136 research outputs found
The resonant magnetic mode: a common feature of high- superconductors
Inelastic neutron scattering experiments in high- cuprates have
evidenced a new magnetic excitation present in the superconducting state. In
particular, recent experiments on single layer TlBaCuO, performed near optimum doping ( K), provide evidence of a
sharp magnetic resonant mode below , similar to previous reports on the
YBCO and BSCCO bilayer systems. This result supports models that ascribe a key
role to magnetic excitations in the mechanism of superconductivity.Comment: Proceedings of the LT23 conference (Hiroshima-Aug2002
Spin Susceptibility in Underdoped
We report a comprehensive polarized and unpolarized neutron scattering study
of the evolution of the dynamical spin susceptibility with temperature and
doping in three underdoped single crystals of the \YBCO{6+x} high temperature
superconductor: \YBCO{6.5} (Tc = 52 K), \YBCO{6.7} (Tc = 67 K), and \YBCO{6.85}
(T_c = 87 K). Theoretical implications of these data are discussed, and a
critique of recent attempts to relate the spin excitations to the
thermodynamics of high temperature superconductors is given.Comment: minor revisions, to appear in PR
Neutron scattering search for static magnetism in oxygen ordered YBa2Cu3O6.5
We present elastic and inelastic neutron scattering results on highly oxygen
ordered YBa2Cu3O6.5 ortho-II. We find no evidence for the presence of ordered
magnetic moments to a sensitivity of 0.003 Bohr magnetons, an order of
magnitude smaller than has been suggested in theories of orbital or
d-density-wave (DDW) currents. The absence of sharp elastic peaks, shows that
the d-density-wave phase is not present, at least for the superconductor with
the doping of 6.5 and the ordered ortho-II structure. We cannot exclude the
possibility that a broad peak may exist with extremely short-range DDW
correlations. For less ordered or more doped crystals it is possible that
disorder may lead to static magnetism. We have also searched for the large
normal state spin gap that is predicted to exist in an ordered DDW phase.
Instead of a gap we find that the Q-correlated spin susceptibility persists to
the lowest energies studied, 6 meV. Our results are compatible with the
coexistence of superconductivity with orbital currents, but only if they are
dynamic, and exclude a sharp phase transition to an ordered d-density-wave
phase.Comment: 6 pages 4 figures RevTex Submitted to Phys Rev B January 23, 200
Competing orders in a magnetic field: spin and charge order in the cuprate superconductors
We describe two-dimensional quantum spin fluctuations in a superconducting
Abrikosov flux lattice induced by a magnetic field applied to a doped Mott
insulator. Complete numerical solutions of a self-consistent large N theory
provide detailed information on the phase diagram and on the spatial structure
of the dynamic spin spectrum. Our results apply to phases with and without
long-range spin density wave order and to the magnetic quantum critical point
separating these phases. We discuss the relationship of our results to a number
of recent neutron scattering measurements on the cuprate superconductors in the
presence of an applied field. We compute the pinning of static charge order by
the vortex cores in the `spin gap' phase where the spin order remains
dynamically fluctuating, and argue that these results apply to recent scanning
tunnelling microscopy (STM) measurements. We show that with a single typical
set of values for the coupling constants, our model describes the field
dependence of the elastic neutron scattering intensities, the absence of
satellite Bragg peaks associated with the vortex lattice in existing neutron
scattering observations, and the spatial extent of charge order in STM
observations. We mention implications of our theory for NMR experiments. We
also present a theoretical discussion of more exotic states that can be built
out of the spin and charge order parameters, including spin nematics and phases
with `exciton fractionalization'.Comment: 36 pages, 33 figures; for a popular introduction, see
http://onsager.physics.yale.edu/superflow.html; (v2) Added reference to new
work of Chen and Ting; (v3) reorganized presentation for improved clarity,
and added new appendix on microscopic origin; (v4) final published version
with minor change
On the relative positions of the peaks in Raman and tunneling spectra of d-wave superconductors
We study Raman intensity and the density of states
in isotropic 2D d-wave superconductors. For an ideal gas,
and have sharp peaks at and , respectively, where is the maximum value of the gap.
We study how the peak positions are affected by the fermionic damping due to
impurity scattering.
We show that while the damping generally shifts the peak positions to larger
frequencies, the peak in still occurs at almost twice the peak
position in and therefore cannot account for the experimentally
observed downturn shift of the peak frequency in in underdoped
cuprates compared to twice that in . We also discuss how the
fermionic damping affects the dynamical spin susceptibility.Comment: 5 pages, 2 figure
Organic and inorganic constituents of salt tolerant taro (Colocasia esculenta var Antiquorum) tissues cultured in saline media
Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model
We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h095%=3.47×10-25 when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering. © 2019 American Physical Society
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society
Erratum: "A Gravitational-wave Measurement of the Hubble Constant Following the Second Observing Run of Advanced LIGO and Virgo" (2021, ApJ, 909, 218)
[no abstract available
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