2,518 research outputs found
Proximity effect thermometer for local temperature measurements on mesoscopic samples
Using the strong temperature dependent resistance of a normal metal wire in
proximity to a superconductor, we have been able to measure the local
temperature of electrons heated by flowing a dc current in a metallic wire to
within a few tens of millikelvin at low temperatures. By placing two such
thermometers at different parts of a sample, we have been able to measure the
temperature difference induced by a dc current flowing in the sample. This
technique may provide a flexible means of making quantitative thermal and
thermoelectric measurements on mesoscopic metallic samples
Evolution of transport properties of BaFe2-xRuxAs2 in a wide range of isovalent Ru substitution
The effects of isovalent Ru substitution at the Fe sites of BaFe2-xRuxAs2 are
investigated by measuring resistivity and Hall coefficient on high-quality
single crystals in a wide range of doping (0 < x < 1.4). Ru substitution
weakens the antiferromagnetic (AFM) order, inducing superconductivity for
relatively high doping level of 0.4 < x < 0.9. Near the AFM phase boundary, the
transport properties show non-Fermi-liquid-like behaviors with a
linear-temperature dependence of resistivity and a strong temperature
dependence of Hall coefficient with a sign change. Upon higher doping, however,
both of them recover conventional Fermi-liquid behaviors. Strong doping
dependence of Hall coefficient together with a small magnetoresistance suggest
that the anomalous transport properties can be explained in terms of
anisotropic charge carrier scattering due to interband AFM fluctuations rather
than a conventional multi-band scenario.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Thickness dependent magnetotransport in ultra-thin manganite films
To understand the near-interface magnetism in manganites, uniform, ultra-thin
films of La_{0.67}Sr_{0.33}MnO_3 were grown epitaxially on single crystal (001)
LaAlO_3 and (110) NdGaO_3 substrates. The temperature and magnetic field
dependent film resistance is used to probe the film's structural and magnetic
properties. A surface and/or interface related dead-layer is inferred from the
thickness dependent resistance and magnetoresistance. The total thickness of
the dead layer is estimated to be for films on NdGaO_3 and for films on LaAlO_3.Comment: 11 pages, 4 figure
Theoretical studies of the kinetics of mechanical unfolding of cross-linked polymer chains and their implications for single molecule pulling experiments
We have used kinetic Monte Carlo simulations to study the kinetics of
unfolding of cross-linked polymer chains under mechanical loading. As the ends
of a chain are pulled apart, the force transmitted by each crosslink increases
until it ruptures. The stochastic crosslink rupture process is assumed to be
governed by first order kinetics with a rate that depends exponentially on the
transmitted force. We have performed random searches to identify optimal
crosslink configurations whose unfolding requires a large applied force
(measure of strength) and/or large dissipated energy (measure of toughness). We
found that such optimal chains always involve cross-links arranged to form
parallel strands. The location of those optimal strands generally depends on
the loading rate. Optimal chains with a small number of cross-links were found
to be almost as strong and tough as optimal chains with a large number of
cross-links. Furthermore, optimality of chains with a small number of
cross-links can be easily destroyed by adding cross-links at random. The
present findings are relevant for the interpretation of single molecule force
probe spectroscopy studies of the mechanical unfolding of load-bearing
proteins, whose native topology often involves parallel strand arrangements
similar to the optimal configurations identified in the study
Positive exchange bias in ferromagnetic La0.67Sr0.33MnO3 / SrRuO3 bilayers
Epitaxial La0.67Sr0.33MnO3 (LSMO)/ SrRuO3 (SRO) ferromagnetic bilayers have
been grown on (001) SrTiO3 (STO) substrates by pulsed laser deposition with
atomic layer control. We observe a shift in the magnetic hysteresis loop of the
LSMO layer in the same direction as the applied biasing field (positive
exchange bias). The effect is not present above the Curie temperature of the
SRO layer (), and its magnitude increases rapidly as the temperature is lowered
below . The direction of the shift is consistent with an antiferromagnetic
exchange coupling between the ferromagnetic LSMO layer and the ferromagnetic
SRO layer. We propose that atomic layer charge transfer modifies the electronic
state at the interface, resulting in the observed antiferromagnetic interfacial
exchange coupling.Comment: accepted to Applied Physics Letter
Electron-hole asymmetry in Co- and Mn-doped SrFe2As2
Phase diagram of electron and hole-doped SrFe2As2 single crystals is
investigated using Co and Mn substitution at the Fe-sites. We found that the
spin-density-wave state is suppressed by both dopants, but the superconducting
phase appears only for Co (electron)-doping, not for Mn (hole)-doping. Absence
of the superconductivity by Mn-doping is in sharp contrast to the hole-doped
system with K-substitution at the Sr sites. Distinct structural change, in
particular the increase of the Fe-As distance by Mn-doping is important to have
a magnetic and semiconducting ground state as confirmed by first principles
calculations. The absence of electron-hole symmetry in the Fe-site-doped
SrFe2As2 suggests that the occurrence of high-Tc superconductivity is sensitive
to the structural modification rather than the charge doping.Comment: 7 pages, 6 figure
Quantum Hall Ferromagnetism in a Two-Dimensional Electron System
Experiments on a nearly spin degenerate two-dimensional electron system
reveals unusual hysteretic and relaxational transport in the fractional quantum
Hall effect regime. The transition between the spin-polarized (with fill
fraction ) and spin-unpolarized () states is accompanied
by a complicated series of hysteresis loops reminiscent of a classical
ferromagnet. In correlation with the hysteresis, magnetoresistance can either
grow or decay logarithmically in time with remarkable persistence and does not
saturate. In contrast to the established models of relaxation, the relaxation
rate exhibits an anomalous divergence as temperature is reduced. These results
indicate the presence of novel two-dimensional ferromagnetism with a
complicated magnetic domain dynamic.Comment: 15 pages, 5 figure
- …