Dissipative Random Quantum Ashkin-Teller Model Exhibits Smearing of Three Out of Three Phase Transitions

The interplay between disorder and dissipation profoundly impacts phase transitions in complex systems, and researchers are now revealing how these forces combine to alter critical behaviour. Pedro S. Farinas from the Universidade de São Paulo, Rajesh Narayanan from the Indian Institute of Technology Madras, and José A. Hoyos, also from the Universidade de São Paulo, investigate this phenomenon within a generalized version of the random Ashkin-Teller model. Their work demonstrates that introducing dissipation alongside inherent disorder effectively blurs the boundaries of two out of three critical points, fundamentally altering the system’s behaviour. Importantly, the team’s analytical theory explains why one critical point remains distinct, revealing a delicate balance where dissipation effects cancel, preserving the system’s unique characteristics and offering new insights into the nature of phase transitions in disordered environments.

By extending the strong-disorder renormalization group technique, the team investigates how dissipation alters the typical critical behaviour observed in isolated quantum systems, revealing that even weak dissipation can significantly modify the critical properties and universality class of the system.

Through adiabatic renormalisation, the team explored a model with three phases and three quantum phase transitions, demonstrating that the combined effect of Ohmic dissipation and quenched disorder smears two of these transitions. Their analytical theory explains why one transition remains sharp, attributing this to a cancellation of dissipation effects arising from the intertwined order parameter of one of the phases.

Disorder and Interactions Drive Quantum Phase Transitions

This research explores the behaviour of materials where atomic arrangements are not perfectly regular, leading to unique and unpredictable electronic properties. Scientists investigate quantum phase transitions, which occur at zero temperature and are driven by quantum fluctuations, and how these transitions are affected by disorder and interactions between electrons, employing the strong-disorder renormalization group to analyse these strongly disordered systems. Through a combination of strong-disorder renormalization group and adiabatic renormalization techniques, scientists demonstrate that the interplay of Ohmic dissipation and quenched disorder significantly alters the phase transitions within the model, specifically blurring two out of three critical points.

The findings reveal that dissipation selectively smears the transition between the product and ferromagnetic phases, leaving the transition between the product and paramagnetic phases unaffected, a robustness that persists regardless of the specific form of the system-bath coupling.