TODAY - SPECIAL COLLOQUIUM - Rolando Valdes Aguilar, Los Alamos National Lab - 11:30am, Smith Seminar Room

[Longbrake, Patricia]

Please join us for a "Special Colloquium" presented by Rolando Valdes Aguilar from Los Alamos National Laboratory, Center for Integrated Nanotechnologies at 11:30am TODAY in the Smith Seminar Room.

Terahertz transport properties of the topological insulator Bi2Se3.

Ordered states of matter are typically categorized by their broken symmetries. With the ordering of spins in a ferromagnet or the freezing of a liquid into a solid, the loss of symmetry distinguishes the ordered state from the disordered one. In contrast, topological states are distinguished by specific topological properties that are encoded in their quantum mechanical wave functions. Topological insulators are states of matter characterized by an inverted band structure driven by strong spin-orbit coupling (SOC). In this talk I will provide an introduction to the subject of Topological Insulators and will show results of the studies of the transport properties at terahertz (THz) frequencies in thin films of the material Bi2Se3. At low frequencies, transport is essentially thickness independent showing the dominant contribution of the surface electrons. These surfaces exhibit robust properties including narrow, almost thickness-independent Drude peaks, and an unprecedentedly large polarization rotation of linearly polarized light reflected in an applied magnetic field. This Kerr rotation can be as large as 65° and can be explained by a cyclotron resonance effect of the surface states. In addition, the topological phase transition into a trivial insulating state was investigated by studying the THz conductivity in (Bi1-xInx)2Se3 thin films, where Indium substitution tunes SOC. Above a thickness dependent substitution threshold, a sudden collapse in the transport lifetime is observed, which indicates that the surface states have lost their topological protection, a signature of the destruction of the topological phase, and of a transition to a topologically trivial state.

Thank you,
Trisch
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