There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, such as the formation of charge density wave or polaron...There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, such as the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe5. It is found that a three-dimensional topological Dirac semimetal state emerges only at around Tp （at which the resistivity shows a pronounced peak）, as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe5. Our work not only provides the first evidence of a temperature-induced critical topological phase transition inHfTe5 but also gives a reasonable explanation on the long-lasting question.展开更多
Single crystals of RSeTe2 （R =La, Ce, Pr, Nd） are synthesized using LiC1/RbCI flux. Transport and magnetic properties in the directions parallel and perpendicular to the a-c plane are investigated. We find that the ...Single crystals of RSeTe2 （R =La, Ce, Pr, Nd） are synthesized using LiC1/RbCI flux. Transport and magnetic properties in the directions parallel and perpendicular to the a-c plane are investigated. We find that the resistivity anisotropy P⊥/P∥ lies in the range 486-615 for different compounds at 2K, indicating the highly two-dimensional character. In both the orientations, the charge-density-wave transitions start near Tcow = 284（3）K, 316（3）K, 359（3）K for NdSeTe2, PrSeTe2, CeSeTe2, respectively, with a considerable increase in dc resistivity. While for LaSeTe2, no obvious resistivity anomaly is observed up to 380K. The value of TCDW increases monotonically with the increasing lattice parameters. Below TCDW, slight anomalies can be observed in NdSeTe2, PrSeTe2 and CeSeTe2 with onset temperature at 193（3）K, 161（3）K, 108（3）K, respectively, decreasing as lattice parameters increase. Magnetic susceptibility measurements show that the valence state of rare earth ions are trivalenee in these compounds. Antiferromagnetie-type magnetic order is formed in CeSeTe2 at 2.1 K, while no magnetic transition is observed in PrSeTe2 and NdSeTe2 down to 1.8 K.展开更多
We revisit the reversible magnetocaloric effect of itinerant ferromagnet Mn3GaC near the ferromagnetic to paramagnetic phase transition by adopting the experimental and theoretical methods and critical behavior of Mn-...We revisit the reversible magnetocaloric effect of itinerant ferromagnet Mn3GaC near the ferromagnetic to paramagnetic phase transition by adopting the experimental and theoretical methods and critical behavior of Mn-rich Mn3GaC with an enhanced FM interaction.Landau theory model cannot account for temperature dependent magnetic entropy change which is estimated from thermal magnetic methods only considering magnetoelastic coupling and the electron-electron interaction,apart from molecular mean-field model.Critical behavior is studied by adopting the modified Arrott plot,Kouvel-Fisher plot,and critical isotherm analysis.With these critical exponents,experimental data below and above Tc collapse into two universal branches,fulfilling the single scaling equation m=f±(h),where m and h are renormalized magnetization and field.Critical exponents are confirmed by Widom scaling law and just between mean-field model and three-dimensional Heisenberg model,as the evidence for the existence of long-range ferromagnetic interaction.With increasing the Mn content,Tc increases monotonously and critical exponents increases accordingly.The exchange distance changes from J(r)~r^-4.68 for x=0 to J(r)~r^-4.71 for x=0.08,respectively,which suggests the competition of the Mn-Mn direct interaction and the itinerant Mn-C-Mn hybridization.The possible mechanism is proposed.展开更多
We synthesize a set of Pd-doped polycrystalline samples PdxNdSeTe2 and measure their physical properties. Compared with pure NdSeTe2, the charge density wave （CDW） order is continuously suppressed with the Pdinterca...We synthesize a set of Pd-doped polycrystalline samples PdxNdSeTe2 and measure their physical properties. Compared with pure NdSeTe2, the charge density wave （CDW） order is continuously suppressed with the Pdintercalation. Bulk superconductivity first appears at x = 0.06 with Tc nearly 2.5I〈, coexisting with a CDW transition at 176K. Further Pd-doping enhances Tc, until it reaches the maximum value 2.84K at x=0.1, meanwhile the CDW transition vanishes. The upper critical field for the optimal doping sample Pdo.lNdSeTe2 is determined from the R-H measurement, which is estimated to be 0.6 T. These results provide another kind of ideal compound for studying the interplay between CDW and superconductivity systematically.展开更多
基金Supported by the National Basic Research Program of China under Grant Nos 2015CB921303 and 2013CB921700the National Key Research Program of China under Grant No 2016YFA0300604the'Strategic Priority Research Program(B)'of the Chinese Academy of Sciences under Grant No XDB07020100
文摘There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe5. Several mechanisms, such as the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe5. It is found that a three-dimensional topological Dirac semimetal state emerges only at around Tp （at which the resistivity shows a pronounced peak）, as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe5. Our work not only provides the first evidence of a temperature-induced critical topological phase transition inHfTe5 but also gives a reasonable explanation on the long-lasting question.
基金Supported by the National Basic Research Program of China under Grant No 2015CB921303the Strategic Priority Research Program(B) of Chinese Academy of Sciences under Grant No XDB07020100
文摘Single crystals of RSeTe2 （R =La, Ce, Pr, Nd） are synthesized using LiC1/RbCI flux. Transport and magnetic properties in the directions parallel and perpendicular to the a-c plane are investigated. We find that the resistivity anisotropy P⊥/P∥ lies in the range 486-615 for different compounds at 2K, indicating the highly two-dimensional character. In both the orientations, the charge-density-wave transitions start near Tcow = 284（3）K, 316（3）K, 359（3）K for NdSeTe2, PrSeTe2, CeSeTe2, respectively, with a considerable increase in dc resistivity. While for LaSeTe2, no obvious resistivity anomaly is observed up to 380K. The value of TCDW increases monotonically with the increasing lattice parameters. Below TCDW, slight anomalies can be observed in NdSeTe2, PrSeTe2 and CeSeTe2 with onset temperature at 193（3）K, 161（3）K, 108（3）K, respectively, decreasing as lattice parameters increase. Magnetic susceptibility measurements show that the valence state of rare earth ions are trivalenee in these compounds. Antiferromagnetie-type magnetic order is formed in CeSeTe2 at 2.1 K, while no magnetic transition is observed in PrSeTe2 and NdSeTe2 down to 1.8 K.
基金Project supported by National Key Research and Development Program of China(Grant Nos.2018YFA0305700 and 2018YFA0305800)One Hundred-Talent Program in Institute of Physics(Grant No.Y7K5031X61)Youth Promotion Association of CAS(Grant No.2018010)。
文摘We revisit the reversible magnetocaloric effect of itinerant ferromagnet Mn3GaC near the ferromagnetic to paramagnetic phase transition by adopting the experimental and theoretical methods and critical behavior of Mn-rich Mn3GaC with an enhanced FM interaction.Landau theory model cannot account for temperature dependent magnetic entropy change which is estimated from thermal magnetic methods only considering magnetoelastic coupling and the electron-electron interaction,apart from molecular mean-field model.Critical behavior is studied by adopting the modified Arrott plot,Kouvel-Fisher plot,and critical isotherm analysis.With these critical exponents,experimental data below and above Tc collapse into two universal branches,fulfilling the single scaling equation m=f±(h),where m and h are renormalized magnetization and field.Critical exponents are confirmed by Widom scaling law and just between mean-field model and three-dimensional Heisenberg model,as the evidence for the existence of long-range ferromagnetic interaction.With increasing the Mn content,Tc increases monotonously and critical exponents increases accordingly.The exchange distance changes from J(r)~r^-4.68 for x=0 to J(r)~r^-4.71 for x=0.08,respectively,which suggests the competition of the Mn-Mn direct interaction and the itinerant Mn-C-Mn hybridization.The possible mechanism is proposed.
基金Supported by the National Basic Research Program of China under Grant No 2015CB921303the Strategic Priority Research Program(B) of the Chinese Academy of Sciences under Grant No XDB07020100
文摘We synthesize a set of Pd-doped polycrystalline samples PdxNdSeTe2 and measure their physical properties. Compared with pure NdSeTe2, the charge density wave （CDW） order is continuously suppressed with the Pdintercalation. Bulk superconductivity first appears at x = 0.06 with Tc nearly 2.5I〈, coexisting with a CDW transition at 176K. Further Pd-doping enhances Tc, until it reaches the maximum value 2.84K at x=0.1, meanwhile the CDW transition vanishes. The upper critical field for the optimal doping sample Pdo.lNdSeTe2 is determined from the R-H measurement, which is estimated to be 0.6 T. These results provide another kind of ideal compound for studying the interplay between CDW and superconductivity systematically.
