7,212 research outputs found
Heat Kernel for Spin-3/2 Rarita-Schwinger Field in General Covariant Gauge
The heat kernel for the spin-3/2 Rarita-Schwinger gauge field on an arbitrary
Ricci flat space-time () is investigated in a family of covariant gauges
with one gauge parameter . The -dependent term of the kernel is
expressed by the spin-1/2 heat kernel. It is shown that the axial anomaly and
the one-loop divegence of the action are -independent, and that the
conformal anomaly has an -dependent total derivative term in
dimensions.Comment: 11 pages, latex, ITP-SB-94-3
Effect of Oscillating Landau Bandwidth on the Integer Quantum Hall Effect in a Unidirectional Lateral Superlattice
We have measured activation gaps for odd-integer quantum Hall states in a
unidirectional lateral superlattice (ULSL) -- a two-dimensional electron gas
(2DEG) subjected to a unidirectional periodic modulation of the electrostatic
potential. By comparing the activation gaps with those simultaneously measured
in the adjacent section of the same 2DEG sample without modulation, we find
that the gaps are reduced in the ULSL by an amount corresponding to the width
acquired by the Landau levels through the introduction of the modulation. The
decrement of the activation gap varies with the magnetic field following the
variation of the Landau bandwidth due to the commensurability effect. Notably,
the decrement vanishes at the flat band conditions.Comment: 7 pages, 6 figures, minor revisio
Modulation Induced Phase Transition from Fractional Quantum Hall to Stripe State at nu=5/3
We have investigated the effect of unidirectional periodic potential
modulation on the fractional quantum Hall (FQH) state at filling factors nu=5/3
and 4/3. For large enough modulation amplitude, we find that the resistivity
minimum at nu=5/3 gives way to a peak that grows with decreasing temperature.
Density matrix renormalization group calculation reveals that phase transition
from FQH state to unidirectional striped state having a period sim 4 l (with l
the magnetic length) takes place at nu=1/3 (equivalent to nu=5/3 by the
particle-hole symmetry) with the increase of the modulation amplitude,
suggesting that the observed peak is the manifestation of the stripe phase.Comment: 4 pages, 6 figures; minor revisio
Phase Variation in the Pulse Profile of SMC X-1
We present the results of timing and spectral analysis of X-ray high state
observations of the high-mass X-ray pulsar SMC X-1 with Chandra, XMM-Newton,
and ROSAT, taken between 1991 and 2001. The source has L_X ~ 3-5 x 10^38
ergs/s, and the spectra can be modeled as a power law plus blackbody with kT_BB
\~ 0.18 keV and reprocessed emission radius R_BB ~ 2 x 10^8 cm, assuming a
distance of 60 kpc to the source. Energy-resolved pulse profiles show several
distinct forms, more than half of which include a second pulse in the soft
profile, previously documented only in hard energies. We also detect
significant variation in the phase shift between hard and soft pulses, as has
recently been reported in Her X-1. We suggest an explanation for the observed
characteristics of the soft pulses in terms of precession of the accretion
disk.Comment: 4 pages, 4 figures, accepted for publication in ApJL; v2 minor
corrections, as will appear in ApJ
Tuning of magnetic quantum criticality in artificial Kondo superlattice CeRhIn5/YbRhIn5
The effects of reduced dimensions and the interfaces on antiferromagnetic
quantum criticality are studied in epitaxial Kondo superlattices, with
alternating layers of heavy-fermion antiferromagnet CeRhIn and 7 layers
of normal metal YbRhIn. As is reduced, the Kondo coherence temperature
is suppressed due to the reduction of effective Kondo screening. The N\'{e}el
temperature is gradually suppressed as decreases and the quasiparticle mass
is strongly enhanced, implying dimensional control toward quantum criticality.
Magnetotransport measurements reveal that a quantum critical point is reached
for superlattice by applying small magnetic fields. Remarkably, the
anisotropy of the quantum critical field is opposite to the expectations from
the magnetic susceptibility in bulk CeRhIn, suggesting that the Rashba
spin-orbit interaction arising from the inversion symmetry breaking at the
interface plays a key role for tuning the quantum criticality in the
two-dimensional Kondo lattice.Comment: Main text: 5 pages, 4 figures; Supplemental material:6 pages, 3
figures. Accepted for publication in Physical Review Letter
Controllable Rashba spin-orbit interaction in artificially engineered superlattices involving the heavy-fermion superconductor CeCoIn5
By using a molecular beam epitaxy technique, we fabricate a new type of
superconducting superlattices with controlled atomic layer thicknesses of
alternating blocks between heavy fermion superconductor CeCoIn_5, which
exhibits a strong Pauli pair-breaking effect, and nonmagnetic metal YbCoIn_5.
The introduction of the thickness modulation of YbCoIn_5 block layers breaks
the inversion symmetry centered at the superconducting block of CeCoIn_5. This
configuration leads to dramatic changes in the temperature and angular
dependence of the upper critical field, which can be understood by considering
the effect of the Rashba spin-orbit interaction arising from the inversion
symmetry breaking and the associated weakening of the Pauli pair-breaking
effect. Since the degree of thickness modulation is a design feature of this
type of superlattices, the Rashba interaction and the nature of pair-breaking
are largely tunable in these modulated superlattices with strong spin-orbit
coupling.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let
Reduced frequency noise in superconducting resonators
We report a reduction of the frequency noise in coplanar waveguide
superconducting resonators. The reduction of 7 dB is achieved by removing the
exposed dielectric substrate surface from the region with high electric fields
and by using NbTiN. In a model-analysis the surface of NbTiN is found to be a
negligible source of noise, experimentally supported by a comparison with NbTiN
on SiOx resonators. The reduction is additive to decreasing the noise by
widening the resonators.Comment: 4 pages, 4 figure
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