Quantum criticality in Ising chains with random hyperuniform couplings

TL;DR

This paper investigates quantum phase transitions in hyperuniform disordered Ising chains, revealing a spectrum of critical behaviors from infinite-randomness points to localized insulating states as disorder correlations vary.

Contribution

It introduces a one-parameter family of models with tunable disorder correlations, uncovering new critical phenomena and phases in quantum Ising chains with hyperuniform couplings.

Findings

Identified a line of infinite-randomness critical points with varying exponents for 0<α<1.

Discovered the critical Ising insulator phase for α>1, with localized excitations and suppressed transport.

Showed absence of Griffiths phases for α>0, contrasting with the α=0 case.

Abstract

We study quantum phase transitions in transverse-field Ising spin chains in which the couplings are random but hyperuniform, in the sense that their large-scale fluctuations are suppressed. We construct a one-parameter family of disorder models in which long-wavelength fluctuations are increasingly suppressed as a parameter $\alpha$ is tuned. For $\alpha = 0$, one recovers the familiar infinite-randomness critical point. For $0 < \alpha < 1$, we find a line of infinite-randomness critical points with continuously varying critical exponents; however, the Griffiths phases that flank the critical point at $\alpha = 0$ are absent at any $\alpha > 0$. When $\alpha > 1$, randomness is a dangerously irrelevant perturbation at the clean Ising critical point, leading to a state we call the critical Ising insulator. In this state, thermodynamics and equilibrium correlation functions behave as in the clean system. However, all finite-energy excitations are localized, thermal transport vanishes, and autocorrelation functions remain finite in the long-time limit. We characterize this line of hyperuniform critical points using a combination of perturbation theory, renormalization-group methods, and exact diagonalization.