1,471 research outputs found
Evidence for two distinct energy scales in the Raman spectra of YBa2(CuNi)O6.95
We report low energy electronic Raman scattering from Ni-substituted
YBa2Cu3O6.95 single crystals with Tc ranging from 92.5 K to 78 K. The fully
symmetrical A1g channel and the B1g channel which is sensitive to the dx2-y2
gap maximum have been explored. The energy of the B1g pair-breaking peak
remains constant under Ni doping while the energy of the A1g peak scales with
Tc (EA1g/Tc=5). Our data show that the A1g peak tracks the magnetic resonance
peak observed in inelastic neutron scattering yielding a key explanation to the
long-standing problem of the origin the A1g peak.Comment: 10 pages, 4 figures and 1 tabl
Anomalously slow spin dynamics and short-range correlations in the quantum spin ice systems Yb2Ti2O7 and Yb2Sn2O7
We report a positive muon spin relaxation and rotation (\muSR) study of the
quantum spin ice materials Yb2Ti2O7 and Yb2Sn2O7 focusing on the low field
response. In agreement with earlier reports, data recorded in small
longitudinal fields evidence anomalously slow spin dynamics in the microsecond
range below the temperature T_c at which the specific heat displays an intense
peak, namely T_c = 0.24 K and 0.15 K, respectively, for the two systems. We
found that slow dynamics extends above T_c up to at least 0.7 K for both
compounds. The conventional dynamical Gaussian Kubo-Toyabe model describes the
\muSR spectra recorded above T_c. At lower temperatures a published analytical
extension of the Gaussian Kubo-Toyabe model provides a good description,
consistent with the existence of short-range magnetic correlations. While the
physical response of the two systems is qualitatively the same, Yb2Ti2O7
exhibits a much larger local magnetic susceptibility than Yb2Sn2O7 below T_c.
Considering previously reported ac susceptibility, neutron scattering and \muSR
results, we suggest the existence of anomalously slow spin dynamics to be a
common physical property of pyrochlore magnetic materials. The possibility of
molecular spin substructures to be associated to the slow dynamics and
therefore the short-range correlations is mentioned. The slow spin dynamics
observed under field does not exclude the presence of much faster dynamics
detected in extremely low or zero field.Comment: 11 pages, 10 figure
Spin Dynamics in Cuprates: Optical Conductivity of HgBa2CuO4
The electron-boson spectral density function I^2ChiOmega responsible for
carrier scattering of the high temperature superconductor HgBa2CuO4 (Tc = 90 K)
is calculated from new data on the optical scattering rate. A maximum entropy
technique is used. Published data on HgBa2Ca2Cu3O8 (Tc = 130 K) are also
inverted and these new results are put in the context of other known cases. All
spectra (with two notable exceptions) show a peak at an energy (Omega_r)
proportional to the superconducting transition temperature Omega_r ~= 6.3
kB.Tc. This charge channel relationship follows closely the magnetic resonance
seen by polarized neutron scattering, Omega_r^{neutron} ~= 5.4 kB.Tc. The
amplitudes of both peaks decrease strongly with increasing temperature. In some
cases, the peak at Omega_r is weak and the spectrum can have additional maxima
and a background extending up to several hundred meV
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