Low temperature vortex phase diagram of Bi2Sr2CaCu2O8 : a magnetic penetration depth study

We report measurements of the magnetic penetration depth \lambda_m(T) in the presence of a DC magnetic field in optimally doped BSCCO-2212 single crystals. Warming, after magnetic field is applied to a zero-field cooled sample, results in a non-monotonic \lambda_m(T), which does not coincide with a curve obtained upon field cooling, thus exhibiting a hysteretic behaviour. We discuss the possible relation of our results to the vortex decoupling, unbinding, and dimensional crossover.Comment: M2S-HTSC-V

Magnetic penetration depth in electron-doped cuprates - evidence for gap nodes

The in-plane penetration depth \lambda(T) is measured in electron-doped single crystals Nd1.85Ce0.15CuO4-x (NCCO) and Pr1.85Ce0.15CuO4-x (PCCO) using a 11 MHz LC resonator. In NCCO, \lambda(T) exhibits a minimum at 3.8 K and a pronounced upturn down to 0.4 K due to the paramagnetic contribution of Nd3+ ions. The London penetration depth contribution is linear in T. The paramagnetic contribution is absent in PCCO, where \lambda(T)~T^2 at low temperatures. Our results indicate the presence of nodes in the superconducting gap, i.e., non s-wave symmetry of the order parameter in electron-doped cuprates.Comment: 2 pages Acrobat-3 optimized PDF. To be presented at M2S-HTSC-V

Campbell Penetration Depth of a Superconductor in the Critical State

The magnetic penetration depth $\lambda(T,H,j)$ was measured in the presence of a slowly relaxing supercurrent, $j$. In single crystal $\mathrm{Bi_2Sr_2CaCu_2O_8}$ below approximately 25 K, $\lambda(T,H,j)$ is strongly hysteretic. We propose that the irreversibility arises from a shift of the vortex position within its pinning well as $j$ changes. The Campbell length depends upon the ratio $j/j_{c}$ where $j_{c}$ is the critical current defined through the Labusch parameter. Similar effects were observed in other cuprates and in an organic superconductor

A SMALL GAS THERMOMETER FOR USE AT LOW TEMPERATURES

On décrit un petit thermomètre à gaz à volume constant qui utilise un oscillateur à diode tunnel. Ce thermomètre a une sensibilité de 0,2 mK et il est très linéaire entre 0,71 K et 10 K.A small constant volume gas thermometer utilizing a self-contained tunnel diode oscillator is described. It has a sensitivity of 0.2 mK and is highly linear between 0.71 and 10 K