Correlation of the vortex order-disorder transition with the symmetry of the crystal lattice inV3Si

Abstract

The transitions from the ordered Bragg glass into the disordered vortex states at low and high fields are investigated by magnetization measurements varying the angle between magnetic field and crystal lattice orientations in a distinct manner. A single crystalline sphere is used to obtain an uniform demagnetization and not to introduce vortex disorder from sample edges. No angular dependence was observed when the pinning energy dominates. However, if the elastic energy of the vortex lattice is superior, the formation of the Bragg glass depends strongly on the relative orientation of both lattices. If the sphere is rotated around the ͓100͔ direction of the crystal with the field being perpendicular to it, a fourfold symmetry, both of the transition fields and of the strength of the vortex metastability, is found. The recent observation by Yethiraj et al. ͓Phys. Rev. Lett. 82, 5112 ͑1999͔͒, that the vortex lattice reflects the symmetry of the crystal lattice also in V 3 Si is in good agreement with our investigations. Comparative measurements made on the sphere and on a crystal with edges revealed the influence of disorder on the Bragg glass induced by the sample shape.

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

“…This indicates that the observation of the disordered/Bragg Glass phase transition by means of 1 st harmonics measurements is limited to an intermediate field/temperature region. A very similar behavior was earlier reported in the V 3 Si system [25], another A15 type compound: the Bragg Glass Phase extends without a transition up to the vortex liquid state, for high magnetic fields (H > 7 T). Nevertheless, the theoretical models [3] predict that this transition should be present, even at higher magnetic fields.…”

“…By magnetic measurements, we have no information about the order of the transition. We detected magnetic history effects (which will be reported elsewhere), for temperature lower than the peak temperature (T p ), as in other type II superconductors [24,25,28], but they are not a proof of a first order transition. Recent calorimetric measurements [29], in fact, show that the latent heat is zero around T p , suggesting that it cannot be a first order transition.…”

Frozen disorder and edge contamination in magnetization measurements of the Bragg glass phase

“…This geometry was chosen in order to avoid specific features from the correlation between crystal and vortex lattice at a high-symmetry direction as discussed in Ref. 22.…”

Superconducting properties of a parallelepiped mesoscopic superconductor: A comparative study between the 2D and 3D Ginzburg–Landau models

“…(1)-(3) numerically, we used the linkvariable method as sketched in references [28,29]. 1 Here, we provide a brief description of the numerical setup. The domain Ω is Fig.…”

“…In particular, as a consequence of the demagnetization effects, when the size of the sample along the direction of the applied magnetic field is smaller than the lateral dimensions of its cross section, the local magnetic field near the edges of the sample is enhanced and interacts with the shielding currents. There are many experimental (see for instance [1][2][3][4][5]) and theoretical (see for instance [6][7][8][9][10]) studies in threedimensional (3D) systems. For example, in [11], a superconducting wire with a constriction in the middle was investigated.…”