No abstract

We theoretically show that two-photon coherent control yields electron photoemission from metal nanostructures that is localized in nanosize hot spots whose positions are controllable on a nanometer scale, in agreement with recent experiments. We propose to use silver V-shapes as tailored nanoantennas for which the position of the coherently controllable photoelectron emission hot spot can be deterministically predicted. We predict that the low-frequency, high-intensity (quasi-stationary) excitation of the photoemission leads to an exponentially high contrast of the coherent control. In various fields of nanoscience and nanotechnology, one of the key processes to achieve is controlled photoinduced injection of charges into nanoscopic regions of semiconductor or metal systems or vacuum. It is very important to perform this injection as an ultrafast process, on a femtosecond or subfemtosecond scale, and have a possibility to choose the injection nanosite dynamically with a nanometer-scale resolution. Such processes can be used, for instance, in site-specific, time-resolved electron-excitation spectroscopy of molecules and nanoobjects; its technological applications are possible in superfast nano-optoelectronics to transfer signals from optical to electronic components. There are, however, major obstacles to implementation of such processes. One of them is that light cannot be focused to nanoscopic regions directly. Using the adiabatic transformation, it is possible to transfer the optical excitation energy and coherence to the nanoscale; 1 however, such a concentration and the electron photoemission caused by it are static in space. Coherent control has been employed to dynamically change spectrum of photoelectrons emitted in a two-photon process from the Cu(111) surface. 2 We have proposed to use the coherent control to dynamically concentrate the optical excitation energy in space and time on the nanometer-femtosecond scale. 3,4 For nonlinear photoprocesses, such a concentration is possible and the time integral is coherently controllable. 3 This phenomenon has been later observed for two-photon electron emission from random nanostructured metal systems using two-pulse, interferometric coherent control in combination with electron microscopy. 5 In this Letter, we pursue two related goals: (a) We show that the two-photon (interferometric) coherent control allows one to dynamically control electron emission from randomly rough surfaces, which is localized within a few nanometers; we also propose metal nanoantennas whose photoelectron emission is predictable, highly localized, and coherently controllable. (b) We predict that the photoelectron emission from metal nanostructures in the strong field (quasi-stationary) regime allows for coherent control with extremely high contrast, suitable for nanoelectronics applications. Consider a specific variant of the coherent control where a femtosecond excitation pulse consists of two identical laser subpulses with a controllable temporal delay τ between them, as shown in Fig...

No abstract

We introduce a quantum dot in topological insulator nanofilm as a bump at the surface of the nanofilm. Such a quantum dot can localize an electron if the size of the dot is large enough, ≳5 nm. The quantum dot in topological insulator nanofilm has states of two types, which belong to two ('conduction' and 'valence') bands of the topological insulator nanofilm. We study the energy spectra of such defined quantum dots. We also consider intraband and interband optical transitions within the dot. The optical transitions of the two types have the same selection rules. While the interband absorption spectra have multi-peak structure, each of the intraband spectra has one strong peak and a few weak high frequency satellites.

No abstract