Importance of subleading corrections for the Mott critical point

The interaction-induced metal-insulator transition should be in the Ising universality class. Experiments on layered organic superconductors suggest instead that the observed critical endpoint of the first-order Mott transition in d = 2 does not belong to any of the known universality classes for thermal phase transitions. In particular, it is found that delta = 2. Given the quantum nature of the two phases involved in the transition, we use dynamical mean-field theory and a cluster generalization to investigate whether the unusual exponents could arise as transient quantum behavior preceding the asymptotic critical behavior. In the cluster calculation, a canonical transformation that minimizes the sign problem in continuous-time quantum Monte Carlo calculations allows large improvements in accuracy. Our results show that there are important subleading corrections in the mean-field regime that can lead to an apparent exponent delta = 2. Experiments on optical lattices could verify our predictions for double occupancy.