Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 47: Correlated Electrons: Spin Systems and Itinerant Magnets 2
TT 47.9: Vortrag
Freitag, 30. März 2012, 11:45–12:00, H 0104
Unconventional phase transition in the classical triangular-lattice Heisenberg antiferromagnet in applied magnetic field — •Luis Seabra1, Tsutomu Momoi2, Philippe Sindzingre3, and Nic Shannon4 — 1Max-Planck-Institut für Physik komplexer System, Dresden, Germany — 2Condensed Matter Theory Laboratory, RIKEN, Wako, Japan — 3LPTMC, Université P. et M. Curie, Paris, France — 4H. H. Wills Physics Laboratory, University of Bristol, U. K.
The classical Heisenberg antiferromagnet on a two-dimensional triangular lattice is a paradigmatic problem in frustrated magnetism. Its ``120 degree" classical ground state gives rise to three distinct low-temperature phases under the combined effect of magnetic field and thermal fluctuations. However, many of the details of the magnetic phase diagram remain surprisingly obscure. We address this problem using modern Monte Carlo simulation techniques. At low to intermediate values of magnetic field, we find evidence for a continuous three-state Potts phase transition from the paramagnet into the one-third magnetisation plateau. We also find evidence for conventional Kosterlitz-Thouless transitions from the magnetisation plateau into the canted ``Y-state", and into the 2:1 canted phase. However, at higher fields, the phase transition from the paramagnet into the 2:1 canted phase, while continuous, does not appear to fall into any conventional universality class, being instead described by continuously varying exponents. We argue that this deserves further study as an interesting example of a finite-temperature phase transition with compound order-parameter symmetry.