arXiv subjects

Yoichi Tanabe

Publications and source records attributed to Yoichi Tanabe.

22 records · Page 2Linked to original sources

arXiv2011

Evidence for line nodes in the energy gap of the overdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ from low-temperature specific heat measurements

Low-temperature specific heat (SH) is measured on Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ single crystals in a wide doping region under different magnetic fields. For the overdoped sample, we find the clear evidence for the presence of $T^2$ term in the data, which is absent both for the underdoped and optimal doped samples, suggesting the presence of line nodes in the energy gap of the overdoped samples. Moreover, the field induced electron specific heat coefficient $Δγ(H)$ increases more quickly with the field for the overdoped sample than the underdoped and optimal doped ones, giving another support to our arguments. Our results suggest that the superconducting gap(s) in the present system may have different structures strongly depending on the doping regions.

cond-mat.supr-con↗

arXiv2011

Electron and hole Dirac cone states in-pairs in Ba(FeAs)$_2$ confirmed by magnetoresistance

The quantum transport of Dirac cone states in the iron pnictide Ba(FeAs)$_2$ with a d-\,multiband system is studied by using single crystal samples. The transverse magnetoresistance develops linearly against magnetic field at low temperatures. The transport phenomena are interpreted in terms of the 0$^{th}$ Landau level by applying the theory predicted by Abrikosov. The results of the semiclassical analyses of a two carrier system under low magnetic field limit show that both electron and hole reside as the high mobility states, being indicative to the fact that both electron- and hole Dirac cone states should be taken into account in pairs for having the real interpretation of low temperature electronic states in iron pnictides, being in contrast to the previous reports.

cond-mat.str-el↗

arXiv2010

Change of the Ground State upon Hole Doping Unveiled by Ni Impurity in High-$T_{\rm c}$ Cuprates

The electronic ground state in high-$T_{\rm c}$ cuprates where the superconducting state is suppressed by Ni substitution has been investigated in La$_{2-x}$Sr$_x$Cu$_{1-y}$Ni$_y$O$_4$ from the specific heat and muon spin relaxation measurements. It has been found that the ground state changes from a magnetically ordered state with the strong hole-trapping by Ni to a metallic state with the Kondo effect of Ni with increasing hole-concentration. Moreover, the analysis of the results has revealed that a phase separation into the magnetically ordered phase and the metallic phase occurs around the boundary of two phases.

cond-mat.supr-con↗

arXiv2007

Magnetic-field-induced enhancement of the vortex pinning in the overdoped regime of La$_{2-x}$Sr$_x$CuO$_4$ : Relation to the microscopic phase separation

In order to investigate the inhomogeneity of the superconducting (SC) state in the overdoped high-$T_{\rm c}$ cuprates, we have measured the magnetic susceptibility, $χ$, of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) single crystals in the overdoped regime in magnetic fields parallel to the c-axis up to 7 T on warming after zero-field cooling. It has been found for $x$ = 0.198 and 0.219 that the temperature dependence of $χ$ in 1 T shows a plateau, that is, $χ$ is almost independent of temperature in a moderate temperature-range in the SC state. Moreover, a so-called second peak in the magnetization curve has markedly appeared in these crystals. These results indicate an anomalous enhancement of the vortex pinning and strongly suggest the occurrence of a $microscopic$ phase separation into SC and normal-state regions in the overdoped high-$T_{\rm c}$ cuprates.

cond-mat.supr-con↗