Bose Glass State Research Articles

Indications of pair electron effect above field induced superconductor–insulator transition in amorphous ultra thin W films with Si/W/Si structure

We present the measurements of the superconductor–insulator transition (SIT) driven by both thickness and magnetic field for the Si/a–W/Si system. The thickness of the W-film was varied over a range from 1 to 5 nm. We found the universal quantum sheet resistance at SIT driven by thickness. Field induced SIT for two samples with 1.6 and 3 nm W thick was investigated in detail. In the insulator side, the evidence of Bose glass state for our homogeneous disordered two dimensional system is inferred by comparing SIT field B c with the upper critical field at 0 K H c2(0) estimated from measurements of d H c2/d T| T c and the field dependent magneto-resistance at various temperatures.

Bose-glass behavior of the vortex system in epitaxial Bi2Sr2CaCu2O8+ delta films with columnar defects.

A continuous transition of the vortex ensemble into a Bose-glass state in epitaxial ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ films with columnar defects along the c axis, induced by irradiation with 2.7 GeV $^{238}\mathrm{U}$ ions was observed. The temperature variation of the resistivity, measured with the magnetic field B=${\mathrm{\ensuremath{\mu}}}_{0}$H applied parallel to the c axis, fits the expression \ensuremath{\rho}(T)\ensuremath{\sim}(T-${\mathit{T}}_{\mathrm{BG}}$${)}^{\ensuremath{\nu}(\mathit{z}\mathrm{\ensuremath{-}}2)}$ at low levels, with a field-independent exponent up to B\ensuremath{\approxeq}2 T. At very low fields, the magnetic-field dependence of the Bose-glass transition temperature ${\mathit{T}}_{\mathrm{BG}}$ is in good agreement with the predictions of theory of boson localization in the presence of correlated disorder, 1/${\mathit{T}}_{\mathrm{BG}}$-1/${\mathit{T}}_{\mathit{c}0}$\ensuremath{\sim}${\mathit{B}}^{1/4}$. However, for applied field values significantly larger than the dose-equivalent field ${\mathit{B}}_{\mathrm{\ensuremath{\varphi}}}$=1 T, the vortex delocalization in our samples seems to proceed via melting, the magnetic-field exponent becoming very close to 1/2. The occurrence of the Bose-glass transition in the case of intrinsically very anisotropic superconductors, as ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$, can be understood through an increase of the tilt modulus in the vortex ensemble in the presence of correlated disorder, which promotes vortex localization.

Vortex dynamics and correlated disorder in high- Tc superconductors

We develop a theory for the vortex motion in the presence of correlated disorder in the form of twin boundaries and columnar defects. Mapping vortex trajectories onto boson world lines enables us to establish the duality of the vortex transport in systems with correlated disorder and the hopping conductivity of charged particles in 2D systems. A glassy-like dynamics of the vortex lines with zero linear resistivity and strongly nonlinear current-voltage behavior as V ∝ exp(-const/ J μ) in a Bose glass state is predicted.