We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility,specific heat and electrical resistivity measurements as well as hig...We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility,specific heat and electrical resistivity measurements as well as high pressure effect.Magnetic measurements reveal that an antiferromagnetic order develops below T_(m)~10.4 K with magnetic moments orientated in the ab plane.The enhanced electronic specific heat coefficient and the negative logarithmic slope in the resistivity of CeGaSi indicate that the title compound belongs to the family of Kondo system with heavy fermion ground states.The max magnetic entropy change-ΔS_(M)^(max)(μ_(0)H⊥c,μ_(0)H=7 T) around T_(m) is found to reach up to 11.85 J·kg^(-1)·K^(-1).Remarkably,both the antiferromagnetic transition temperature and-ln T behavior increase monotonically with pressure applied to 20 kbar(1 bar=10~5 Pa),indicating that much higher pressure will be needed to reach its quantum critical point.展开更多
In this review article, we give a brief overview of heavy fermions, which are prototype examples of strongly correlated electron systems. We introduce the application of physical pressure in heavy fermion systems to c...In this review article, we give a brief overview of heavy fermions, which are prototype examples of strongly correlated electron systems. We introduce the application of physical pressure in heavy fermion systems to construct their pressure phase diagrams and to study the close relationship between superconductivity（SC） and other electronic instabilities, such as antiferromagnetism（AFM）, ferromagnetism（FM）, and valence transitions. Field-angle dependent heat capacity and point-contact spectroscopic measurements under pressure are taken as examples to illustrate their ability to investigate novel physical properties of the emergent electronic states.展开更多
We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system ...We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn5.Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt2In7. The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt2In7. A comparison of the common features of the electronic structure of CePt2In7and CeCoIn5indicates that CeCoIn5shows a much stronger band renormalization effect than CePt2In7. These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems.展开更多
We successfully synthesize a series of polycrystalline CeRuxFe1-xCe3（0≤x≤0.5）samples,which are characterized using powder x-ray diffraction,resistivity and specific heat measurements.The expansion of the lattice c...We successfully synthesize a series of polycrystalline CeRuxFe1-xCe3（0≤x≤0.5）samples,which are characterized using powder x-ray diffraction,resistivity and specific heat measurements.The expansion of the lattice constants with increasing x demonstrates the successful doping of Ru into the CeFeGe3 lattice.Upon doping,it is found that the temperature up to which Landau-Fermi liquid behavior is observed in the resistivity is reduced.Meanwhile,there is also a pronounced increase in the resistivity coefficient and residual resistivity,as well as a clear upturn in C/T at low temperatures,suggesting that Ru doping may tune the system towards a quantum critical point.展开更多
The recent discovery of high-temperature superconductivity in iron-based pnictides （chalcogenides） not only trig- gers tremendous enthusiasm in searching for new superconducting materials, but also opens a new avenu...The recent discovery of high-temperature superconductivity in iron-based pnictides （chalcogenides） not only trig- gers tremendous enthusiasm in searching for new superconducting materials, but also opens a new avenue to the study of the Kondo physics. CeFeAsO is a parent compound of the 1111-type iron-based superconductors. It shows 3d- antiferromagnetic （AFM） ordering below 139 K and 4f-AFM ordering below 4 K. On the other hand, the phosphide CeFePO is a ferromagnetically corelated heavy-fermion （HF） metal with Kondo scale TK 10 K. These properties set up a new platform for research of the interplay among magnetism, Kondo effect, and superconductivity （SC）. In this review, we present the recent progress in the study of chemical pressure effect in CeFeAsOl_yFy （y = 0 and 0.05）. This P/As-doping in CeFeAsO serves as an effective controlling parameter which leads to two magnetic critical points, Xcl -- 0.4 and Xc2 - 0.92, associated with suppression of 3d and 4f magnetism, respectively. We also observe a turning point of AFM-FM ordering of Ce3＋ moment at Xc3 - 0.37. The SC is absent in the phase diagram, which is attributed to the destruction to Cooper pair by Ce-FM fluctuations in the vicinity of Xcl. We continue to investigate CeFeAsl-xPxO0.95Fo.os. With the separation of xcl and xc3, this chemical pressure results in a broad SC region 0〈 x 〈 0.53, while the original HF behavior is driven away by 5% F- doping. Different roles of P and F dopings are addressed, and the interplay between SC and Ce-4f magnetism is also discussed.展开更多
We report an optical spectroscopy study on intermediate valence system Ybl-xLuxA13 with x = 0, 0.25, 0.5, 0.75, and 1. The Kondo temperature in the system is known to increase with increasing Lu concentration. Therefo...We report an optical spectroscopy study on intermediate valence system Ybl-xLuxA13 with x = 0, 0.25, 0.5, 0.75, and 1. The Kondo temperature in the system is known to increase with increasing Lu concentration. Therefore, it is expected that the energy scale of the hybridization gap should increase with increasing Lu concentration based on the periodic Anderson model. On the contrary, we find that the spectral structure associated with the hybridization effect shifts monotonically to lower energy. Furthermore, the Lu substitution results in a substantial increase of the free carrier spectral weight and less pronounced plasma frequency reduction upon lowering temperature. We attribute the effect to the disruption of the Kondo lattice periodicity by the random substitution of Yb by Lu. The work highlights the importance of the lattice periodicity of the rare earth element for understanding the Kondo lattice phenomena.展开更多
High-quality single crystals of A-site ordered perovskite oxides CaCu3Ru4O12 were synthesized by flux method with Cu O serving as a flux. The typical size of these single crystals was around 1 × 1 × 1 mm^3 a...High-quality single crystals of A-site ordered perovskite oxides CaCu3Ru4O12 were synthesized by flux method with Cu O serving as a flux. The typical size of these single crystals was around 1 × 1 × 1 mm^3 and the lattice constant was determined to be 7.430 ± 0.0009 ？A by using x-ray single crystal diffraction. The surfaces of the samples were identified to be（100） surface. The high quality of the single crystal samples was confirmed by the rocking curve data which have a full width at half maximum of approximately 0.02 degree. The x-ray photoelectron spectroscopy measurement was performed and the temperature-dependent specific heat, magnetic susceptibility, and electric resistivity were measured along the [100]direction of the single crystals. All these measurements showed that the physical properties of Ca Cu3Ru4O12 single crystals are similar to that of polycrystals. However, the single crystals have a lower Curie susceptibility tail and a smaller residual resistivity than polycrystals, which indicates that the amount of paramagnetic impurities can be controlled by tuning the number of defects in CaCu3Ru4O12 samples.展开更多
Needle-like single crystals of CeAu_(2)In_(4)have been grown from In flux and characterized as a new candidate of quasi-one-dimensional Kondo lattice compound by crystallographic,magnetic,transport,and specific-heat m...Needle-like single crystals of CeAu_(2)In_(4)have been grown from In flux and characterized as a new candidate of quasi-one-dimensional Kondo lattice compound by crystallographic,magnetic,transport,and specific-heat measurements down to very low temperatures.We observe an antiferromagnetic transition at T_(N)≈0.9 K,a highly non-mean-field profile of the corresponding peak in specific heat,and a large Sommerfeld coefficientγ=369 mJ·mol^(-1)·K^(-2).The Kondo temperature T_(K)is estimated to be 1.1 K,being low and comparable to TN.While Fermi liquid behavior is observed deep into the magnetically ordered phase,the Kadowaki-Woods ratio is much reduced relative to the expected value for Ce compounds with Kramers doublet ground state.Markedly,this feature shares striking similarities to that of the prototypical quasi-one-dimensional compounds YbNi_(4)P_(2) and CeRh_(6)Ge_(4) with tunable ferromagnetic quantum critical point.Given the shortest Ce-Ce distance along the needle direction,CeAu_(2)In_(4)appears to be an interesting model system for exploring antiferromagnetic quantum critical behaviors in a quasi-one-dimensional Kondo lattice with enhanced quantum fluctuations.展开更多
The magnetic and electronic properties of spinel oxide LiV2O4 have been systematically studied by using the spin-polarized first-principles electronic structure calculations.We find that a series of magnetic states,in...The magnetic and electronic properties of spinel oxide LiV2O4 have been systematically studied by using the spin-polarized first-principles electronic structure calculations.We find that a series of magnetic states,in which the ferromagnetic(FM)V4 tetrahedra are linked together through the corner-sharing antiferromagnetic(AFM)V4 tetrahedra,possess degenerate energies lower than those of other spin configurations.The large number of these energetically degenerated states being the magnetic ground state give rise to strong magnetic frustration as well as large magnetic entropy in LiV2O4.The corresponding band structure and density of states of such a typical magnetic state in this series,i.e.,the ditetrahedron(DT)AFM state,demonstrate that LiV2O4 is in the vicinity of a metal-insulator transition.Further analysis suggests that the t2g and eg orbitals of the V atoms play different roles in the magnetic exchange interactions.Our calculations are consistent with previous experimental measurements and shed light on understanding the exotic magnetism and the heavy-fermion behavior of LiV2O4.展开更多
Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport pr...Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single- and poly-crystalline samples. The electrical resistivity p （T） is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high- and low-temperature windows are found to increase with pressure. A flat p（T） observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 12274440)the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB33010100)+1 种基金the Fund from the Ministry of Science and Technology of China (Grant No. 2022YFA1403903)the Fund of the Synergetic Extreme Condition User Facility (SECUF)。
文摘We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility,specific heat and electrical resistivity measurements as well as high pressure effect.Magnetic measurements reveal that an antiferromagnetic order develops below T_(m)~10.4 K with magnetic moments orientated in the ab plane.The enhanced electronic specific heat coefficient and the negative logarithmic slope in the resistivity of CeGaSi indicate that the title compound belongs to the family of Kondo system with heavy fermion ground states.The max magnetic entropy change-ΔS_(M)^(max)(μ_(0)H⊥c,μ_(0)H=7 T) around T_(m) is found to reach up to 11.85 J·kg^(-1)·K^(-1).Remarkably,both the antiferromagnetic transition temperature and-ln T behavior increase monotonically with pressure applied to 20 kbar(1 bar=10~5 Pa),indicating that much higher pressure will be needed to reach its quantum critical point.
基金Project supported by the National Basic Research Program of China(Grant No.2011CBA00103)the National Natural Science Foundation of China(Grant Nos.11174245 and 11374257)+1 种基金the Science Challenge Program of Chinathe Fundamental Research Funds for the Central Universities of China
文摘In this review article, we give a brief overview of heavy fermions, which are prototype examples of strongly correlated electron systems. We introduce the application of physical pressure in heavy fermion systems to construct their pressure phase diagrams and to study the close relationship between superconductivity（SC） and other electronic instabilities, such as antiferromagnetism（AFM）, ferromagnetism（FM）, and valence transitions. Field-angle dependent heat capacity and point-contact spectroscopic measurements under pressure are taken as examples to illustrate their ability to investigate novel physical properties of the emergent electronic states.
基金The ARPES experimental work is supported by the National Natural Science Foundation of China(Grant No.11574360)the National Basic Research Program of China(Grant Nos.2015CB921300,2013CB921700,and 2013CB921904)+3 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB07020300)supported by the National Natural Science Foundation of China(Grant No.91421304)the Fundamental Research Funds for the Central Universities of Chinathe Research Funds of Renmin University of China(Grant Nos.14XNLQ03 and16XNLQ01)
文摘We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn5.Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt2In7. The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt2In7. A comparison of the common features of the electronic structure of CePt2In7and CeCoIn5indicates that CeCoIn5shows a much stronger band renormalization effect than CePt2In7. These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474251,11604291 and U1632275the National Key Research and Development Program of China under Grant Nos 2017YFA0303100 and 2016YFA0300202the Science Challenge Project of China under Grant No TZ2016004
文摘We successfully synthesize a series of polycrystalline CeRuxFe1-xCe3（0≤x≤0.5）samples,which are characterized using powder x-ray diffraction,resistivity and specific heat measurements.The expansion of the lattice constants with increasing x demonstrates the successful doping of Ru into the CeFeGe3 lattice.Upon doping,it is found that the temperature up to which Landau-Fermi liquid behavior is observed in the resistivity is reduced.Meanwhile,there is also a pronounced increase in the resistivity coefficient and residual resistivity,as well as a clear upturn in C/T at low temperatures,suggesting that Ru doping may tune the system towards a quantum critical point.
基金supported by the National Basic Research Program of China(Grant Nos.2011CBA00103 and 2010CB923003)the National Natural Science Foundation of China
文摘The recent discovery of high-temperature superconductivity in iron-based pnictides （chalcogenides） not only trig- gers tremendous enthusiasm in searching for new superconducting materials, but also opens a new avenue to the study of the Kondo physics. CeFeAsO is a parent compound of the 1111-type iron-based superconductors. It shows 3d- antiferromagnetic （AFM） ordering below 139 K and 4f-AFM ordering below 4 K. On the other hand, the phosphide CeFePO is a ferromagnetically corelated heavy-fermion （HF） metal with Kondo scale TK 10 K. These properties set up a new platform for research of the interplay among magnetism, Kondo effect, and superconductivity （SC）. In this review, we present the recent progress in the study of chemical pressure effect in CeFeAsOl_yFy （y = 0 and 0.05）. This P/As-doping in CeFeAsO serves as an effective controlling parameter which leads to two magnetic critical points, Xcl -- 0.4 and Xc2 - 0.92, associated with suppression of 3d and 4f magnetism, respectively. We also observe a turning point of AFM-FM ordering of Ce3＋ moment at Xc3 - 0.37. The SC is absent in the phase diagram, which is attributed to the destruction to Cooper pair by Ce-FM fluctuations in the vicinity of Xcl. We continue to investigate CeFeAsl-xPxO0.95Fo.os. With the separation of xcl and xc3, this chemical pressure results in a broad SC region 0〈 x 〈 0.53, while the original HF behavior is driven away by 5% F- doping. Different roles of P and F dopings are addressed, and the interplay between SC and Ce-4f magnetism is also discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11327806 and GZ1123)the National Key Research and Development Program of China(Grant Nos.2016YFA0300902 and 2017YFA0302904)
文摘We report an optical spectroscopy study on intermediate valence system Ybl-xLuxA13 with x = 0, 0.25, 0.5, 0.75, and 1. The Kondo temperature in the system is known to increase with increasing Lu concentration. Therefore, it is expected that the energy scale of the hybridization gap should increase with increasing Lu concentration based on the periodic Anderson model. On the contrary, we find that the spectral structure associated with the hybridization effect shifts monotonically to lower energy. Furthermore, the Lu substitution results in a substantial increase of the free carrier spectral weight and less pronounced plasma frequency reduction upon lowering temperature. We attribute the effect to the disruption of the Kondo lattice periodicity by the random substitution of Yb by Lu. The work highlights the importance of the lattice periodicity of the rare earth element for understanding the Kondo lattice phenomena.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB821404)the National Natural Science Foundation of China(Grant Nos.51172166 and 61106005)+1 种基金the National Science Fund for Talent Training in Basic Science of China(Grant No.J1210061)the Doctoral Fund of Ministry of Education of China(Grant No.20110141110007)
文摘High-quality single crystals of A-site ordered perovskite oxides CaCu3Ru4O12 were synthesized by flux method with Cu O serving as a flux. The typical size of these single crystals was around 1 × 1 × 1 mm^3 and the lattice constant was determined to be 7.430 ± 0.0009 ？A by using x-ray single crystal diffraction. The surfaces of the samples were identified to be（100） surface. The high quality of the single crystal samples was confirmed by the rocking curve data which have a full width at half maximum of approximately 0.02 degree. The x-ray photoelectron spectroscopy measurement was performed and the temperature-dependent specific heat, magnetic susceptibility, and electric resistivity were measured along the [100]direction of the single crystals. All these measurements showed that the physical properties of Ca Cu3Ru4O12 single crystals are similar to that of polycrystals. However, the single crystals have a lower Curie susceptibility tail and a smaller residual resistivity than polycrystals, which indicates that the amount of paramagnetic impurities can be controlled by tuning the number of defects in CaCu3Ru4O12 samples.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774404 and 52088101)the National Key R&D Program of China(Grant No.2017YF A0303100)the Chinese Academy of Sciences through the Strategic Priority Research Program(Grant No.XDB33000000).
文摘Needle-like single crystals of CeAu_(2)In_(4)have been grown from In flux and characterized as a new candidate of quasi-one-dimensional Kondo lattice compound by crystallographic,magnetic,transport,and specific-heat measurements down to very low temperatures.We observe an antiferromagnetic transition at T_(N)≈0.9 K,a highly non-mean-field profile of the corresponding peak in specific heat,and a large Sommerfeld coefficientγ=369 mJ·mol^(-1)·K^(-2).The Kondo temperature T_(K)is estimated to be 1.1 K,being low and comparable to TN.While Fermi liquid behavior is observed deep into the magnetically ordered phase,the Kadowaki-Woods ratio is much reduced relative to the expected value for Ce compounds with Kramers doublet ground state.Markedly,this feature shares striking similarities to that of the prototypical quasi-one-dimensional compounds YbNi_(4)P_(2) and CeRh_(6)Ge_(4) with tunable ferromagnetic quantum critical point.Given the shortest Ce-Ce distance along the needle direction,CeAu_(2)In_(4)appears to be an interesting model system for exploring antiferromagnetic quantum critical behaviors in a quasi-one-dimensional Kondo lattice with enhanced quantum fluctuations.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0302903 and 2019YFA0308603)the National Natural Science Foundation of China(Grant Nos.11774422,11774424,and 11674374)+1 种基金the CAS Interdisciplinary Innovation Team,the Fundamental Research Funds for the Central Universities,Chinathe Research Funds of Renmin University of China(Grant No.19XNLG13).
文摘The magnetic and electronic properties of spinel oxide LiV2O4 have been systematically studied by using the spin-polarized first-principles electronic structure calculations.We find that a series of magnetic states,in which the ferromagnetic(FM)V4 tetrahedra are linked together through the corner-sharing antiferromagnetic(AFM)V4 tetrahedra,possess degenerate energies lower than those of other spin configurations.The large number of these energetically degenerated states being the magnetic ground state give rise to strong magnetic frustration as well as large magnetic entropy in LiV2O4.The corresponding band structure and density of states of such a typical magnetic state in this series,i.e.,the ditetrahedron(DT)AFM state,demonstrate that LiV2O4 is in the vicinity of a metal-insulator transition.Further analysis suggests that the t2g and eg orbitals of the V atoms play different roles in the magnetic exchange interactions.Our calculations are consistent with previous experimental measurements and shed light on understanding the exotic magnetism and the heavy-fermion behavior of LiV2O4.
基金Project supported by the Ministry of Science and Technology of China(Grant Nos.2015CB921303 and 2017YFA0303103)the National Natural Science Foundation of China(Grant Nos.11474332 and 11774404)the Chinese Academy of Sciences through the Strategic Priority Research Program(Grant No.XDB07020200)
文摘Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single- and poly-crystalline samples. The electrical resistivity p （T） is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high- and low-temperature windows are found to increase with pressure. A flat p（T） observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.
