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The rich landscape of orientational phases
报告人：Ke Liu，Ludwig Maximilian University of Munich
时间：10月10日（周二）10:30
单位：中科院物理研究所
地点：M830
The notion of spontaneous symmetry breaking plays a vital role in modern physics. It has been intensively applied in many fields to explore physical laws and to search for new states of matter. However, an obvious aspect has often been overlooked: a symmetry can spontaneously break down to any of its subgroups. Each of these subgroups corresponds to phases with distinctive long range orders. In this talk, I will attempt to give a perspective onto the great diversity of orientational phases by breaking O(n) symmetries, and discuss their relevance to both hard and soft condensed matter systems. This task actually exceeds the reach of standard Ginzburg-Landau theory, while lattice gauge theory is utilized. We will see how the latter can be adopted as a productive tool for classifying the tensor order parameter of those phases and studying the associated phase transitions, highlighting the relation between symmetries and fluctuations. Moreover, it also reveals a chiral liquid phase that is reminiscent of recent observations of experiments on crystal melting.
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Superconductivity mediated by quantum critical antiferromagnetic fluctuations: the rise and fall of hot spots
报告人：Rafael Fernandes，University of Minnesota
时间：10月11日（周三）10:30
单位：中科院物理研究所
地点：M830
In this talk, we present a combined analytical and sign-problem-free Quantum Monte Carlo investigation of the spin-fermion model – a widely studied low-energy model for the interplay between superconductivity and magnetic fluctuations. By engineering a series of band dispersions that interpolate between near-nested and open Fermi surfaces, and by also varying the strength of the spin-fermion interaction, we find that the hot spots of the Fermi surface provide the dominant contribution to the pairing instability in this model. We show that the analytical expressions for Tc and for the pairing susceptibility, obtained within a large-N Eliashberg approximation to the spin-fermion model, agree well with the Quantum Monte Carlo data, even in the regime of interactions comparable to the electronic bandwidth.
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Deforming PSL(n,R) Hitchin component and Goldman symplectic form
报告人：孙哲，YMSC Tsinghua
