5,585 research outputs found
Electronic phase separation due to magnetic polaron formation in the semimetallic ferromagnet EuB - A weakly-nonlinear-transport study
We report measurements of weakly nonlinear electronic transport, as measured
by third-harmonic voltage generation , in the low-carrier density
semimetallic ferromagnet EuB, which exhibits an unusual magnetic ordering
with two consecutive transitions at \,K and \,K. Upon cooling in zero magnetic field through the ferromagnetic
transition, the dramatic drop in the linear resistivity at the upper transition
coincides with the onset of nonlinearity, and upon further cooling is
followed by a pronounced peak in at the lower transition
. Likewise, in the paramagnetic regime, a drop of the material's
magnetoresistance precedes a magnetic-field-induced peak in nonlinear
transport. A striking observation is a linear temperature dependence of
. We suggest a picture where at the upper transition
the coalescing MP form a conducting path giving rise to a strong
decrease in the resistance. The MP formation sets in at around \,K below which these entities are isolated and strongly fluctuating, while
growing in number. The MP then start to form links at , where
percolative electronic transport is observed. The MP merge and start forming a
continuum at the threshold . In the paramagnetic temperature regime
, MP percolation is induced by a magnetic field, and the
threshold accompanied by charge carrier delocalization occurs at a single
critical magnetization.Comment: to appear in J. Kor. Phys. Soc (ICM2012 conference contribution
Evidence for electron-phonon interaction in FeMSb (M=Co, Cr) single crystals
We have measured polarized Raman scattering spectra of the
FeCoSb and FeCrSb (00.5)
single crystals in the temperature range between 15 K and 300 K. The highest
energy symmetry mode shows significant line asymmetry due to phonon
mode coupling width electronic background. The coupling constant achieves the
highest value at about 40 K and after that it remains temperature independent.
Origin of additional mode broadening is pure anharmonic. Below 40 K the
coupling is drastically reduced, in agreement with transport properties
measurements. Alloying of FeSb with Co and Cr produces the B mode
narrowing, i.e. weakening of the electron-phonon interaction. In the case of
A symmetry modes we have found a significant mode mixing
Kondo insulator SmB6 under strain: surface dominated conduction near room temperature
SmB6 is a strongly correlated mixed-valence Kondo insulator with a newly
discovered surface state, proposed to be of non-trivial topological origin.
However, the surface state dominates electrical conduction only below T* ~ 4 K
limiting its scientific investigation and device application. Here, we report
the enhancement of T * in SmB6 under the application of tensile strain. With
0.7% tensile strain we report surface dominated conduction at up to a
temperature of 240 K, persisting even after the strain has been removed. This
can be explained in the framework of strain-tuned temporal and spatial
fluctuations of f-electron configurations, which might be generally applied to
other mixed-valence materials. We note that this amount of strain can be indued
in epitaxial SmB6 films via substrate in potential device applications.Comment: to appear in Nature Material
Radio Frequency Tunable Oscillator Device Based on SmB6 Microcrystal
Radio frequency tunable oscillators are vital electronic components for
signal generation, characterization, and processing. They are often constructed
with a resonant circuit and a 'negative' resistor, such as a Gunn-diode,
involving complex structure and large footprints. Here we report that a piece
of SmB6, 100 micron in size, works as a current-controlled oscillator in the 30
MHz frequency range. SmB6 is a strongly correlated Kondo insulator that was
recently found to have a robust surface state likely to be protected by the
topology of its electronics structure. We exploit its non-linear dynamics, and
demonstrate large AC voltage outputs with frequencies from 20 Hz to 30 MHz by
adjusting a small DC bias current. The behaviors of these oscillators agree
well with a theoretical model describing the thermal and electronic dynamics of
coupled surface and bulk states. With reduced crystal size we anticipate the
device to work at higher frequencies, even in the THz regime. This type of
oscillator might be realized in other materials with a metallic surface and a
semiconducting bulk.Comment: v3 to appear in Physical Review Letter
Strong pinning of vortices by antiferromagnetic domain boundaries in CeCo(InCd)
We have studied the isothermal magnetization of
CeCo(InCd) with = 0.0075 and 0.01 down to 50 mK. Pronounced
field-history dependent phenomena occur in the coexistence regime of the
superconducting and antiferromagnetic phases. At low-fields, a phenomenological
model of magnetic-flux entry well explains implying the dominance of
bulk pinning effect. However, unless crystallographic quenched disorder is
hysteretic, the asymmetric peak effect (ASPE) which appears at higher fields
cannot be explained by the pinning of vortices due to material defects. Also
the temperature dependence of the ASPE deviates from the conventional scenario
for the peak effect. Comparison of our thermodynamic phase diagrams with those
from previous neutron scattering and magnetoresistance experiments indicates
that the pinning of vortices takes place at the field-history dependent
antiferromagnetic domain boundaries.Comment: 13 pages,4 figures, to be published in New Journal of Physic
- …