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Meissner effect in Ag and Cu backed with superconducting Pb
Solid State Communications,
Vol. 9, pp. 895—897, 1971.
Pergamon Press.
Printed in Great Britain
MEISSNER EFFECT IN Ag AND Cu BACKED WITH SUPERCONDUCTING Pb C. Vallette Physique des Solides, Faculté des Sciences, 91
—
Orsay (France)
(Received 15 February 1971 by P.G. de Gennes)
The diamagnetic properties of silver and copper backed with a thick lead layer have been studied as a function of their normal state electrical resistivity and of the temperature. The agreement between our experimental results and the theory’ is good, and allows for a dc~erminationof the electron—electron interaction, which is found to be weakly attractive both in silver and in copper.
THE SAMPLES were prepared by the successive evaporations of the lead (5) and of the the normal metal (\“j~ onto a rotating hollow glass cylinder. Simultaneously, separate layers of S and .\ were deposited onto similar cylinders. The electrical resistance of these layers was measured at room temperature and at 4.2°K, in order to determine their thickness (maintained between 1~.and 2.~) and their residual normal state resistivity. It turned out that the resistivity of the normal layers was not always the same when they were deposited directly on the glass and when they were deposited on the lead layer. For the silver and silver alloys the conductance of the binary samples was, in general, equal to the sum of the conductances of the two layers deposited separately within the experimental accuracy. For the copper and the dilute copper alloy samples, on the other hand, the films deposited on the lead had a systematically higher resistivity. A similar observation has been reported previously.
to the axis of the cylinders and the frequency is recorded as a function of the field (see Fig. 1). Typically there is a first small decrease in the frequency (several hundred cycles) which continues up to a field of about 200G at which the Meissner effect is destroyed in the normal metal.
(arb units)
_______________
The Meissner effect is measured b~’the method of Shawlow and Devlin.~A pick-up coil surrounding the specimen closely and a 2700pF capacitor
0
oscillate with the help of a back-diode (BD General Electric), all immersed in the helium bath.
*
\
200
~öo
~
A static magnetic field is then applied parallel
FIG. 1. Field dependence of the resonant frequency The low field variation reflects the progressive destruction of the superconducting properties of the silver, whereas the sharper high field decrease
: Ag and Ag Al alloys, Cu and Cu Ge alloys.
is due to the bulk transition of the lead as its thermodynamical critical field. 895
896
MEISSNER EFFECT IN Ag AND Cu BACKED WITH SUPERCONDUCTING Pb
Vol. 9, No. 12
p97
~xoo
FIG.2. The screening distance p in the silver times q(q: ~
(p1~
~__
in ~S2 cm, T,
=
fivpl/67rkBT) as a function of
=
7. 18°K, the critical temperature of lead)
p~
_____
C~
22
25
0 15,
.3
~ NVr..16
27
38
~
.5~
o
.7
.8
9
+
1
1.1
1.2
13
11.
1.5
1.6
1.7
1.8
FIG. 3. Experimental results for copper (same notations as in Fig. 2). At higher fields there is a new decrease when the
field penetrates into the lead layer, and then a very sharp drop (several thousand cycles) .at the bulk critical field H~of the lead. Above this field only the surface sheath of the lead at the interface with the glass remains superconducting, up to its critical field H~3.
The sensitivity of the pick-up coil is deterby the ratio of the frequency drop at H~ to the thickness of the lead, and is typically 0.2 —0.3 cycle per Angstom. It is now possible to determine the the thickness corresponding to the initial frequency drop, which is defined to be the screening distance p. 1
mined
Vol. 9, No. 12
MEISSNER EFFECT IN Ag
AND
Cu BACKED WITH SUPERCONDUCTING Pb
897
The screening distance is a decreasing function of the temperature and of the resistivity
the critical temperature of lead) for different samples of various resistivities, at different
prn,. For a pure Ag film (p~ 0.8~.Lflcm)we obtained p 850A at 4.2°Kand p 2810 A at
temperatures. For a given sample, the variation of pq0 as a function of the temperature follows the theoretical predictions, except for two cases: (1) if the resistivity of the normal metal is too low (P~r’~0.5.~1cm, clean limit); (2) if the temperature is lower than about 2°K: in that case p q0 remains constant, because of sat4 Theseprobably two cases are explicitly uration outside effects. the range of va4idity of the theoretical treatment of reference 1.
‘~
“-j
2.17°K.For a 0.75% at Ag Al,alloy (pj,,~, 2.2 we obtained p 240A at 4.2°K and p 780A at 2.17°K.As explained above, the resistivity of the copper films was always rather high; typically, for pj~” 2.2 ~ cm we obtained p 130A at 4.2°Kand p 620A at 2.17°K. The results are reproducible on different samples, even if the pressure during the evaporation 5.iO~Torr to 10~Tort), and the time interval between the end of the lead evaporation and the beginning of the Ag or Cu evaporation ‘-
(20 sec—90 sec) are different. The regular decrease of the screening distance as a function of p~,(varied from O.8~I/cm—45~~/cm) is also an indication that the metallurgical characteristics near the S/N interface are controlled by the impurity concentration in the normal metal, and notthe by Salloying tween and the or N diffusion layers. processes be-
The dispersion of the results in the case of Ag is somewhat stronger than for Cu, probably because the range of variation of p 1,,~,is much larger in Ag than in Cu. In both cases one may conclude that 0
Following the indications of the theory’ we have represented (Fig. 2 and Fig, 3) the variation
of pqc(q~ = ~ v.~-J/&rrkBT)as a function of
Acknowledgements I would like to thank Dr. G. Deutscher for his help in the analysis of the —
K 00 ~
p1~ T/TC (p1,,~in~.clcm, T~8= 7.18~K,
experimental data.
REFERENCES
1.
Supercurrents in the proximity effect, DEUTSCHER G. (Preceeding paper).
2. 3.
FISCHER G. and KLEIN R., Phvs. cond. Mar. 7, 12 (1968). SCHAWLOW and DEVLIN, Phvs. Rev. 113, 120 (1959).
4.
DEUTSCHER G., LINDENFELD P. and WOLF S., Phys. Rev. Lett. 23, 1102 (1969).
5.
DEUTSCHER G., LINDENFELD P. and WOLF S., (to be published).
On a étudié les propriétés diamagnétiques de l’argent et du cuivre au contact d’un film épais de plomb, en. fonction de leur résistivite électrique a l’état normal. L’accord entre nós résultats experimentaux et la théorie est bon, et permet une determination de l’interaction electron—electron, que l’on trouve faiblement attractive aussi bien pour l’argent que pour le cuivre.
Vol. 9, pp. 895—897, 1971.
Pergamon Press.
Printed in Great Britain
MEISSNER EFFECT IN Ag AND Cu BACKED WITH SUPERCONDUCTING Pb C. Vallette Physique des Solides, Faculté des Sciences, 91
—
Orsay (France)
(Received 15 February 1971 by P.G. de Gennes)
The diamagnetic properties of silver and copper backed with a thick lead layer have been studied as a function of their normal state electrical resistivity and of the temperature. The agreement between our experimental results and the theory’ is good, and allows for a dc~erminationof the electron—electron interaction, which is found to be weakly attractive both in silver and in copper.
THE SAMPLES were prepared by the successive evaporations of the lead (5) and of the the normal metal (\“j~ onto a rotating hollow glass cylinder. Simultaneously, separate layers of S and .\ were deposited onto similar cylinders. The electrical resistance of these layers was measured at room temperature and at 4.2°K, in order to determine their thickness (maintained between 1~.and 2.~) and their residual normal state resistivity. It turned out that the resistivity of the normal layers was not always the same when they were deposited directly on the glass and when they were deposited on the lead layer. For the silver and silver alloys the conductance of the binary samples was, in general, equal to the sum of the conductances of the two layers deposited separately within the experimental accuracy. For the copper and the dilute copper alloy samples, on the other hand, the films deposited on the lead had a systematically higher resistivity. A similar observation has been reported previously.
to the axis of the cylinders and the frequency is recorded as a function of the field (see Fig. 1). Typically there is a first small decrease in the frequency (several hundred cycles) which continues up to a field of about 200G at which the Meissner effect is destroyed in the normal metal.
(arb units)
_______________
The Meissner effect is measured b~’the method of Shawlow and Devlin.~A pick-up coil surrounding the specimen closely and a 2700pF capacitor
0
oscillate with the help of a back-diode (BD General Electric), all immersed in the helium bath.
*
\
200
~öo
~
A static magnetic field is then applied parallel
FIG. 1. Field dependence of the resonant frequency The low field variation reflects the progressive destruction of the superconducting properties of the silver, whereas the sharper high field decrease
: Ag and Ag Al alloys, Cu and Cu Ge alloys.
is due to the bulk transition of the lead as its thermodynamical critical field. 895
896
MEISSNER EFFECT IN Ag AND Cu BACKED WITH SUPERCONDUCTING Pb
Vol. 9, No. 12
p97
~xoo
FIG.2. The screening distance p in the silver times q(q: ~
(p1~
~__
in ~S2 cm, T,
=
fivpl/67rkBT) as a function of
=
7. 18°K, the critical temperature of lead)
p~
_____
C~
22
25
0 15,
.3
~ NVr..16
27
38
~
.5~
o
.7
.8
9
+
1
1.1
1.2
13
11.
1.5
1.6
1.7
1.8
FIG. 3. Experimental results for copper (same notations as in Fig. 2). At higher fields there is a new decrease when the
field penetrates into the lead layer, and then a very sharp drop (several thousand cycles) .at the bulk critical field H~of the lead. Above this field only the surface sheath of the lead at the interface with the glass remains superconducting, up to its critical field H~3.
The sensitivity of the pick-up coil is deterby the ratio of the frequency drop at H~ to the thickness of the lead, and is typically 0.2 —0.3 cycle per Angstom. It is now possible to determine the the thickness corresponding to the initial frequency drop, which is defined to be the screening distance p. 1
mined
Vol. 9, No. 12
MEISSNER EFFECT IN Ag
AND
Cu BACKED WITH SUPERCONDUCTING Pb
897
The screening distance is a decreasing function of the temperature and of the resistivity
the critical temperature of lead) for different samples of various resistivities, at different
prn,. For a pure Ag film (p~ 0.8~.Lflcm)we obtained p 850A at 4.2°Kand p 2810 A at
temperatures. For a given sample, the variation of pq0 as a function of the temperature follows the theoretical predictions, except for two cases: (1) if the resistivity of the normal metal is too low (P~r’~0.5.~1cm, clean limit); (2) if the temperature is lower than about 2°K: in that case p q0 remains constant, because of sat4 Theseprobably two cases are explicitly uration outside effects. the range of va4idity of the theoretical treatment of reference 1.
‘~
“-j
2.17°K.For a 0.75% at Ag Al,alloy (pj,,~, 2.2 we obtained p 240A at 4.2°K and p 780A at 2.17°K.As explained above, the resistivity of the copper films was always rather high; typically, for pj~” 2.2 ~ cm we obtained p 130A at 4.2°Kand p 620A at 2.17°K. The results are reproducible on different samples, even if the pressure during the evaporation 5.iO~Torr to 10~Tort), and the time interval between the end of the lead evaporation and the beginning of the Ag or Cu evaporation ‘-
(20 sec—90 sec) are different. The regular decrease of the screening distance as a function of p~,(varied from O.8~I/cm—45~~/cm) is also an indication that the metallurgical characteristics near the S/N interface are controlled by the impurity concentration in the normal metal, and notthe by Salloying tween and the or N diffusion layers. processes be-
The dispersion of the results in the case of Ag is somewhat stronger than for Cu, probably because the range of variation of p 1,,~,is much larger in Ag than in Cu. In both cases one may conclude that 0
Following the indications of the theory’ we have represented (Fig. 2 and Fig, 3) the variation
of pqc(q~ = ~ v.~-J/&rrkBT)as a function of
Acknowledgements I would like to thank Dr. G. Deutscher for his help in the analysis of the —
K 00 ~
p1~ T/TC (p1,,~in~.clcm, T~8= 7.18~K,
experimental data.
REFERENCES
1.
Supercurrents in the proximity effect, DEUTSCHER G. (Preceeding paper).
2. 3.
FISCHER G. and KLEIN R., Phvs. cond. Mar. 7, 12 (1968). SCHAWLOW and DEVLIN, Phvs. Rev. 113, 120 (1959).
4.
DEUTSCHER G., LINDENFELD P. and WOLF S., Phys. Rev. Lett. 23, 1102 (1969).
5.
DEUTSCHER G., LINDENFELD P. and WOLF S., (to be published).
On a étudié les propriétés diamagnétiques de l’argent et du cuivre au contact d’un film épais de plomb, en. fonction de leur résistivite électrique a l’état normal. L’accord entre nós résultats experimentaux et la théorie est bon, et permet une determination de l’interaction electron—electron, que l’on trouve faiblement attractive aussi bien pour l’argent que pour le cuivre.