Topic: Tutorial session: Physics in graphene (Part I and Part II)

Speaker: Xiao Li (李潇)

　　　　 Department of Physics, University of Texas, Austin, USA

Time: 14:30-16:00 PM (Part I),  Jul. 24 (Wed.), 2013

　　　09:30-11:00 AM (Part II), Jul. 25 (Thur.), 2013

Venue: Room 457, Lee Hsun Building, IMR CAS

Welcome to attend！

Abstract:

In this tutorial, I will provide relevant background information for my talk “Quantum Hall and Many-body physics in graphene” on Friday. The relevant topics will include

(1) Electronic properties of graphene, and the newly discovered transition metal dichalcogenides;

(2) Quantum Hall physics in graphene;

(3) Pseudo-spin ferromagnetism in graphene;

(4) Hartree-Fock theory of electron-electron interaction;

(5) Optical spectroscopy in bilayer graphene.

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Topic: Quantum Hall and Many-body physics in graphene

Speaker: Xiao Li (李潇)

　　　　 Department of Physics, University of Texas, Austin, USA

Time: 15:00-17:00 PM, Jul. 26 (Fri.), 2013

Venue: Room 468, Lee Hsun Building, IMR CAS

Welcome to attend！

Abstract:

In this talk I will discuss the various novel states driven by electron-electron interaction in graphene. It consists of three different but related works. In the first part, I will talk about the quantum Hall physics in monolayer molybdenum disulfide (MoS2), a newly discovered platform of two-dimensional electron gas system. The honeycomb lattice structure of a monolayer MoS2 (when viewed from the top) and its low-energy Dirac physics are reminiscent of graphene. However, strong spin-orbit coupling arising from broken inversion symmetry substantially modifies the behavior of electrons in a magnetic field. I will discuss the Landau level structure, as well as its consequences. This work is published in Physical Review Letters [PRL 110, 066803 (2013)].

In the second part, I will talk about spontaneous domain wall formation in bilayer graphene. Due to its non-vanishing density of states at the charge neutrality point and large pseudo-spin chirality, electron-electron interaction plays an important role in the low energy physics of bilayer graphene. There have been extensive studies on the existence of interaction driven broken symmetry ground states. In this talk I will discuss how topological defects above the broken symmetry ground states can modify the critical temperature for metal-insulator transition in bilayer graphene. I will also compare this to the story in two-dimensional superconductors, where topological defects can also produce a new critical temperature, but the underlying physics is very different. In the third part, I will turn to the discussion of how electron-electron interaction can modify the optical Drude weight in bilayer graphene. It is known that in conventional semiconductors, the Galilean invariance of the band edge states will prevent the optical Drude weight from interaction corrections. However, in graphene, due to the additional pseudo-spin degrees, Galilean invariance is broken even for the band edge states. Therefore, the measured Drude weight is expected to be different from estimations in a single-particle picture. Indeed, several experiments have seen such a deviation, and I will argue how electron-electron interaction modifies the Drude weight.

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