Vortex imaging and vortex lattice transitions in superconducting Sr2RuO4single crystals

Abstract

Scanning Hall probe microscopy has been used to study vortex structures in very-high-quality single crystals of the unconventional superconductor Sr 2 RuO 4 (T c ∼ = 1.5 K). In none of our samples do we find credible evidence for the existence of the spontaneous fields or chiral domains predicted for the expected time-reversal symmetry-breaking order parameter. Even in our highest-quality samples we observe very strong vortex pinning and anomalous broadening of vortex profiles. The best samples also exhibit a clear field-driven triangular to square vortex lattice transition at low fields, as predicted by extended London theory calculations. In stark contrast, slightly less well-ordered samples exhibit pronounced vortex chaining/banding that we tentatively attribute to an extrinsic source of disorder.

Unconventional quantum oscillations in mesoscopic rings of spin-triplet superconductor Sr2RuO4

“…Neutron scattering study revealed the existence of a square rather than the traditional triangular vortex lattice over a large range of temperatures and magnetic fields applied along the c axis [6]. Surprisingly, vortex lattices were observed [7] at a field much lower than the lower critical field H c1 c = 50 Oe [8]. More specifically, the triangular Abrikosov vortex lattice was observed at a field as low as 5.4 Oe and a wellordered square lattice was found to form for fields above 12.7 Oe.…”

“…In an applied magnetic field, previous studies of the few-vortex states of mesoscopic Type II superconductors suggest that the free energy of the sample will be minimized if the ring is decorated by vortices [21]. In small fields, these vortices will be driven in and out of the ring because of the weak pinning potentials in crystalline Sr 2 RuO 4 and the lack of sample space to form a square vortex lattice expected for this field regime [7]. For the two thick-wall rings, on which two different periods of resistance oscillations were found, we note that the wall thickness, (w ∼ 4.8ξ(0)) and (w ∼ 5.5ξ(0)), respectively, would allow two vortices along the radial direction of the ring (the nominal size of the normal core of a vortex is 2ξ(0)).…”

Effect of electron irradiation on the fluctuation conductivity in YBa2Cu3O7−δ single crystals

“…According to contemporary concepts (see, for example, [5][6][7]), such a behavior of the ρ ab (Т) dependences can be caused by the transition to the so-called pseudogap state, characteristic for the "underdoped" compositions of HTSC compounds. A certain role in this is played by the presence of structural and kinematic anisotropy in the system [38][39][40][41][42]. On the other hand, it cannot be completely excluded that this feature can also be partially caused due to the presence of an additive contribution to the conductivity from impurity phases with higher T c .…”

Electro- and Heat Transfer in $$\mathbf{Cd}_{\mathbf{0.22}}\mathbf{\hbox {Hg}}_{\mathbf{0.78}}{} \mathbf{Te}$$ Cd 0.22 Hg

“…3 and, for example, [11]). A certain role in this is played by the presence of structural and kinematic anisotropy in the system [12][13][14][15].…”