201,949 research outputs found
Evidence for very strong electron-phonon coupling in YBa_{2}Cu_{3}O_{6}
From the observed oxygen-isotope shift of the mid-infrared two-magnon
absorption peak of YBaCuO, we evaluate the oxygen-isotope
effect on the in-plane antiferromagnetic exchange energy . The exchange
energy in YBaCuO is found to decrease by about 0.9% upon
replacing O by O, which is slightly larger than that (0.6%) in
LaCuO. From the oxygen-isotope effects, we determine the lower
limit of the polaron binding energy, which is about 1.7 eV for
YBaCuO and 1.5 eV for LaCuO, in quantitative
agreement with angle-resolved photoemission data, optical conductivity data,
and the parameter-free theoretical estimate. The large polaron binding energies
in the insulating parent compounds suggest that electron-phonon coupling should
also be strong in doped superconducting cuprates and may play an essential role
in high-temperature superconductivity.Comment: 4 pages, 1 figur
Oxygen-isotope effect on the in-plane penetration depth in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} as revealed by muon-spin rotation
The oxygen-isotope (^16O/^18O) effect (OIE) on the in-plane penetration depth
in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} was studied by
muon-spin rotation. A pronounced OIE on was observed
with a relative isotope shift of
=-5(2)% for x =0.3 and -9(2)% for
x=0.4. It arises mainly from the oxygen-mass dependence of the in-plane
effective mass . The OIE exponents of T_{c} and of
exhibit a relation that appears to be generic for
cuprate superconductors.Comment: 4 pages, 4 eps figures, RevTex
Indirect Detection Signatures for the Origin of Asymmetric Dark Matter
We study the decay signatures of Asymmetric Dark Matter (ADM) via higher
dimension operators which are responsible for generating the primordial dark
matter (DM) asymmetry. Since the signatures are sensitive both to the nature of
the higher dimension operator generating the DM asymmetry and to the sign of
the baryon or lepton number that the DM carries, indirect detection may provide
a window into the nature of the mechanism which generates the DM asymmetry. We
consider in particular dimension-6 fermionic operators of the form , where (or operators related through a Hermitian conjugate) with
the scale around or just below the GUT scale. We derive constraints on ADM
particles both in the natural mass range (around a few GeV), as well as in the
range between 100 GeV to 10 TeV. For light ADM, we focus on constraints from
both the low energy gamma ray data and proton/anti-proton fluxes. For heavy
ADM, we consider -rays and proton/anti-proton fluxes, and we fit
data from AMS-02 and H.E.S.S. (neglecting the Fermi charged particle
fluxes which disagree with AMS-02 below 100 GeV). We show that, although the
best fit regions from electron/positron measurement are still in tension with
other channels on account of the H.E.S.S. measurement at high energies,
compared to an ordinary symmetric dark matter scenario, the decay of DM with a
primordial asymmetry reduces the tension. Better measurement of the flux at
high energy will be necessary to draw a definite conclusion about the viability
of decaying DM as source for the signals.Comment: Constraint from H.E.S.S. for heavy ADM scenario is included.
Constraint from anti-proton flux for light ADM scenario is included. Matched
to the version of publicatio
- β¦