Energy gap structure and tunneling characteristics of layered superconductors Page: 15 of 34
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A set of DOS curves is shown in Fig.9 for model parameters used in Fig.7 except that
J1/Teo ranges from 0.1 to 5. The bottommost curve for weak hopping is BCS-like, with
peaks at A1, i.e. the dominant OP. The topmost curve for strong hopping has threshold
at f(01 - A2) and main peaks at f(A1 + A2). The DOS curve increases continuously
between the threshold and the peak on both sides. The origin of these features has been
discussed in Ref.3-5, and is reiterated here using a different language. Recall the definition
of A. and its complex conjugate Ab in Eqs.(28) and (29). The real part of A8 or Aj given
Rea. = A1 cos[kzd + (kz)] + A2 cos[kzd' - 4(kz)}, (40)
which is an even function of k2., is the intraband OP discussed in early papers,3-5 while
the imaginary part, an odd function of kz given by:
Ima8 = A1 sin[kzd + 0(kz)] - A2 sin[kzd' - q(kz)], (41).
is the interband OP. It can be shown without much difficulty that the imaginary part van-. .
ishes in the strong hopping limit, leaving the intraband OP as the only order parameter. A
little algebra yields that-the extremal values of the right-hand-side of Eq(39) are A1 A2
obtained at kz = 0 and kz = fir/s respectively. Therefore, the inner structure reflects the
c-axis versus ab-plane anisotropy of the gap function [3-5]. The main peaks are logarith-
mic singularities because of the kz dependence of the gap function. In the intermediate
hopping regime the DOS curves exhibit two sets of peaks in addition to structures inside
of the inner peaks. It will be discussed in the Appendix that both sets of peaks are loga-
rithmic singularities, but it is not straightforward to write down analytic expressions for
the threshold and the positions of the singularities. Nonetheless, one can establish that,
just like the intralayer pairing case, the outer peaks are associated with interband pairing.
In contrast to the intralayer problem, however, the interband peaks may be stronger than
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Liu, S.H. & Klemm, R.A. Energy gap structure and tunneling characteristics of layered superconductors, report, June 1, 1993; Illinois. (digital.library.unt.edu/ark:/67531/metadc682733/m1/15/: accessed July 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.