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Register a new userParity Violation in a Single Domain of Spin-Triplet Sr2RuO4 Superconductors
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We observed an unconventional parity-violating vortex in single domain Sr2RuO4 single crystals using a transport measurement. The current-voltage characteristics of submicron Sr2RuO4 shows that the induced voltage has anomalous components which are even function of the bias current. The results may suggest that the vortex itself has a helical internal structure characterized by a Hopf invariant (a topological invariant). We also discuss that the hydrodynamics of such a helical vortex causes the parity violation to retain the topological invariant.
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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.
We report on tunneling spectroscopy measurements using a Scanning Tunneling Microscope (STM) on the spin triplet superconductor Sr2RuO4. We find a negligible density of states close to the Fermi level and a fully opened gap with a value of $Delta$=0.28 meV, which disappears at T$_c$ = 1.5 K. $Delta$ is close to the result expected from weak coupling BCS theory ($Delta_0$=1.76kBT$_c$ = 0.229 meV). Odd parity superconductivity is associated with a fully isotropic gap without nodes over a significant part of the Fermi surface.
We show that mixed-parity superconductors may exhibit equal-spin pair correlations that are odd-in-time and can be tuned by means of an applied field. The direction and the amplitude of the pair correlator in the spin space turn out to be strongly dependent on the symmetry of the order parameter, and thus provide a tool to identify different types of singlet-triplet mixed configurations. We find that odd-in-time spin-polarized pair correlations can be generated without magnetic inhomogeneities in superconducting/ferromagnetic hybrids when parity mixing is induced at the interface.
The field dependence of the specific heat gamma(H) at lower temperatures in Sr2RuO4 is analyzed by solving microscopic Eilenberger equation numerically. We find that systematic gamma(H) behaviors from a concaved sqrt H to a convex H^{alpha} (alpha>1) under H orientation change are understood by taking account of the Pauli paramagnetic effect. The magnetizations are shown to be consistent with it. This implies either a singlet pairing or a triplet one with d-vector locked in the basal plane, which allows us to explain other mysteries of this compound in a consistent way.
Odd-parity, spin-triplet superconductor Sr2RuO4 has been found to feature exotic vortex physics including half-flux quanta trapped in a doubly connected sample and the formation of vortex lattices at low fields. The consequences of these vortex states on the low-temperature magnetoresistive behavior of mesoscopic samples of Sr2RuO4 were investigated in this work using ring device fabricated on mechanically exfoliated single crystals of Sr2RuO4 by photolithography and focused ion beam. With the magnetic field applied perpendicular to the in-plane direction, thin-wall rings of Sr2RuO4 were found to exhibit pronounced quantum oscillations with a conventional period of the full-flux quantum even though the unexpectedly large amplitude and the number of oscillations suggest the observation of vortex-flow-dominated magnetoresistance oscillations rather than a conventional Little-Parks effect. For rings with a thick wall, two distinct periods of quantum oscillations were found in high and low field regimes, respectively, which we argue to be associated with the lock-in of a vortex lattice in these thick-wall rings. No evidence for half-flux-quantum resistance oscillations were identified in any sample measured so far without the presence of an in-plane field.
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