Finite-temperature semimetal-insulator transition on the honeycomb lattice

A semimetal-insulator transition in the Hubbard model on the honeycomb lattice is studied by using the dynamical mean-field theory. Electrons in the honeycomb lattice resemble the Dirac electron liquid and for weak interactions the system is semimetal. With increasing the local interaction, a semimetal-insulator transition occurs. We find a nonanalytical structure of the phase transition which consists of a first-order transition line ending in a second-order transition point and high-temperature crossover line. A phase separation of semimetal and insulator occurs at low temperatures. Maxwell construction is performed to determine the first-order transition line. The phase diagram is also presented.