Temperature-driven change of Fermi surface has been attracting attention recently as it is fundamental and essential to understand a metallic system.We report the magnetotransport anomalies in the semimetal HfTe_(2) s...Temperature-driven change of Fermi surface has been attracting attention recently as it is fundamental and essential to understand a metallic system.We report the magnetotransport anomalies in the semimetal HfTe_(2) single crystals.The magnetoresistance behavior at high temperatures obeys Kohler's rule which can lead to the field-induced resistivity upturn behavior as observed.When the temperature is decreased to around 30 K,Kohler's rule becomes inapplicable,indicating the change of the Fermi surface in HfTe_(2).The Hall analyses and extended Kohler's plot reveal abrupt change of carrier densities and mobilities near 30 K.These results suggest that the chemical potential may shift as the temperature increases and the shift causes an electron pocket to vanish.Our work of the temperature-driven Lifshitz transition in HfTe_(2) is relevant to understanding of the transport anomalies and exotic physical properties in transition-metal dichalcogenides.展开更多
Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity...Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity has been discovered in Nd_(0.8)Sr_(0.2)NiO_(2)films.Herein,we report structural,electronic transport,magnetic,and thermodynamic characterizations of single crystals of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6).La_(3)Ni_(2)O_(7)is metallic with mixed Ni^(2+)and Ni^(3+)valent states.Resistivity measurements yield two transition-like kinks at~110 and 153 K.The kink at 153 K is further revealed from magnetization and specific heat measurements,indicative of the formation of charge and spin density waves.La_(3)Ni_(2)O_(6)single crystals obtained from the topochemical reduction of La_(3)Ni_(2)O_(7)are insulating and show an anomaly at~176 K on magnetic susceptibility.The transition-like behaviors of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6)are analogous to those observed in La_(4)Ni_(3)O_(10) and La_(4)Ni_(3)O_(8),suggesting that charge and spin density waves are a common feature in the ternary La-Ni-O system with mixed-valent states of nickel.展开更多
基金the National Natural Science Foundation of China(Grant Nos.21BAA01133,12004441,92165204,11974431,11774434,and U2130101)the Natural Science Foundation of Guangdong Province of China(Grant No.2023A1515010487)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011109)the Fundamental Research Funds for the Central Universities(Grant No.22hytd07).
文摘Temperature-driven change of Fermi surface has been attracting attention recently as it is fundamental and essential to understand a metallic system.We report the magnetotransport anomalies in the semimetal HfTe_(2) single crystals.The magnetoresistance behavior at high temperatures obeys Kohler's rule which can lead to the field-induced resistivity upturn behavior as observed.When the temperature is decreased to around 30 K,Kohler's rule becomes inapplicable,indicating the change of the Fermi surface in HfTe_(2).The Hall analyses and extended Kohler's plot reveal abrupt change of carrier densities and mobilities near 30 K.These results suggest that the chemical potential may shift as the temperature increases and the shift causes an electron pocket to vanish.Our work of the temperature-driven Lifshitz transition in HfTe_(2) is relevant to understanding of the transport anomalies and exotic physical properties in transition-metal dichalcogenides.
基金supported by the National Natural Science Foundation of China(Grant Nos.12174454,11904414,11904416,and U2130101)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011123)the National Key Research and Development Program of China(Grant Nos.2019YFA0705702,2020YFA0406003,2021YFA1400401,and 2021YFA0718900)。
文摘Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity has been discovered in Nd_(0.8)Sr_(0.2)NiO_(2)films.Herein,we report structural,electronic transport,magnetic,and thermodynamic characterizations of single crystals of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6).La_(3)Ni_(2)O_(7)is metallic with mixed Ni^(2+)and Ni^(3+)valent states.Resistivity measurements yield two transition-like kinks at~110 and 153 K.The kink at 153 K is further revealed from magnetization and specific heat measurements,indicative of the formation of charge and spin density waves.La_(3)Ni_(2)O_(6)single crystals obtained from the topochemical reduction of La_(3)Ni_(2)O_(7)are insulating and show an anomaly at~176 K on magnetic susceptibility.The transition-like behaviors of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6)are analogous to those observed in La_(4)Ni_(3)O_(10) and La_(4)Ni_(3)O_(8),suggesting that charge and spin density waves are a common feature in the ternary La-Ni-O system with mixed-valent states of nickel.
