231 research outputs found
Impurity effects on optical response in a finite band electronic system coupled to phonons
The concepts, which have traditionally been useful in understanding the
effects of the electron--phonon interaction in optical spectroscopy, are based
on insights obtained within the infinite electronic band approximation and no
longer apply in finite band metals. Impurity and phonon contributions to
electron scattering are not additive and the apparent strength of the coupling
to the phonon degrees of freedom is substantially reduced with increased
elastic scattering. The optical mass renormalization changes sign with
increasing frequency and the optical scattering rate never reaches its high
frequency quasiparticle value which itself is also reduced below its infinite
band value
Giant Carrier Mobility in Single Crystals of FeSb2
We report the giant carrier mobility in single crystals of FeSb2. Nonlinear
field dependence of Hall resistivity is well described with the two-carrier
model. Maximum mobility values in high mobility band reach ~10^5 cm^2/Vs at 8
K, and are ~10^2 cm^2/Vs at the room temperature. Our results point to a class
of materials with promising potential for applications in solid state
electronics.Comment: 5 pages, 3 figures. Applied Physics Letters (in press
Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2
We have investigated anisotropy in magnetic and electrical transport
properties of Fe1-xCrxSb2 (0<= x <=1) single crystals. The magnetic ground
state of the system evolves from paramagnetic to antiferromagnetic with gradual
substitution of Fe with Cr. Anisotropy in electrical transport diminishes with
increased Cr substitution and fades away by x=0.5. We find that the variable
range hopping (VRH) conduction mechanism dominates at low temperatures for
0.4<= x <=0.75.Comment: 5 pages, 6 figure
Anisotropy in magnetic and transport properties of Fe1-xCoxSb2
Anisotropic magnetic and electronic transport measurements were carried out
on large single crystals of Fe1-xCoxSb2 (0<= x <=1). The semiconducting state
of FeSb2 evolves into metallic and weakly ferromagnetic by substitution of Fe
with Co for x<0.5. Further doping induces structural transformation from
orthorhombic Pnnm structure of FeSb2 to monoclinic P21/c structure of CoSb2
where semiconducting and diamagnetic ground state is restored again. Large
magnetoresistance and anisotropy in electronic transport were observed.Comment: 7 pages, 6 figure
Comment on ``Texture in the Superconducting Order Parameter of CeCoIn Revealed by Nuclear Magnetic Resonance''
The study of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been of
considerable recent interest. Below the temperature which is believed to
be the transition temperature () to the FFLO phase in CeCoIn, K.
Kakuyanagi et al. (Phys. Rev. Lett. 94, 047602 (2005)) reported a composite NMR
spectrum with a tiny component observed at frequencies corresponding to the
normal state signal. The results were interpreted as evidence for the emergence
of an FFLO state. This result is inconsistent with two other NMR studies of V.
F. Mitrovi{\'c} et al. (Phys. Rev. Lett. 97, 117002 (2006)) and B.-L. Young et
al. (Phys. Rev. Lett. 98, 036402 (2007)). In this comment we show that the
findings of K. Kakuyanagi et al. do not reflect the true nature of the FFLO
state but result from excess RF excitation power used in that experiment.Comment: 1 page, to appear in PR
Changes in Optical Conductivity due to Readjustments in Electronic Density of States
Within the model of elastic impurity scattering, we study how changes in the
energy dependence of the electronic density of states (EDOS)
around the Fermi energy are reflected in the frequency-dependent
optical conductivity . While conserving the total number of
states in we compute the induced changes in as a
function of and in the corresponding optical scattering rate
. These quantities mirror some aspects of the EDOS
changes but the relationship is not direct. Conservation of optical oscillator
strength is found not to hold, and there is no sum rule on the optical
scattering rate although one does hold for the quasiparticle scattering.
Temperature as well as increases in impurity scattering lead to additional
changes in optical properties not seen in the constant EDOS case. These effects
have their origin in an averaging of the EDOS around the Fermi energy
on an energy scale set by the impurity scattering.Comment: 13 pages, 7 figure
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