Deconfined quantum phase transition on the kagome lattice: Distinct velocities of spinon and string excitations

TL;DR

This paper numerically demonstrates that in a deconfined quantum phase transition on the kagome lattice, spinon and string excitations exhibit distinct velocities, challenging existing theories of Lorentz symmetry in such transitions.

Contribution

It reveals the existence of two different excitation velocities in a DQPT on the kagome lattice, indicating a breakdown of conventional Lorentz-invariant theories.

Findings

Two linear dispersions with different velocities were observed.

The results negate the possibility of emergent Lorentz symmetry.

The velocities may correspond to fractional excitations and quantum strings.

Abstract

Deconfined quantum phase transition (DQPT) provides an extraordinary possibility of the quantum phase transition beyond the Ginzburg-Landau paradigm, which is interwoven with numerous exotic phenomena of the strongly correlated quantum many-body system, e.g. fractional excitation, emergent symmetries, and gauge field. However, various candidates of DQPT have been demonstrated to be weakly first-order, and the conformal field theory (CFT) has to be altered into a non-unitary one. Here we numerically found two linear dispersions with different velocities in one of the few survivors of DQPT -- the extended hard-core Bose-Hubbard model on the Kagome lattice. Such counterintuitive results directly lead to the negation of possible emergent Lorentz symmetry, and the breakdown of conventional theory of DQPT. Furthermore, the snapshots of boson configuration hint that these two velocities may correspond to the dynamics of the fractional excitations and quantum strings, respectively. Our work will inspire the revisit of the theory of DQPT and benefit the field of quantum materials and quantum simulations.