Prof. Dietmar Ebert, Humboldt-University, Berlin

Phase transitions in hexagonal, graphen-like lattice sheets and nanotubes

This talk considers a class of (2+1)D schematic models with four-fermion interactions that are effectively used in studying condensed-matter systems with planar structure, and especially graphene. Symmetry breaking in these models occurs due to a possible appearance of condensates. Condensates as well as fermion-antifermion exciton bound states are calculated. Moreover, nanotubes with corresponding boundary conditions are considered and their relation with the effect of an applied external magnetic field is discussed. To study phase transitions, the effective potential for the nanotube model including effects of finite temperature, density and an external magnetic field is calculated. Finally, the phase structure of the nanotube model under the influence of the Aharonov-Bohm effect is considered.