A polar conductor with Rashba spin-orbit coupling is a potential material platform for exotic quantum transport and spintronic functionalities [1,2]. One of their inherent properties is the nonreciprocal transport, where the magnetoresistance becomes inequivalent between the rightward and leftward current directions, because of the breaking of both spatial inversion and time reversal symmetries. Such a rectification effect reflecting polar symmetry has been studied at the interface or bulk polar semiconductor [3,4]. However, the mechanism of the nonreciprocity in a polar superconductor remains elusive.
To elucidate the noncentrosymmetric nature of the Rashba superconductor, we have investigated the nonreciprocal transport in gated SrTiO₃, which is known as a 2D Rashba superconductor. We found the gigantic enhancement in the nonlinear resistance in the amplitude and phase fluctuation regions. Also, we discuss the possible origins of nonreciprocity in the 2D Rashba superconductor, such as paraconductivity with a parity mixing in the Cooper pairs and rectified vortex-antivortex motions.
[1] E. Lesne et al., Nat. Mater. 15, 1261 (2016).
[2] R. Ohshima et al., Nat. Mater. 16, 609 (2017).
[3] P. He et al., Phys. Rev. Lett. 120, 266802 (2018).
[4] T. Ideue et al., Nat. Phys. 13, 578 (2017).