MOBILITY OF POSITIVE IONS IN NORMAL AND SUPERFLUID 3He

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MOBILITY OF POSITIVE IONS IN NORMAL AND

SUPERFLUID 3He

J. Kokko, M. Paalanen, W. Schoepe, Y. Takano

To cite this version:

J. Kokko, M. Paalanen, W. Schoepe, Y. Takano.

MOBILITY OF POSITIVE IONS IN

JOURNAL DE PHYSIQUE

Colloque C6, suppliment au no 8, Tome 39, aozit 1978, page

C6-68

M O B I L I T Y OF P O S I T I V E I O N S I N NORMAL AND S U P E R F L U I D

3He

J

.

Kokko, M.A. Paalanen, W. ~ c h o e p e * and Y. Takano

Lou

Temperature Laboratory, Helsinki University of TechrzoZogy

SF-02150

Espoo

15,

Finland

Rdsum6.- La m o b i l i t d d e s i o n s p o s i t i f s dans l f 3 H e l i q u i d e a Q t 6 mesurge en dessous d e 200

mK.

Dans l a phase normale on observe aux p l u s b a s s e s tempgratures un comportement non l i n e a i r e d e l a v i t e s s e d e d d r i v e pour d e s champs d l e c t r i q u e s a u s s i f a i b l e s que 30 V / m . On d o i t donc u t i l i - s e r des champs i n h a b i t u e l l e m e n t f a i b l e s pour determiner 1-1. La v a r i a t i o n thermique d e P a i n s i que l e s e f f e t s non l i n g a i r e s en champ o n t dtL Ltudids dans l e s phases normale e t s u p e r f l u i d e . Abstract.- P o s i t i v e i o n m o b i l i t y i n l i q u i d 3 ~ e h a s been measured below 200 mK. A t t h e lowest temperature i n t h e normal phase t h e d r i f t v e l o c i t y o f t h e i o n s was found t o be n o n l i n e a r with r e s p e c t t o e l e c t r i c f i e l d f o r E a s low a s 30

Vim.

T h i s means t h a t u n u s u a l l y low f i e l d s were used to determine t h e m o b i l i t y . The temperature dependence of t h e m o b i l i t y and t h e e l e c t r i c f i e l d dependence o f t h e d r i f t v e l o c i t y were s t u d i e d i n t h e n o b a l and s u p e r f l u i d phases.

The 3 ~ e sample w i t h 30 ppm 'He i m p u r i t y was cooled by t h e n u c l e a r demagnetization technique / I / . Temperatures were measured using platinum

NMR. The

time of f l i g h t method t o measure t h e i o n m o b i l i t y was s i m i l a r t o t h e one used i n our p r e v i o u s n e g a t i v e i o n experiments 1 2 1 , 131.

Fig. 1 : D r i f t v e l o c i t y i n t h e normal phase v e r s u s e l e c t r i c f i e l d . + , 1.5 mK, 0.5 b a r . A t 6 b a r

,

2.66 mK; o , 5.14 mK, o , 8.42 mK. A t 28 b a r :

A ,

3.11 mK; A , 5.71 mK.

a t s e v e r a l temperatures a s a f u n c t i o n of t h e e l e c - t r i c f i e l d E from 9 t o 100 V/cm. A t t h e lowest temperatures we found a pronounced n o n l i n e a r i t y i n t h e d a t a , which a r e shown i n f i g u r e 1 i n compari- son w i t h t h e h i g h temperature d a t a . A t 6 b a r and 28 b a r f o r temperatures above 5 and 8 mK, respec- t i v e l y , we observed a l i n e a r d r i f t v e l o c i t y i n o u r f i e l d range.

Fig. 2 : M o b i l i t y i n t h e normal phase a t 6 b a r (0) I n o r d e r t o determine t h e m o b i l i t y of posi- and 28 b a r

0')

t i v e i o n s y = VIE, t h e d r i f t v e l o c i t y v was measured

I n f i g u r e 2 we show t h e m o b i l i t i e s a t t h e s e p r e s s u r e s determined e i t h e r from t h e low f i e l d r Permanent a d d r e s s : Z e n t r a l i n s t i t u t fiir Tieftempe-

r a t u r f o r s c h u n g d e r Bayerischen Akademie d e r Wissen s l o p e of t h e v-E p l o t o r from t h e v/E r a t i o taken. s c h a f t e n , 8046 Garching, W. Germany _{i n t h e l i n e a r regime. The anomalous jump i n t h e}

m o b i l i t y a t around 100 mK i s s i m i l a r t o t h e impuri- king, v = AlpF, where

A

i s t h e energy gap and PF t y e f f e c t observed by Roach e t a l . 141. The m o b i l i t y t h e Fermi momentum of 3 ~ e q u a s i p a r t i c l e s (V % 7cm/s a t lower t e m p e r a t u r e s i n c r e a s e d l o g a r i t h m i c a l l y w i t h a t zero temperature and 28 b a r ) . A s t h e d r i f t velo- d e c r e a s i n g temperature down t o T

.

The r e s u l t s by

Alexander e t a l . 151 a t 5 bar and 27 b a r a r e c o n s i s - t e n t w i t h o u r s whereas t h e d a t a by Roach e t a l . de- v i a t e s i g n i f i c a n t l y a t temperatures below 1 0 mK probably due t o t h e r a t i o v/E being taken i n t h e n o n l i n e a r regime.

A s with t h e d a t a of Alexander e t a l . , b e t - ween 90 V/cm and 2000 ~ / c m , our d a t a i n f i g u r e 1

p l o t t e d i n I / v a g a i n s t 1/E c a n a l s o be f i t t e d t o a

c i t y exceeds t h i s v e l o c i t y , t h e c u r v e s a r e more o r l e s s p a r a l l e l t o t h e normal phase d a t a taken i n t h e v i c i n i t y of T

.

I n t h e normal phase b o t h t h e temperature de- pendence o f t h e m o b i l i t y and t h e pronounced n o n l i - n e a r i t y i n t h e e l e c t r i c f i e l d dependence of t h e d r i f t v e l o c i t y a r e important i n s t u d i e s of t h e ener- gy exchange between t h e i o n s and 3 ~ e q u a s i p a r t i c l e s Bowley's c a l c u l a t i o n 161 has y i e l d e d t h e l o g a r i t h - r e a s o n a b l y s t r a i g h t l i n e e x c e p t i n t h e low f i e l d mic temperature dependence b u t i t s p r e s s u r e depen- regime where t h e l i n e a r i t y h o l d s . The m o b i l i t y ob- c e i s i n c o n s i s t e n t w i t h our d a t a i f t h e snowball t a i n e d from t h e s l b p e of such a l i n e , however, model / 7 / of t h e p o s i t i v e i o n s t r u c t u r e i s assumed. t e n d s t o b e l a r g e r than t h e low f i e l d m o b i l i t y . The

d i s c r e p a n c y f o r t h e 0.5 b a r d a t a a t 1 . 5 mK i s 6 2. When t h e l i q u i d e n t e r s t h e s u p e r f l u i d pha- s e s t h e m o b i l i t y of t h e i o n s i n c r e a s e s s t e e p l y . The i n c r e a s e of t h e m o b i l i t y normalized t o t h e v a l u e a t Tc, however, i n c r e a s e s c o n d i d e r a b l y l e s s t h a n f o r n e g a t i v e i o n s ; i n t h e B phase, a t t e m p e r a t u r e s be- low TIT % 0 . 9 , i t becomes l e s s t h a n one h a l f of

t h e n e g a t i v e i o n i n c r e a s e . The d r i f t v e l o c i t y i s s t r o n g l y n o n l i n e a r i n t h e f i e l d a s shown i n f i g u r e 3. 20 15 0 3 11 mK normot 20 LO 50 80 Fig. 3 : D i r f t v e l o c i t y a s a f u n c t i o n of t h e e l e c t r i c f i e l d E i n t h e s u p e r f l u i d a t 28 b a r . The magnetic f i e l d was a p p l i e d p a r a l l e l t o E. The arrow i n d i c a t e s Landau's c r i t i c a l velo- c i t y f o r p a i r breaking a t zero temperature.

A t t e m p e r a t u r e s below TITc 0.8, t h e d r i f t v e l o c i t y became n o n l i n e a r i n even t h e lowest f i e l d (5 V/cm)

References

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