A. V. Stier

Terahertz Response and Colossal Kerr Rotation from the Surface States of the Topological Insulator Bi2Se3

We report the THz response of thin films of the topological insulator Bi2Se3. At low frequencies, transport is essentially thickness independent showing the dominant contribution of the surface electrons. Despite their extended exposure to ambient conditions, 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.

A sudden collapse in the transport lifetime across the topological phase transition in (Bi1-xInx)2Se3

The quantum phase transition from a topological to a conventional insulator in In-doped Bi2Se3 occurs when the topological phase is destroyed by the hybridization of states on opposite surfaces. This is characterized by a sudden change in the transport lifetime, measured by means of optical spectroscopy.

Polarization modulation time-domain terahertz polarimetry

We present high precision measurements of polarization rotations in the frequency range from 0.1 to 2.5 THz using a polarization modulation technique. A motorized stage rotates a polarizer at ~ 80 Hz, and the resulting modulation of the polarization is measured by a lock-in technique. We achieve an accuracy of 0.050° (900 μrad) and a precision of 0.02° (350 μrad) for small rotation angles. A detailed mathematical description of the technique is presented, showing its ability to fully characterize elliptical polarizations from 0.1 to 2.5 THz.

Aging and reduced bulk conductance in thin films of the topological insulator Bi2Se3

We report on the effect of exposure to atmospheric conditions on the THz conductivity of thin films of the topological insulator Bi2Se3. We find (1) two contributions of mobile charge carriers to the THz conductivity immediately after growth and (2) the spectral weight of the smaller of these decays significantly over a period of several days as the film is exposed to ambient conditions, while the other remains relatively constant. We associate the former with a bulk response and the latter with the surface. The surface response exhibits the expected robustness of the carriers from 2D topological surface states. We find no evidence for a third spectral feature derived from topologically trivial surface states.

Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu 2 Ge 2

We present time-domain THz spectroscopy data of a thin film of the Kondo-lattice antiferromagnet CeCu

Mixed-valence-driven heavy-fermion behavior and superconductivity in KNi2Se2

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Electric field modulated topological magnetoelectric effect in Bi2Se3

Ge

Spatial extent of the excited exciton states in WS2 monolayers from diamagnetic shifts

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Electrodynamics of the topological insulator (Bi

. The low frequency complex conductivity has been obtained down to temperatures below the onset of magnetic order. At low temperatures a narrow Drude-like peak forms, which is similar to ones found in other heavy fermion compounds that do not exhibit magnetic order. Using this data in conjunction with DC resistivity measurements, we obtain the frequency dependence of the scattering rate and effective mass through an extended Drude model analysis. The zero frequency limit of this analysis yields evidence for large mass renormalization even in the magnetic state, the scale of which agrees closely with that obtained from thermodynamic measurements.