Thermodynamic Properties of Glasses

The main low temperature p r o p e r t i e s of g l a s s e s a r e reviewed and analyzed i n terms of t h e "two l e v e l systemsv model. A new mechanism of i n t e r a c t i o n between f l u o r e s c e n t molecules and f l u c t u a t i n g s t r a i n f i e l d s c rea ted by t h e two l e v e l systems involving t h e concept of e l a s t i c quadrupoles is proposed i n view of exp la in ing t h e T ' . ~ law of t h e homogeneous f luorescence l inewid ths f o r amorphous h o s t s . I THE TUNNELING MODEL The tunne l ing model has been b u i l t up on t h e purpose t o exp la in t h e low temperature s p e c i f i c hea t and thermal conduc t iv i ty of g l a s s e s measured i n 1 9 7 1 by Z e l l e r and Pohl 111. Anderson, Halper in , Varma / 2 / and W. P h i l l i p s 1 3 1 assume t h a t t h e insu la t i n g g l a s s e s have s p e c i f i c d e f e c t s named tunnel ing d e f e c t s . They a r e r e s i d u a l motion of atoms o r group of atoms cha rac te r i zed by a double we l l p o t e n t i a l . The assymmetry energy is A = €2 €1 while t h e tunne l ing energy A, = where wo is t h e typ ica l c u r v a r t u r e of l o c a l minimum and A t h e dimensionless tunnel ing parameter. The o r i g i n a l assumptions of t h e a u t h o r s was t o assume A and A a s uniform random v a r i a b l e a t low energy (whi te no i se ) . The tunne l ing parameter A : A = @ d (1) wA where d is t h e d i s t a n c e between t h e two minima, m t h e mass, V t h e average p o t e n t i a l b a r r i e r and wo t h e c h a r a c t e r i s t i c frequency of p a r t i c l e motion This tunne l ing motion changes t h e s p l i t t i n g GI . . . . . . energy E of t h e two l e v e l :