Emergent moments and random singlet physics in a Majorana spin liquid

TL;DR

This paper presents an exactly solvable SU(2) symmetric Majorana spin liquid model with quenched disorder, exhibiting random-singlet behavior and a distinctive low-temperature susceptibility, advancing understanding of disordered quantum spin liquids.

Contribution

It introduces a new exactly solvable model of a Majorana spin liquid with quenched disorder, demonstrating emergent random-singlet physics and specific susceptibility behavior.

Findings

Low-temperature susceptibility follows a specific power-law form with a Curie tail.

Disorder induces a random singlet phase similar to known spin chain systems.

Vacancy-induced spin textures contribute to intrinsic magnetic response.

Abstract

We exhibit an exactly solvable example of a SU(2) symmetric Majorana spin liquid phase, in which quenched disorder leads to random-singlet phenomenology. More precisely, we argue that a strong-disorder fixed point controls the low temperature susceptibility $\chi(T)$ of an exactly solvable $S=1/2$ model on the decorated honeycomb lattice with quenched bond disorder and/or vacancies, leading to $\chi(T) = {\mathcal C}/T+ {\mathcal D} T^{\alpha(T) - 1}$ where $\alpha(T) \rightarrow 0$ as $T \rightarrow 0$. The first term is a Curie tail that represents the emergent response of vacancy-induced spin textures spread over many unit cells: it is an intrinsic feature of the site-diluted system, rather than an extraneous effect arising from isolated free spins. The second term, common to both vacancy and bond disorder (with different $\alpha(T)$ in the two cases) is the response of a random singlet phase, familiar from random antiferromagnetic spin chains and the analogous regime in phosphorus-doped silicon (Si:P).