12 research outputs found
Inter-grain tunneling in the half-metallic double-perovskites SrBB'O (BB'-- FeMo, FeRe, CrMo, CrW, CrRe
The zero-field conductivities () of the polycrystaline title
materials, are governed by inter-grain transport. In the majority of cases
their (T) can be described by the "fluctuation induced tunneling"
model. Analysis of the results in terms of this model reveals two remarkable
features: 1. For \emph{all} SrFeMoO samples of various microstructures,
the tunneling constant (barrier width inverse decay-length of the
wave-function) is 2, indicating the existence of an intrinsic insulating
boundary layer with a well defined electronic (and magnetic) structure. 2. The
tunneling constant for \emph{all} cold-pressed samples decreases linearly with
increasing magnetic-moment/formula-unit.Comment: 10 pages, 2 tables, 3 figure
Pulsed versus DC I-V characteristics of resistive manganites
We report on pulsed and DC I-V characteristics of polycrystalline samples of
three charge-ordered manganites, Pr_{2/3}Ca_{1/3}MnO_3, Pr_{1/2}Ca_{1/2}MnO_3,
Bi_{1/2}Sr_{1/2}MnO_3 and of a double-perovskite Sr_2MnReO_6, in a temperature
range where their ohmic resistivity obeys the Efros-Shklovskii variable range
hopping relation. For all samples, the DC I(V) exhibits at high currents
negative differential resistance and hysteresis, which mask a perfectly ohmic
or a moderately nonohmic conductivity obtained by pulsed measurements. This
demonstrates that the widely used DC I-V measurements are usually misleading.Comment: 6 pages, 4 figures. Accepted for publication to AP
Proximity induced superconductivity by Bi in topological and films: Evidence for a robust zero energy bound state possibly due to Majorana Fermions
Point contact conductance measurements on topological and
films reveal a signature of superconductivity below 2-3 K. In
particular, critical current dips and a robust zero bias conductance peak are
observed. The latter suggests the presence of zero energy bound states which
could be assigned to Majorana Fermions in an unconventional topological
superconductor. We attribute these novel observations to proximity induced
local superconductivity in the films by small amounts of superconducting Bi
inclusions or segregation to the surface, and provide supportive evidence for
these effects.Comment: Accepted for publication in Physical Review B (Dec. 20, 2011), 15
figures. Version V1: arXiv:1111.3445v1 [cond-mat.supr-con] 15 Nov 201
Inter-grain tunnelling in the half-metallic double-perovskites Sr2BB'O6 (BB'= FeMo, FeRe, CrMo, CrW, CrRe)
The zero-field conductivities (σ) of polycrystalline title materials, are governed by intergrain transport. In the majority of cases their σ(T) can be described by the "fluctuation induced tunnelling" model. Analysis of the results in terms of this model reveals two remarkable features: 1. For all Sr2FeMoO6 samples of various microstructures, the tunnelling constant (barrier width × inverse decay-length of the wave-function) is ~ 2, indicating the existence of an intrinsic insulating boundary layer with a well-defined electronic (and magnetic) structure. 2. The tunnelling constant for all cold-pressed samples decreases linearly with increasing magnetic-moment/formula-unit
I-V Characteristics of Resistive Oxides: DC versus Pulsed Measurements
We investigated pulsed and DC I-V characteristics of a variety of resistive oxides. Examples of pulsed, compared with DC characteristics, are shown for samples of LaSrMnO (a double layer manganite), Pr Ca MnO and Bi Sr MnO (charge-ordered manganites), SrFeMoO, SrCrWO and BaMnReO (double perovskites). For pulsed measurements, single pulses in the ms range were applied. For short-rise-time square pulses, the Joule heating is negligible, as long as the response remains independent of time. The DC I-V characteristics were measured up to current runaway in the negative resistance regime;Δ T never exceeded a fraction of a degree. In most cases the DC characteristics mask a perfectly ohmic or moderately non-ohmic conductivity obtained by pulsed measurements. This demonstrates that the widely used DC I-V measurements in the high current regime are frequently misleading
Evolution of the fermi surface of a doped topological insulator with carrier concentration
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