# Condensed-Matter Physics & Materials Science Seminar

## "TBATopological Nodal-Line Fermions in Strong Spin-Orbit Metal PbTaSe2"

#### Presented by Tay-Rong Chang, National Tsing Hua University Taiwan, Taiwan

Thursday, October 8, 2015, 1:30 pm — ISB Bldg. 734, Conf. Rm. 201 (upstairs)

In a typical three-dimensional metal, the low-energy excitations are found on a two-dimensional closed Fermi surface in momentum space. Topological semimetals, by contrast, can support one-dimensional Fermi lines or zero-dimensional Fermi-Weyl points, at locations in momentum space, where the valence and conduction bands touch. While the degeneracy points in Weyl semimetals are robust against any perturbation that preserves translational symmetry, nodal lines require protection by additional crystalline symmetries such as mirror reflection. In this talk, I will demonstrate the prediction of topological nodal-line states in the non-centrosymmetric compound single-crystalline PbTaSe2 with strong spin-orbit coupling based on the first-principles electronic structure calculations. Remarkably, the spin-orbit nodal lines in PbTaSe2 are not only protected by the reflection symmetry but also characterized by an integer topological invariant. Our theoretical analysis illustrate the physical mechanism underlying the formation of the topological nodal-line states and associated surface states. The calculated surface states for (001) surface with Pb-termination are in good agreement with angle-resolved photoemission (ARPES) measurements [1]. [1] arXiv:1505.03069, G. Bian, T.-R. Chang, R. Sankar, et al.

Hosted by: Wei Ku

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