Suggested question: identify experimental tests for the latest developments in the theory of the SIT
Experiments suggested to check recent theories of S-I transition:
1) RF stimulation of activated conductance. Can be used to probe the nature of insulating state which contains (according to theory of Feigelman, Ioffe, Mezard) energy threshold for delocalized excitation, ωd(g) which vanishes when coupling constant g approaches the critical point gc RF excitation with frequency ω which is a bit above ωd may lead to strong increase of conductivity due to specific excitation
of mobile excitations without much heating of the sample.
2) Mapping of supercurrent distribution. According to the theory, close to SIT supercurrent is distributed very inhomogeneously along the sample. It would be important to measure distribution of supercurrents experimentally. Possible methods could include, for example, magnetic AFM or magnetic-field-sensitive NV-centers in diamond, both methods being able to measure magnetic field produced by super-current with a good spatial resolution.
3) Spatial correlation of peak heights and gap widths.
More extensive STM studies are needed to investigate correlation functions of the spatial inhomogeneities of the superconducting state. The spatial evolution of the gap and coherence peak height correlation functions as a function of disorder would be of great interest for understanding how disorder transforms superconductors into insulators.
4) Fate of pseudogap while moving away from SIT ?
According to theoretical description of strongly disordered superconductors, the size of pseudogap is expected to decrease while switching to less disordered samples. Thus it would be important to study if pseudogap features (e.g. seen in InOx near S-I transition) are diminished for less disordered samples, with higher Tc values (like ones used in the phase slip experiment by Oleg Astafiev, or in high-frequency measurements reported Peter Armitage ).
Prepared by B.Sacepe and M. Feigel’man
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