology. Recently, many quantum systems have been proposed to realize non-reciprocity, but stable non-recipr...Besides its fundamental importance, non-reciprocity has also found many potential applications in quantum technology. Recently, many quantum systems have been proposed to realize non-reciprocity, but stable non-reciprocal process is still experimentally difficult in general, due to the needed cyclical interactions in artificial systems or operational difficulties in solid state materials. Here, we propose a new kind of interaction induced non-reciprocal operation, based on the conventional stimulated-Raman-adiabatic-passage (STIRAP) setup, which removes the experimental difficulty of requiring cyclical interaction, and thus it is directly implementable in various quantum systems. Furthermore, we also illustrate our proposal on a chain of three coupled superconducting transmons, which can lead to a non-reciprocal circulator with high fidelity without a ring coupling configuration as in the previous schemes or implementations. Therefore, our protocol provides a promising way to explore fundamental non-reciprocal quantum physics as well as realize non-reciprocal quantum device.展开更多
We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via co...We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of using the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a nmch easier manner. Our proposal overcomes the major drawback of the method used by Creffield et al [Phys. Rev. Lett. 99 （2007） 110501], and can be implemented, in principle, in any one-dimensional optical lattice. Some potential applications of the scheme are also discussed.展开更多
We investigate the quantum transport properties through a special kind of quantum dot（QD） system composed of a serially coupled multi-QD-pair（multi-QDP） chain and side-coupled Majorana bound states（MBSs） by usin...We investigate the quantum transport properties through a special kind of quantum dot（QD） system composed of a serially coupled multi-QD-pair（multi-QDP） chain and side-coupled Majorana bound states（MBSs） by using the Green functions method,where the conductance can be classified into two kinds：the electron tunneling（ET） conductance and the Andreev reflection（AR） one.First we find that for the nonzero MBS-QDP coupling a sharp AR-induced zero-bias conductance peak with the height of e^2/h is present（or absent） when the MBS is coupled to the far left（or the other） QDP.Moreover,the MBS-QDP coupling can suppress the ET conductance and strengthen the AR one,and further split into two sub-peaks each of the total conductance peaks of the isolated multi-QDPs,indicating that the MBS will make obvious influences on the competition between the ET and AR processes.Then we find that the tunneling rate ΓLis able to affect the conductances of leads L and R in different ways,demonstrating that there exists a ΓL-related competition between the AR and ET processes.Finally we consider the effect of the inter-MBS coupling on the conductances of the multi-QDP chains and it is shown that the inter-MBS coupling will split the zero-bias conductance peak with the height of e^2/h into two sub-peaks.As the inter-MBS coupling becomes stronger,the two sub-peaks are pushed away from each other and simultaneously become lower,which is opposite to that of the single QDP chain where the two sub-peaks with the height of about e^2/2h become higher.Also,the decay of the conductance sub-peaks with the increase of the MBS-QDP coupling becomes slower as the number of the QDPs becomes larger.This research should be an important extension in studying the transport properties in the kind of QD systems coupled with the side MBSs,which is helpful for understanding the nature of the MBSs,as well as the MBS-related QD transport properties.展开更多
This paper investigates Kondo transport properties in a quadruple quantum dot （QD） based on the slave-boson mean field theory and the non-equilibrium Green＇s function. In the quadruple QD structure one Kondo-type Q...This paper investigates Kondo transport properties in a quadruple quantum dot （QD） based on the slave-boson mean field theory and the non-equilibrium Green＇s function. In the quadruple QD structure one Kondo-type QD sandwiched between two leads is side coupled to two separate QD structures： a single-QD atom and a double-QD molecule. It shows that the conductance valleys and peaks always appear in pairs and by tuning the energy levels in three side QDs, the one-, two-, or three-valley conductance pattern can be obtained. Furthermore, it finds that whether the valley and the peak can appear is closely dependent on the specific values of the interdot couplings and the energy level difference between the two QDs in the molecule. More interestingly, an extra novel conductance peak can be produced by the coexistence of the two different kinds of side QD structures.展开更多
We theoretically investigate coherent scattering of single photons and quantum entanglement of two giant atoms with azimuthal angle differences in a waveguide system.Using the real-space Hamiltonian,analytical express...We theoretically investigate coherent scattering of single photons and quantum entanglement of two giant atoms with azimuthal angle differences in a waveguide system.Using the real-space Hamiltonian,analytical expressions are derived for the transport spectra scattered by these two giant atoms with four azimuthal angles.Fano-like resonance can be exhibited in the scattering spectra by adjusting the azimuthal angle difference.High concurrence of the entangled state for two atoms can be implemented in a wide angle-difference range,and the entanglement of the atomic states can be switched on/off by modulating the additional azimuthal angle differences from the giant atoms.This suggests a novel handle to effectively control the single-photon scattering and quantum entanglement.展开更多
Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum lock...Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum locking in nonmagnetic systems provides a new platform for developing spintronics, while previous studies were mostly based on magnetic materials.In this study, the spin transport measurement of Dirac semimetal Cd_(3)As_(2) was studied by three-terminal geometry, and a hysteresis loop signal with high resistance and low resistance state was observed. The hysteresis was reversed by reversing the current direction, which illustrates the spin–momentum locking feature of Cd_(3)As_(2). Furthermore, we realized the on–off states of the spin signals through electric modulation of the Fermi arc via the three-terminal configuration, which enables the great potential of Cd_(3)As_(2) in spin field-effect transistors.展开更多
According to the well-established light-to-electricity conversion theory,resonant excited carriers in the quantum dots will relax to the ground states and cannot escape from the quantum dots to form photocurrent,which...According to the well-established light-to-electricity conversion theory,resonant excited carriers in the quantum dots will relax to the ground states and cannot escape from the quantum dots to form photocurrent,which have been observed in quantum dots without a p–n junction at an external bias.Here,we experimentally observed more than 88% of the resonantly excited photo carriers escaping from In As quantum dots embedded in a short-circuited p–n junction to form photocurrent.The phenomenon cannot be explained by thermionic emission,tunneling process,and intermediate-band theories.A new mechanism is suggested that the photo carriers escape directly from the quantum dots to form photocurrent rather than relax to the ground state of quantum dots induced by a p–n junction.The finding is important for understanding the low-dimensional semiconductor physics and applications in solar cells and photodiode detectors.展开更多
Using a transfer matrix method, we investigate spin transport through a chain of polygonal rings with Dresselhaus spin-orbit coupling（DSOC）. The spin conductance is dependent on the number of sides in the polygons. ...Using a transfer matrix method, we investigate spin transport through a chain of polygonal rings with Dresselhaus spin-orbit coupling（DSOC）. The spin conductance is dependent on the number of sides in the polygons. When DSOC is considered in a chain which also has Rashba spin-orbit coupling（RSOC） of the same magnitude, the total conductance is the same as that for the same chain with no SOC. However, when the two types of SOC have different values, there results a unique anisotropic conductance.展开更多
Quantum spin transport in a mesoscopic Aharonov-Bohm ring with two leads subject to a magnetic field with circular configuration is investigated by means of one-dimensional quantum waveguide theory. Within the framewo...Quantum spin transport in a mesoscopic Aharonov-Bohm ring with two leads subject to a magnetic field with circular configuration is investigated by means of one-dimensional quantum waveguide theory. Within the framework of Landauer-Bfittiker formalism, the polarization direction of transmitted electrons can be controlled either by the AB magnetic flux or by the tangent magnetic field. In particular, the spin flips can be induced by hopping the AB magnetic flux or the tangent field.展开更多
The ionized dopants, working as quantum dots in silicon nanowires, exhibit potential advantages for the development of atomic-scale transistors. We investigate single electron tunneling through a phosphorus dopant ind...The ionized dopants, working as quantum dots in silicon nanowires, exhibit potential advantages for the development of atomic-scale transistors. We investigate single electron tunneling through a phosphorus dopant induced quantum dots array in heavily n-doped junctionless nanowire transistors. Several subpeaks splittings in current oscillations are clearly observed due to the coupling of the quantum dots at the temperature of 6 K. The transport behaviors change from resonance tunneling to hoping conduction with increased temperature. The charging energy of the phosphorus donors is approximately 12.8 meV. This work helps clear the basic mechanism of electron transport through donor-induced quantum dots and electron transport properties in the heavily doped nanowire through dopant engineering.展开更多
An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in I...An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in In Sb nanowires grown by molecular-beam epitaxy contacted by superconductor electrodes. At an elevated temperature, clear conductance plateaus are observed at zero magnetic field and in agreement with calculations based on the Landauer formula. At lower temperature, we have observed characteristic Fabry–Pérot patterns which confirm the ballistic nature of charge transport.Furthermore, the magnetoconductance measurements in the ballistic regime reveal a periodic variation related to the Fabry–Pérot oscillations. The result can be reasonably explained by taking into account the impact of magnetic field on the phase of ballistic electron＇s wave function, which is further verified by our simulation. Our results pave the way for better understanding of the quantum interference effects on the transport properties of In Sb nanowires in the ballistic regime as well as developing of novel device for topological quantum computations.展开更多
Transport properties in a multi-terminal regular polygonal quantum ring with Rashba spin-orbit coupling （SOC） are investigated analytically using quantum networks and the transport matrix metLod. The results show th...Transport properties in a multi-terminal regular polygonal quantum ring with Rashba spin-orbit coupling （SOC） are investigated analytically using quantum networks and the transport matrix metLod. The results show that conduc- tances remain at exactly the same values when the output leads are located at axisymmetric positions. However, for the nonaxisymmetrical case, there is a phase difference between the upper and lower arm, which leads to zero conductances appearing periodically. An isotropy of the conductance is destroyed by the Rashba SOC effect in the axisymmetric case. In addition, the position of zero conductance is regulated with the strength of the Rashba SOC.展开更多
Using the tight-binding approximation and the transfer matrix method, this paper studies the electronic transport properties through a periodic array of quantum-dot （QD） rings threaded by a magnetic flux. It demonst...Using the tight-binding approximation and the transfer matrix method, this paper studies the electronic transport properties through a periodic array of quantum-dot （QD） rings threaded by a magnetic flux. It demonstrates that the even^odd parity of the QD number in a single ring and the number of the QD rings in the array play a crucial role in the electron transmission. For a single QD ring, the resonance and antiresonance transmission depend not only on the applied magnetic flux but also on the difference between the number of QDs on the two arms of the ring. For an array of QD rings, the transmission properties are related not only to the even-odd parity of the number No of QDs in the single ring but also to the even-odd parity of the ring number N in the array. When the incident electron energy is aligned with the site energy, for the array of N rings with No = odd the antiresonance transmission cannot occur but the resonance transmission may occur and the transmission spectrum has N resonance peaks （N - 1 resonance peaks） in a period for N = odd （for N = even）. For the array of N rings with No = even the transmission properties depend on the flux threading the ring and the QD number on one arm of the ring. These results may be helpful in designing QD devices.展开更多
The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and witho...The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p-n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p-n junction escape from quantum wells and form photoeurrent rather than relax to the ground state of the quantum wells. The photo absorption coei^cient of multiple quantum wells is also enhanced by a p-n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure.展开更多
We propose a theoretical method to investigate the effect of the Dresselhaus spin–orbit coupling（DSOC） on the spin transport properties of a regular polygonal quantum ring with an arbitrary number of segments. We f...We propose a theoretical method to investigate the effect of the Dresselhaus spin–orbit coupling（DSOC） on the spin transport properties of a regular polygonal quantum ring with an arbitrary number of segments. We find that the DSOC can break the time reversal symmetry of the spin conductance in a polygonal ring and that this property can be used to reverse the spin direction of electrons in the polygon with the result that a pure spin up or pure spin down conductance can be obtained by exchanging the source and the drain. When the DSOC is considered in a polygonal ring with Rashba spin–orbit coupling（RSOC） with symmetric attachment of the leads, the total conductance is independent of the number of segments when both of the two types of spin–orbit coupling（SOC） have the same value. However, the interaction of the two types of SOC results in an anisotropic and shape-dependent conductance in a polygonal ring with asymmetric attachment of the leads. The method we proposed to solve for the spin conductance of a polygon can be generalized to the circular model.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974215,21933002,and 12274264)。
文摘With an extended Su–Schrieffer–Heeger model and Green's function method, the spin–orbit coupling(SOC) effects on spin admixture of electronic states and quantum transport in organic devices are investigated. The role of lattice distortion induced by the strong electron–lattice interaction in organics is clarified in contrast with a uniform chain. The results demonstrate an enhanced SOC effect on the spin admixture of frontier eigenstates by the lattice distortion at a larger SOC,which is explained by the perturbation theory. The quantum transport under the SOC is calculated for both nonmagnetic and ferromagnetic electrodes. A more notable SOC effect on total transmission and current is observed for ferromagnetic electrodes, where spin filtering induced by spin-flipped transmission and suppression of magnetoresistance are obtained.Unlike the spin admixture, a stronger SOC effect on transmission exists for the uniform chain rather than the organic lattices with distortion. The reason is attributed to the modified spin-polarized conducting states in the electrodes by lattice configuration, and hence the spin-flip transmission, instead of the spin admixture of eigenstates. This work is helpful to understand the SOC effect in organic spin valves in the presence of lattice distortion.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0200503)the Program for Innovative Research Team(in Science and Technology) in University of Henan Province,China(Grant No.18IRTSTHN016)the National Natural Science Foundation of China(Grant Nos.61376096,61327813,and 61404126)
文摘We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation. Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorus- doped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.
基金Project supported partly by the National Basic Research Program of China(Grant No.2010CB934104)the National Natural Science Foundation of China(Grant Nos.61376069 and 61327813)
文摘Single and multiple n-channel junctionless nanowire transistors （JNTs） are fabricated and experimentally investigated at variable temperatures. Clear current oscillations caused by the quantum-confinement effect are observed in the curve of drain current versus gate voltage acquired at low temperatures （10 K-100 K） and variable drain bias voltages （10 mV- 90 mV）. Transfer characteristics exhibit current oscillation peaks below flat-band voltage （VFB） at temperatures up to 75 K, which is possibly due to Coulomb-blocking from quantum dots, which are randomly formed by ionized dopants in the just opened n-type one-dimensional （1D） channel of silicon nanowires. However, at higher voltages than VFB, regular current steps are observed in single-channel JNTs, which corresponds to the fully populated subbands in the 1D channel. The subband energy spacing extracted from transconductance peaks accords well with theoretical predication. However, in multiple-channel JNT, only tiny oscillation peaks of the drain current are observed due to the combination of the drain current from multiple channels with quantum-confinement effects.
基金supported by the Natural Science Foundation of Zhejiang Province,China(Grant Nos.Y6110250 and Y201018926)
文摘We use the transfer matrix method and the Green function technique to theoretically study the quantum tunnelling through a DNA-type molecule. Ferromagnetic electrodes are used to produce the spin-polarized transmission probability and therefore the spin current. The distance-dependent crossover comes from the topological variation from the one- dimensional to the two-dimensional model transform as we switch on the interstrand coupling; a new base pair will present N - 1 extrachannels for the charge and spin as N being the total base pairs. This will restrain the decay of the transmission and improve the stability of the quantum transport. The spin and charge transfer through the DNA-type molecule is consistent with the quantum tunneling barrier.
基金the National Key Research and Development Program of China(Grant No.2016YFA0200503).
文摘We investigate the influence of source and drain bias voltages(V_(DS))on the quantum sub-band transport spectrum in the 10-nm width N-typed junctionless nanowire transistor at the low temperature of 6 K.We demonstrate that the transverse electric field introduced from V_(DS) has a minor influence on the threshold voltage of the device.The transverse electric field plays the role of amplifying the gate restriction effect of the channel.The one-dimensional(1D)-band dominated transport is demonstrated to be modulated by V_(DS) in the saturation region and the linear region,with the sub-band energy levels in the channel(E_(channel))intersecting with Fermi levels of the source(E_(fS))and the drain(E_(fD))in turn as V_(g) increases.The turning points from the linear region to the saturation region shift to higher gate voltages with V_(DS) increase because the higher Fermi energy levels of the channel required to meet the situation of E_(fD)=E_(channel).We also find that the bias electric field has the effect to accelerate the thermally activated electrons in the channel,equivalent to the effect of thermal temperature on the increase of electron energy.Our work provides a detailed description of the bias-modulated quantum electronic properties,which will give a more comprehensive understanding of transport behavior in nanoscale devices.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11874156 and 11904111)the Project funded by China Postdoctoral Science Foundation(Grant No.2019M652684).
文摘Besides its fundamental importance, non-reciprocity has also found many potential applications in quantum technology. Recently, many quantum systems have been proposed to realize non-reciprocity, but stable non-reciprocal process is still experimentally difficult in general, due to the needed cyclical interactions in artificial systems or operational difficulties in solid state materials. Here, we propose a new kind of interaction induced non-reciprocal operation, based on the conventional stimulated-Raman-adiabatic-passage (STIRAP) setup, which removes the experimental difficulty of requiring cyclical interaction, and thus it is directly implementable in various quantum systems. Furthermore, we also illustrate our proposal on a chain of three coupled superconducting transmons, which can lead to a non-reciprocal circulator with high fidelity without a ring coupling configuration as in the previous schemes or implementations. Therefore, our protocol provides a promising way to explore fundamental non-reciprocal quantum physics as well as realize non-reciprocal quantum device.
基金Supported by the National Basic Research Program of China under Grant No 2011CBA00200the National Natural Science Foundation of China under Grant No 11074244+3 种基金ARO(W911NF-12-1-0334)DARPA-YFA(N66001-10-1-4025)AFOSR(FA9550-11-1-0313)NSF-PHY(1104546)
文摘We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of using the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a nmch easier manner. Our proposal overcomes the major drawback of the method used by Creffield et al [Phys. Rev. Lett. 99 （2007） 110501], and can be implemented, in principle, in any one-dimensional optical lattice. Some potential applications of the scheme are also discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274040 and 10974015)the Program for New Century Excellent Talents in University of China(Grant No.NCET-08-0044)
文摘We investigate the quantum transport properties through a special kind of quantum dot（QD） system composed of a serially coupled multi-QD-pair（multi-QDP） chain and side-coupled Majorana bound states（MBSs） by using the Green functions method,where the conductance can be classified into two kinds：the electron tunneling（ET） conductance and the Andreev reflection（AR） one.First we find that for the nonzero MBS-QDP coupling a sharp AR-induced zero-bias conductance peak with the height of e^2/h is present（or absent） when the MBS is coupled to the far left（or the other） QDP.Moreover,the MBS-QDP coupling can suppress the ET conductance and strengthen the AR one,and further split into two sub-peaks each of the total conductance peaks of the isolated multi-QDPs,indicating that the MBS will make obvious influences on the competition between the ET and AR processes.Then we find that the tunneling rate ΓLis able to affect the conductances of leads L and R in different ways,demonstrating that there exists a ΓL-related competition between the AR and ET processes.Finally we consider the effect of the inter-MBS coupling on the conductances of the multi-QDP chains and it is shown that the inter-MBS coupling will split the zero-bias conductance peak with the height of e^2/h into two sub-peaks.As the inter-MBS coupling becomes stronger,the two sub-peaks are pushed away from each other and simultaneously become lower,which is opposite to that of the single QDP chain where the two sub-peaks with the height of about e^2/2h become higher.Also,the decay of the conductance sub-peaks with the increase of the MBS-QDP coupling becomes slower as the number of the QDPs becomes larger.This research should be an important extension in studying the transport properties in the kind of QD systems coupled with the side MBSs,which is helpful for understanding the nature of the MBSs,as well as the MBS-related QD transport properties.
基金supported by National Natural Science Foundation of China (Grant Nos. 10604005 and 10974015)supported by Program for New Century Excellent Talents in University of China (Grant No. NCET-08-0044)
文摘This paper investigates Kondo transport properties in a quadruple quantum dot （QD） based on the slave-boson mean field theory and the non-equilibrium Green＇s function. In the quadruple QD structure one Kondo-type QD sandwiched between two leads is side coupled to two separate QD structures： a single-QD atom and a double-QD molecule. It shows that the conductance valleys and peaks always appear in pairs and by tuning the energy levels in three side QDs, the one-, two-, or three-valley conductance pattern can be obtained. Furthermore, it finds that whether the valley and the peak can appear is closely dependent on the specific values of the interdot couplings and the energy level difference between the two QDs in the molecule. More interestingly, an extra novel conductance peak can be produced by the coexistence of the two different kinds of side QD structures.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12365003,12364024,and 11864014)the Jiangxi Provincial Natural Science Foundation(Grant Nos.20212BAB201014 and 20224BAB201023)。
文摘We theoretically investigate coherent scattering of single photons and quantum entanglement of two giant atoms with azimuthal angle differences in a waveguide system.Using the real-space Hamiltonian,analytical expressions are derived for the transport spectra scattered by these two giant atoms with four azimuthal angles.Fano-like resonance can be exhibited in the scattering spectra by adjusting the azimuthal angle difference.High concurrence of the entangled state for two atoms can be implemented in a wide angle-difference range,and the entanglement of the atomic states can be switched on/off by modulating the additional azimuthal angle differences from the giant atoms.This suggests a novel handle to effectively control the single-photon scattering and quantum entanglement.
基金Project supported by the National Key Research and Development Program of China (Grant Nos.2020YFA0309300 and 2022YFA1403700)the National Natural Science Foundation of China (Grant Nos.12004158,12074162,and 91964201)+2 种基金the Key-Area Research and Development Program of Guangdong Province (Grant No.2018B030327001)Guangdong Provincial Key Laboratory (Grant No.2019B121203002)Guangdong Basic and Applied Basic Research Foundation (Grant No.2022B1515130005)。
文摘Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum locking in nonmagnetic systems provides a new platform for developing spintronics, while previous studies were mostly based on magnetic materials.In this study, the spin transport measurement of Dirac semimetal Cd_(3)As_(2) was studied by three-terminal geometry, and a hysteresis loop signal with high resistance and low resistance state was observed. The hysteresis was reversed by reversing the current direction, which illustrates the spin–momentum locking feature of Cd_(3)As_(2). Furthermore, we realized the on–off states of the spin signals through electric modulation of the Fermi arc via the three-terminal configuration, which enables the great potential of Cd_(3)As_(2) in spin field-effect transistors.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574362,61210014,11374340,and 11474205)the Innovative Clean-Energy Research and Application Program of Beijing Municipal Science and Technology Commission,China(Grant No.Z151100003515001)
文摘According to the well-established light-to-electricity conversion theory,resonant excited carriers in the quantum dots will relax to the ground states and cannot escape from the quantum dots to form photocurrent,which have been observed in quantum dots without a p–n junction at an external bias.Here,we experimentally observed more than 88% of the resonantly excited photo carriers escaping from In As quantum dots embedded in a short-circuited p–n junction to form photocurrent.The phenomenon cannot be explained by thermionic emission,tunneling process,and intermediate-band theories.A new mechanism is suggested that the photo carriers escape directly from the quantum dots to form photocurrent rather than relax to the ground state of quantum dots induced by a p–n junction.The finding is important for understanding the low-dimensional semiconductor physics and applications in solar cells and photodiode detectors.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61176089 and 11504083)the Foundation of Shijiazhuang University,China(Grant No.XJPT002)
文摘Using a transfer matrix method, we investigate spin transport through a chain of polygonal rings with Dresselhaus spin-orbit coupling（DSOC）. The spin conductance is dependent on the number of sides in the polygons. When DSOC is considered in a chain which also has Rashba spin-orbit coupling（RSOC） of the same magnitude, the total conductance is the same as that for the same chain with no SOC. However, when the two types of SOC have different values, there results a unique anisotropic conductance.
基金Project supported by the Youth Science Foundation of Shanxi Province, China （Grant No 20031003）.
文摘Quantum spin transport in a mesoscopic Aharonov-Bohm ring with two leads subject to a magnetic field with circular configuration is investigated by means of one-dimensional quantum waveguide theory. Within the framework of Landauer-Bfittiker formalism, the polarization direction of transmitted electrons can be controlled either by the AB magnetic flux or by the tangent magnetic field. In particular, the spin flips can be induced by hopping the AB magnetic flux or the tangent field.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFA0200503)the National Natural Science Foundation of China(Grant Nos.11947115,61376096,61327813,and 61404126)。
文摘The ionized dopants, working as quantum dots in silicon nanowires, exhibit potential advantages for the development of atomic-scale transistors. We investigate single electron tunneling through a phosphorus dopant induced quantum dots array in heavily n-doped junctionless nanowire transistors. Several subpeaks splittings in current oscillations are clearly observed due to the coupling of the quantum dots at the temperature of 6 K. The transport behaviors change from resonance tunneling to hoping conduction with increased temperature. The charging energy of the phosphorus donors is approximately 12.8 meV. This work helps clear the basic mechanism of electron transport through donor-induced quantum dots and electron transport properties in the heavily doped nanowire through dopant engineering.
基金Project supported by the National Key Basic Research and Development Project of the Ministry of Science and Technology of China(Grant No.2016YFA0300601)the National Natural Science Foundation of China(Grant Nos.91221202,91421303,11374019,and 61321001)
文摘An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in In Sb nanowires grown by molecular-beam epitaxy contacted by superconductor electrodes. At an elevated temperature, clear conductance plateaus are observed at zero magnetic field and in agreement with calculations based on the Landauer formula. At lower temperature, we have observed characteristic Fabry–Pérot patterns which confirm the ballistic nature of charge transport.Furthermore, the magnetoconductance measurements in the ballistic regime reveal a periodic variation related to the Fabry–Pérot oscillations. The result can be reasonably explained by taking into account the impact of magnetic field on the phase of ballistic electron＇s wave function, which is further verified by our simulation. Our results pave the way for better understanding of the quantum interference effects on the transport properties of In Sb nanowires in the ballistic regime as well as developing of novel device for topological quantum computations.
基金Project supported by the National Natural Science Foundation of China(Grant No.61176089)Hebei Provincial Natural Science Foundation,China(Grant No.A2011205092)
文摘Transport properties in a multi-terminal regular polygonal quantum ring with Rashba spin-orbit coupling （SOC） are investigated analytically using quantum networks and the transport matrix metLod. The results show that conduc- tances remain at exactly the same values when the output leads are located at axisymmetric positions. However, for the nonaxisymmetrical case, there is a phase difference between the upper and lower arm, which leads to zero conductances appearing periodically. An isotropy of the conductance is destroyed by the Rashba SOC effect in the axisymmetric case. In addition, the position of zero conductance is regulated with the strength of the Rashba SOC.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10774094 and 10775091)National Fundamental Fund of Personnel Training (Grant No. J0730317)Natural Science Foundation of Shanxi Province of China (GrantNo. 2009011001-1)
文摘Using the tight-binding approximation and the transfer matrix method, this paper studies the electronic transport properties through a periodic array of quantum-dot （QD） rings threaded by a magnetic flux. It demonstrates that the even^odd parity of the QD number in a single ring and the number of the QD rings in the array play a crucial role in the electron transmission. For a single QD ring, the resonance and antiresonance transmission depend not only on the applied magnetic flux but also on the difference between the number of QDs on the two arms of the ring. For an array of QD rings, the transmission properties are related not only to the even-odd parity of the number No of QDs in the single ring but also to the even-odd parity of the ring number N in the array. When the incident electron energy is aligned with the site energy, for the array of N rings with No = odd the antiresonance transmission cannot occur but the resonance transmission may occur and the transmission spectrum has N resonance peaks （N - 1 resonance peaks） in a period for N = odd （for N = even）. For the array of N rings with No = even the transmission properties depend on the flux threading the ring and the QD number on one arm of the ring. These results may be helpful in designing QD devices.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11574362,61210014,and 11374340the Innovative Clean-Energy Research and Application Program of Beijing Municipal Science and Technology Commission under Grant No Z151100003515001
文摘The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p-n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p-n junction escape from quantum wells and form photoeurrent rather than relax to the ground state of the quantum wells. The photo absorption coei^cient of multiple quantum wells is also enhanced by a p-n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure.
基金supported by the National Natural Science Foundation of China(Grant No.61176089)the Natural Science Foundation of Hebei Province,China(Grant No.A2011205092)the Foundation of Shijiazhuang University,China(Grant No.XJPT002)
文摘We propose a theoretical method to investigate the effect of the Dresselhaus spin–orbit coupling（DSOC） on the spin transport properties of a regular polygonal quantum ring with an arbitrary number of segments. We find that the DSOC can break the time reversal symmetry of the spin conductance in a polygonal ring and that this property can be used to reverse the spin direction of electrons in the polygon with the result that a pure spin up or pure spin down conductance can be obtained by exchanging the source and the drain. When the DSOC is considered in a polygonal ring with Rashba spin–orbit coupling（RSOC） with symmetric attachment of the leads, the total conductance is independent of the number of segments when both of the two types of spin–orbit coupling（SOC） have the same value. However, the interaction of the two types of SOC results in an anisotropic and shape-dependent conductance in a polygonal ring with asymmetric attachment of the leads. The method we proposed to solve for the spin conductance of a polygon can be generalized to the circular model.
