Dynamical Spectral Function of the Kagome Quantum Spin Liquid

TL;DR

This paper uses advanced tensor-network methods to compute the dynamical spectral function of the kagome Heisenberg model, revealing spectral signatures of a gapless U(1) Dirac spin liquid phase.

Contribution

It provides the first full dynamical spectral function of the kagome quantum spin liquid using tensor-network techniques, bridging theory and experiment.

Findings

Strong spin-wave renormalization as J2 decreases

Flattening and merging of modes into a continuum

Identification of the gapless U(1) Dirac spin liquid

Abstract

Quantum spin liquids (QSLs) host exotic fractionalized magnetic and gauge-field excitations whose microscopic origins and experimental verification remain frustratingly elusive. In the absence of static magnetic order, the spin excitation spectrum constitutes the crucial probe of QSL behavior, but its theoretical computation remains a serious challenge. Here we employ state-of-the-art tensor-network methods to obtain the full dynamical spectral function of the $J_1$-$J_2$ kagome Heisenberg model and benchmark our results by tracking their evolution across the magnetically ordered and QSL phases. Reducing $|J_2|/J_1$ causes increasingly strong spin-wave renormalization, flattening these modes then merging them into a continuum characteristic of deconfined spinons at all finite energies in the QSL. The low-energy continuum and the occurrence of gap closure at multiple high-symmetry points identify this gapless QSL as the U(1) Dirac spin liquid. These results establish a unified understanding of spin excitations in highly frustrated quantum magnets and provide clear spectral fingerprints for experimental detection in candidate kagome QSL materials.