42 research outputs found
Dynamical theory of superfluidity in one dimension
A theory accounting for the dynamical aspects of the superfluid response of
one dimensional (1D) quantum fluids is reported. In long 1D systems the onset
of superfluidity is related to the dynamical suppression of quantum phase slips
at low temperatures. The effect of this suppression as a function of frequency
and temperature is discussed within the framework of the relevant correlation
function that is accessible experimentally, namely the momentum response
function. Application of these results to the understanding of the superfluid
properties of helium confined in nanometer-size pores, edge dislocations in
solid He, and ultra-cold atomic gases is also briefly discussed.Comment: 4.4 pages, 2 eps figures, and 1 page of supplementary informatio
Thermalization and Quantum Correlations in Exactly Solvable Models
The generalized Gibbs ensemble introduced for describing few body
correlations in exactly solvable systems following a quantum quench is related
to the nonergodic way in which operators sample, in the limit of infinite time
after the quench, the quantum correlations present in the initial state. The
nonergodicity of the correlations is thus shown \emph{analytically} to imply
the equivalence with the generalized Gibbs ensemble for quantum Ising and
XX spin chains as well as for the Luttinger model the thermodynamic limit,
and for a broad class of initial states and correlation functions of both local
and nonlocal operators.Comment: 12 pages, 4 figures. Expanded in response to Referee criticis
Anomalous Nonlocal Resistance and Spin-charge Conversion Mechanisms in Two-Dimensional Metals
We uncover two anomalous features in the nonlocal transport behavior of
two-dimensional metallic materials with spin-orbit coupling. Firstly, the
nonlocal resistance can have negative values and oscillate with distance, even
in the absence of a magnetic field. Secondly, the oscillations of the nonlocal
resistance under an applied in-plane magnetic field (Hanle effect) can be
asymmetric under field reversal. Both features are produced by direct
magnetoelectric coupling, which is possible in materials with broken inversion
symmetry but was not included in previous spin diffusion theories of nonlocal
transport. These effects can be used to identify the relative contributions of
different spin-charge conversion mechanisms. They should be observable in
adatom-functionalized graphene, and may provide the reason for discrepancies in
recent nonlocal transport experiments on graphene.Comment: 5 pages, 3 figures, and Supplementary Materials, to appear in Phys.
Rev. Let
Magnetic phases in the one-dimensional Kondo chain on a metallic surface
We study the low-temperature properties of a one-dimensional spin-1/2 chain
of magnetic impurities coupled to a (normal) metal environment by means of
anisotropic Kondo exchange. In the case of easy-plane anisotropy, we obtain the
phase diagram of this system at T=0. We show that the in-plane Kondo coupling
destabilizes the Tomonaga-Luttinger phase of the spin-chain, and leads to two
different phases: i) At strong Kondo coupling, the spins in the chain form
Kondo singlets and become screened by the metallic environment, and ii) At weak
and intermediate Kondo coupling, we find a novel dissipative phase
characterized by diffusive gapless spin excitations. The two phases are
separated by a quantum critical point of the Wilson-Fisher universality class
with dynamical exponent .Comment: 15 pages, 3 figures. New version contains clarifications about the
specific approximations. Accepted for publication in PR
Control of Spin Diffusion and Suppression of the Hanle Effect by the Coexistence of Spin and Valley Hall Effects
In addition to spin, electrons in many materials possess an additional
pseudo-spin degree of freedom known as 'valley'. In materials where the spin
and valley degrees of freedom are weakly coupled, they can be both excited and
controlled independently. In this work, we study a model describing the
interplay of the spin and valley Hall effects in such two-dimensional
materials. We demonstrate the emergence of an additional longitudinal neutral
current that is both spin and valley polarized. The additional neutral current
allows to control the spin density by tuning the magnitude of the valley Hall
effect. In addition, the interplay of the two effects can suppress the Hanle
effect, that is, the oscillation of the nonlocal resistance of a Hall bar
device with in-plane magnetic field. The latter observation provides a possible
explanation for the absence of the Hanle effect in a number of recent
experiments. Our work opens also the possibility to engineer the conversion
between the valley and spin degrees of freedom in two-dimensional materials.Comment: 15 pages, 2 figure
Graphene Electrodynamics in the presence of the Extrinsic Spin Hall Effect
We extend the electrodynamics of two dimensional electron gases to account
for the extrinsic spin Hall effect (SHE). The theory is applied to doped
graphene decorated with a random distribution of absorbates that induce
spin-orbit coupling (SOC) by proximity. The formalism extends previous
semiclassical treatments of the SHE to the non-local dynamical regime. Within a
particle-number conserving approximation, we compute the conductivity,
dielectric function, and spin Hall angle in the small frequency and wave vector
limit. The spin Hall angle is found to decrease with frequency and wave number,
but it remains comparable to its zero-frequency value around the frequency
corresponding to the Drude peak. The plasmon dispersion and linewidth are also
obtained. The extrinsic SHE affects the plasmon dispersion in the long
wavelength limit, but not at large values of the wave number. This result
suggests an explanation for the rather similar plasmonic response measured in
exfoliated graphene, which does not exhibit the SHE, and graphene grown by
chemical vapor deposition, for which a large SHE has been recently reported.
Our theory also lays the foundation for future experimental searches of SOC
effects in the electrodynamic response of two-dimensional electron gases with
SOC disorder.Comment: 12 pages, 4 figure