Spin-triplet superfluids can support exotic objects, such as half-quantum vortices characterized by the nontrivial winding of the spin structure. We present cantilever magnetometry measurements performed on mesoscopic samples of Sr(2)RuO(4), a spin-triplet superconductor. With micrometer-sized annular-shaped samples, we observed transitions between integer fluxoid states as well as a regime characterized by "half-integer transitions"--steps in the magnetization with half the height of the ones we observed between integer fluxoid states. These half-height steps are consistent with the existence of half-quantum vortices in superconducting Sr(2)RuO(4).

We measure quantum and thermal phase-slip rates using the standard deviation of the switching current in superconducting nanowires. Our rigorous quantitative analysis provides firm evidence for the presence of quantum phase slips (QPS) in homogeneous nanowires at high bias currents. We observe that as temperature is lowered, thermal fluctuations freeze at a characteristic crossover temperature Tq, below which the dispersion of the switching current saturates to a constant value, indicating the presence of QPS. The scaling of the crossover temperature Tq with the critical temperature Tc is linear, Tq ∝ Tc, which is consistent with the theory of macroscopic quantum tunneling. We can convert the wires from the initial amorphous phase to a single crystal phase, in situ, by applying calibrated voltage pulses. This technique allows us to probe directly the effects of the wire resistance, critical temperature and morphology on thermal and quantum phase slips.

We present a variational analysis for a half-quantum vortex (HQV) in the equal-spin-pairing superfluid state which, under suitable conditions, is believed to be realized in Sr2RuO4 and 3 He-A. Our approach is based on a description of the HQV in terms of a BCS-like wave function with a spin-dependent boost. We predict a novel feature: the HQV, if stable, should be accompanied by a non-zero spin polarization. Such a spin polarization would exist in addition to the one induced by the Zeeman coupling to the external field and hence may serve as an indicator in experimental search for HQV. When3 He is liquified and cooled into the millidegree regime it enters a new phase which has been proved to possess a spin triplet paired condensate. There also exists by now a growing body of experimental evidence that Sr 2 RuO 4 below 1.5 K is a spin triplet superconductor [1]. This implies the possibility of many interesting phenomena not expected in systems with spin singlet pairing. One of them is the existence of half-quantum vortices (HQV's) in the equal-spin-pairing (ESP) state of the spin triplet condensate [2,3].The pairing symmetry for 3 He is well established and the so-called A phase is confidently believed to realize an ESP spin triplet state [4,5]. While there is, to the best of our knowledge, no unambiguous observation of HQV in 3 He-A [6], there is a strong theoretical argument in favor of their existence at least under some assumptions on the geometry of the experiment. On the contrary, the pairing state of Sr 2 RuO 4 is currently poorly understood and the observation (or not) of HQV, along with other experimental information, would facilitate identification of the underlying pairing symmetry. In addition, there is a significant interest in HQV for topological quantum computing [13].It should be noted right away that the identification of the superconducting phase of Sr 2 RuO 4 with an ESP state does not by itself guarantee thermodynamic stability of HQV in this compound. Even under the assumption of negligible spin-orbit coupling, the kinetic energy of unscreened spin currents which accompany HQV disfavors its formation vis-à-vis the formation of a regular vortex where electromagnetic currents are screened over the length of the penetration depth. Such an unfavorable energy balance can be avoided by limiting the sample size to a few microns [7]. This however further complicates the experimental detection of HQV in Sr 2 RuO 4 .One of the most direct ways for detection of HQV is to look for spin currents which circulate around it. The usual techniques for spin current detection are based on the accumulation of spin and their straightforward application to this situation seems to be difficult. One can however use a fact that spin currents generate electric field. A very rough conservative estimate shows that for a ring of size 1µ the quadrupole electric field generated by the spin currents of HQV will create a potential difference of 1nV across the ring -quite small, but not beyond the capabilities of current exper...

We study the stochastic nature of switching current in hysteretic current-voltage characteristics of superconductor-graphene-superconductor junctions. We find that the dispersion of the switching current distribution scales with temperature as σ(I) proportional to T(α(G)) with α(G) as low as 1/3. This observation is in sharp contrast to the known Josephson junction behavior where σ(I) proportional to T(α(J)) with α(J)=2/3. We propose an explanation using a generalized version of Kurkijärvi's theory for the flux stability in rf-SQUID and attribute this anomalous effect to the temperature dependence of the critical current which persists down to low temperatures.