Finite-Momentum Pairing State in Unconventional Rashba Systems

TL;DR

This paper predicts a finite-momentum pairing state in unconventional Rashba systems without external magnetic fields, explaining recent experimental observations and proposing detection methods via Josephson effects.

Contribution

It introduces a microscopic model for phase transition to finite-momentum pairing and highlights the role of multi-orbital degrees of freedom in these states.

Findings

Finite-momentum pairing can occur without magnetic fields.

Coexistence of zero-momentum and LO-type pairings explains PDW states.

Detection via Josephson current measurements is feasible.

Abstract

In systems with unconventional Rashba bands, we propose that a finite-momentum pairing state can emerge without the need for an external magnetic field. We analyze the phase transition from a zero-momentum Bardeen-Cooper-Schrieffer (BCS) state to a finite-momentum pairing state using a microscopic interaction model. We demonstrate that the coexistence of zero-momentum and Larkin-Ovchinnikov (LO)-type pairings in different channels provides a well understanding of recent experimental observations of pair-density-wave (PDW) states. Furthermore, we propose that an s-wave BCS superconductor-unconventional Rashba metal (SC-URM) junction can generate an LO-type pairing state via an orbital-selective proximity effect. This nontrivial state can be detected by measuring the Josephson current in an SC-URM-SC junction or through Josephson scanning tunneling microscopy/spectrosscopy (JSTM/S). Our results reveal that the internal multi-orbital degrees of freedom play a crucial role in facilitating finite-momentum pairing states.