Layered superconductors with anisotropic energy gap: specific heat and infrared absorption

Jha, Sudhanshu S. (1990) Layered superconductors with anisotropic energy gap: specific heat and infrared absorption Pramana - Journal of Physics, 34 (4). pp. 259-277. ISSN 0304-4289

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New oxide superconductors with layered structure are expected to have anisotropic energy gap in the generalized BCS pairing theory. The gap parameter 2Δ(k^) can be quite different for (k^) perpendicular to the plane of the layers as compared tok parallel to layer planes. Because of short coherence lengths ξ, quite small compared to the normal state carrier meanfree pathl, the effect of these anisotropies do not average out, as in many of the conventional superconductors. For a proper comparison of experimental results with the correct predictions of the pairing theory, a formulation is developed to obtain important physical quantities like specific heat and infrared absorption in the superconducting state of such anisotropic systems. This includes a brief account of the pairing theory generalized to layered crystals with arbitrary number of layers per unit cell, not necessarily equidistant. In an explicit model for the anisotropy of the gap parameter ink-space, with a simple form for the nonspherical Fermi-surface, it is shown that the low-temperature specific heat can have even a linear or a power-law temperature-dependence in the superconducting state. Even if the gap parameter does not vanish anywhere, its smeared-out exponential temperature-dependence may be difficult to be distinguished experimentally from a power-law behaviour. Similarly, it is shown that in the case of appreciable anisotropy, infrared absorption can take place much below the in-plane gap parameter 2Δt(k^)t), where kt is the wavevector in the plane of the layers.

Item Type:Article
Source:Copyright of this article belongs to Indian Academy of Sciences.
Keywords:Layered Superconductors; Anisotropic Energy Gap; Specific Heat; Infrared Absorption
ID Code:66513
Deposited On:24 Oct 2011 09:13
Last Modified:18 May 2016 14:01

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