arXiv subjects

F. Bernd Mueller-Allinger

Publications and source records attributed to F. Bernd Mueller-Allinger.

3 recordsLinked to original sources

arXiv2000

Reentrance of the induced diamagnetism in gold-niobium proximity cylinders

We discuss the magnetic response of gold-niobium proximity cylinders in the temperature range 100 μK<T<9 K. The temperature dependence of the susceptibility in the diamagnetic regime is described well by the quasiclassical Eilenberger theory including an elastic mean-free path l. In the mesoscopic regime, the temperature dependence of the reentrant paramagnetic susceptibility χ_para(T) \propto \exp[-L/3ξ^d_N(T)] is governed by the dirty limit coherence length ξ^d_N(T)=\sqrt{1/3ξ_N l_N}, with ξ_N the clean limit coherence length obtained from breakdown field measurements and l_N the measured mean-free path in the gold layer. At T=100 μK, χ_para compensates about 1/5 of the induced diamagnetic susceptibility in gold.

cond-mat.mes-hall↗

arXiv2000

Paramagnetic reentrant effect in high purity mesoscopic AgNb proximity structures

We discuss the magnetic response of clean Ag coated Nb proximity cylinders in the temperature range 150 μK < T < 9 K. In the mesoscopic temperature regime, the normal metal-superconductor system shows the yet unexplained paramagnetic reentrant effect, discovered some years ago [P. Visani, A. C. Mota, and A. Pollini, Phys. Rev. Lett. 65, 1514 (1990)], superimposing on full Meissner screening. The logarithmic slope of the reentrant paramagnetic susceptibility chi_para(T) \propto \exp(-L/ξ_N) is limited by the condition ξ_N=n L, with ξ_N=\hbar v_F/2 πk_B T, the thermal coherence length and n=1,2,4. In wires with perimeters L=72 μm and L=130 μm, we observe integer multiples n=1,2,4. At the lowest temperatures, χ_para compensates the diamagnetic susceptibility of the \textit{whole} AgNb structure.

cond-mat.mes-hall↗

arXiv1998

Diamagnetic response of cylindrical normal metal - superconductor proximity structures with low concentration of scattering centers

We have investigated the diamagnetic response of composite NS proximity wires, consisting of a clean silver or copper coating, in good electrical contact to a superconducting niobium or tantalum core. The samples show strong induced diamagnetism in the normal layer, resulting in a nearly complete Meissner screening at low temperatures. The temperature dependence of the linear diamagnetic susceptibility data is successfully described by the quasiclassical Eilenberger theory including elastic scattering characterised by a mean free path l. Using the mean free path as the only fit parameter we found values of l in the range 0.1-1 of the normal metal layer thickness d_N, which are in rough agreement with the ones obtained from residual resistivity measurements. The fits are satisfactory over the whole temperature range between 5 mK and 7 K for values of d_N varying between 1.6 my m and 30 my m. Although a finite mean free path is necessary to correctly describe the temperature dependence of the linear response diamagnetic susceptibility, the measured breakdown fields in the nonlinear regime follow the temperature and thickness dependence given by the clean limit theory. However, there is a discrepancy in the absolute values. We argue that in order to reach quantitative agreement one needs to take into account the mean free path from the fits of the linear response. [PACS numbers: 74.50.+r, 74.80.-g]

cond-mat.mes-hall↗