arXiv subjects

Hechang Lei

Publications and source records attributed to Hechang Lei.

187 records · Page 11Linked to original sources

arXiv2011

Anisotropy in transport and magnetic properties of K0.64Fe1.44Se2

We report a study of anisotropy in transport and magnetic properties of K0.64Fe1.44Se2.00 single crystals. The anisotropy in resistivity is up to one order of magnitude between 1.8 K and 300 K. Magnetic susceptibility exhibits weak temperature dependence in the normal state with decrease in temperature with no significant anomalies. The lower critical fields Hc1 of K0.64Fe1.44Se2.00 are only about 3 Oe and the anisotropy of Hc1,c/Hc1,ab is about 1. The critical currents for H||ab and H||c are about 10-10^3 A/cm2, smaller than in iron pnictides and in FeTe_{1-x}Se_{x} and nearly isotropic.

cond-mat.supr-con↗

arXiv2011

Spin glass behavior of insulating K0.8Fe2-xS2

We report the discovery of KxFe2-yS2 single crystals, isostructural to KxFe2-ySe2 superconductors. The sulfide compound is a small gap semiconductor and shows spin-glass behavior below 32 K. Our results indicate that stoichiometry, defects, and the local environment of FeCh (Ch = S,Se) tetrahedra have important effects on the physical properties of isostructural and isoelectronic KxFe2-yCh2 compounds.

cond-mat.supr-con↗

arXiv2011

Evolution of correlation strength in KxFe(2-y)Se2 superconductor doped with S

We report the evolution of thermal transport properties of iron-based superconductor K$_x$Fe$_{2-y}$Se$_2$ with sulfur substitution at Se sites. Sulfur doping suppresses the superconducting $T_c$ as well as the Seebeck coefficient. The Seebeck coefficient of all crystals in the low temperature range can be described very well by diffusive thermoelectric response model. The zero-temperature extrapolated value of Seebeck coefficient divided by temperature $S/T$ gradually decreases from $-0.48 μV/K^2$ to a very small value $\sim$ 0.03 $μ$V/K$^2$ where $T_c$ is completely suppressed. The normal state electron Sommerfeld term ($γ_n$) of specific heat also decreases with the increase of sulfur content. The dcrease of $S/T$ and $γ_n$ reflects a suppression of the density of states at the Fermi energy, or a change in the Fermi surface that would induce the suppression of correlation strength.

cond-mat.supr-con↗

arXiv2011

Thermoelectric studies of KxFe2-ySe2: weakly correlated superconductor

We report thermal transport measurement of KxFe2-ySe2 superconducting single crystal. Significant peak anomaly in thermal conductivity is observed at nearly TC/2 indicating a large phonon mean-free-path in the superconducting state. The zero-temperature extrapolated thermoelectric power is smaller than the value in typical strongly correlated superconductors, implying large normalized Fermi temperature. In contrast to other iron superconductors, thermoelectric power in our sample does not exhibit significant anomalies. These findings indicate that KxFe2-ySe2 is a weakly or intermediately correlated superconductor without significant Fermi surface nesting.

cond-mat.supr-con↗

arXiv2010

Thermally activated energy and flux flow Hall effect of Fe1+y(Te1-xSx)z

Thermally activated flux flow (TAFF) and flux flow Hall effect (FFHE) of Fe(Te,S) single crystal in the mixed state are studied in magnetic fields up to 35 T. Thermally activated energy (TAE) is analyzed using conventional Arrhenius relation and modified TAFF theory which is closer to experimental results. The results indicate that there is a crossover from single-vortex pinning region to collective creep pinning region with increasing magnetic field. The temperature dependence of TAE is different for H//ab and H//c. On the other hand, the analysis of FFHE in the mixed state indicates that there is no Hall sign reversal. We also observe scaling behavior |Rhoxy(H)| = A*Rhoxx(H)^beta.

cond-mat.supr-con↗

arXiv2010

Pauli-limited upper critical field in Fe1+yTe1-xSex

In this work we investigated the temperature dependence of the upper critical field u0Hc2(T) of Fe1.02(3)Te0.61(4)Se0.39(4) and Fe1.05(3)Te0.89(2)Se0.11(2) single crystals by measuring the magnetotransport properties in stable dc magnetic fields up to 35 T. Both crystals show that u0Hc2(T) in the ab-plane and along the c-axis exhibit saturation at low temperatures. The anisotropy of u0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic when the temperature T->0. Furthermore, u0Hc2(0) deviates from the conventional Werthamer-Helfand-Hohenberg (WHH) theoretical prediction values for both field directions. Our analysis indicates that the spin-paramagnetic pair-breaking effect is responsible for the temperature-dependent behavior of u0Hc2(T) in both field directions.

cond-mat.supr-con↗

arXiv2010

Effects of excess Fe on upper critical field and magnetotransport in Fe1+y(Te1-xSx)z

We have investigated the upper critical field anisotropy and magnetotransport properties of Fe1.14(1)Te0.91(2)S0.09(2) single crystals in stable magnetic fields up to 35 T. The results show that u0Hc2(T) along the c axis and in the ab-plane exhibit saturation at low temperatures. The anisotropy of u0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic for T->0. Our analysis indicates that the spin-paramagnetic pair-breaking with spin-orbital scattering is responsible for the behavior of u0Hc2(T). Furthermore, from analysis of the normal state properties, we show evidence that the excess Fe acting as Kondo-type impurities is a key factor determining the normal and superconducting state physical properties.

cond-mat.supr-con↗