Recent progress in condesned matter theory at KIAS on Friday, September 2nd, 2016.

We will have a condensed matter theory workshop. The location is room 1503, the 5th floor of building no.1 at KIAS. Everyone is invited to attend and participate. Please let us know(kkim@kias.re.kr) if you have any questions. More information on speakers and their talks are following:

10:30-11:15am. Speaker: Myung-Joon Han (KAIST).
Title: Toward the better first-principles description of correlated materials: Branching ratio, magnetic exchange, and dynamical electron correlation
Abstract: In this talk, I will try to give a brief overview of recent progress in my research group for developing first-principle computation methods based on our 'OpenMX' code (www.openmx-square.org). In the first part, a simple technique to directly calculate branching ratio through spin-orbit coupling L.S will be presented. We applied this method to iridium oxide compounds and found a good agreement with experiments. In the second part, a calculation method of magnetic exchange parameter based on force theorem is discussed. It was originally implemented for the case of molecule and now is extended for the bulk case. Finally, I will report our on-going progress toward the DFT+DMFT to better describe dynamical correlation effect. The non-interacting Hamiltonian is extracted from first-principles band structure based on Wannier-function technique and then the interactions are described within single-site DMFT with ALPS Solver. The application to LaTiO3-based superlattice will be presented.

11:15-12:00pm. Speaker: Cheol Hwan Park (SNU).
Title:Light-matter interaction in materials with spin-orbit coupling
Abstract: theoretical prediction of ours that the spin polarization of photoelectrons emitted from a topological insulator is highly tunable such that almost 100 % polarization along any arbitrary direction can be achieved by tuning the polarization of light was followed by a number of independent experimental confirmations. However, there are some experimental results that cannot be explained by previous theoretical descriptions. In this talk, I will discuss our recent theoretical investigation of the photoemission process from topological insulators. I will also discuss how the electronic structure, photoemission and optical absorption are affected by spin-orbit coupling.

Lunch

2:00-2:45pm. Speaker: Jung Hoon Han (SKKU).
Title:Entanglement and corner Hamiltonian spectra of integrable open spin chains
Abstract: We investigate the entanglement entropy (EE) and entanglement spectra (ES) of critical SU(N) (N=2,3,4) spin chains and other integrable models of finite length with the density matrix renormalization group method. For all models under investigation, we find a remarkable agreement of the level spacings and the degeneracy structure of the ES with the spectrum of the corner Hamiltonian (CS), defined as the generator of the associated corner transfer matrix. The correspondence holds between ES(n) at the n-th cut position from the edge of the spin model, and the spectrum CS(n) of the corner Hamiltonian of length n, for all values of n that we have checked. The cut position dependence of the ES shows a period-N oscillatory behavior for a given SU(N) chain, reminiscent of the oscillatory part of the entanglement entropy observed in the past for the same models. However, the oscillations of the ES do not die out in the bulk of the chain, in contrast to the asymptotically vanishing oscillation of the entanglement entropy. We further present a heuristic argument based on Young tableaux construction that can explain the period-N structure of the ES qualitatively. This work was done in collaboration with Panjin Kim (SKKU), Hosho Katsura (TU), and Nandini Trivedi (OSU).

2:45-3:30pm. Speaker: Bohm Jung Yang (SNU).
Title: Quantum criticality of topological phase transitions
Abstract:

Break

4:00-4:45pm. Speaker: Eun Gook Moon (KAIST).
Title: Anomaly realization in condensed matter
Abstract: We argue that a lattice translation symmetry in even space-time dimensions may play a role as a ``chiral'' symmetry of quantum states in a low energy Hilbert-space. A ``chiral anomaly'' is realized with the lattice translation symmetry, and we argue that the anomaly guarantees the absence of energy gap in the thermodynamic limit: the gaplessness is protected by the presence of the lattice translation, but its spontaneous symmetry breaking does not protect the gaplessness. This is in sharp contrast to one of the 't Hooft anomaly matching in high-energy physics. Criteria of realization of the anomaly are provided, and naturally, our results are consistent with the previously well-studied Hasting-Oshikawa-Lieb-Shultz-Mattis (HOLSM) and its extension to generic lattice models. We also identify connection between the ``chiral anomaly'' and symmetry-protected topological states and compare our results to the recently proposed duality of the half-filled quantum Hall state. If time permits, I will also discuss how anomaly plays a role to classify novel quantum criticality in three spatial dimensions.