Tractable model for a fractionalized Fermi liquid (FL$^*$) on a square lattice

TL;DR

This paper introduces an analytically solvable microscopic model of a fractionalized Fermi liquid (FL*) on a square lattice, relevant to cuprates, featuring a Majorana Fermi surface and Fermi arcs.

Contribution

It presents a new solvable model of FL* with a Z2 spin liquid and Majorana fermions, elucidating Fermi surface reconstruction without symmetry breaking.

Findings

Identifies two phases: hybridized Fermi surface and decoupled fractionalized fermions.

Derives momentum-dependent coherence factors responsible for Fermi arcs.

Predicts a strong diamagnetic response and a divergent Sommerfeld coefficient at the pseudogap onset.

Abstract

Motivated by the continued interest in Fermi-surface reconstruction without symmetry breaking, we present an analytically tractable microscopic model of a fractionalized Fermi liquid (FL$^*$) on a square lattice and discuss its potential relevance to the cuprates. As in ancilla-qubit constructions, the model is related to Kondo lattice systems, but in this case, the conduction electrons interact with a $\mathbb{Z}_2$ spin liquid of the Yao--Lee type, with a Majorana Fermi surface. The associated $\mathbb Z_2$ gauge theory is static so that the model can be analytically solved to leading-logarithic accuracy. There are two phases: one in which the fractionalized fermions of the spin liquid hybridize with conduction electrons to form a common Fermi surface violating the naive Luttinger count, and one in which they remain decoupled. We discuss the salient features of the small Fermi-surface phase, including analytically derived momentum dependent coherence factors responsible for the appearance of Fermi arcs \`{a} la Yang-Rice-Zhang. We further discuss the impact of quantum and thermal fluctuations, including a strong diamagnetic response and a logarithmically divergent Sommerfeld coefficient at the onset of the pseudogap.