Superconductivity from a confinement transition out of a fractionalized Fermi liquid with $\mathbb{Z}_2$ topological and Ising-nematic orders

TL;DR

This paper explores how doping a $ ext{Z}_2$ spin liquid on a frustrated square lattice can lead to a fractionalized Fermi liquid and a subsequent transition into a modulated superconducting state, revealing new insights into unconventional superconductivity.

Contribution

It introduces a fermionic spinon description of the $ ext{Z}_2$ spin liquid and describes a Higgs transition to a modulated superconducting phase, connecting topological order with superconductivity.

Findings

Stable $ ext{Z}_2$ spin liquid with Ising-nematic order identified.

Doping leads to a fractionalized Fermi liquid with small Fermi pockets.

Transition to a modulated superconducting state via Higgs mechanism described.

Abstract

The Schwinger-boson theory of the frustrated square lattice antiferromagnet yields a stable, gapped $\mathbb{Z}_2$ spin liquid ground state with time-reversal symmetry, incommensurate spin correlations and long-range Ising-nematic order. We obtain an equivalent description of this state using fermionic spinons (the fermionic spinons can be considered to be bound states of the bosonic spinons and the visons). Upon doping, the $\mathbb{Z}_2$ spin liquid can lead to a fractionalized Fermi liquid (FL*) with small Fermi pockets of electron-like quasiparticles, while preserving the $\mathbb{Z}_2$ topological and Ising-nematic orders. We describe a Higgs transition out of this deconfined metallic state into a confining superconducting state which is usually of the Fulde-Ferrell-Larkin-Ovchinnikov type, with spatial modulation of the superconducting order.