I would like to ask if it makes sense to make Tauc Plots (either Direct or Indirect band gap ones) for a material that the literature claims to be a superconductor.
Supposing that I had obtained a reasonable value (about 1.5 eV) for one of the type of Tauc plot. What would be the meaning of this band gap obtained? Is it still the gap energy between valence and conduction band?
Some additional information: I got the Tauc plot from absorption spectra of a suspension of the material, at room temperature. And the critical temperature for this superconductor according to literature is about 4.4 K.
Thank you so much for your attention
Optical gap is different from the quasi-particle gap (at least in the conventional BCS theory for bulk materials, the superconducting gap coincides with the quasi-particle gap arising from paring). In optical experiments (and Tauc plot is used for determining optical gap) one excites particles that remain to interact with the hole they leave behind; in contrast, in photo-emission (and inverse photo-emission) experiments, one truly removes (adds) particles from (to) systems. The optical gap is in general smaller than the quasi-particle gap, the difference being the binding energy of the bound states that electrons can form with holes (forming excitons). This binding energy can be small, whereby optical gap can be very close to the quasi-particle gap, but this is not in general the case. Incidentally, because bound states cannot be calculated by means of finite-order perturbation theory, calculation of the optical gap in general requires solving the relatively complicated Bethe-Salpeter equations.
Thank you so much Mr. Behnam Farid. Could you indicate some reference related to the concept you explained me? I mean, some paper about this difference between optical and quasi-particle gap?
You are welcome Alexandre. Regarding photo-emission spectroscopy, see the review article by Damascelli et al., the link to which I attach below. Regarding optical gap and the attendant issues, see the book Many-Body Aspects of Solid State Spectroscopy, by M. Balkanski (Elsevier, Amsterdam, 1986). For excitons and excitonic effects, see the book Principles of the Theory of Solids, 2nd edition, by J. M. Ziman (Cambridge University Press, 1972); see in particular Sec. 6.7 herein.
http://journals.aps.org/rmp/abstract/10.1103/RevModPhys.75.473
Hi, colleagues! We recently published a new method of spectrophotometric data analysis very similar to the Tauc method but with many advantages over it. In the Tauc method, the main problem is to determine the energy gap without knowing the nature of the optical transition (described with the parameter m). Our method does not require knowledge of the parameter m. The value of energy gap and parameter m can be obtained simultaneously thanks to one linear fit. Other advantages and description of how to use this method are described in the article. We encourage you to read the paper!
Article Inverse logarithmic derivative method for determining the en...
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Optics