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Submitted on 1 Jan 1978
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EXPERIMENTAL EVIDENCE FOR THE
EXISTENCE OF REMANENT
SUPERCONDUCTIVITY IN ALUMINIUM AND ITS
EFFECT ON THE TEMPERATURE DEPENDENCE
OF THE NORMAL PHASE RESISTIVITY
E. Zair, M. Sinvani, B. Levy, A. Greenfield
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplPment au no 8, Tome 39, aolit 1978, page C6-496
EXPERIMENTAL E V I D E N C E FOR THE E X I S T E N C E OF REMANENT SUPERCONDUCTIVITY I N A L U M I N I U M AND ITS EFFECT ON THE TEMPERATURE DEPENDENCE OF THE NORMAL PHASE RESISTIVITY+
E. Zair, M. Sinvani, B. Levy and A.J. Greenfield
Department of Physics, Bar-IZan University, Ramat-Gan, IsraeZ
R6sumd.- I1 est rendu compte de l'existence d'une superconductivitC rsmanente dans la phase nomale de Al, bien au-dessus de T,. Cette superconductivitd rdmanente permet d'expliquer les differents rd- sultats experimentaux P propos de la dspendance en temperature de A1 au-dessus de 4 K.
Abstract.- The existence is reported of remanent-superconductivity in the normal phase of A1 well above Tc. This remanent superconductivity is shown to explain the different experimental findings in the temperature dependence of the electrical resistivity of A1 below 4 K.
Remanent superconductivity above the transi- tion temperature has been reported both for thin films/l/ and for bulk specimens for very dirty al- loys/2/. We here report the first observation of a similar phenomenon for bulk samples of a pure metal. Measurements have been made for several samples of A1 having residual resistance ratios (RRR) ranging from 360 to 13 100. For all our samples, we clearly observe remanent superconductivity up to at least 4 K. The prerequisite for observing this effect over such a large temperature range above T = 1.18 K is the use of very low current densities. Our current density was about 1 Amp/cm2.
We are here concerned with the implications of these results for the normal-phase resistivity. Exa- mination of the literature shows that there is di- sagreement regarding the temperature dependence of the 11~basured electrical resistivity p (T) of Al.
exPt
This is particularly so for measurements below 4.2 K where different workers/3-61 report either a T~ dependence or a T~ dependence or something varying between them. This situation has been attributed131 to the difficulty in obtaining the required very high precision for distinguishing a power law de- pendence with. reasonable certainty.
We propose that these discrepancies are in fact due to remanent superconductivity. For those experiments/4/ where the magnetic field resulting from the electrical current used in the measure- ment, is sufficiently large to destroy the remanent
superconductivity, a T~ dependence is found for Pexp t (T). However, when the measuring current is sufficiently low that the associated magnetic field
+ Research supported by the Israel Conrmission for the Basic Research.
does not destroy the remanent superconductivity, then an apparent T~ dependence is found/3/ for 'exp t (T). This T' dependence is in fact a combina- tion of the T~ dependence of the normal resistivity together with the remanent superconductivity, which has a (T-TC)'I2 dependence/?/ over most of the tem- perature range from T to about 4 K.
This effect has been found for samples having three different purities. The magnitude of the rema- nent superconductivity is smallest for the highest purity sample and is progressively larger with in- creasing impurity.
In figure 1, we plot for each of three samples *Pexp t (T) = pexpt(T) -po, where p is the residual 0
resistivity. The extent of the remanent superconduc- tivity is clearly obvious for the dirtiest sample but is also noticeable for the other two samples when the vertical scale is appropriately expanded.
In figure 2 we show haw remanent superconducti- vity can affect the measured temperature dependence of pexpt(T) by plotting pexpt(T) against both T' and T ~ . Below 5 K, one obtains almost a straight line for p (T) vs T~
,
except for the points veryexp t
close to the superconducting transition temperature Tc. By contrast, the curve p (T) vs T~ shows a
exp t
downward curvature. These results are very similar to those obtained by Garland/3/. Since the data of Garland do not extend below 1.5 K, he did not see the sharp downward curvature apparent in our data near to T
.
In fact, the high purity of his samples would make it nearly impossible to see this down- ward curvature due to remanent superconductivity near T.
The above results are in marked contrast to tho- se reported by Senoussi and Campbell/4/ who find a
D A R R R =l3100
.
RRR.4400 m D R R R = 360 - DFig. 1 : Plot of raw data minus the constant value p for 3 samples.
0
Fig. 2 : Values for pexpt(T) VS. T2 and VS. T3 sho- wing T2 dependence.
pure T3 dependence. These differing results are due to the different magnitudes of the magnetic field present on the sample resulting from the differing measuring currents and sample sizes in each case
(= 0.1 gauss and = 40 gauss)
.
In figure 3, we show a plot of our measure-
Fig. 3 : Normal-phase resistivity pN(T) vs. 'T and T3 showing T3 dependence.
removed leaving only the normal contribution. The data clearly lie on a straight line up to 6 K when plotted against T3. By contrast, the data show a marked curvature when plotted against T2.
References
/ l / Glover,III, R.E., Physica
55
(1971) 3 /2/ Hake,R.R., Phys. Rev. Letters23
(1969) 1105 /3/ Garland,J.C. and Van Harlingen,D.J., J. Phys.F
8
1 (1978) 117/4/ Senoussi,S. and Campbell,I.A., J. Phys. F
2
(1973) 119/5/ Ekin,J.W. and Maxfield,B.W., Phys. Rev. Lett. 26 (1971) 635
-
161 Van Kempen, tc be published
171 Aslamazov,L.G. and Larkin,A.I., Phys. Lett. 2 A (1968) 238
