Berlin 2018 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 88: Quantum-Critical Phenomena III
TT 88.6: Vortrag
Donnerstag, 15. März 2018, 12:45–13:00, H 3010
Emergent symmetry in quantum critical Dirac systems — •Lukas Janssen1, Igor F. Herbut2, and Michael M. Scherer3 — 1Institut für Theoretische Physik, Technische Universität Dresden, Germany — 2Department of Physics, Simon Fraser University, Burnaby, Canada — 3Institut für Theoretische Physik, Universität Köln, Germany
Within the standard Landau-Ginzburg paradigm, O(N) symmetry, when not present explicitly on the microscopic level, can emerge dynamically at some critical point only for small N < 3. We show that this classical conclusion becomes severely overturned in the presence of gapless fermion degrees of freedom. We study the quantum multicritical point in 2+1D Dirac systems between the semimetallic phase and two ordered phases that are characterized by anticommuting mass terms with O(N1) and O(N2) symmetry, respectively. Using є expansion around the upper critical space-time dimension of four, we demonstrate that the multicritical point is characterized by an emergent O(N1+N2) symmetry for arbitrary values of N1 and N2 and fermion flavor numbers Nf, as long as the corresponding representation of the Clifford algebra exists. Put differently, small O(N)-breaking perturbations near the chiral O(N) fixed point are irrelevant for all N > 1.