Orientation Of Vortex Lattice Research Articles

Rotation of the magnetic vortex lattice in Ru7B3 driven by the effects of broken time-reversal and inversion symmetry

We observe a hysteretic reorientation of the magnetic vortex lattice in the noncentrosymmetric superconductor Ru7B3, with the change in orientation driven by altering magnetic field below Tc. Normally a vortex lattice chooses either a single or degenerate set of orientations with respect to a crystal lattice at any given field or temperature, a behavior well described by prevailing phenomenological and microscopic theories. Here, in the absence of any typical VL structural transition, we observe a continuous rotation of the vortex lattice which exhibits a pronounced hysteresis and is driven by a change in magnetic field. We propose that this rotation is related to the spontaneous magnetic fields present in the superconducting phase, which are evidenced by the observation of time-reversal symmetry breaking, and the physics of broken inversion symmetry. Finally, we develop a model from the Ginzburg-Landau approach which shows that the coupling of these to the vortex lattice orientation can result in the rotation we observe.

Vortex patterns and the critical rotational frequency in rotating dipolar Bose-Einstein condensates

Based on the two-dimensional mean-field equations for pancake-shaped dipolar Bose-Einstein condensates in a rotating frame with both attractive and repulsive dipole-dipole interaction (DDI) as well as arbitrary polarization angle, we study the profiles of the single vortex state and show how the critical rotational frequency change with the s-wave contact interaction strengths, DDI strengths and the polarization angles. In addition, we find numerically that at the `magic angle' $\vartheta=\arccos(\sqrt{3}/3)$, the critical rotational frequency is almost independent of the DDI strength. By numerically solving the dipolar GPE at high rotational speed, we identify different patterns of vortex lattices which strongly depend on the polarization direction. As a result, we undergo a study of vortex lattice structures for the whole regime of polarization direction and find evidence that the vortex lattice orientation tends to be aligned with the direction of the dipoles.

Vortex lattice structure inBaFe2(As0.67P0.33)2via small-angle neutron scattering

We have observed a magnetic vortex lattice (VL) in ${\mathrm{BaFe}}_{2}({\mathrm{As}}_{0.67}{\mathrm{P}}_{0.33}){}_{2}$ (BFAP) single crystals by small-angle neutron scattering. With the field along the $c$ axis, a nearly isotropic hexagonal VL was formed in the field range from 1 to 16 T, and no symmetry changes in the VL were observed. The temperature dependence of the VL signal was measured and confirms the presence of (non-$d$-wave) nodes in the superconducting gap structure for measurements at 5 T and below. The nodal effects were suppressed at high fields. At low fields, a VL reorientation transition was observed between 1 and 3 T, with the VL orientation changing by ${45}^{\ensuremath{\circ}}$. Below 1 T, the VL structure was strongly affected by pinning and the diffraction pattern had a fourfold symmetry. We suggest that this (and possibly also the VL reorientation) is due to pinning to defects aligned with the crystal structure, rather than being intrinsic. The temperature dependence of the scaled intensity suggests that BFAP possesses at least one full gap and one nodal gap with circular symmetry. Judging from the symmetry, the node structure should take the form of an ``accidental'' circular line node, which is consistent with recent angle-resolved photoemission spectroscopy results [Y. Zhang, Z. R. Ye, Q. Q. Ge, F. Chen, J. Jiang, M. Xu, B. P. Xie, and D. L. Feng, Nature Physics 8, 371 (2012).].

Rotation of Triangular Vortex Lattice in the Two-Band Superconductor MgB2

To identify the contributions of the multiband nature and the anisotropy of a microscopic electronic structure to a macroscopic vortex lattice morphology, we develop a method based on the Eilenberger theory near \(H_{\text{c2}}\) combined with the first-principles band calculation to estimate the stable vortex lattice configuration. For a typical two-band superconductor MgB2, successive transitions of vortex lattice orientation that have been observed recently by small angle neutron scattering [Das et al.: Phys. Rev. Lett. 108 (2012) 167001] are explained by the characteristic field-dependence of two-band superconductivity and the competition of sixfold anisotropy between the σ- and π-bands. The reentrant transition at low temperature reflects the Fermi velocity anisotropy of the σ-band.

Vortex Lattice Studies inCeCoIn5withH⊥c

We present small angle neutron scattering studies of the vortex lattice (VL) in CeCoIn5 with magnetic fields applied parallel (H) to the antinodal [100] and nodal [110] directions. For H || [100], a single VL orientation is observed, while a 90 degree reorientation transition is found for H || [110]. For both field orientations and VL configurations we find a distorted hexagonal VL with an anisotropy, Gamma = 2.0 +/- 0.05. The VL form factor shows strong Pauli paramagnetic effects similar to what have previously been reported for H || [001]. At high fields, above which the upper critical field (Hc2) becomes a first-order transition, an increased disordering of the VL is observed.

Vortex lattice reorientation and anisotropy in MgB 2––effects of two-band superconductivity

We present small-angle neutron scattering (SANS) measurements of the vortex lattice (VL) in single crystal MgB 2––a two-band superconductor. Bragg diffraction of neutrons visualizes the structure and orientation of the VL while the scattered intensity probes the super-carrier density. Superconductivity in the π-band is rapidly suppressed with increasing field with a corresponding decrease in scattered intensity and a re-orientation of the VL between 0.5 and 0.9 T. Both these observations are consistent with superconductivity in the π-band being weaker than in the σ-band ( Δ π< Δ σ), and a changing influence of different parts of the Fermi surface determining the VL orientation. SANS measurements of the VL for fields applied at an angle to the c-axis allow the penetration depth anisotropy, γ λ , to be estimated.

Spin-Orbit Coupling and the in-Plane Anisotropy of the Upper Critical Field in Sr2RuO4

The anomalous temperature dependence of the in-plane H c 2 anisotropy of Sr 2 RuO 4 is discussed based on a model which includes spin-orbit coupling effects. While the basic superconducting state corresponds to a chiral p -wave state, the in-plane magnetic field generates a nonunitary state which leads to the observed anomalous anisotropy. Although this effect is connected with spin-orbit coupling and multi-band effects, it does not affect anisotropy parameters which determine the vortex lattice structure in the mixed state for fields parallel to the c -axis. In this manner the discrepancy between low-temperature in-plane anisotropy and c -axis vortex lattice orientation is resolved.

Commensurate and incommensurate vortex states in superconductors with periodic pinning arrays

As a function of applied field, we find a rich variety of ordered and partially-ordered vortex lattice configurations in systems with square or triangular arrays of pinning sites. We present formulas that predict the matching fields at which commensurate vortex configurations occur and the vortex lattice orientation with respect to the pinning lattice. Our results are in excellent agreement with recent imaging experiments on square pinning arrays [K. Harada et al., Science 274, 1167 (1996)].

Vortex lattice orientation and the anisotropy of Hc2 in type II superconductors

In single crystals of pure or dirty superconductors the orientation of the vortex lattice is always related to the anisotropic properties of the conduction electrons, i.e. the anisotropy of H c 2 and not to the magnetic elastic strain interaction.