Zeeman effect in superconducting two-leg ladders: irrational magnetization plateaus and exceeding the Pauli limit

TL;DR

This paper explores how magnetic fields influence superconducting two-leg ladders, revealing irrational magnetization plateaus, coexistence of triplet and singlet correlations, and mechanisms for surpassing the Pauli limit, supported by numerical analysis.

Contribution

It demonstrates the connection between irrational magnetization plateaus and magnetic resonant modes, and explains how the Pauli limit can be exceeded in these systems.

Findings

Irrational magnetization plateau at hole density

Coexistence of triplet and singlet correlations above plateau

Mechanism for exceeding the Pauli limit

Abstract

The effect of a parallel magnetic field on superconducting two-leg ladders is investigated numerically. The magnetization curve displays an irrational plateau at a magnetization equal to the hole density. Remarkably, its stability is fundamentally connected to the existence of a well-known magnetic resonant mode. Once the zero-field spin gap is suppressed by the field, pairs acquire a finite momentum characteristic of a Fulde-Ferrell-Larkin-Ovchinnikov phase. In addition, S^z=0 triplet superconducting correlations coexist with singlet ones above the irrational plateau. This provides a simple mechanism in which the Pauli limit is exceeded as suggested by recent experiments.