How to compare the applicability of point contact Andreev reflection spectroscopy (PCAR) and angle-resolved angle-resolved photoemission spectroscopy to characterize the superconducting gap?
Dear Nilabja Kanti Sarkar,
I will take a stab at the question and hoe someone that knows a bit more will take over…
I am not particularly knowledgeable in PCAR but after reading these articles: https://arxiv.org/pdf/1210.6054.pdf and https://www.bnl.gov/isd/documents/93558.pdfI think it is similar to scanning tunneling spectroscopy (STS), as article number 2 uses a STM to conduct the measurements. In such case the STS probe the occupied and unoccupied local density of states (LDOS) or if a broader tip is used, I guess it is less local than STS of single atoms could be.
ARPES (see for example this review: https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.93.025006) probes the band structure of a material. If a UV lamp or other means of excitation is used it probes the occupied density of states. It is possible to probe unoccupied states using pump-probe laser setups or access parts of unoccupied states by doping.
The difference in this case would be that the STS measures the intensity of states for a range of binding energies whereas ARPES measures the reciprocal resolved intensity electron density for a set of binding energies. For one excitation energy you get k-parallel resolved band structure and if you vary energy you can get information about k perpendicular as well.
With ARPES you get occupied band structure (if using a standard setup not with laser or at a synchrotron) and with STS you get LDOS (also unoccupied states).
Best regards,
John
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