Session+notes

After talk by G. Luke:
Q: What other materials show TRSB sigantures in muSR experiments? A: All that show evidence are also considered TRSB candidates for other reasons, but are not firmly established as such. The most relevant materials are UPt3, Sr2RuO4, PrOs4Sb12, and some other doped compound.

Q: What is the nature of these other candidate materials, such as their order parameter symmetry? A: They are still under depate. The orbital symmetry class seems to be E_2, but it is unclear whether the d-vector is locked by SO coupling or not. UPt3 belongs to a high-dimensional representation and appears to have multiple phases. It is possible that the field distribution leading to the muSR signal has relatively long tails, and the field scale could be somewhat larger if it occupies only a fraction of the sample volume.

Q: Could muons themselve create a local moment? A: This should produce a signal corresponding to a more homogeneous field, since there are only few non-equivalent muon stopping sites. Thus, it is not a likely explanation for the observed signal.

Q: Could on tune the muon energy? A: In principle yes, but it requires a different procedure for muon production with a lower yield. No one has attempted the integration of a He3 or dilution fridge into an appropriate beamline.

Q: Some other material break gauge symmetry before TR symmetry. Is it of any significance that TRSB sets in right at Tc for Sr2RuO4? The general consensus seemed to be that this is not the case. It was also noted that one enocunters different temperature dependences. The muSR TRSB signal varies linearly near Tc for Sr2RuO4, but as a square root for other materials.

After talk by J. Kirtley:
Q: Is there room for different surface state? The general consesus was that while the surface may have an effect through various measurements, it is unlikely to explain the apparent absence of chiral currents, since the surface state would have to extend several penetration depths into the sample in order for any lower lying edge currents to be fully screeened.

After talk by C. Hicks:
It was noted that a smooth cutoff in the gap Delta as a function of energy should not affect chiral currents. Similarly, edge scattering should not lead to a large change.

There was a general discussion on chiral currents in He3. They have no been detected directly, but there is one indirect magnetization measurement based on acoustic attenuation in a field, for which a small asymmetry was predicted. The experiment appeared to be troubled by hysteresis upon field reversal. If there were null-results, they were not published. The expected Faraday effect is still debated by one order of magnitude, and would be near the noise limit of the Kapitulnik group.

It was discussed whether the phase sensitive measurement by the Liu group imply small domains, and pointed out that many pi phase shifts would still give long range coherence. Ying Liu believes this scenario to be unlikely, and noted that there was no evidence of dynamic switching.

V. Yakovenko proposed a scanning experiment to directly probe the triplet pairing: Consider a junction between a singlet and a triplet superconductor, with d||z_hat for the latter. Assume paring amplitude in the off diagonal gap- matrix elements. -> diffetence between singlet and triplet pairing is just a sign in the gap matrix. The Andreev states (obtained from BdG) should have a well defined spin projection. Their energies for spin up and down, plotted as function of the phase difference across the junction, will have opposite signs because the sign difference in one of the off-diagonal paring amplitudes. A junction without external leads will minimize the energy w.r.t. the phase difference. Since this minimum depends on spins, the system should break summetry. Only Andreev states with the lower energy spin will be occupied, leading to a spin accumulation. Its magnitude might be on the order of 1 spin per surface atom. The temperature scale, i.e. difference between up and down energy, is set by the transparency of the junction.

Experimental evidence for the A-phase in He-3: - NMR - acoustic spectrum indicating collective modes. - fractional vortices on a texture.