Abstract for Seminar by Tasrief Surungan.




Tasrief Surungan
Hasanuddin University, Indonesia


Tuesday, October 26, 3.00pm,
Seminar Room, First Floor, Physics, University of Adelaide



Critical properties of 2D complex planar spin systems.



Abstract:

Critical properties of frustrated and diluted two-dimensional (2-d) discrete planar spin systems are studied using hybrid Monte Carlo methods. The analysis is based on the calculation of the ratio of the correlation functions which is more straightforward for probing critical behavior of 2-d systems. For the frustration, we study the antiferromagnet triangular (AFT) lattice and the Villain model of the square lattice, where The Kosterlitz-Thouless (KT) transition and the chiral transition were observed. Both transitions occur at slightly different temperatures. We found additional KT transition in the AFT at a lower temperature due to the discrete symmetry of the clock model. Our estimates of the decay exponents of correlation function at both KT transitions suggest that the KT transitions are universal even for the fully frustrated case. Meanwhile, for the critical phenomena of chiral transition, the exponent of correlation length suggests that the transition deviates from the Ising universality class. In diluted 6-state clock model, we observed a monotonic decrease of KT transition temperatures as the concentration of missing bonds increases. Only at the concentration very close to the percolation threshold are KT transitions completely ruled out. The decay exponents with various dilution concentrations indicate that the KT transitions of the diluted problem are in the same universality class as the pure case.


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