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 new 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 previously unattainable precision. Our results show that there are important subleading corrections in the mean-field regime that can lead to an {\it apparent} exponent $\delta=2$. Experiments on optical lattices could verify our predictions for double occupancy. P. S\'emon and A.-M.S. Tremblay, Phys. Rev. B 85, 201101(R)/1-5 (2012).