4 research outputs found
Frequency and temperature dependence of the anomalous Hall conductivity in a chiral px+ipy superconductor with impurities
We calculate frequency and temperature dependence of the anomalous ac Hall
conductivity induced by impurity scattering in a chiral px+ipy superconductor,
such as Sr2RuO4, with spontaneous time-reversal-symmetry breaking in the
absence of an external magnetic field. We consider two models of disorder,
Gaussian and non-Gaussian, characterized by the second and third moments of the
random impurity potential, respectively. Within both models, we find that the
anomalous Hall conductivity has a finite real value at zero frequency, exhibits
singularities at the threshold of photon absorption across the superconducting
gap, and decays as some power of the high frequency \Omega. The Hall
conductivity increases linearly with the decrease of temperature below the
superconducting transition and saturates at zero temperature. Using our results
for the high-frequency Hall conductivity, we estimate the polar Kerr angle for
light reflection from the material and compare it with the experimental
measurements in Sr2RuO4 by Xia et al., Phys. Rev. Lett. 97, 167002 (2006).Comment: 22 pages, 12 figures
Gauge-invariant electromagnetic response of a chiral px+ipy superconductor
We present a gauge-invariant theory of the electromagnetic response of a
chiral px+ipy superconductor in the clean limit. Due to the spontaneously
broken time-reversal symmetry, the effective action of the system contains an
anomalous term not present in conventional superconductors. As a result, the
electromagnetic charge and current responses contain anomalous terms, which
depend explicitly on the chirality of the superconducting order parameter.
These terms lead to a number of unusual effects, such as coupling of the
transverse currents to the collective plasma oscillations and a possibility of
inducing the charge density by the magnetic field perpendicular to the
conducting planes. We calculate the antisymmetric part of the conductivity
tensor (the intrinsic Hall conductivity) and show that it depends on the wave
vector of the electromagnetic field. We also show that the Mermin-Muzikar
magnetization current and the Hall conductivity are strongly suppressed at high
frequencies. Finally, we discuss implications of the theory to the experiments
in Sr2RuO4.Comment: 22 pages, 4 figures, final version as published in PR
Polar Kerr Effect as Probe for Time-Reversal Symmetry Breaking in Unconventional Superconductors
The search for broken time reversal symmetry (TRSB) in unconventional
superconductors intensified in the past year as more systems have been
predicted to possess such a state. Following our pioneering study of TRSB
states in SrRuO using magneto-optic probes, we embarked on a systematic
study of several other of these candidate systems. The primary instrument for
our studies is the Sagnac magneto-optic interferometer, which we recently
developed. This instrument can measure magneto-optic Faraday or Kerr effects
with an unprecedented sensitivity of 10 nanoradians at temperatures as low as
100 mK. In this paper we review our recent studies of TRSB in several systems,
emphasizing the study of the pseudogap state of high temperature
superconductors and the inverse proximity effect in superconductor/ferromagnet
proximity structures.Comment: A review pape
Evaluation of Spin-Triplet Superconductivity in Sr2RuO4
This review presents a summary and evaluations of the superconducting
properties of the layered ruthenate Sr2RuO4 as they are known in the autumn of
2011. This paper appends the main progress that has been made since the
preceding review by Mackenzie and Maeno was published in 2003. Here, special
focus is placed on the critical evaluation of the spin-triplet, odd-parity
pairing scenario applied to Sr2RuO4. After an introduction to superconductors
with possible odd-parity pairing, accumulated evidence for the pairing symmetry
of Sr2RuO4 is examined. Then, significant recent progress on the theoretical
approaches to the superconducting pairing by Coulomb repulsion is reviewed. A
section is devoted to some experimental properties of Sr2RuO4 that seem to defy
simple explanations in terms of currently available spin-triplet scenario. The
next section deals with some new developments using eutectic boundaries and
micro-crystals, which reveals novel superconducting phenomena related to chiral
edge states, odd-frequency pairing states, and half-fluxoid states. Some of
these properties are intimately connected with the properties as a topological
superconductor. The article concludes with a summary of knowledge emerged from
the study of Sr2RuO4 that are now more widely applied to understand the physics
of other unconventional superconductors, as well as with a brief discussion of
relatively unexplored but promising areas of ongoing and future studies of
Sr2RuO4.Comment: 31 pages, 35 figures, published in J. Phys. Soc. Jpn. as a review
article of Special Topic