G. Baskaran, RESONANT PAIR TUNNELING AND SINGULAR EFFECTS OF C-AXIS DISORDER IN CUPRATE AND ORGANIC SUPERCONDUCTORS, Philosophical magazine. B. Physics of condensed matter. Statistical mechanics, electronic, optical and magnetic, 76(2), 1997, pp. 119-129
In the interlayer pair tunnelling theory of superconductivity, the lar
ge scale of T-c has its origin in the k-space locality of the pair tun
nelling matrix elements. We give a complementary interpretation of the
same physics as a process of resonant pair tunnelling and illustrate
it through Cooper pair analysis. This interpretation is used to give a
mechanism which leads to a singular suppression of T-c as a function
of c-axis (off-plane or off-axis) disorder. In this mechanism the nonr
esonant tunnelling processes arising from the c-axis disorder in gener
al contributes a pair binding energy which is reduced by a factor of t
he order of T-J/epsilon(F), where T-J is the interlayer pair tunnellin
g matrix element and epsilon(F) is the Fermi energy. This leads to a s
imple theorem which states that the scale of T-c is controlled by the
space average value of the bare one-electron interlayer hopping matrix
element. After briefly discussing the fact that the organic supercond
uctors based on ET and tetramethyltetraselenafulvalene molecules are s
trongly correlated narrow-band systems, the dramatic reduction in T-c
due to anion disorder in organic superconductors is explained by our m
echanism. Off-plane disorder effects in some of the cuprates are also
discussed.