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

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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 ω. 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. At finite T 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 ν||. This opens a new way to investigate the non-universal character of ν|| without penetrating the true critical regime. On the other hand, the emergent interfacial quantum critical regime shows no signatures of non-universality.