Prominence of Terahertz Acoustic Surface Plasmon Excitation in Gas-Surface Interaction with Metals

Acoustic Plasmons in Nickel and Its Modification upon Hydrogen Uptake

In this work, we study, in the framework of the ab initio linear-response time-dependent density functional theory, the low-energy collective electronic excitations with characteristic sound-like dispersion, called acoustic plasmons, in bulk ferromagnetic nickel. Since the respective spatial oscillations in slow and fast charge systems involve states with different spins, excitation of such plasmons in nickel should result in the spatial variations in the spin structure as well. We extend our study to NiHx with different hydrogen concentrations x. We vary the hydrogen concentration and trace variations in the acoustic plasmons properties. Finally, at x=1 the acoustic modes disappear in paramagnetic NiH. The explanation of such evolution is based on the changes in the population of different energy bands with hydrogen content variation.

Impact of the energy dispersion anisotropy on the plasmonic structure in a two-dimensional electron system

The effect of the band structure anisotropy (triangular, square, and hexagonal wrapping) on the electronic collective excitations (plasmons) in a two-dimensional electron gas (2DEG) is studied in the framework of the random-phase approximation. We show that the dynamical dielectric response in these systems strongly depends on the direction of the in-plane momentum transfer q. The effect is so pronounced that it results in a different number of electronic collective excitations in some q regions, both with - and ∼q-like energy dispersions. This finding is in striking contrast to the conventional 2DEG case with isotropic energy band dispersion where only a single plasmon with dispersion can exist. Our prediction of acoustic modes (with the ∼q dispersion) in a one-energy-band electron system expands the previous knowledge that such kind of plasmon can be realized only in two-component systems.

Surface electronic corrugation of a one-dimensional topological metal: Bi(114)

The surface of Bi(114) is a striking example where the reduced dimensionality gives rise to structural rearrangement and new states at the surface. Here, we present a study of the surface structure and electronic corrugation of this quasi one-dimensional topological metal based on helium atom scattering (HAS) measurements. In contrast to low-index metal surfaces, upon scattering from the stepped (114) truncation of Bi, a large proportion of the incident beam is scattered into higher order diffraction channels which in combination with the large surface unit cell makes an analysis challenging. The surface electronic corrugation of Bi(114) is determined, using measurements upon scattering normal to the steps, together with quantum mechanical scattering calculations. Therefore, minimisation routines that vary the shape of the corrugation are employed, in order to minimise the deviation between the calculations and experimental scans. Furthermore, we illustrate that quantum mechanical scattering calculations can be used to determine the orientation of the in- and outgoing beam with respect to the stepped surface structure.