Could you explain it a little bit more? How do you measured it ?

Hello, 

Thank you for your interest. We contact the sample sides to  two Ag contacts at 0.8 cm length and 0.2 width. The sample is inserted into a closed cycle cryogenic cryostat (He) the system is   brought at vacuum of 10^-5 mbar. then ohmic test is verified, there after temperature is lowered  to 200 K, then I-V test i verified each 5 K. after delay of stability of 60 sec at each step 

Greeting 

    The topological insulator has a very different behaviour on its surface (a semimetal with gap zero) and on the bulk which is an insulator. What is the activation energy that you find higher than the energy gap?

thank u for the response we read about 0.6 ev

   Thank you. That is quite a lot, that is 0.6 eV for the excess of the gap energy. Where do you take the this gap energy in the surface or in the bulk? Do you distinguish these two different parts of the material?

no I am able to do . Most probably we are measuring the surface because the measurements are carried out by the Hall bar technique

  Thus if you consider that on the surface the band energy gap is zero ( are you doing that?), this means that you have 0.6 eV of activation energy which you could coincide with an effective energy gap thermally induced. Why do you distinguish the energy gap from the activation energy?

Thank u. you are mostly right as I believe. I distinguish between them because I am not sure about the value. If I said this is Eg then I must be sure. but why there is conflect btwn the thermal and optical gap. Thank u