6,622 research outputs found
Evolution of the Fermi surface of BiTeCl with pressure
We report measurements of Shubnikov-de Haas oscillations in the giant Rashba
semiconductor BiTeCl under applied pressures up to ~2.5 GPa. We observe two
distinct oscillation frequencies, corresponding to the Rashba-split inner and
outer Fermi surfaces. BiTeCl has a conduction band bottom that is split into
two sub-bands due to the strong Rashba coupling, resulting in two
spin-polarized conduction bands as well as a Dirac point. Our results suggest
that the chemical potential lies above this Dirac point, giving rise to two
Fermi surfaces. We use a simple two-band model to understand the pressure
dependence of our sample parameters. Comparing our results on BiTeCl to
previous results on BiTeI, we observe similar trends in both the chemical
potential and the Rashba splitting with pressure.Comment: 6 pages, 5 figure
Parametric resonance and spin-charge separation in 1D fermionic systems
We show that the periodic modulation of the Hamiltonian parameters for 1D
correlated fermionic systems can be used to parametrically amplify their
bosonic collective modes. Treating the problem within the Luttinger liquid
picture, we show how charge and spin density waves with different momenta are
simultaneously amplified. We discuss the implementation of our predictions for
cold atoms in 1D modulated optical lattices, showing that the fermionic
momentum distribution directly provides a clear signature of spin-charge
separation.Comment: 6 pages, 3 figures, published versio
The Hawking-Penrose singularity theorem for -Lorentzian metrics
We show that the Hawking--Penrose singularity theorem, and the generalisation
of this theorem due to Galloway and Senovilla, continue to hold for Lorentzian
metrics that are of -regularity. We formulate appropriate weak
versions of the strong energy condition and genericity condition for
-metrics, and of -trapped submanifolds. By regularisation, we
show that, under these weak conditions, causal geodesics necessarily become
non-maximising. This requires a detailed analysis of the matrix Riccati
equation for the approximating metrics, which may be of independent interest.Comment: Minor amendments in v4: Removed non-equivalent condition from Def.
2.2 and adapted Lemma 3.5 and the proof of Lemma 3.
Two-channel point-contact tunneling theory of superconductors
We introduce a two-channel tunneling model to generalize the widely used BTK
theory of point-contact conductance between a normal metal contact and
superconductor. Tunneling of electrons can occur via localized surface states
or directly, resulting in a Fano resonance in the differential conductance
. We present an analysis of within the two-channel model when
applied to soft point-contacts between normal metallic silver particles and
prototypical heavy-fermion superconductors CeCoIn and CeRhIn at high
pressures. In the normal state the Fano line shape of the measured is well
described by a model with two tunneling channels and a large
temperature-independent background conductance. In the superconducting state a
strongly suppressed Andreev reflection signal is explained by the presence of
the background conductance. We report Andreev signal in CeCoIn consistent
with standard -wave pairing, assuming an equal mixture of
tunneling into [100] and [110] crystallographic interfaces. Whereas in
CeRhIn at 1.8 and 2.0 GPa the signal is described by a -wave
gap with reduced nodal region, i.e., increased slope of the gap opening on the
Fermi surface. A possibility is that the shape of the high-pressure Andreev
signal is affected by the proximity of a line of quantum critical points that
extends from 1.75 to 2.3 GPa, which is not accounted for in our description of
the heavy-fermion superconductor.Comment: 13 pages, 13 figure
Quantum oscillations and a non-trivial Berry phase in the noncentrosymmetric superconductor BiPd
We report the measurements of de Haas-van Alphen (dHvA) oscillations in the
noncentrosymmetric superconductor BiPd. Several pieces of a complex multi-sheet
Fermi surface are identified, including a small pocket (frequency 40 T) which
is three dimensional and anisotropic. From the temperature dependence of the
amplitude of the oscillations, the cyclotron effective mass is (
0.1) . Further analysis showed a non-trivial -Berry phase is
associated with the 40 T pocket, which strongly supports the presence of
topological states in bulk BiPd and may result in topological superconductivity
due to the proximity coupling to other bands.Comment: 5 pages, 3 figure
Functional modulation of the transient outward current Ito by KCNE beta-subunits and regional distribution in human non-failing and failing hearts
Objectives: The function of Kv4.3 (KCND3) channels, which underlie the transient outward current I,, in human heart, can be modulated by several accessory subunits such as KChIP2 and KCNE1-KCNE5. Here we aimed to determine the regional expression of Kv4.3, KChIP2, and KCNE mRNAs in non-failing and failing human hearts and to investigate the functional consequences of subunit coexpression in heterologous expression systems.
Methods: We quantified mRNA levels for two Kv4.3 isoforms, Kv4.3-S and Kv4.3-L, and for KChIP2 as well as KCNE1-KCNE5 with real-time RT-PCR. We also studied the effects of KCNEs on Kv4.3 + KChIP2 current characteristics in CHO cells with the whole-cell voltage-clamp method.
Results: In non-failing hearts, low expression was found for KCNE1, KCNE3, and KCNE5, three times higher expression for KCNE2, and 60 times higher for KCNE4. Transmural gradients were detected only for KChIP2 in left and right ventricles. Compared to non-failing tissue, failing hearts showed higher expression of Kv4.3-L and KCNE1 and lower of Kv4.3-S, KChIP2, KCNE4, and KCNE5. In CHO cells, Kv4.3 + KChIP2 currents were differentially modified by co-expressed KCNEs: time constants of inactivation were shorter with KCNE1 and KCNE3-5 while time-to-peak was decreased, and V-0.5 of steady-state inactivation was shifted to more negative potentials by all KCNE subunits. Importantly, KCNE2 induced a unique and prominent 'overshoot' of peak current during recovery from inactivation similar to that described for human I-to while other KCNE subunits induced little (KCNE4,5) or no overshoot.
Conclusions: All KCNEs are expressed in the human heart at the transcript level. Compared to It. in native human myocytes, none of the combination of KChIP2 and KCNE produced an ideal congruency in current characteristics, suggesting that additional factors contribute to the regulation of the native I-to channel
Local suppression of the hidden order phase by impurities in URu2Si2
We consider the effects of impurities on the enigmatic hidden order (HO)
state of the heavy-fermion material URu2Si2. In particular, we focus on local
effects of Rh impurities as a tool to probe the suppression of the HO state. To
study local properties we introduce a lattice free energy, where the time
invariant HO order parameter "psi" and local antiferromagnetic (AFM) order
parameter M are competing orders. Near each Rh atom the HO order parameter is
suppressed, creating a hole in which local AFM order emerges as a result of
competition. These local holes are created in the fabric of the HO state like
in a Swiss cheese and "filled" with droplets of AFM order. We compare our
analysis with recent NMR results on URu2Si2 doped with Rh and find good
agreement with the data.Comment: 8 pages, 6 figure
Quantum response of dephasing open systems
We develop a theory of adiabatic response for open systems governed by
Lindblad evolutions. The theory determines the dependence of the response
coefficients on the dephasing rates and allows for residual dissipation even
when the ground state is protected by a spectral gap. We give quantum response
a geometric interpretation in terms of Hilbert space projections: For a two
level system and, more generally, for systems with suitable functional form of
the dephasing, the dissipative and non-dissipative parts of the response are
linked to a metric and to a symplectic form. The metric is the Fubini-Study
metric and the symplectic form is the adiabatic curvature. When the metric and
symplectic structures are compatible the non-dissipative part of the inverse
matrix of response coefficients turns out to be immune to dephasing. We give
three examples of physical systems whose quantum states induce compatible
metric and symplectic structures on control space: The qubit, coherent states
and a model of the integer quantum Hall effect.Comment: Article rewritten, two appendices added. 16 pages, 2 figure
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