Quantum Annealed Criticality

Experimentally there exist several materials with classical first-order transitions that display quantum criticality, and here we provide a theoretical basis for this observed behavior. At a first-order transition the quartic mode-mode coupling of the effective action becomes negative. A common mechanism for this phenomenon, studied by Larkin and Pikin, involves the coupling of the critical energy density to the lattice; the singular nature of the specific heat drives the bulk modulus negative leading to a first-order transition. Here we generalize the Larkin-Pikin criterion in terms of response functions. Furthermore we show that if the T=0 quantum system lies above its upper critical dimension, the line of first-order transitions ends in a quantum critical point (continuous quantum phase transition). We discuss specific measurements to probe this behavior and also extensions to metallic systems.