11,235 research outputs found
Symmetry Considerations for the Detection of Second-Harmonic Generation in Cuprates in the Pseudogap phase
A proposal to test the proposed time-reversal and inversion breaking phase in
the Pseudogap region of the Cuprate compounds through the variation of
Second-harmonic generation intensity with temperature and polarization and
angle of incidence is presented.Comment: 7 pages, 2 figures include
Theory of Superconductivity in the Cuprates
The quantum critical fluctuations of the time-reversal breaking order
parameter which is observed in the pseudogap regime of the Cuprates are shown
to couple to the lattice equivalent of the local angular momentum of the
fermions. Such a coupling favors scattering of fermions through angles close to
which is unambiguously shown to promote d-wave pairing. The right
order of magnitude of both and the normalized zero temperature gap
are calculated using the same fluctuations which give the
temperature, frequency and momentum dependence of the the anomalous normal
state properties for dopings near the quantum-critical value and with two
parameters extracted from fit to such experiments.Comment: Accepted for publication in PRB with the title "Theory of the
coupling of quantum-critical fluctuations to fermions and d-wave
superconductivity in the cuprates
Detecting Dichroism in Angle Resolved Photoemission
Recently, the time-reversal violation predicted for the pseudogap phase of
the cuprates, which was observed by dichroism experiments using Angle-Resolved
Photoemission has also been observed by polarized neutron diffraction. Earlier
derivation of dichroism in angle resolved photoemission due to time-reversal
violation relied on existence of mirror planes in the crystal. Here the theory
of the effect is generalized to the case that mirror plane symmetry is weakly
violated due to perturbing potentials such as a superstructure.Comment: Addenda to Simon and Varma, Phys. Rev. Lett. vol. 89, 247003-1 (2002)
and A. Kaminski, et al., Nature, vol. 416, 610 (2002
Gyrotropic Birefringence in the Under-doped Cuprates
The optical effects due to the loop-current order parameter in under-doped
cuprates are studied in order to understand the recent observation of unusual
birefringence in electromagnetic propagation in under-doped cuprates. It is
shown why birefringence occurs even in multiple domains of order with size of
domains much smaller than the wave-length and in twinned samples. Not only is
there a rotation of polarization of incident light but also a rotation of the
principal optical axis from the crystalline axes. Both are calculated in
relative agreement with experiments in terms of the same parameters. The
magnitude of the effect is orders of magnitude larger than the unusual Kerr
effect observed in under-doped cuprates earlier. The new observations,
including their comparison with the Kerr effect, test the symmetry of the
proposed order decisively and confirm the conclusions from polarized neutron
scattering
Some Experimental Signatures to look for Time-reversal Violating superconductors
We discuss some experimental signatures associated with the topological
structures of unconventional superconductor order parameters of form
, where , or . Specifically, we study
the topological surface states on the and equivalent surfaces of such
superconductors which are observable in Andreev tunneling experiments, as well
as evaluate the magnetic flux trapped in superconducting rings of such
superconductors with multiple grain-boundary Josephson junctions. Previous
experiments are examined and several new experiments suggested.Comment: 11 pages, 3 figure
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