# Recent content by physengineer

1. ### Best material for IR absorption

Thank you, Cthugha! Yes, I want it for a detector. I can cool it down to 4.2K too. Single photon sensitivity is also required. I need the maximum absorption for the thinnest possible film, say a few nano meter. Spectral resolution is not an issue as long as either telecom freqs i.e. 1310 or 1550...
2. ### Best material for IR absorption

Hi ThereIam, No, not cell phones. Just detecting few photons of 1550nm or 1310nm photons at the end of an optical fiber. Thanks
3. ### Best material for IR absorption

Thank you, f95toli! In fact, I am interested in telecom wavelengths: 1550 nm or 1310 nm. Since the number of photons are very limited we need to absorb as much as we can.
4. ### Best material for IR absorption

Hi all, I am looking for the best material for IR (infra red) absorption, preferably something that I can make it into a thin film; any material that would work from semiconductors, metals to more exotic materials like graphene or... I appreciate your help. Thank you
5. ### What is kinetic capacitance in superconductors or in solid state in general?

Thanks, Sambristol! In fact my question on "kinetic capacitance" comes from studying "quantum phase slip". I understand it as a combination of coefficients with the dimension of capacitance in the "effective action" introduced by Golubev and Zaikin; however, I was hoping to get some physical...
6. ### What is kinetic capacitance in superconductors or in solid state in general?

What is "kinetic capacitance" in superconductors or in solid state in general? Hi, I would appreciate it if anyone could explain to me what "kinetic capacitance" is, particularly in the context of superconductors or solids. I understand "kinetic inductance" which comes from the kinetic...
7. ### Instanton contribution to two point function

Hello, I would appreciate it if anyone could help me with this problem: can there be any instantonic contribution to the following generic two-points function? \left \langle \varphi(x) \varphi(y) \right\rangle= \int D\varphi D A \varphi(x) \varphi(y) \exp \left( -S_E...
8. ### Kramers-Kronig relations for limited data point

Hello, I need to measure the complex-optical conductivity of some materials. The problem is that I can only measure the imaginary part of the complex conductivity only for limited wavelengths between 1030 nm and 2300 nm. From Kramers-Kronig relations, we know that the real and imaginary...
9. ### Replacing cathodoluminesc. by gates

Hi, I appreciate any help in this regard: People have used cathodoluminescence to study defects in insulators by having energetic electron beam on the defect and observing the luminescence. I want to see if I can do the same thing instead by putting gates around that defect. I can also...
10. ### Nonlocal electrodynamics of superconductors

Hello, Conductivity \sigma (\omega, k) in Fourier space is defined by J(\omega, k)= \sigma (\omega, k) A(\omega, k) In most cases the local limit of k\rightarrow 0 is a good approximation particulalry in type I superconductors and HTC superconductors. I am interested in cases...
11. ### Symmetry, Lagrangian, Qm, and diff eqs.

I am not sure if I understood your question exactly and my reply may sound trivial. Anyway, when you have a symmetry there are invariants associated with each of those symmetries (Noether's Theorem). In other words some quantities will be conserved during, let's say, a collision experiment like...
12. ### Effective action from the background field

Hello, Assuming that I have a pure U(1) gauge theory. The partition function can be written as Z=\int D(A) \exp (-F_{\mu\nu} F^{\mu\nu}) If I want to find the effective action in terms of an external classical field I can write it in terms of A\rightarrow A+B where B is background and then...
13. ### Connection between Free Energy and Action

Could anyone please, explain the connection between the Free Energy and the Action? I know the definitions of each but not sure about the connection. I read somewhere that the free energy is the same as the action when calculated "on-shell". What does this "on-shell" thing mean in this...
14. ### Conductivity from path integral and Kubo formlism

Thanks, DrDu! I appreciate your help.
15. ### Conductivity from path integral and Kubo formlism

Thanks a lot, DrDU! I am just not sure if I understood exactly what you meant for (2) My effective action is complex and non local but fortunately remains quadratic in terms of A and \psi or combination of these two. Therefore I can technically integrate over both A and \psi in the path...