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Surface plasmon assisted electron pair formation in strong electromagnetic field

The basis of low-temperature superconductivity has been set to be the pair formation of electrons, due to their effective attraction. The appearance of an effective attraction potential has also been predicted for electron-electron scattering in the presence of a strong, inhomogeneous radiation field. In the present work the strong electromagnetic fields were created by femtosecond Ti:Sa lasers, used to excite surface plasmons in gold films at room temperature, in the Kretschmann geometry. Experimental investigations were carried out using a surface plasmon near-field scanning tunneling microscope, by measuring its response to the excitation at hot spots on the gold surface. Furthermore, the spectra of photoelectrons, liberated by multi-plasmon absorption, have also been measured by a time-of-flight spectrometer. In both cases new type of anomalies in the electon signal have been measured in the same intensity range, whose existence may be qualitatively understood, by using the intensity-dependent expression for the effective electon-electron scattering potential, derived earlier in a different context.