155,999 research outputs found
Unconventional superconducting pairing symmetry induced by phonons
The possibility of non-s-wave superconductivity induced by phonons is
investigated using a simple model that is inspired by SrRuO. The model
assumes a two-dimensional electronic structure, a two-dimensional
spin-fluctuation spectrum, and three-dimensional electron-phonon coupling.
Taken separately, each interaction favors formation of spin-singlet pairs (of s
symmetry for the phonon interaction and d symmetry for the spin
interaction), but in combination, a variety of more unusual singlet and triplet
states are found, depending on the interaction parameters. This may have
important implications for SrRuO, providing a plausible explanation of
how the observed spin fluctuations, which clearly favor d pairing,
may still be instrumental in creating a superconducting state with a different
(e.g., p-wave) symmetry. It also suggests an interpretation of the large
isotope effect observed in SrRuO. These results indicate that phonons
could play a key role in establishing the order-parameter symmetry in
SrRuO, and possibly in other unconventional superconductors.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
Virial expansion for a strongly correlated Fermi gas with imbalanced spin populations
Quantum virial expansion provides an ideal tool to investigate the
high-temperature properties of a strongly correlated Fermi gas. Here, we
construct the virial expansion in the presence of spin population imbalance. Up
to the third order, we calculate the high-temperature free energy of a unitary
Fermi gas as a function of spin imbalance, with infinitely large, attractive or
repulsive interactions. In the latter repulsive case, we show that there is no
itinerant ferromagnetism when quantum virial expansion is applicable. We
therefore estimate an upper bound for the ferromagnetic transition temperature
. For a harmonically trapped Fermi gas at unitarity, we find that
, where is the Fermi temperature at the center
of the trap. Our result for the high-temperature equations of state may
confront future high-precision thermodynamic measurements.Comment: 7 pages, 5 figures, accepted in Phys. Rev.
Identification of photons in double beta-decay experiments using segmented germanium detectors - studies with a GERDA Phase II prototype detector
The sensitivity of experiments searching for neutrinoless double beta-decay
of germanium was so far limited by the background induced by external
gamma-radiation. Segmented germanium detectors can be used to identify photons
and thus reduce this background component.
The GERmanium Detector Array, GERDA, will use highly segmented germanium
detectors in its second phase. The identification of photonic events is
investigated using a prototype detector. The results are compared with Monte
Carlo data.Comment: 20 pages, 7 figures, to be submitted to NIM-
Pulse shape simulation for segmented true-coaxial HPGe detectors
A new package to simulate the formation of electrical pulses in segmented
true-coaxial high purity germanium detectors is presented. The computation of
the electric field and weighting potentials inside the detector as well as of
the trajectories of the charge carriers is described. In addition, the
treatment of bandwidth limitations and noise are discussed. Comparison of
simulated to measured pulses, obtained from an 18-fold segmented detector
operated inside a cryogenic test facility, are presented.Comment: 20 pages, 16 figure
Stripe, checkerboard, and liquid-crystal ordering from anisotropic p-orbital Fermi surfaces in optical lattices
We study instabilities of single-species fermionic atoms in the p-orbital
bands in two-dimensional optical lattices at noninteger filling against
interactions. Charge density wave and orbital density wave orders with stripe
or checkerboard patterns are found for attractive and repulsive interactions,
respectively. The superfluid phase, usually expected of attractively
interacting fermions, is strongly suppressed. We also use field theory to
analyze the possible phase-transitions from orbital stripe order to
liquid-crystal phases and obtain the phase diagram. The condition of
nearly-perfect Fermisurface nesting, which is key to the above results, is
shown robustly independent of fermion fillings in such p-orbital systems, and
the momentum of density wave oscillation is highly tunable.
Such remarkable features show the promise of making those exotic orbital
phases, which are of broad interest in condensed-matter physics, experimentally
realizable with optical lattice gases.Comment: final version, 8 pages, 5 figure
Local electronic structures on the superconducting interface
Motivated by the recent discovery of superconductivity on the heterointerface
, we theoretically investigate its local electronic
structures near an impurity considering the influence of Rashba-type spin-orbit
interaction (RSOI) originated in the lack of inversion symmetry. We find that
local density of states near an impurity exhibits the in-gap resonance peaks
due to the quasiparticle scattering on the Fermi surface with the reversal sign
of the pairing gap caused by the mixed singlet and RSOI-induced triplet
superconducting state. We also analyze the evolutions of density of states and
local density of states with the weight of triplet pairing component determined
by the strength of RSOI, which will be widely observed in thin films of
superconductors with surface or interface-induced RSOI, or various
noncentrosymmetric superconductors in terms of point contact tunneling and
scanning tunneling microscopy, and thus reveal an admixture of the spin singlet
and RSOI-induced triplet superconducting states.Comment: Phys. Rev. B 81, 144504 (2010)
Light-cone Distribution Amplitudes of Xi and their Applications
We present the light-cone distribution amplitudes of the Xi baryons up to
twist six on the basis of QCD conformal partial wave expansion to the leading
order conformal spin accuracy. The nonperturbative parameters relevant to the
DAs are determined in the framework of the QCD sum rule. The light-cone QCD sum
rule approach is used to investigate both the electromagnetic form factors of
Xi and the exclusive semileptonic decay of Xi_c as applications. Our
estimations on the magnetic moments are and
. The decay width of the process Xi_c->Xi
e^+\nu_e is evaluated to be , which is in
accordance with the experimental measurements and other theoretical approaches.Comment: 23 pages, 8 figures, version to appear in Phys. Rev.
Comparison of gluon flux-tube distributions for quark-diquark and quark-antiquark hadrons
The distribution of gluon fields in hadrons is of fundamental interest in
QCD. Using lattice QCD we have observed the formation of gluon flux tubes
within 3 quark (baryon) and quark plus antiquark (meson) systems for a wide
variety of spatial distributions of the color sources. In particular we have
investigated three quark configurations where two of the quarks are close
together and the third quark is some distance away, which approximates a quark
plus diquark string. We find that the string tension of the quark-diquark
string is the same as that of the quark-antiquark string on the same lattice.
We also compare the longitudinal and transverse profiles of the gluon flux
tubes for both sets of strings, and find them to be of similar radii and to
have similar vacuum suppression.Comment: 6 pages, 9 figures and 1 tabl
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