arXiv subjects

K. Yada

Publications and source records attributed to K. Yada.

3 recordsLinked to original sources

arXiv2019

Identification of Spin-Triplet Superconductivity through a Helical-Chiral Phase Transition in Sr$_2$RuO$_4$ Thin-Films

Despite much effort for over the two decades, the paring symmetry of a Sr$_2$RuO$_4$ superconductor has been still unclear. In this Rapid Communication, motivated by the recent rapid progress in fabrication techniques for Sr$_2$RuO$_4$ thin-films, we propose a promising strategy for identifying the spin-triplet superconductivity in the thin-film geometry by employing an antisymmetric spin-orbit coupling potential and a Zeeman potential due to an external magnetic field. We demonstrate that a spin-triplet superconducting thin-film undergoes a phase transition from a helical state to a chiral state by increasing the applied magnetic field. This phase transition is accompanied by a drastic change in the property of surface Andreev bound states. As a consequence, the helical-chiral phase transition, which is unique to the spin-triplet superconductors, can be detected through a sudden change in a tunneling conductance spectrum of a normal-metal/superconductor junction. Importantly, our proposal is constructed by combining fundamental and rigid concepts regarding physics of spin-triplet superconductivity.

cond-mat.supr-con↗

arXiv2015

The Josephson current in Fe-based superconducting junctions: theory and experiment

We present theory of dc Josephson effect in contacts between Fe-based and spin-singlet $s$-wave superconductors. The method is based on the calculation of temperature Green's function in the junction within the tight-binding model. We calculate the phase dependencies of the Josephson current for different orientations of the junction relative to the crystallographic axes of Fe-based superconductor. Further, we consider the dependence of the Josephson current on the thickness of an insulating layer and on temperature. Experimental data for PbIn/Ba$_{1-x}$K$_{x}$(FeAs)$_2$ point-contact Josephson junctions are consistent with theoretical predictions for $s_{\pm}$ symmetry of an order parameter in this material. The proposed method can be further applied to calculations of the dc Josephson current in contacts with other new unconventional multiorbital superconductors, such as $Sr_2RuO_4$ and superconducting topological insulator $Cu_xBi_2Se_3$.

cond-mat.supr-con↗

arXiv2014

Anomalous surface states at interfaces in p-wave superconductors

We present the results of theoretical study of surface state properties in a two-dimensional model for triplet $p$-wave superconductors. We derive boundary conditions for Eilenberger equations at rough interfaces and develop the approach for self-consistent solution for the spatial dependence of $p_{x}$ and $p_{x}+i~p_{y}$ -wave pair potentials. In the $p_{x}$ case we demonstrate the robustness of the zero-energy peak in the density of states (DoS) with respect to surface roughness, in contrast to the suppression of such a peak in the case of $d_{xy}$ symmetry. This effect is due to stability of odd-frequency pairing state at the surface with respect to disorder. In the case of the chiral $p_{x}+i~p_{y}$ state we demonstrate the appearance of a complex multi-peak subgap structure in the spectrum with increasing surface roughness.

cond-mat.supr-con↗