Emergent $D_8^{(1)}$ spectrum and topological soliton excitation in CoNb$_2$O$_6$

TL;DR

This paper reveals that near a quantum critical point, CoNb$_2$O$_6$ exhibits an emergent $D_8^{(1)}$ spectrum with topological solitons, expanding understanding beyond the previously predicted $E_8$ structure.

Contribution

The study identifies a new $D_8^{(1)}$ Lie algebra spectrum and topological soliton excitations in CoNb$_2$O$_6$, challenging prior $E_8$ based predictions and broadening the scope of quantum critical phenomena.

Findings

The spectrum near the 1D QCP is characterized by the $D_8^{(1)}$ Lie algebra.

Robust topological soliton excitations are present in the spectrum.

The $D_8^{(1)}$ spectrum can be realized in various interacting quantum systems.

Abstract

Quantum integrability emerging near a quantum critical point (QCP) is manifested by exotic excitation spectrum that is organized by the associated algebraic structure. A well known example is the emergent $E_8$ integrability near the QCP of a transverse field Ising chain (TFIC), which was long predicted theoretically and initially proposed to be realized in the quasi-one-dimensional (q1D) quantum magnet CoNb$_2$O$_6$. However, later measurements on the spin excitation spectrum of this material revealed a series of satellite peaks that cannot be described by the $E_8$ Lie algebra. Motivated by these experimental progresses, we hereby revisit the spin excitations of CoNb$_2$O$_6$ by combining numerical calculation and analytical analysis. We show that, as effects of strong interchain fluctuations, the spectrum of the system near the 1D QCP is characterized by the $D_{8}^{(1)}$ Lie algebra with robust topological soliton excitation. We further show that the $D_{8}^{(1)}$ spectrum can be realized in a broad class of interacting quantum systems. Our results advance the exploration of integrability and manipulation of topological excitations in quantum critical systems.