24,942 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
Microwave-induced resistance oscillations in a back-gated GaAs quantum well
We performed effective mass measurements employing microwave-induced
resistance oscillation in a tunable-density GaAs/AlGaAs quantum well. Our main
result is a clear observation of an effective mass increase with decreasing
density, in general agreement with earlier studies which investigated the
density dependence of the effective mass employing Shubnikov- de Haas
oscillations. This finding provides further evidence that microwave-induced
resistance oscillations are sensitive to electron-electron interactions and
offer a convenient and accurate way to obtain the effective mass.Comment: 4 pages, 4 figure
Lattice QCD calculation of scattering length
We study s-wave pion-pion () scattering length in lattice QCD for
pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered
fermion formulation, we calculate the four-point functions for isospin
I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order
to extrapolate our simulation results. Extrapolating to the physical pion mass
gives the scattering lengths as and for isospin I=2 and 0 channels, respectively. Our lattice
simulation for scattering length in the I=0 channel is an exploratory
study, where we include the disconnected contribution, and our preliminary
result is near to its experimental value. These simulations are performed with
MILC 2+1 flavor gauge configurations at lattice spacing fm.Comment: Remove some typo
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
Collective quantum phase slips in multiple nanowire junctions
Realization of robust coherent quantum phase slips represents a significant
experimental challenge. Here we propose a new design consisting of multiple
nanowire junctions to realize a phase-slip flux qubit. It admits good
tunability provided by gate voltages applied on superconducting islands
separating nanowire junctions. In addition, the gates and junctions can be
identical or distinct to each other leading to symmetric and asymmetric setups.
We find that the asymmetry can improve the performance of the proposed device,
compared with the symmetric case. In particular, it can enhance the effective
rate of collective quantum phase slips. Furthermore, we demonstrate how to
couple two such devices via a mutual inductance. This is potentially useful for
quantum gate operations. Our investigation on how symmetry in multiple nanowire
junctions affects the device performance should be useful for the application
of phase-slip flux qubits in quantum information processing and quantum
metrology.Comment: 12 pages, 6 figure
Two-component model for the chemical evolution of the Galactic disk
In the present paper, we introduce a two-component model of the Galactic disk
to investigate its chemical evolution. The formation of the thick and thin
disks occur in two main accretion episodes with both infall rates to be
Gaussian. Both the pre-thin and post-thin scenarios for the formation of the
Galactic disk are considered. The best-fitting is obtained through
-test between the models and the new observed metallicity distribution
function of G dwarfs in the solar neighbourhood (Hou et al 1998). Our results
show that post-thin disk scenario for the formation of the Galactic disk should
be preferred. Still, other comparison between model predictions and
observations are given.Comment: 23 pages, 7 figure
AN INTELLIGENT PERSONAL NAVIGATOR INTEGRATING GNSS, RFID AND INS FOR CONTINUOUS POSITION DETERMINATION
Most of the developed pedestrian navigators rely on the use of satellite positioning (GNSS), sometimes also in combination with other sensors and positioning methods. In the project “Ubiquitous Cartography for Pedestrian Navigation” (UCPNAVI) we have integrated active Radio Frequency Identification (RFID) in combination with GNSS and Inertial Navigation Systems (INS) for continuous positioning. RFID can be employed in areas where no satellite positioning is possible due to obstructions, e.g. in urban canyons and indoor environments. In RFID positioning the location estimation is based on Received Signal Strength Indication (RSSI) which is a measurement of the power present in a received radio signal. The receiver can compute its position using various methods based on RSSI. In total, three different methods have been developed and investigated, i.e., cell-based positioning, trilateration and RFID location fingerprinting. These methods can be employed depending on the density of the RFID tags in the surrounding environment providing different levels of positioning accuracies. By integrating the three methods for positioning into an intelligent software package and developing a knowledge-based system it is possible to determine the pedestrian position automatically and ubiquitously. The concept of the intelligent software package is presented and described in the paper. For improvement of the positioning accuracy of cell-based positioning a modification has been developed, the so-called time-ased Cell of Origin (CoO) positioning method. This method uses also the measured RSSI above a certain threshold which is measured only if the user is located very close to the RFID tag. The test results showed that the accuracy of positioning using time-based CoO is in the range of 1.30 m. For continuous positioning of the pedestrian user, a low-cost INS is employed in addition. Since the INS components produce small measurement errors that accumulate over time and cause drift errors, the positions determined by RFID would be needed regularly for update. For the combined positioning of RFID and INS a time-varying Kalman filter is employed. The approach is tested in indoor environment in an office building of our university. For the combined positioning, an accuracy of around 1.00 m for continuous position determination is achieved. The new approach and the test results are also described in this paper.
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