Quantum wetting transitions in two dimensions: An alternative path to non-universal interfacial singularities

We consider two-dimensional $(d=2)$ systems with short-ranged microscopic interactions, where interface unbinding (wetting) transitions occur in the limit of vanishing temperature T. For T = 0 the transition is characterized by non-universal critical properties analogous to those established for thermal wetting transitions in d = 3, albeit with a redefined capillary parameter $\tilde{\omega }$. Within a functional renormalization-group treatment of an effective interfacial model, we compute the finite-temperature phase diagram, exhibiting a line of interface unbinding transitions, terminating at T = 0 with an interfacial quantum-critical point. We identify distinct scaling regimes, reflecting the interplay between quantum and thermal interfacial fluctuations. A crossover line marking the onset of the quantum-critical regime is described by the d = 3 interfacial correlation-length exponent ${\nu }_{||}$. This potentially opens another way to investigate the non-universal character of ${\nu }_{||}$. On the other hand, the emergent interfacial quantum-critical regime shows no signatures of non-universality. (letter)