27,777 research outputs found
Large magnetoresistance in the antiferromagnetic semi-metal NdSb
There has been considerable interest in topological semi-metals that exhibit
extreme magnetoresistance (XMR). These have included materials lacking
inversion symmetry such as TaAs, as well Dirac semi-metals such as Cd3As2.
However, it was reported recently that LaSb and LaBi also exhibit XMR, even
though the rock-salt structure of these materials has inversion symmetry, and
the band-structure calculations do not show a Dirac dispersion in the bulk.
Here, we present magnetoresistance and specific heat measurements on NdSb,
which is isostructural with LaSb. NdSb has an antiferromagnetic groundstate,
and in analogy with the lanthanum monopnictides, is expected to be a
topologically non-trivial semi-metal. We show that NdSb has an XMR of 10^4 %,
even within the AFM state, illustrating that XMR can occur independently of the
absence of time reversal symmetry breaking in zero magnetic field. The
persistence of XMR in a magnetic system offers promise of new functionality
when combining topological matter with electronic correlations. We also find
that in an applied magnetic field below the Neel temperature there is a first
order transition, consistent with evidence from previous neutron scattering
work.Comment: 5 pages, 6 figure
Nuclear Magnetic Relaxation Rate in a Noncentrosymmetric Superconductor
For a noncentrosymmetric superconductor such as CePt3Si, we consider a Cooper
pairing model with a two-component order parameter composed of spin-singlet and
spin-triplet pairing components.
We demonstrate that such a model on a qualitative level accounts for
experimentally observed features of the temperature dependence of the nuclear
spin-lattice relaxation rate 1/T1, namely a peak just below Tc and a line-node
gap behavior at low temperatures.Comment: 4 page
Efficient Magnetization Reversal with Noisy Currents
We propose to accelerate reversal of the ferromagnetic order parameter in
spin valves by electronic noise. By solving the stochastic equations of motion
we show that the current-induced magnetization switching time is drastically
reduced by a modest level of externally generated current (voltage) noise. This
also leads to a significantly lower power consumption for the switching
process.Comment: 4 pages, 3 figure
Stress engineering at the nanometer scale: Two-component adlayer stripes
Spontaneously formed equilibrium nanopatterns with long-range order are
widely observed in a variety of systems, but their pronounced temperature
dependence remains an impediment to maintain such patterns away from the
temperature of formation. Here, we report on a highly ordered stress-induced
stripe pattern in a two-component, Pd-O, adsorbate monolayer on W(110),
produced at high temperature and identically preserved at lower temperatures.
The pattern shows a tunable period (down to 16 nm) and orientation, as
predicted by a continuum model theory along with the surface stress and its
anisotropy found in our DFT calculations. The control over thermal fluctuations
in the stripe formation process is based on the breaking/restoring of
ergodicity in a high-density lattice gas with long-range interactions upon
turning off/on particle exchange with a heat bath.Comment: 6 pages, 4 figure
Collective rearrangement at the onset of flow of a polycrystalline hexagonal columnar phase
Creep experiments on polycrystalline surfactant hexagonal columnar phases
show a power law regime, followed by a drastic fluidization before reaching a
final stationary flow. The scaling of the fluidization time with the shear
modulus of the sample and stress applied suggests that the onset of flow
involves a bulk reorganization of the material. This is confirmed by X-ray
scattering under stress coupled to \textit{in situ} rheology experiments, which
show a collective reorientation of all crystallites at the onset of flow. The
analogy with the fracture of heterogeneous materials is discussed.Comment: to appear in Phys. Rev. Let
Spin heat accumulation and its relaxation in spin valves
We study the concept of spin heat accumulation in excited spin valves, more
precisely the effective electron temperature that may become spin dependent,
both in linear response and far from equilibrium. A temperature or voltage
gradient create non-equilibrium energy distributions of the two spin ensembles
in the normal metal spacer, which approach Fermi-Dirac functions through energy
relaxation mediated by electron-electron and electron-phonon coupling. Both
mechanisms also exchange energy between the spin subsystems. This inter-spin
energy exchange may strongly affect thermoelectric properties spin valves,
leading, e.g., to violations of the Wiedemann-Franz law.Comment: 4 pages, 4 figures, close to published versio
Degree Sequences and the Existence of -Factors
We consider sufficient conditions for a degree sequence to be forcibly
-factor graphical. We note that previous work on degrees and factors has
focused primarily on finding conditions for a degree sequence to be potentially
-factor graphical.
We first give a theorem for to be forcibly 1-factor graphical and, more
generally, forcibly graphical with deficiency at most . These
theorems are equal in strength to Chv\'atal's well-known hamiltonian theorem,
i.e., the best monotone degree condition for hamiltonicity. We then give an
equally strong theorem for to be forcibly 2-factor graphical.
Unfortunately, the number of nonredundant conditions that must be checked
increases significantly in moving from to , and we conjecture that
the number of nonredundant conditions in a best monotone theorem for a
-factor will increase superpolynomially in .
This suggests the desirability of finding a theorem for to be forcibly
-factor graphical whose algorithmic complexity grows more slowly. In the
final section, we present such a theorem for any , based on Tutte's
well-known factor theorem. While this theorem is not best monotone, we show
that it is nevertheless tight in a precise way, and give examples illustrating
this tightness.Comment: 19 page
- …