20,793 research outputs found
Zeeman-Induced Gapless Superconductivity with Partial Fermi Surface
We show that an in-plane magnetic field can drive two-dimensional
spin-orbit-coupled systems under superconducting proximity effect into a
gapless phase where parts of the normal state Fermi surface are gapped, and the
ungapped parts are reconstructed into a small Fermi surface of Bogoliubov
quasiparticles at zero energy. Charge distribution, spin texture, and density
of states of such "partial Fermi surface" are discussed. Material platforms for
its physical realization are proposed.Comment: 5 pages, 2 figure
Unconventional Superconductivity and Density Waves in Twisted Bilayer Graphene
We study electronic ordering instabilities of twisted bilayer graphene with
electrons per supercell, where correlated insulator state and
superconductivity are recently observed. Motivated by the Fermi surface nesting
and the proximity to Van Hove singularity, we introduce a hot-spot model to
study the effect of various electron interactions systematically. Using
renormalization group method, we find /-wave superconductivity and
charge/spin density wave emerge as the two types of leading instabilities
driven by Coulomb repulsion. The density wave state has a gapped energy
spectrum at and yields a single doubly-degenerate pocket upon doping to
. The intertwinement of density wave and superconductivity and the
quasiparticle spectrum in the density wave state are consistent with
experimental observations.Comment: 15 pages, 12 figures; updated discussion and analysis on density wave
state
Non-Fermi liquid states in the pressurized system: two critical points
In the archetypal strongly correlated electron superconductor CeCuSi
and its Ge-substituted alloys CeCu(SiGe) two quantum
phase transitions -- one magnetic and one of so far unknown origin -- can be
crossed as a function of pressure \cite{Yuan 2003a}. We examine the associated
anomalous normal state by detailed measurements of the low temperature
resistivity () power law exponent . At the lower critical point
(at , ) depends strongly on Ge
concentration and thereby on disorder level, consistent with a
Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic
fluctuations. By contrast, is independent of at the upper quantum
phase transition (at , ), suggesting critical
scattering from local or Q=0 modes, in agreement with a density/valence
fluctuation approach.Comment: 4 pages, including 4 figures. New results added. Significant changes
on the text and Fig.
Edelstein effect and supercurrent diode effect
We self-consistently calculate the supercurrent diode effect from microscopic
models of quasi one- and two-dimensional clean superconductors with spin-orbit
coupling under external Zeeman fields, and show that the Edelstein effect is
responsible for the supercurrent diode effect. In turn, the supercurrent diode
effect may serve as a direct measurement of the Edelstein effect as its
application.Comment: 4 pages+ 1 page references, 1 figur
The upper critical field and its anisotropy in LiFeAs
The upper critical field of LiFeAs single crystals has
been determined by measuring the electrical resistivity using the facilities of
pulsed magnetic field at Los Alamos. We found that of LiFeAs
shows a moderate anisotropy among the layered iron-based superconductors; its
anisotropic parameter monotonically decreases with decreasing
temperature and approaches as . The upper
critical field reaches 15T () and 24.2T () at
1.4K, which value is much smaller than other iron-based high
superconductors. The temperature dependence of can be
described by the Werthamer-Helfand-Hohenberg (WHH) method, showing orbitally
and (likely) spin-paramagnetically limited upper critical field for and , respectively.Comment: 5 pages,5 figure
The magnetoresistance and Hall effect in CeFeAsO: a high magnetic field study
The longitudinal electrical resistivity and the transverse Hall resistivity
of CeFeAsO are simultaneously measured up to a magnetic field of 45T using the
facilities of pulsed magnetic field at Los Alamos. Distinct behaviour is
observed in both the magnetoresistance Rxx({\mu}0H) and the Hall resistance
Rxy({\mu}0H) while crossing the structural phase transition at Ts \approx 150K.
At temperatures above Ts, little magnetoresistance is observed and the Hall
resistivity follows linear field dependence. Upon cooling down the system below
Ts, large magnetoresistance develops and the Hall resistivity deviates from the
linear field dependence. Furthermore, we found that the transition at Ts is
extremely robust against the external magnetic field. We argue that the
magnetic state in CeFeAsO is unlikely a conventional type of spin-density-wave
(SDW).Comment: 4 pages, 3 figures SCES2010, To appear in J. Phys.: Conf. Ser. for
SCES201
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