Single Molecule Spectroscopy as a possible tool to study the electric field in superconductors

– We discuss the influence of the superconducting transition in a film on the fluorescence spectrum of a single molecule located nearby. We show that single molecule spectroscopy (SMS) should be an appropriate tool to detect the electric charge associated with a vortex line. Also we argue that an electric field must appear at the boundaries between normal and superconducting regions of the intermediate phase and SMS could be useful to study this effect. Introduction. – The studies of the electric field effects in superconductors have a rather long history (see Ref. [1] and articles cited there). In spite of a large number of theoretical works there exist only a few experimental hints on the experimental observation of electric field in superconductors. A regain of interest to this subject has been stimulated by the prediction of the existence of an electric charge of the vortex core (see Ref. [2]). It was argued there that the vortex charge can be responsible for the sign change in the Hall effect below Tc. Subsequent studies [3] stressed the importance of the metallic screening which strongly reduces the vortex core charge. For the moment, there is no direct experimental evidence of the charge of a single vortex. Note that high-resolution nuclear quadrupole frequency measurements revealed a change in the local electric field at the transition into the mixed state in YBaCuO [4]. However, this behavior can also be explained by a magnetostriction effect due to the coupling between the vortex lattice and the crystal structure. Therefore, it remains of considerable interest to directly observe the charge of a single vortex. Another interesting example of electric field generation in a superconductor is the intermediate state in type I material. This state involves a sequence of normal and superconducting regions and appears for example in superconducting films submitted to a perpendicular magnetic field. The electric charge in this case appears at the boundaries between the normal and