Nonreciprocal transport in gate-induced polar superconductor SrTiO ₃

Abstract

Polar conductors/superconductors with Rashba-type spin-orbit interaction are potential material platforms for quantum transport and spintronic functionalities. One of their inherent properties is the nonreciprocal transport, where the rightward and leftward currents become inequivalent, reflecting spatial inversion/time-reversal symmetry breaking. Such a rectification effect originating from the polar symmetry has been recently observed at interfaces or bulk Rashba semiconductors, while its mechanism in a polar superconductor remains elusive. Here, we report the nonreciprocal transport in gate-induced two-dimensional superconductor SrTiO 3 , which is a Rashba superconductor candidate. In addition to the gigantic enhancement of nonreciprocal signals in the superconducting fluctuation region, we found kink and sharp peak structures around critical temperatures, which reflect the crossover behavior from the paraconductivity origin to the vortex origin, based on a microscopic theory. The present result proves that the nonreciprocal transport is a powerful tool for investigating the interfacial/polar superconductors without inversion symmetry, where rich exotic features are theoretically prognosticated.

SrTiO3—Glimpses of an Inexhaustible Source of Novel Solid State Phenomena

“…Moreover, nonreciprocal transport is observed, which reflects the ratio of odd versus even pairing interactions. A similar highlight was observed in a gate-induced 2D SC of interfacial STO [44]. Due to its Rashba-type spin orbit interaction, it reveals nonreciprocal transport, where the inequivalent rightward and leftward currents reflect simultaneous spatial inversion and time-reversal symmetry breaking-an exciting prospect of forthcoming research on STO.…”

Nonreciprocal superconducting NbSe2 antenna

“…These include superconducting non-centrosymmetric gated-MoS 2 12 , Bi 2 Te 3 /FeTe heterostructures 13 and MoGe/Y 3 Fe 5 O 12 bilayers 14 , where the nonreciprocal response is markedly enhanced by several orders of magnitude compared to non-superconducting systems due to the large energy scale difference between the Fermi energy and the superconducting gap 12 , 15 . Apart from being a powerful tool to study the interplay between superconductivity and chirality in non-centrosymmetric superconductors 6 , 16 , nonreciprocal charge transport also promises great potential in superconducting device applications such as vortex diodes 17 and flux lenses 18 , both of which are in great demand for future electrical circuits.…”

Nonreciprocal charge transport up to room temperature in bulk Rashba semiconductor α-GeTe

“…Such a UMR sparks a surge of interest in realizing two-terminal rectification, memory, and logic devices 7 , 14 , 15 . To date, more efforts to hunt for the materials with larger γ values by taking the spin–orbit interaction and Fermi energy into account are being made in interface/surface Rashba systems 9 , 15 , 16 . However, given the low Rashba spin splitting energy, e.g., 3 meV (~35 k B ) in LaAlO 3 /SrTiO 3 9 , 5 meV (~58 k B ) in Ge(111) 15 , nonreciprocal transport can only be observed at very low temperature, and here γ -value decreases dramatically with increasing temperature due to the thermal fluctuation.…”