Signatures of Temperature-Driven Lifshitz Transition in Semimetal Hafnium Ditelluride

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.

Superconductivity and Charge Density Wave in Iodine-Doped CuIr_(2)Te_(4)

We report a systematic investigation on the evolution of the structural and physical properties,including the charge density wave(CDW) and superconductivity of the polycrystalline CuIr_(2)Te_(4-x)Ix for 0.0 ≤x≤ 1.0.Xray diffraction results indicate that both of a and c lattice parameters increase linearly when 0.0 ≤ x ≤ 1.0.The resistivity measurements indicate that the CDW is destabilized with slight x but reappears at x≥0.9 with very high TCDW.Meanwhile,the superconducting transition temperature Tc enhances as x increases and reaches a maximum value of around 2.95 K for the optimal composition CuIr_(2)Te_(1.9)I_(0.1) followed by a slight decrease with higher iodine doping content.The specific heat jump(ΔC/γTc) for the optimal composition CuIr_(2)Te_(3.9)I_(0.1) is approximately 1.46,which is close to the Bardeen-Cooper-Schrieffer value of 1.43,indicating that it is a bulk superconductor.The results of thermodynamic heat capacity measurements under different magnetic fields |Cp(T,H)],magnetization M(T,H) and magneto-transport ρ(T,H) measurements further suggest that CuIr_(2)Te_(4-x)Ix bulks are type-Ⅱ superconductors.Finally,an electronic phase diagram for this CuIr_(2)Te_(4-x)Ix system has been constructed.The present study provides a suitable material platform for further investigation of the interplay of the CDW and superconductivity.