157 research outputs found
Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB6
As an exemplary Kondo insulator, SmB6 has been studied for several decades;
however, direct evidence for the development of the Kondo coherent state and
the evolution of the electronic structure in the material has not been obtained
due to the rather complicated electronic and thermal transport behavior.
Recently, these open questions attracted increasing attention as the emergence
of a time-reversal invariant topological surface state in the Kondo insulator
has been suggested. Here, we use point-contact spectroscopy to reveal the
temperature dependence of the electronic states in SmB6. We demonstrate that
SmB6 is a model Kondo insulator: below 100 K, the conductance spectra reflect
the Kondo hybridization of Sm ions, but below ~ 30 K, signatures of inter-ion
correlation effects clearly emerge. Moreover, we find evidence that the
low-temperature insulating state of this exemplary Kondo lattice compound
harbors conduction states on the surface, in support of predictions of
nontrivial topology in Kondo insulators.Comment: Accepted for publication in Physical Review
Spatially resolved femtosecond pump-probe study of topological insulator Bi2Se3
Carrier and phonon dynamics in Bi2Se3 crystals are studied by a spatially
resolved ultrafast pump-probe technique. Pronounced oscillations in
differential reflection are observed with two distinct frequencies, and are
attributed to coherent optical and acoustic phonons, respectively. The rising
time of the signal indicates that the thermalization and energy relaxation of
hot carriers are both sub-ps in this material. We found that the thermalization
and relaxation time decreases with the carrier density. The expansion of the
differential reflection profile allows us to estimate an ambipolar carrier
diffusion coefficient on the order of 500 square centimeters per second. A
long-term slow expansion of the profile shows a thermal diffusion coefficient
of 1.2 square centimeters per second.Comment: 8 pages, 6 figure
Terahertz Kerr and Reflectivity Measurements on the Topological Insulator Bi2Se3
We report the first terahertz Kerr measurements on bulk crystals of the
topological insulator Bi2Se3. At T=10K and fields up to 8T, the real and
imaginary Kerr angle and reflectance measurements utilizing both linearly and
circularly polarized incident radiation were measured at a frequency of
5.24meV. A single fluid free carrier bulk response can not describe the
line-shape. Surface states with a small mass and surprisingly large associated
spectral weight quantitatively fit all data. However, carrier concentration
inhomogeneity has not been ruled out. A method employing a gate is shown to be
promising for separating surface from bulk effects.Comment: 10 pages, 5 figure
Magnetothermoelectric properties of Bi2Se3
We present a study of entropy transport in Bi2Se3 at low temperatures and
high magnetic fields. In the zero-temperature limit, the magnitude of the
Seebeck coefficient quantitatively tracks the Fermi temperature of the 3D Fermi
surface at \Gamma-point as the carrier concentration changes by two orders of
magnitude (10 to 10cm). In high magnetic fields, the
Nernst response displays giant quantum oscillations indicating that this
feature is not exclusive to compensated semi-metals. A comprehensive analysis
of the Landau Level spectrum firmly establishes a large -factor in this
material and a substantial decrease of the Fermi energy with increasing
magnetic field across the quantum limit. Thus, the presence of bulk carriers
significantly affects the spectrum of the intensively debated surface states in
Bi2Se3 and related materials.Comment: 10 pages, 9 figure
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