Parity-violating current-voltage curves in a single domain of Sr2RuO4 superconductors

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Abstract

We have found parity-violating current-voltage (IV) curves in a single domain of Sr2RuO4 superconductors. The induced voltage V is an even function of bias current I below superconducting transition temperature. The anomalous IV curves show that positive voltage is detected regardless of the current direction. The result implies the parity violation of IV curves.

Introduction

Anisotropic superconductors [1], [2], [3] stimulate much interest in a nontrivial order parameter field. Since the internal degrees of freedom of the order parameter provide domain configurations, the experimental data of millimeter-scale superconductors could be considered as a result of ensemble-averaging over domain configurations. Sr2RuO4 crystals form domains with different chirality by the angular momentum of Cooper pairs [2]. The size of a single chiral order parameter domain is suggested to be 150μm. Thus, it is important to extract peculiar effects by measuring the only single domain. However, transport measurements of the single domain are still limited [4].

Section snippets

Experiment

Sr2RuO4 crystals were grown with a solid-phase reaction. The samples were dispersed in dichloroethane by sonication and deposited on an oxidized Si substrate. We selected microscale Sr2RuO4 single crystals from the chemical composition and crystallinity. We confirmed that the dispersed crystals had no boundaries nor ruthenium inclusions on the surface by observing the crystal orientation using the electron backscatter diffraction pattern. On the analyzed samples, we fabricated gold electrodes

Result and discussion

We observed anomalous the IV curves in zero magnetic field. Fig. 1(b) shows IV curves at temperatures with typical flat tail resistances of R*0.16Ω. The transition temperature Tc is 1.69 K. Finite resistivity shows the flow of vortices due to quantum fluctuations of the phase. In general, the voltage in IV curves for metals, quantum Hall systems and Josephson junction is always odd function of bias current (i.e., change signs under the space inversion), which is a result of parity

Summary

We studied the transport properties in a chiral single domain of microscale Sr2RuO4 single crystals. Sr2RuO4 single crystals were selected by detailed analyses. Gold electrodes were attached durably by welding with electron beam irradiation. The parity-violating IV curves were observed.

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