Direct evidence of correlated two-electron tunneling in field emission resonance revealed through light emission on Ag(100) surfaces

Our Previous study discovered that the linewidth of the field emission resonance (FER) observed on MoS 2 surfaces varies significantly, resulting from the combined effects of correlated two-electron tunneling (CTET) and mechanisms involving spin flip, light emission, quantum trapping, and the Pauli exclusion principle. Due to CTET, the quantized state in FER can be simultaneously occupied by two electrons with opposite spins, in contrast to the conventional viewpoint that the quantized state is occupied by only one electron. Therefore, it is crucial to experimentally search for direct evidence of CTET in FER. In this study, we investigate whether the light emission associated with FER provides evidence of paired electrons on the Ag(100) surface, which possesses an energy gap above the vacuum level that may enhance the probability of CTET. This energy gap prevents electrons in the first-order FER from transmitting into the surface, thereby enabling light emission to reveal characteristics of triplet states and Auger-type excitation, both of which require two electrons occupying the quantized state, indicating that direct evidence of CTET has been obtained. Moreover, surface plasmons can be induced by electrons in the zeroth-order FER, and their radiative decay can also trigger Auger-type excitation.