The energy gap can be determined from the specific heat measurements, but one has to be very careful about subtracting the lattice contribution. The electronic contribution to the heat capacity from the superconducting state has exponential form with an argument proportional to -1/T, suggestive of excitation of the electrons across the gap. A better determination of the gap can be done by tunneling experiments. Please read first Kittel's textbook and then more advanced book by Tinkham, de Gennes and Schriffer.

Thank you so much. Sir, Is there any possibility that there is no jump (exponetial below Tc) in specific heat. I mean its not clear from specific heat data(or it may be problem in the measurements).

It is extremely difficult to extract the energy gap from the specific heat data correctly. So even if you cannot do it from your specific heat data you cannot say that there is no gap. The tunneling experiment is much more sensitive. Pratap Raychaudhuri in TIFR is a specialist for tunneling measurements. You may perhaps contact him.

What type of superconductor do you have. What type of sample have you prepared? Single crystals are more suitable for such experiments. Even heat capacity measurements on single crystals may reveal energy gap. So try to grow single crystals if that is possible.

The formation of energy gap can be observed in FTIR spectra across Tc, and you can define the energy gap value in the range of formation. For specific heat measurement, the jump or discontinuity at Tc not visible for some classes.

Thank you both of you. @TC I start working on AFe2As2 where A is monovalent elements with tetragonal ThCr2Si2-type structure at room temperature. WE are using here vacuum sealed tube for making bulk samples. I ll try to contact Pratap Raychaudhuri regarding these measurements. Tunneling experiments, sir you mean STM at low temperature or Andrew reflection measurements?

I was just thinking of simple electron tunneling experiment first developed and used by I. Giaever (Phys. Rev. Lett 5, 147 (1960)) to determine the superconducting gap in elemental metallic superconductors. You can read about it in Tinkham's book in section 2-8 on p. 43. But electron tunneling method has been greatly developed for investigating all these new exotic superconductors. So you should consult recent literature as well. Pratap is a specialist in these experimental methods. Once I visited his laboratory at TIFR and was greatly impressed. But I guess you should have single crystals for the success. Small single crystals would do.

I think in this lab (for me new) small crystals can be found while making bulk samples. I ll try to see this possibly. I am interested to know about gaps and their origin. Thank you.

@tapan Chatterji?: I have another question for you, in lines of this, so if it is a s wave superconducter we an use specific heat measurments to find out the Gap, what if it is like D wave or others where gap is dependent on the direction you observe... Does specific heat really capture this .. I am theorist I would like to know., Thanks,...@ Brajesh so do you know what is symmetry of the cooper pair in your material?

@ Janani AFe2As2 amd AFe2Se2 type superconductor I am working now. Some papers say it has nodal s wave symmetry. But ralsy I dont have clear idea about symmetry of Cooper pair. Please tell a good reference to understand from a lay man point of view.

Some papers http://www.sciencemag.org/content/337/6100/1314.full.pdf

http://www.nature.com/nphys/journal/v9/n6/full/nphys2617.html

See your facebook....

@Janani: Unfortunately specific heat measurements often do not give the gap values especially for high Tc superconductors. Measurement on single crystals are much better. Better method is electron tunneling as I indicated before.

Electronic specific heat measurements can give an indication of the symmetry, s-wave or d-wave, but not the value of the gap. The specific heat is exponential in an s-wave, and goes T^2 in a d-wave. But as Tapan says, these measurements are themselves highly non-trivial.