Vortex Flow and Transverse Flux Screening at the Bose Glass Transition

Abstract

We study the vortex phase diagram in untwinned YBCO crystals with columnar defects. These randomly distributed defects are expected to induce a "Bose glass" phase of localized vortices exhibiting a vanishing resistance and Meissner effect for magnetic fields H Ќ transverse to the columns. We directly observe the transverse Meissner effect using a Hall probe array. As predicted, the Meissner state breaks down at temperatures T s that decrease linearly as H Ќ increases. However, T s lies far below the conventional melting temperature T m determined by a vanishing resistivity, suggesting a regime where vortices are effectively localized even when rotated off the columnar defects.PACS numbers: 74.60. Ge, 74.25.Bt Weak pinning, large anisotropy, and prodigious thermal fluctuations in high temperature superconductors permit magnetic vortices to exist in a liquid phase which flows easily in response to an external current [1]. This technologically undesirable state of finite electrical resistance is quelled only at sufficiently low temperatures when vortex-vortex interactions precipitate a solid phase [2][3][4]. Columnar defects, a form of strong disorder correlated across many CuO 2 planes, serve as an effective strategy to bolster the constraining effects of the interaction potential, localizing the vortices on the disordered array of columns. The resulting "Bose glass" phase [5] exhibits two characteristic signatures: a diverging vortex viscosity leading to a zero resistance state, as well as a diverging tilt modulus resulting in vortex alignment with the columns even as the external magnetic field rotates. A large rotation of the external field, however, will melt the glass at fixed temperature. We monitor both the onset of a resistive response (vortex mobility) and the onset of transverse flux penetration (vortex alignment). In contrast to theory, we find that these two events yield widely different demarcations for the Bose glass phase.Amorphous columnar tracks created by heavy ion bombardment of cuprate superconductors are of nearly optimal size and geometry to pin vortices over their entire length. Thermal excitations, however, permit some segment of a vortex line to wander off its pinning site. Nelson and Vinokur [5] have mapped this statistical mechanics problem onto the quantum mechanical problem of two-dimensional bosons in the presence of point disorder [6]. They find a sharp phase transition between a high-temperature vortex liquid of delocalized and entangled vortex lines and a low temperature Bose glass dominated by the spatial disorder in the columnar defect distribution. The predictions of scaling theory [5,[7][8][9] have been tested [10][11][12][13][14][15][16][17][18][19] by measuring the vortex mobility subjected to a driving current at the approach to the glass transition temperature, T BG . These experiments vary widely on values for the critical exponents and on the angular dependence of T BG . We consider an additional prediction of the theory, that below

Vortex solid state inYBa2Cu3O7−Maiorov1, Osquiguil2 2001Phys. Rev. B136100View full textAdd to dashboardCite

“…An interesting point related to the shape of the cusp, however, has gone unnoticed in the literature. While in samples with columnar defects the transition curve is well described by T BG ()ϳ1Ϫ͉͉ at small angles, 8,10,11 in twinned crystals a nonlinear transition curve 6,7,9,12,13 is observed. Monte Carlo simulations of the Bose-glass melting 4 in a vortex system interacting with linear defects gave Ϸ1, which, through Eq.…”

Generalized Anisotropic Scaling Theory and the Transverse Meissner Transition

“…The TM effect has been studied experimentally [7][8][9][10][11][12][13][14]. The phase diagram for small tilt angles has been determined and shows a characteristic cusp around zero tilt [4,15,16].…”

Unscreened universality class for superconductors with columnar disorder

“…The columnar defects are often produced as damage tracks by irradiating the sample with high-energy heavy ions. Such correlated disorder strongly affects the phase transition from the SC to normal state and there is an ongoing theoretical and experimental effort to investigate the phase diagram and properties of the transition [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Below a critical temperature the vortices freeze into a glassy SC state, known as a Bose glass, which replaces the Abrikosov vortex lattice of the clean system.…”