935 research outputs found
Measurement of the topological surface state optical conductance in bulk-insulating Sn-doped BiSbTeS single crystals
Topological surface states have been extensively observed via optics in thin
films of topological insulators. However, in typical thick single crystals of
these materials, bulk states are dominant and it is difficult for optics to
verify the existence of topological surface states definitively. In this work,
we studied the charge dynamics of the newly formulated bulk-insulating Sn-doped
BiSbTeS crystal by using time-domain terahertz
spectroscopy. This compound shows much better insulating behavior than any
other bulk-insulating topological insulators reported previously. The
transmission can be enhanced an amount which is 5 of the zero-field
transmission by applying magnetic field to 7 T, an effect which we believe is
due to the suppression of topological surface states. This suppression is
essentially independent of the thicknesses of the samples, showing the
two-dimensional nature of the transport. The suppression of surface states in
field allows us to use the crystal slab itself as a reference sample to extract
the surface conductance, mobility, charge density and scattering rate. Our
measurements set the stage for the investigation of phenomena out of the
semi-classical regime, such as the topological magneto-electric effect.Comment: 5 pages, 3 figures, submitted in Augus
Anomalous conductivity tensor in the Dirac semimetal Na_3Bi
Na3Bi is a Dirac semimetal with protected nodes that may be sensitive to the
breaking of time-reversal invariance in a magnetic field B. We report
experiments which reveal that both the conductivity and resistivity tensors
exhibit robust anomalies in B. The resistivity is B-linear up to 35
T, while the Hall angle exhibits an unusual profile approaching a
step-function. The conductivities and share
identical power-law dependences at large B. We propose that these significant
deviations from conventional transport result from an unusual sensitivity of
the transport lifetime to B. Comparison with Cd3As2 is made.Comment: 8 pages, 5 figure
Experimental tests of the chiral anomaly magnetoresistance in the Dirac-Weyl semimetals NaBi and GdPtBi
In the Dirac/Weyl semimetal, the chiral anomaly appears as an "axial" current
arising from charge-pumping between the lowest (chiral) Landau levels of the
Weyl nodes, when an electric field is applied parallel to a magnetic field . Evidence for the chiral anomaly was obtained from the longitudinal
magnetoresistance (LMR) in NaBi and GdPtBi. However, current jetting
effects (focussing of the current density ) have raised general concerns
about LMR experiments. Here we implement a litmus test that allows the
intrinsic LMR in NaBi and GdPtBi to be sharply distinguished from pure
current jetting effects (in pure Bi). Current jetting enhances along the
mid-ridge (spine) of the sample while decreasing it at the edge. We measure the
distortion by comparing the local voltage drop at the spine (expressed as the
resistance ) with that at the edge (). In Bi,
sharply increases with but decreases (jetting effects are
dominant). However, in NaBi and GdPtBi, both and
decrease (jetting effects are subdominant). A numerical simulation allows the
jetting distortions to be removed entirely. We find that the intrinsic
longitudinal resistivity in NaBi decreases by a factor of
10.9 between = 0 and 10 T. A second litmus test is obtained from the
parametric plot of the planar angular magnetoresistance. These results
strenghthen considerably the evidence for the intrinsic nature of the
chiral-anomaly induced LMR. We briefly discuss how the squeeze test may be
extended to test ZrTe.Comment: 17 pages, 8 figures, new co-authors added, new Fig. 6a added. In
press, PR
Scattering of elastic waves by periodic arrays of spherical bodies
We develop a formalism for the calculation of the frequency band structure of
a phononic crystal consisting of non-overlapping elastic spheres, characterized
by Lam\'e coefficients which may be complex and frequency dependent, arranged
periodically in a host medium with different mass density and Lam\'e
coefficients. We view the crystal as a sequence of planes of spheres, parallel
to and having the two dimensional periodicity of a given crystallographic
plane, and obtain the complex band structure of the infinite crystal associated
with this plane. The method allows one to calculate, also, the transmission,
reflection, and absorption coefficients for an elastic wave (longitudinal or
transverse) incident, at any angle, on a slab of the crystal of finite
thickness. We demonstrate the efficiency of the method by applying it to a
specific example.Comment: 19 pages, 5 figures, Phys. Rev. B (in press
Simple Procedures for Left and Right Keys of semi-standard Young tableaux
We give simple procedures to obtain the left and right keys of a
semi-standard Young tableau.Comment: 17 page
Au9+ swift heavy ion irradiation of Zn[CS(NH2)2]3SO4 crystal: Crystalline perfection and optical properties
The single crystal of tris(thiourea)zinc sulphate (Zn[CS(NH2)2]3SO4) was
irradiated by 150 MeV Au9+ swift heavy ions and analyzed in comparison with
pure crystal for crystalline perfection and optical properties. The Fourier
transform infrared and x-ray powder diffraction inferred that swift ions lead
the disordering and breaking of molecular bonds in lattice without formation of
new structural phases. High resolution X-ray diffraction (HRXRD) revealed the
abundance of point defects, and formation of mosaics and low angle grain
boundaries in the irradiated region of crystal. The swift ion irradiation found
to affect the lattice vibrational modes and functional groups significantly.
The defects induced by heavy ions act as the color centers and resulted in
enhance of photoluminescence emission intensity. The optical transparency and
band gap found to be decreased.Comment: 7 page
Unique Measure for Geometrical Shape Object Detection-based on Area Matching
Object classifier often operates by making decisions based on the values of several shape properties measured from an image of the object. The paper introduces a unique definition of measure for 2-D geometrical object shape detection. Using this definition different object shapes can be identified on the basis of their degree of fitness parameter. Basically, we have fitted a 2-D polygon/curve on the object as a best fitted polygon/curve and computed the parameter degree of fitness which is the ratio of the matching area and non-matching area due to the fitted polygon/curve and the object both. The results show the effectiveness of the proposed measure.Defence Science Journal, 2012, 62(1), pp.58-66, DOI:http://dx.doi.org/10.14429/dsj.62.94
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