Transition temperature depression in quench condensed Zn-Mn dilute alloy films

Abstract

The depression of the superconducting transition temperature has been investigated for uhv quench condensed Zn-Mn alloy films, containing 5-50 ppm Mn. Within accuracy limits the result for the initial depression dTc[dC=285 +_ 30 K[at % is in agreement with the bulk material value of 305 K/at%, supporting the equivalence between quench condensed fills and bulk material alloys. A detailed analysis of the data within the framework of the Zittartz-Mtiller-Hartmann theory shows, that for the "Kondo-system" Zn-Mn (with Tk/T c 0 ~ 1 and S= 3/2) the thin film results follow the theoretical T e depression curve better than the bulk material values. This is due to the early onset of impurity-impurity interactions in the bulk alloys, which are reduced in quenched films because of reduced mean free path of the conduction electrons.

Different behaviour of magnetic impurities in crystalline and amorphous states of superconductors

“…We suggest that a more systematic experimental investigation is necessary for the different behavior of the magnetic impurities in crystalline and amorphous superconductors. * quench-condensed films * * ion implantation at low temperatures References: a): [32]; b): [33]; c): [34]; d): [2]; e): [13]; f): [35]; g): [7]; h): [3]; i): [20]; j): [6]; k): [4]; l): [36]; m): [8]; n): [1]; o): [37]; p): [38]; q): [39]; ∆T c (K)…”

“…Here T c0 values are the experimental results. 13 Note that quench condensed amorphous Zn films also show significantly rounded transition curves, 46 which explains somewhat bigger value for the mean free path of curve (a). But for curve (b) our mean free path value is reasonable compared to dilute ZnMn alloys data.…”

“…25 It is clear that the initial T c decrease depends on the sample quality and is not the universal constant suggested by Abrikosov and Gor'kov. 26 Note that In-Mn, 4,5,8 Sn-Mn, 28 Zn-Mn, 13 and Cd-Mn 35 show the Kondo anomalies at low temperatures.…”

“…Here T c0 values are the experimental results. 13 Therefore, the change of the initial slope of the T c decrease may be explained in terms of the change of the Cooper pair size caused by the variation of the mean free path ℓ. We used ω D = 327K, and v F = 1.82 × 10 8 cm/sec.…”

“…In Table I, most of the values from the literature for the initial decrease of T c for the Zn-Mn system are listed, which shows this behavior spectacularly. Data are from Falke et al 13 As can be seen, the initial slope of the T c decrease by magnetic impurities is not universal but dependent on the sample quality and sample preparation methods. Note that Zn-Mn alloys show all the Kondo anomalies at low temperatures.…”