Spin-triplet pair density wave superconductors

TL;DR

This paper theoretically demonstrates the emergence of a spin-triplet pair density wave in a one-dimensional superconductor model with spin-orbit coupling, revealing its topological properties and potential relevance to experimental observations.

Contribution

It provides the first concrete theoretical model of a pure spin-triplet PDW state in a 1D superconductor with spin-orbit coupling, showing its topological nature and experimental relevance.

Findings

Spin-triplet PDW emerges in the ground state of the model.

The t-PDW state is fully gapped and topologically nontrivial.

Majorana zero modes are localized at the chain ends.

Abstract

Recent experiments have shown that the nonzero center of mass momentum pair density wave (PDW) is a widespread phenomenon observed over different superconducting materials. However, concrete theoretical model realizations of the PDW order have remained elusive. Here, we study a one-dimensional model with nearest-neighbor pairing attraction, i.e. a spinful Kitaev chain, under generic spin-orbit couplings such that the spin-rotation symmetry is fully broken. The most general superconducting order parameter is described by a spatial dependent $\mathbf{d}_i$-vector. We show that a spin-triplet pair density wave (t-PDW) emerges in the ground state and occupies a large part of the phase diagram. The $\mathbf{d_i}$-vector of the t-PDW rotates with a pitch $Q_{\rm pdw}$ along the chain and spans an ellipsoid. The pure t-PDW is fully gapped and realizes a class-DIII topological superconductor, characterized by two Majorana zero modes localized at each end of the chain and protected by time-reversal symmetry. Our findings reveal unprecedented insights into the exotic pure PDW superconductor and provide a possible explanation for the one-dimensional PDW detected along domain walls in monolayer iron-based superconductor Fe(Te,Se) and potentially realizable using other quantum structures in unconventional superconductors.