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SEARCH FOR SUPERCONDUCTIVITY IN
RUBIDIUM AT HIGH PRESSURE
K. Ullrich, C. Probst, J. Wittig
To cite this version:
K. Ullrich, C. Probst, J. Wittig.
SEARCH FOR SUPERCONDUCTIVITY IN RUBIDIUM
JOURNAL DE PHYSIQUE Colloque C6, supplément au n° 8, Tome 39, août 1978, page C6-463
SEARCH FOR SUPERCONDUCTIVITY IN RUBIDIUM AT HIGH PRESSURE
K. U l l r i c h , C. Profast
+and J . Wittig
Institut ficr Festkorperforsahung, KFA Jul-Ceh, D-5170 Jul-ieh, Germany
Résumé.- La résistance électrique de Rb a été mesurée jusqu'à 140 Kbar à l'aide de la technique des 4 pointes. On ne détecte pas de supraconductivité en descendant jusqu'à la très basse température de 0.045 K. Ce résultat appuie l'hypothèse qu'à haute pression Cs est un métal de bande 4f.
Abstract.- The electrical resistance of Rb has been measured up to 140 kbar by a four probe techni-que. No superconductivity was detected down to a lowest temperature of 0.045 K. The result lends some support to the hypothesis that Cs is a 4f-band metal at high pressure.
Cesium is the only alkali metal which has been found to become superconducting. Thus far super-conductivity has been observed in a high pressure phase (Cs V) above - 100 kbar. T is approximately
1 . 5 K / 1 / , It is hence an interesting question, whether the other alkali metals (Rb,...) will also become superconducting at high pressure. An unpre-cedented increase of the electrical resistance with pressure has been reported for Rb and K by Stager and Drickamer /2/. The room temperature resistance of Rb increases by a factor of = 30 between normal pressure and ^ 150 kbar; see also our data in figu-re 1. This may hint at a strong incfigu-rease of the elec-tron-phonon coupling with pressure. We present pre-liminary data of a study of Rb up TO 140 fcbar. Our search for superconductivity was extended down to a lowest temperature of 0.045 K.
Liquid Rb was filled into thin-walled glas capillaries under an argon atmosphere. The capilla-ries were cut to the proper length under molten pa-raffin. The paraffin-sealed samples were mounted be-tween polyethylene disks in a high pressure cell des-cribed previously /3/. Upon application of pressure the capillaries shatter and electrical shatter and electrical contact is established between the over-lyring electrodes and the Rb sample. The pressure is generated by a mechanical press which subsequen-tly can be cooled in a 3He/"He dilution refregerator /4/. The pressure was determined from the T of a Pb manometer sample.
Figure 1 shows the room-temperature resistan-ce as a function of pressure for one particular resistan-cell.
New address : ZTF Bayer. Akademie d. Wiss., D-8046 Garching
Our data confirm Stager and Drickamer's finding 111
that the resistance of Rb increases dramatically with pressure toward the Rbll/III phase
transforma-tion. a if 2000- ° o
I Rb
t/j $ 1500- ° T=300K o1000-%
^
0J*
0l o — i — ° ^ i i i 0 30 60 90 120 PRESSURE/kbarFig. 1 : Room-temperature resistance of Rb vs. pressure.
A discountinuous rise of the resistance by a factor of - 3 occurs at the RbII-*III phase change.
Figure 2 shows R-T data for pure Rblll and also two other runs in which the sample re-transformed to Rbll upon cooling. It is seen that the hystere-tic RbII->-III transformation shifts to lower tem-peratures with decreasing pressure. Figure 3 is a P-T diagram containing all of our data for the Rbll/III phase boundary. We have investigated Rblll for superconductivity at 130 and 140 M>ar, the sample remaining normal down to a temperature of 0.045 K. The same result was obtained for Rbll at - 100 kbar, i.e. in the pretransitional range (fi-gure 1) of the Rbll III phase change. Our samples
31
C6-464
r e v e a l e d a r e s i d u a l r e s i s t a n c e r a t i o of about 60. "good" s u p e r c o n d u c t i v i t y of Cs and o t h e r anomalies
may be i n t i m a t e l y l i n k e d t o t h e appearance of
4f
c h a r a c t e r i n the conduction e l e c t r o n wave f uric t i o n s 181. C l e a r l y , such 4f c h a r a c t e r cannot appear i n Rb
o r K. Hence t h e absence of s u p e r c o n d u c t i v i t y i n Rb
up t o 140 kbar lends some support t o t h e hypothesis
181
t h a t Cs has n o t - n e g l i g i b l e 4f c h a r a c t e r a t t h eFermi s u r f a c e a t high p r e s s u r e . I n p u r s l i n g t h i s con-
c e p t t h e experiments w i l l be extended t o higher pro-
p r e s s u r e , lower temperatures and p u r e r samples.
-800
References
0 100 200
m
TEMPERATUREIK
/ I / W i t t i g , J . , Phys. Rev. L e t t . (1970) 812.
/ 2 / S t a g e r , R.A. and Drickamer, H.G., Phys. Rev.
Fig. 2 : R e s i s t a n c e v s . temperature f o r Rb a t i n d i -
-
132 (1963) 124.c a t e d p r e s s u r e .
Fig. 3 : Rudimentary P-T diagram f o r
Rb.
The d a t ap o i n t near 70 kbar i n d i c a t e s t h e R b I / I I phase chan- ge f i r s t observed by Bundy. At 300 K the R b I I + I I I t r a n s f o r m a t i o n ran simultaneously w i t h t h e PbI +I1 t r a n s f o r m a t i o n (130 k b a r ) . 300- 200- 100- Oo We t h i n k i t i s a remarkable r e s u l t t h a t Rb i s
n o t a superconductor down t o 0.045 K whereas Cs pos-
-
s e s s e s a T of t h e o r d e r of 1 K i n t h e same p r e s s u r e
range. It has been suggested by s e v e r a l a u t h o r s
15-7/ t h a t the heavy a l k a l i m e t a l s
(K,
Rb and Cs)a r e turned i n t o d - t r a n s i t i o n m e t a l s a t high p r e s s u r e . The s u p e r c o n d u c t i v i t y of Cs has t h u s been a t t r i b u t e d t o a c o n s i d e r a b l e 5d c h a r a c t e r of t h e Bloch waves.
/5-7/ I n l i n e w i t h t h i s p i c t u r e i t has been specula-
ted t h a t Rb and K w i l l a l s o become superconducting because of i n c r e a s i n g d admixture. /5,7/ One of t h e p r e s e n t a u t h o r s however has suggested t h a t t h e
I
n
BUNW Rb-
5
I I 4 30 W 90 120/ 3 / E i c h l e r , A. and W i t t i g , J . , Z. Angew. Phys.
25
(1968) 319.
PRESSURElkbor
/ 4 / W i t t i g , J. and P r o b s t , C . , Proceedings of t h e
I n t . Conf. on High P r e s s u r e and Low Temp. Physics Cleveland 1927.
/5/ Stocks, G.M., Gaspari, D.G. and Gyorffy, B.L.,
J. Phys. F : Metal Phys.
2
(1972) L 123./6/ Louie, S.G. and Cohen,
M.L.,
Phys. Rev, B E(1974) 3237 and r e f e r e n c e s t h e r e i n .
/7/ Gandel'man, G.M. and I t s k o v i c h , 0. Yu., High
Temp.-High P r e s s .
1
(1975) 682 and r e f e r e n c e st h e r e i n .
/8/ W i t t i g , J . , i n ~ e s t k ; j r p e r p r o b l e m e XIIT. (H. J .
