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Submitted on 1 Jan 1978
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ON MOBILITY OF SURFACE ELECTRONS IN
LIQUID HELIUM AT TEMPERATURES UP TO 20
mK
B. Eselson, A. Rybalko, Yu. Kovdrya, A. Golub, S. Sokolov
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, suppl6ment au no 8, Tome 39, aoiit 1978, page C6-338
ON MOBILITY OF SURFACE ELECTRONS I N L I Q U I D HELIUM AT TEMPERATURES UP TO 20 mK B.N.Eselson, A.S.Rybalko, Yu.Z.Kovdrya, A.A. Golub and S.S.Sokolov
Physico-Technical I n s t i t u t e of Lou Temperatures, UkrSSR Academy of Sciences, 47, Lenin Prospect, Kharkov, 310164, USSR
RdsumC.- On a mesurd la mobilitd Clectronique sur la surface de l'hslium liquide 2 des temperatures de 20 mK 1 1 K. On a ddterminC la mobilitd des dlectrons superficiels au moyen de l'absorption d'd- nergie du champ 6lectromagndtique. Les auteurs ont constat6 que dans cette gamme de tempdrature la ddpendance de la mobilitd dlectronique en fonction de la temperature est voisine de T-l.
Abstract.- The mobility of electrons across the liquid helium surface has been measured in the tem- perature range of 20 mK-1 K. The mobility of surface electrons is estimated by the electromagnetic energy absorption. It has been found that in the temperature range studied, the temperature depen- dence of the electron mobility is close to T-'.
The mobility of surface electrons is one of their most important features. By the theorical concepts available, the motion of electrons at ra-
ther low temperatures is due to their interaction with thermal excitations of the liquid helium surfa-
ce (ripplons). The mobility, p, can be measured by various experimental techniques /1,2,3/. To deter- mine the mobility, p, we measured the electromagne-
tic energy absorption by surfaceelectrons. The ab- sorption was determined by the value of loss in the measuring resonance circuit.
The relation between the mobility of charged particles and the power P absorbed is given by the expression /I/ :
P = e N p ~ ~
where N is a number of charges per unit area, e the electron charge, and E the a.c. amplitude.
The concentration of surface electrons was given by the holding electric field and was
lo5-
10' el/cm2. The experiments were performed at the frequencies of 12 and 25 Mc. The value of absorp- tion was estimated to an accuracy of 'L 30%.
The measurements were made in the temperature range of 2x10-'
-
I K, a continuous-circulation di- lution refrigerator /4/ being used to obtain tempe-ratures down to 20 mK.
The experimental results indicated that in the temperature range studied the temperature depen- dence of the electron mobility is essentially given by p ' ~ T-'. The results for T > 0.3 K are in satis- factory agreement with the theory 151 describing the ripplon scattering of electrons. At lower tem-
peratures a comparison between the experimental de- pendence p(T) an the theory becomes difficult b e
cause in this temperature range for the electron concentration studied the energy of the charge Coulomb interaction becomes larger than the thermal
energy of particles.
References
/1/ Rybalko, A.S.,Kovdrya,Yu.Z. and Eselson,B.N., Pisma v ZhETF
2
( 1 975) 569./2/ Grimes,C.C. and Adams,G., Phys.Rev.Lett.
36
(1976) 145.131 Edelman,V.S., Pisma v ZhETF
2
(1976) 510 /4/ Babiichuk,V.P.,Golub,A.A., Medyanik,A.N. and Serbin, I.A., Fiz.kondens.sost.Trudy Ftint an UkrSSR, XXX (1974) 134./5/ Monarkha,Yu.P., Fiz.nizk.temp.
