报告题目：Topological excitations in frustrated lattices

报告人：  张学锋 博士

Technical University of Kaiserslautern, Germany

时间：  2015.9.7  上午9：00

地点：  理论物理研究所报告厅

 

 

abstract：We analyze the repulsive hard core bosons in the optical kagome lattice with cylindrical boundary condition [1]. By using quantum Monte Carlo (QMC) simulations and an effective single string excitation model, we found that fractional charges can be excited in this system. Depending on their chiralities, they exist on different edges to form an edge liquid phase. Meanwhile, the strings between them fluctuate in the bulk. These results not only show a possible proposal to find the fractional charge and string excitations in optical lattice systems [2], but also shed a light on understanding the spin liquid phase in condensed matter physics. Meanwhile, the string type topological excitaion is not limited to the kagome system, but also in the triangular lattice. Recently, we investigate the XXZ model on the triangular lattice with anisotropic ferromagnetic xy coupling and antiferromagnetic z coupling [3]. In previous studies, an incommensurate supersolid phase was found when introducing anisotropy of interactions in different directions [4]. However, the mechanism of the incommensurate phase is still unknown. In the strong coupling region where interactions in the z direction are larger than in the xy plane, we found that quantum fluctuation of domain wall excitations can reduce the energy and cause the incommensurate order. By using QMC simulations, we confirmed our theoretical analysis and found that the number of domain walls and the incommensurate k-vector      monotonically increase with the anisotropy.     

[1] X.-F. Zhang and S. Eggert, Phys. Rev. Lett. 111, 147201 (2013)     

[2] X.-F. Zhang, T.Wang, S. Eggert, andA. Pelster, Phys. Rev. B 92, 014512 (2015)     

[3] X.-F. Zhang, S.-J. Hu,A. Pelster, and S. Eggert, in preparation.     

[4] S. V. Isakov, et al. EPL, 87 36002 (2009)