404 research outputs found
Spin Hall Effect of Excitons
Spin Hall effect for excitons in alkali halides and in Cu_2O is investigated
theoretically. In both systems, the spin Hall effect results from the Berry
curvature in k space, which becomes nonzero due to lifting of degeneracies of
the exciton states by exchange coupling. The trajectory of the excitons can be
directly seen as spatial dependence of the circularly polarized light emitted
from the excitons. It enables us to observe the spin Hall effect directly in
the real-space time.Comment: 5 pages, 2 figure
Coherent inelastic backscattering of intense laser light by cold atoms
We present a nonperturbative treatment of coherent backscattering of intense
laser light from cold atoms, and predict a nonvanishing backscattering signal
even at very large intensities, due to the constructive (self-)interference of
inelastically scattered photons.Comment: minor change
Thermoelectric response near a quantum critical point of beta-YbAlB4 and YbRh2Si2: A comparative study
The thermoelectric coefficients have been measured on the Yb-based heavy
fermion compounds beta-YbAlB4 and YbRh2Si2 down to a very low temperature. We
observe a striking difference in the behavior of the Seebeck coefficient, S in
the vicinity of the Quantum Critical Point (QCP) in the two systems. As the
critical field is approached, S/T enhances in beta-YbAlB4 but is drastically
reduced in YbRh2Si2. While in the former system, the ratio of
thermopower-to-specific heat remains constant, it drastically drops near the
QCP in YbRh2Si2. In both systems, on the other hand, the Nernst coefficient
shows a diverging behavior near the QCP. The results provide a new window to
the way various energy scales of the system behave and eventually vanish near a
QCP
Quantum Criticality without Tuning in the Mixed Valence Compound beta-YbAlB4
Fermi liquid theory, the standard theory of metals, has been challenged by a
number of observations of anomalous metallic behavior found in the vicinity of
a quantum phase transition. The breakdown of the Fermi liquid is accomplished
by fine-tuning the material to a quantum critical point using a control
parameter such as the magnetic field, pressure, or chemical composition. Our
high precision magnetization measurements of the ultrapure f-electron based
superconductor {\beta}-YbAlB4 demonstrate a scaling of its free energy
indicative of zero-field quantum criticality without tuning in a metal. The
breakdown of Fermi-liquid behavior takes place in a mixed-valence state, in
sharp contrast with other known examples of quantum critical f-electron systems
that are magnetic Kondo lattice systems with integral valence.Comment: 26 pages, 7 figures including supporting online matelial
Strong valence fluctuation in the quantum critical heavy fermion superconductor beta-YbAlB4: A hard x-ray photoemission study
Electronic structures of the quantum critical superconductor beta-YbAlB4 and
its polymorph alpha-YbAlB4 are investigated by using bulk-sensitive hard x-ray
photoemission spectroscopy. From the Yb 3d core level spectra, the values of
the Yb valence are estimated to be ~2.73 and ~2.75 for alpha- and beta-YbAlB4,
respectively, thus providing clear evidence for valence fluctuations. The
valence band spectra of these compounds also show Yb2+ peaks at the Fermi
level. These observations establish an unambiguous case of a strong mixed
valence at quantum criticality for the first time among heavy fermion systems,
calling for a novel scheme for a quantum critical model beyond the conventional
Doniach picture in beta-YbAlB4.Comment: 4 pages, 3 figures, revised version accepted for publication in PR
Deterministic Weak Localization in Periodic Structures
The weak localization is found for perfect periodic structures exhibiting
deterministic classical diffusion. In particular, the velocity autocorrelation
function develops a universal quantum power law decay at 4 times Ehrenfest
time, following the classical stretched-exponential type decay. Such
deterministic weak localization is robust against weak enough randomness (e.g.,
quantum impurities). In the 1D and 2D cases, we argue that at the quantum limit
states localized in the Bravis cell are turned into Bloch states by quantum
tunnelling.Comment: 5 pages, 2 figure
- …