Energy gap structure and tunneling characteristics of layered superconductors Page: 5 of 34
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All copper oxide based high-Ta superconductors have stratified structures, in which the
quasiparticles move freely within the layers but hop weakly between layers. It has occurred
to a number of authors that the nearly two-dimensional geometry may play an important
role in the phenomenology of these materials [1-8]. Much of this effort has been stimulated
by the tunneling spectroscopy data, which exhibit far more complex structure than low-T.
superconductors. In general, the theories predict that in the weak hopping limit in which
the interlayer hopping strengths of the quasiparticles are weak compared with the critical
temperature- T, the DOS curves have peaks at the energy gaps or order parameters of
individual layers [1-2]. In the strong hopping limit, however, the main features in the DOS
curve should be identified with the OP's of the bands [3-5]. The present work carries this
line of inquiry into the interesting and perhaps most relevant parameter range,.namely,
where the hopping strengths are comparable to the OP's or. T. For simplicity, we limit our
work to two distinct layers in a unit cell with intralayer or interlayer pairing. It is found
that the results of both weak hopping and strong hopping theories are incomplete and
potentially misleading. The features in DOS are not directly identifiable with the OP's
of the layers, but are shifted and modified by the band dispersion along the c-direction.
The singularities in DOS curves are logarithmic, which are less pronounced than those for
BCS superconductors. We conclude that the tunneling curves for layered superconductors
should be interpreted with caution.
The papers is organized as follows. Section 2 contains the analysis of a two-layer
intralayer pairing model, showing the basic algebraic steps leading to our new conclusions.
Section 3 extends the consideration to the interlayer pairing case. Section 4 discusses how
the results of the last two sections may be applied to real systems.
2. The Intralayer Pairing Model
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Liu, S.H. & Klemm, R.A. Energy gap structure and tunneling characteristics of layered superconductors, report, June 1, 1993; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc682733/m1/5/: accessed March 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.