L. S. Bilbro

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.

Temporal correlations of superconductivity above the transition temperature in La2-xSrxCuO4 probed by terahertz spectroscopy

Above the superconducting temperature for a given material, correlations between pairs of electrons are already present. Many experiments indicate that such correlations may exist up to 100 K above the transition. However, a temporal probe of the superconducting fluctuations suggests that correlations only exist within a narrow temperature range.

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.

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.

Pair-breaking effects and coherence peak in the terahertz conductivity of superconductingBaFe2−2xCo2xAs2thin films

R. Valdés Aguilar, ∗ L.S. Bilbro, S. Lee, J. Jiang, J.D. Weiss, E.E. Hellstrom, D.C. Larbalestier, C.B. Eom, and N. P. Armitage † The Institute of Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218 Department of Material Science and Engineering, University of Wisconsin, Madison, WI 53706 National High Magnetic Field Laboratory, Florida State University, Talahassee, FL 32310 (Dated: July 27, 2010)

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

An abrupt change in transport dynamics across the topological phase transition in the (Bi

_2

_{1-x}

Ge

In

_2

_x

. 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.