1,978 research outputs found
Nernst effect in the electron-doped cuprates
We calculate the normal state Nernst signal in the cuprates resulting from a
reconstruction of the Fermi surface due to spin density wave order. An order
parameter consistent with the reconstruction of the Fermi surface detected in
electron-doped materials is shown to sharply enhance the Nernst signal close to
optimal doping. Within a semiclassical treatment, the obtained magnitude and
position of the enhanced Nernst signal agrees with Nernst measurements in
electron-doped cuprates.Comment: 9 pages, 5 figures, revised version as accepted by Phys. Rev. B,
changed several citations and reference
Theory of cooling by flow through narrow pores
We consider the possibility of adding a stage to a dilution refrigerator to
provide additional cooling by ``filtering out'' hot atoms. Three methods are
considered: 1) Effusion, where holes having diameters larger than a mean-free
path allow atoms to pass through easily; 2) Particle waveguide-like motion
using very narrow channels that greatly restrict the quantum states of the
atoms in a channel. 3) Wall-limited diffusion through channels, in which the
wall scattering is disordered so that local density equilibrium is established
in a channel. We assume that channel dimension are smaller than the mean-free
path for atom-atom interactions. The particle waveguide and the wall-limited
diffusion methods using channels on order of the de Broglie wavelength give
cooling. Recent advances in nano-filters give this method some hope of being
practical.Comment: 10 pages, 3 figures. Corrected typos and made some minor wording
change
Scattering of charge carriers by point defects in bilayer graphene
Theory of scattering of massive chiral fermions in bilayer graphene by radial
symmetric potential is developed. It is shown that in the case when the
electron wavelength is much larger than the radius of the potential the
scattering cross-section is proportional to the electron wavelength. This leads
to the mobility independent on the electron concentration. In contrast with the
case of single-layer, neutral and charged defects are, in general, equally
relevant for the resistivity of the bilayer graphene.Comment: final versio
Entanglement, purity and energy: Two qubits vs Two modes
We study the relationship between the entanglement, mixedness and energy of
two-qubit and two-mode Gaussian quantum states. We parametrize the set of
allowed states of these two fundamentally different physical systems using
measures of entanglement, mixedness and energy that allow us to compare and
contrast the two systems using a phase diagram. This phase diagram enables one
to clearly identify not only the physically allowed states, but the set of
states connected under an arbitrary quantum operation. We pay particular
attention to the maximally entangled mixed states (MEMS) of each system.
Following this we investigate how efficiently one may transfer entanglement
from two-mode to two-qubit states.Comment: 13 figures. References and 1 figure adde
Kondo Breakdown and Hybridization Fluctuations in the Kondo-Heisenberg Lattice
We study the deconfined quantum critical point of the Kondo-Heisenberg
lattice in three dimensions using a fermionic representation for the localized
spins. The mean-field phase diagram exhibits a zero temperature quantum
critical point separating a spin liquid phase where the hybridization vanishes
and a Kondo phase where it does not. Two solutions can be stabilized in the
Kondo phase, namely a uniform hybridization when the band masses of the
conduction electrons and the spinons have the same sign, and a modulated one
when they have opposite sign. For the uniform case, we show that above a very
small temperature scale, the critical fluctuations associated with the
vanishing hybridization have dynamical exponent z=3, giving rise to a
resistivity that has a T log T behavior. We also find that the specific heat
coefficient diverges logarithmically in temperature, as observed in a number of
heavy fermion metals.Comment: new Figure 2, new results on spin susceptibility, some minor changes
to tex
One-dimensional surface states on a striped Ag thin film with stacking fault arrays
One-dimensional (1D) stripe structures with a periodicity of 1.3 nm are
formed by introduction of stacking fault arrays into a Ag thin film. The
surface states of such striped Ag thin films are studied using a low
temperature scanning tunneling microscope. Standing waves running in the
longitudinal direction and characteristic spectral peaks are observed by
differential conductance (dI/dV) measurements, revealing the presence of 1D
states on the surface stripes. Their formation can be attributed to quantum
confinement of Ag(111) surface states into a stripe by stacking faults. To
quantify the degree of confinement, the effective potential barrier at the
stacking fault for Ag(111) surface states is estimated from independent
measurements. A single quantum well model with the effective potential barrier
can reproduce the main features of dI/dV spectra on stripes, while a
Kronig-Penney model fails to do so. Thus the present system should be viewed as
decoupled 1D states on individual stripes rather than as anisotropic 2D Bloch
states extending over a stripe array.Comment: 10 pages, 6 figure
Evidence for biquadratic exchange in the quasi-two-dimensional antiferromagnet FePS
FePS is a van der Waals compound with a honeycomb lattice that is a good
example of a two-dimensional antiferromagnet with Ising-like anisotropy.
Neutron spectroscopy data from FePS3 were previously analysed using a
straight-forward Heisenberg Hamiltonian with a single-ion anisotropy. The
analysis captured most of the elements of the data, however some significant
discrepancies remained. The discrepancies were most obvious at the Brillouin
zone boundaries. The data are subsequently reanalysed allowing for unequal
exchange between nominally equivalent nearest-neighbours, which resolves the
discrepancies. The source of the unequal exchange is attributed to a
biquadratic exchange term in the Hamiltonian which most probably arises from a
strong magnetolattice coupling. The new parameters show that there are features
consistent with Dirac magnon nodal lines along certain Brillouin zone
boundaries.Comment: 8 pages, 4 figures. The following article has been accepted by the
Journal of Applied Physics. After it is published, it will be found at
(https://publishing.aip.org/resources/librarians/products/journals/). The
article was submitted as part of a special topic edition
(https://publishing.aip.org/publications/journals/special-topics/jap/2d-quantum-materials-magnetism-and-superconductivity/
About the screening of the charge of a proton migrating in a metal
The amount of screening of a proton in a metal, migrating under the influence
of an applied electric field, is calculated using different theoretical
formulations. First the lowest order screening expression derived by Sham
(1975) is evaluated. In addition 'exact' expressions are evaluated which were
derived according to different approaches. For a proton in a metal modeled as a
jellium the screening appears to be 15 +/- 10 %, which is neither negligible
not reconcilable with the controversial full-screening point of view of
Bosvieux and Friedel (1962). In reconsidering the theory of electromigration, a
new simplified linear-response expression for the driving force is shown to
lead to essentially the same result as found by Sorbello (1985), who has used a
rather complicated technique. The expressions allow for a reduction such that
only the scattering phase shifts of the migrating impurity are required.
Finally it is shown that the starting formula for the driving force of Bosvieux
and Friedel leads exactly to the zero-temperature limit of well-established
linear response descriptions, by which the sting of the controversy has been
removed.Comment: 14 pages, 5 figure
When Non-Gaussian States are Gaussian: Generalization of Non-Separability Criterion for Continuous Variables
We present a class of non-Gaussian two-mode continuous variable states for
which the separability criterion for Gaussian states can be employed to detect
whether they are separable or not. These states reduce to the two-mode Gaussian
states as a special case.Comment: Removed 1 figure, added reference
Organized Current Patterns in Disordered Conductors
We present a general theory of current deviations in straight current
carrying wires with random imperfections, which quantitatively explains the
recent observations of organized patterns of magnetic field corrugations above
micron-scale evaporated wires. These patterns originate from the most efficient
electron scattering by Fourier components of the wire imperfections with
wavefronts along the direction. We show that long range
effects of surface or bulk corrugations are suppressed for narrow wires or
wires having an electrically anisotropic resistivity
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