7003全讯入口“博约学术论坛”系列报告
第82期     (2016年第9期)

Title：Quantum Hall ferromagnetism in bilayer graphene and SnTe surface states
报告人：李潇 (Condensed Matter Theory Center, University of Maryland)
时   间：6月20日（周一）下午7：00
地   点：中心教学楼610
ABSTRACT
The interplay between topology and electron-electron interactions often give rise to novel states of matter. In the quantum Hall regime, because the bands are flat, the effect of interactions are much more pronounced, leading to the so-called quantum Hall ferromagnetic states. In this talk I will discuss two such examples.
The first story is about gapped bilayer graphene, where trigonal warping effects produced a novel bandstructure with a C3 rotational symmetry at low energies. As a result, the Landau levels are three-fold degenerate at small magnetic fields, while completely non-degenerate at large magnetic fields. I will also discuss how to visualize such a transition by using momentum mapping of the Landau levels.
The second story is about SnTe, a topological crystalline insulator. The (111) surface of SnTe hosts one isotropic Dirac surface states near the Γ valley, and three degenerate anisotropic ones centered around the M valley. I will show that a nematic phase with spontaneously broken C3 symmetry will occur in the presence of an external magnetic field when the three N = 0 Landau levels near the M valley are 1/3 or 2/3 filled.

Reference:
[1] X. Li, F. Zhang, and A. H. MacDonald, SU(3) Quantum Hall ferromagnetism in SnTe, Phys. Rev. Lett. 116, 026803 (2016).
Curriculum Vitae
Xiao Li received his B. S. from Peking University in 2008. He obtained his PhD in physics from The University of Texas at Austin working on quantum Hall effects in 2D systems including graphene and MoS2. He is currently a postdoc associate at the Condensed Matter Theory Center, University of Maryland. His current research interest is in novel states of matter that arise due to the interplay between disorder, electron-electron interaction, and topology.
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