Proximity-effect-induced superconductivity at millikelvin temperatures

Journal Article · Sun Feb 01 00:00:00 EST 1987 · J. Low Temp. Phys.; (United States)

DOI:https://doi.org/10.1007/BF00681822· OSTI ID:6878653

Bergmann, T; Kuhl, K H; Schroeder, B; Jutzler, M; Pobell, F

A systematic study is reported of the proximity effect in superconductivity of thick Cu layers (4 less than or equal to d/sub n/ less than or equal to 105 ..mu..m) in contact with Nb or Nb-Ti (46 less than or equal to D/sub s/ less than or equal to 1041 ..mu..m) from measurements of the ac susceptibility and of the thermal conductivity. The induced superconducting properties of Cu are studied as a function of temperature (7 mK less than or equal to T less than or equal to 1 K), field (0.4 mG less than or equal to H less than or equal to 10G), and electronic mean free path (0.2 less than or equal to l less than or equal to 14 ..mu..m). The Meissner screening length in Cu increases faster than the coherence length with decreasing temperature and eventually saturates, making the Cu fully superconducting. In this case, superconductivity can be destroyed sharply at a breakdown field H/sub b/; the transition at H/sub b/ is hysteretic. The data are in agreement with numerical solutions of the de Gennes/Ginzburg-Landau theory, as demonstrated by the dependence of the Meissner screening length and of the breakdown field on temperature, field, and electronic mean free path. The data indicate that observation of a reduction in thermal conductivity requires a substantially larger induced pair potential than is necessary even for total field shielding. The concentration of Cooper pairs in Cu in contact to Nb is larger than in Cu in contact to Nb-Ti, even for Nb-Ti/Cu samples with a larger electron mean free path in the Cu part. No measurable superconducting field screening could be induced in the investigated temperature range in Pd(26 less than or equal to d/sub n/ less than or equal to 72 ..mu..m) in contact to Nb/Cu or to Nb (D/sub s/ approx. = 5d/sub n/). This is explained by the fact that the coherence length is at least an order of magnitude smaller in Pd than in Cu. Evaporating a layer of Fe on Cu in the Nb/Cu samples results in a strong depression of the proximity effect.

• Research Organization: Universitaet Bayreuth, West Germany
• OSTI ID: 6878653
• Journal Information: J. Low Temp. Phys.; (United States), Vol. 66:3/4
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COPPER
PROXIMITY EFFECT
SUPERCONDUCTIVITY
COHERENCE LENGTH
COOPER PAIRS
ELECTRONS
GINZBURG-LANDAU THEORY
MAGNETIC SHIELDING
MEAN FREE PATH
NIOBIUM
NIOBIUM ALLOYS
SUPERCONDUCTORS
TEMPERATURE DEPENDENCE
THERMAL CONDUCTIVITY
TITANIUM ALLOYS
ULTRALOW TEMPERATURE
ALLOYS
DIMENSIONS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTARY PARTICLES
ELEMENTS
FERMIONS
LENGTH
LEPTONS
METALS
PHYSICAL PROPERTIES
SHIELDING
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
360104* - Metals & Alloys- Physical Properties