Tuning the order of a deconfined quantum critical point

TL;DR

This paper investigates how adding certain terms to a Su-Schrieffer-Heeger model influences the nature of its quantum phase transition, showing that it can change from a deconfined quantum critical point to a first-order transition.

Contribution

It demonstrates that reinforcing antiferromagnetic order in a specific model can alter the quantum critical point from continuous to first order, independent of model symmetry.

Findings

Adding terms that favor AFM phase lowers the critical phonon frequency.

The transition becomes strongly first order with these modifications.

Results are robust across different model symmetries.

Abstract

We consider a Su-Schrieffer-Heeger model in the assisted hopping limit, where direct electron hopping is subdominant. At fixed electron-phonon coupling and in the absence of Coulomb interactions, the model shows a deconfined quantum critical point (DQCP) between a $(\pi,0)$ valence bond solid in the adiabatic limit and a quantum antiferromagnetic (AFM) phase at high phonon frequencies. Here, we show that by adding terms to the model that reinforce the AFM phase, thereby lowering the critical phonon frequency, the quantum phase transition becomes strongly first order. Our results do not depend on the symmetry of the model. In fact, adding a Hubbard-$U$ term to the model lowers the O(4) symmetry of the model to SU(2) such that the DQCP we observe has the same symmetries as other models that account for similar quantum phase transitions.