20,744 research outputs found
Phase Diagram of the Holstein-Hubbard Two-Leg Ladder
Using a functional renormalization group method, we obtain the phase diagram
of the two-leg ladder system within the Holstein-Hubbard model, which includes
both electron-electron and electron-phonon interactions. Our renormalization
group technique allows us to analyze the problem for both weak and strong
electron-phonon coupling. We show that, in contrast results from conventional
weak coupling studies, electron-phonon interactions can dominate
electron-electron interactions because of retardation effects.Comment: 4 page
Spin Relaxation Times of Single-Wall Carbon Nanotubes
We have measured temperature ()- and power-dependent electron spin
resonance in bulk single-wall carbon nanotubes to determine both the
spin-lattice and spin-spin relaxation times, and . We observe that
increases linearly with from 4 to 100 K, whereas {\em
decreases} by over a factor of two when is increased from 3 to 300 K. We
interpret the trend as spin-lattice relaxation via
interaction with conduction electrons (Korringa law) and the decreasing
dependence of as motional narrowing. By analyzing the latter, we
find the spin hopping frequency to be 285 GHz. Last, we show that the Dysonian
lineshape asymmetry follows a three-dimensional variable-range hopping behavior
from 3 to 20 K; from this scaling relation, we extract a localization length of
the hopping spins to be 100 nm.Comment: 6 pages, 3 figure
Broken time-reversal symmetry in Josephson junction involving two-band superconductors
A novel time-reversal symmetry breaking state is found theoretically in the
Josephson junction between the two-gap superconductor and the conventional
s-wave superconductor. This occurs due to the frustration between the three
order parameters analogous to the two antiferromagnetically coupled XY-spins
put under a magnetic field. This leads to the interface states with the
energies inside the superconducting gap. Possible experimental observations of
this state with broken time-reversal symmetry are discussed.Comment: 9 pages, 1 figur
Stable directions for small nonlinear Dirac standing waves
We prove that for a Dirac operator with no resonance at thresholds nor
eigenvalue at thresholds the propagator satisfies propagation and dispersive
estimates. When this linear operator has only two simple eigenvalues close
enough, we study an associated class of nonlinear Dirac equations which have
stationary solutions. As an application of our decay estimates, we show that
these solutions have stable directions which are tangent to the subspaces
associated with the continuous spectrum of the Dirac operator. This result is
the analogue, in the Dirac case, of a theorem by Tsai and Yau about the
Schr\"{o}dinger equation. To our knowledge, the present work is the first
mathematical study of the stability problem for a nonlinear Dirac equation.Comment: 62 page
Optical Spectroscopic Survey of High-latitude WISE-selected Sources
We report on the results of an optical spectroscopic survey at high Galactic latitude (|b| ≥ 30°) of a sample of WISE-selected targets, grouped by WISE W1 (λ_eff = 3.4 μm) flux, which we use to characterize the sources WISE detected. We observed 762 targets in 10 disjoint fields centered on ultraluminous infrared galaxy candidates using DEIMOS on Keck II. We find 0.30 ± 0.02 galaxies arcmin–2 with a median redshift of z = 0.33 ± 0.01 for the sample with W1 ≥ 120 μJy. The foreground stellar densities in our survey range from 0.23 ± 0.07 arcmin–2 to 1.1 ± 0.1 arcmin–2 for the same sample. We obtained spectra that produced science grade redshifts for ≥90% of our targets for sources with W1 flux ≥120 μJy that also had an i-band flux gsim 18 μJy. We used this for targeting very preliminary data reductions available to the team in 2010 August. Our results therefore present a conservative estimate of what is possible to achieve using WISE's Preliminary Data Release for the study of field galaxies
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Reversible writing of high-mobility and high-carrier-density doping patterns in two-dimensional van der Waals heterostructures
A key feature of two-dimensional materials is that the sign and concentration of their carriers can be externally controlled with techniques such as electrostatic gating. However, conventional electrostatic gating has limitations, including a maximum carrier density set by the dielectric breakdown, and ionic liquid gating and direct chemical doping also suffer from drawbacks. Here, we show that an electron-beam-induced doping technique can be used to reversibly write high-resolution doping patterns in hexagonal boron nitride-encapsulated graphene and molybdenum disulfide (MoS2) van der Waals heterostructures. The doped MoS2 device exhibits an order of magnitude decrease of subthreshold swing compared with the device before doping, whereas the doped graphene devices demonstrate a previously inaccessible regime of high carrier concentration and high mobility, even at room temperature. We also show that the approach can be used to write high-quality p–n junctions and nanoscale doping patterns, illustrating that the technique can create nanoscale circuitry in van der Waals heterostructures
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