23,669 research outputs found
Scaling behavior of temperature-dependent thermopower in CeAu2Si2 under pressure
We report a combined study of in-plane resistivity and thermopower of the
pressure-induced heavy fermion superconductor CeAu2Si2 up to 27.8 GPa. It is
found that thermopower follows a scaling behavior in T/T* almost up to the
magnetic critical pressure pc ~ 22 GPa. By comparing with resistivity results,
we show that the magnitude and characteristic temperature dependence of
thermopower in this pressure range are governed by the Kondo coupling and
crystal-field splitting, respectively. Below pc, the superconducting transition
is preceded by a large negative thermopower minimum, suggesting a close
relationship between the two phenomena. Furthermore, thermopower of a variety
of Ce-based Kondo-lattices with different crystal structures follows the same
scaling relation up to T/T* ~ 2.Comment: 6 pages, 4 figures. Supplementary Material available on reques
Effect of disorder on the pressure-induced superconducting state of CeAu2Si2
CeAu2Si2 is a newly discovered pressure-induced heavy fermion superconductor
which shows very unusual interplay between superconductivity and magnetism
under pressure. Here we compare the results of high-pressure measurements on
single crystalline CeAu2Si2 samples with different levels of disorder. It is
found that while the magnetic properties are essentially sample independent,
superconductivity is rapidly suppressed when the residual resistivity of the
sample increases. We show that the depression of bulk Tc can be well understood
in terms of pair breaking by nonmagnetic disorder, which strongly suggests an
unconventional pairing state in pressurized CeAu2Si2. Furthermore, increasing
the level of disorder leads to the emergence of another phase transition at T*
within the magnetic phase, which might be in competition with
superconductivity.Comment: 7 pages, 7 figure
Nuclear Polarization in Quantum Point Contacts in an In-Plane Magnetic Field
Nuclear spin polarization is typically generated in GaAs quantum point
contacts (QPCs) when an out-of-plane magnetic field gives rise to
spin-polarized quantum Hall edge states, and a voltage bias drives transitions
between the edge states via electron-nuclear flip-flop scattering. Here, we
report a similar effect for QPCs in an in-plane magnetic field, where currents
are spin polarized but edge states are not formed. The nuclear polarization
gives rise to hysteresis in the d.c. transport characteristics, with relaxation
timescales around 100 seconds. The dependence of anomalous QPC conductance
features on nuclear polarization provides a useful test of their
spin-sensitivity.Comment: 5 page
Stabilized hot electron bolometer heterodyne receiver at 2.5 THz
We report on a method to stabilize a hot electron bolometer (HEB) mixer at 2.5 THz. The technique utilizes feedback control of the local oscillator (LO) laser power by means of a swing-arm actuator placed in the optical beam path. We demonstrate that this technique yields a factor of 50 improvement in the spectroscopic Allan variance time which is shown to be over 30 s in a 12 MHz noise fluctuation bandwidth. Furthermore, broadband signal direct detection effects may be minimized by this technique. The technique is versatile and can be applied to practically any local oscillator at any frequency
The branch processes of vortex filaments and Hopf Invariant Constraint on Scroll Wave
In this paper, by making use of Duan's topological current theory, the
evolution of the vortex filaments in excitable media is discussed in detail.
The vortex filaments are found generating or annihilating at the limit points
and encountering, splitting, or merging at the bifurcation points of a complex
function . It is also shown that the Hopf invariant of knotted
scroll wave filaments is preserved in the branch processes (splitting, merging,
or encountering) during the evolution of these knotted scroll wave filaments.
Furthermore, it also revealed that the "exclusion principle" in some chemical
media is just the special case of the Hopf invariant constraint, and during the
branch processes the "exclusion principle" is also protected by topology.Comment: 9 pages, 5 figure
Low Mass Dark Matter and Invisible Higgs Width In Darkon Models
The Standard Model (SM) plus a real gauge-singlet scalar field dubbed darkon
(SM+D) is the simplest model possessing a weakly interacting massive particle
(WIMP) dark-matter candidate. In this model, the parameters are constrained
from dark matter relic density and direct searches. The fact that interaction
between darkon and SM particles is only mediated by Higgs boson exchange may
lead to significant modifications to the Higgs boson properties. If the dark
matter mass is smaller than a half of the Higgs boson mass, the Higgs boson can
decay into a pair of darkons resulting in a large invisible branching ratio.
The Higgs boson will be searched for at the LHC and may well be discovered in
the near future. If a Higgs boson with a small invisible decay width will be
found, the SM+D model with small dark matter mass will be in trouble. We find
that by extending the SM+D to a two-Higgs-doublet model plus a darkon (THDM+D)
it is possible to have a Higgs boson with a small invisible branching ratio and
at the same time the dark matter can have a low mass. We also comment on other
implications of this model.Comment: RevTeX, 15 pages, 11 figures. A few typos corrected and some
references adde
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