Regensburg 2025 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 30: Quantum-Critical Phenomena (joint session TT/DY)

DY 30.11: Talk

Thursday, March 20, 2025, 12:15–12:30, H31

Tunable criticality and pseudo-criticality in a quantum dissipative spin system — •Manuel Weber — Institut für Theoretische Physik and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, Germany

The study of competing orders in two-dimensional quantum magnets was strongly motivated by the prediction of non-Landau quantum phase transitions, but often we found symmetry-enhanced first-order transitions or pseudocriticality with a logarithmic drift of critical exponents. Here we present results for a (0+1) dimensional spin-boson model where all of these phenomena occur due to a fixed-point annihilation within the critical manifold. Our recently-developed wormhole quantum Monte Carlo method for retarded interactions allows us to study the critical properties of this model with unprecedented precision. We find a tunable transition between two ordered phases that can be continuous or first-order, and even becomes weakly first-order in an extended regime close to the fixed-point collision. We provide direct numerical evidence for pseudo-critical scaling on both sides of the collision manifesting in an extremely slow drift of critical exponents. We also find scaling behavior at the symmetry-enhanced first-order transition as described by a discontinuity fixed point. Our study motivates future work in higher-dimensional quantum dissipative spin systems.

Keywords: quantum criticality; pseudo-criticality; fixed-point annihilation; spin-boson model; quantum Monte Carlo