Tight binding simulation of laser-assisted ultrafast field-emission from correlated metal

• Published in: 2023 IEEE Nanotechnology Materials and Devices Conference (NMDC) p. 569
• Main Authors: D'Onofrio, Luciano Jacopo, Avella, Adolfo, Eckstein, Martin
• Format: Conference Proceeding
• Language: English
• Published: IEEE 22.10.2023
• Subjects: Correlation; Electric potential; Metals; Protocols; Pulse measurements; Scattering; Solid modeling
• ISSN: 2473-0718
• DOI: 10.1109/NMDC57951.2023.10343945

The study of nonequilibrium phenomena in correlated lattice systems is an increasingly active research field in condensed matter physics. Indeed, electronic correlations induce interesting phenomena, such as Hubbard-Mott metal-to-insulator transitions [1], whose understanding is a crucial step for the exploitation of novel properties of such systems in future applications. Therefore, it is intriguing to design and possibly implement an experimental set-up capable of detecting and measuring effects induced by interactions. Field-emission can be considered a good starting point, as it is a powerful and well-known spectroscopic technique used to investigate the energy distribution of the emitted electrons. Adding a strong and ultrashort laser pulse [2], [3] can periodically modify the potential barrier for electron tunnelling and, thus, the far-field electron energy distribution, which is representative of the interactions inside of the material.In this work, we provide a theoretical-numerical tool able to analyze how interaction effects, as well as decoherence, manifest in such an energy distribution. According to the cold field-emission protocol, we consider a metallic tip which is initially at equilibrium at room temperature. Electrons in it cannot leave the solid because of a high-step potential barrier given by the metal work function W. Then, the barrier potential profile is bended by applying a voltage V pot between an electrode and the metallic tip, opening a tunneling channel between solid and vacuum. Cold-emitted electrons are then perturbed by an electromagnetic pulse in proximity of the solid-vacuum interface and, finally, the field-emitted current, i.e., electron energy distribution, is measured by a detector placed sufficiently far from that interface. Both the solid and the vacuum are modeled using one-band Hubbard-chains with nearest-neighbour hopping. The out-of-equilibrium electron dynamics of this inhomogeneous system is described using the Keldysh Green's function formalism [1], [4] which, in this case, allows to solve the equations of motion considering the two chains as they were disentangled. While the vacuum-chain problem is solved by means of the Runge-Kutta method, we choose to solve the solid-chain problem by means of the second order Born approximation within a DMFT framework [1], [4], [5] and of the implementation of the NESSi simulation package [6]. Finally, we determine the far-field electron energy distribution by considering an uncorrelated Hubbard-chain dispersion in k-space for the vacuum region. We then analyze these results by exploring various pulse parameters and different values of the correlation term U.