A polar conductor with Rashba-type 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, due to 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]. Here we have report nonreciprocal transport in polar superconductivity achieved in gated SrTiO₃. We found the gigantic enhancement in the nonlinear resistance in the amplitude and phase fluctuation regions [5]. Also, we discuss possible origins of nonreciprocity in the 2D Rashba superconductor, such as paraconductivity with a parity mixing in the Cooper pairs and rectified vortex motions.
[1] E. Lesne et al., Nat. Mater. 15, 1261–1266 (2016).
[2] R. Ohshima et al., Nat. Mater. 16, 609–614 (2017).
[3] P. He et al., Phys. Rev. Lett. 120, 266802 (2018).
[4] T. Ideue et al., Nat. Phys. 13, 578–584 (2017).
[5] Y. M. Itahashi et al., Sci. Adv. 6, eaay9120 (2020).