Polar Kerr effect as probe for time-reversal symmetry breaking in unconventional superconductors

Abstract

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 Sr2RuO4 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.

Frequency and temperature dependence of the anomalous ac Hall conductivity in a chiralpx+ipysuperconductor with impurities

“…In Sec. III, we calculate σ (3) xy (ω) originating from the skew-scattering diagrams for the nonGaussian model of disorder. In Sec.…”

“…Eqs. (29) and (31) give a complete answer for the real and imaginary parts of the anomalous Hall conductivity σ (3) xy (ω) for arbitrary frequency and temperature. Now we focus on the limit T = 0, where the function H(x) can be calculated analytically by setting the tanh function to unity in Eq.…”

“…In this state, the Cooper pairs have the angular momentum L z = ±1 pointing perpendicular to the conducting layers of Sr 2 RuO 4 . This order parameter breaks the timereversal symmetry and is the two-dimensional analogue of the A phase in superfluid 3 He [7][8][9]. There is substantial experimental evidence indicating that Sr 2 RuO 4 is indeed a spin-triplet [10,11] p-wave [12] superconductor.…”

“…These experiments measured the rotation angle θ K of the polarization plane of light upon normal reflected from the material surface. A non-zero value of the Kerr angle θ K indicates the TRSB in the sample [3]. Positive and negative values of θ K represent clockwise and counterclockwise rotation of polarization and indicate two possible ways of spontaneous breaking of the time-reversal symmetry.…”

Spin rotational symmetry breaking by orbital current patterns in two-leg ladders

“…10,11 In this latter case the threeband nature of the system is crucial, since currents flow along closed loops formed by Cu-O bonds in such a way that translational symmetry is preserved, while time-reversal symmetry is broken. On the experimental front specific signatures compatible with uniform currents where observed [12][13][14][15] even if the issue is still controversial. 16,17 On the theoretical side significant efforts were made to probe the possible existence of such a phase, either using numerical approaches [18][19][20] or starting from Mott insulating side.…”