Surface-plasmon–assisted electron pair formation in strong electromagnetic field

Abstract

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 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, measuring it's response to the excitation at hot spots on the gold surface. Furthermore, the spectra of photoelectrons, liberated by multi-plasmon absorption, has also been measured by a timeof-flight spectrometer. In both cases new type of anomalies in the electron signal have been measured in the same intensity range, whose existence may be qualitatively understood, by using the intensity-dependent expression for the effective electronelectron scattering potential, derived earlier in a different context.

Shielding and localization in the presence of long-range hopping

“…This implies that in the gapped regime we have a coexistence of extended (ground state) and localized states (excited states) in the same region of parameters. This might be used to control transport in mesoscopic devices [30].…”

Surface-plasmon–assisted magnetic anomalies on room temperature gold films in high-intensity laser fields

“…These experimental findings were interpreted on the basis of an analogy with an earlier theoretical result on e-e scattering in strong laser field in vacuum [5]. In this theory an effective potential has been derived for each multiphoton absorption (or stimulated emission) channels, containing a Bessel function factor with negative regions, implying electron attraction in these negative parts of the relative potential energy of the electrons [1,5]. Concerning the intensity range, where the anomalous behavior of both the STM and TOF signals were observed, a reasonable agreement was found with our experimental data if an SPO field enhancement factor of 30 was used (which has been taken from one of our previous papers [6]).…”

“…In a recent paper [1] we reported on one such effect, namely an indication to surface plasmon assisted electron pairing in gold films at room temperature. The SPO-s were excited by the ppolarized light of femtosecond Ti:Sa lasers in the Kretschmann geometry, and STM measurements were carried out at near field hot spots on the gold surface where we registered the rectified near field at zero STM bias [4].…”

“…

Supplementing our STM and electron emission studies investigations, concluding in electron pairing in strong laser fields [1], further time-of-flight electron emission studies were carried out, changing the angle of polarization of the incident light, exciting surface plasmon oscillations. It has been found, that those parts of the electron spectrum which have been attributed to electron pairing have a significantly different angular dependence around 80 GW/cm 2 where the pairing effect has been found than outside this region (e.g.

…”

“…The first, highest energy, smallest intensity one has been attributed to electron pairing [1]. The qualitative explanation of the higher energy of these electrons is, that they are emitted from the vicinity of the Fermi-surface, where the density of state may have a maximum [10].…”