arXiv subjects

Oleg Tereshchenko

Publications and source records attributed to Oleg Tereshchenko.

3 recordsLinked to original sources

arXiv2023

Revealing the Microscopic Mechanism of Displacive Excitation of Coherent Phonons in a Bulk Rashba Semiconductor

Changing the macroscopic properties of quantum materials by optically activating collective lattice excitations has recently become a major trend in solid state physics. One of the most commonly employed light-matter interaction routes is the displacive mechanism. However, the fundamental contribution to this process remains elusive, as the effects of free-carrier density modification and raised effective electronic temperature have not been disentangled yet. Here we use time-resolved pump-probe spectroscopy to address this issue in the Rashba semiconductor BiTeI. Exploring the conventional regime of electronic interband transitions for different excitation wavelengths as well as the barely accessed regime of electronic intraband transitions, we answer a long-standing open question regarding the displacive mechanism: the lattice modes are predominantly driven by the rise of the effective electronic temperature. In the intraband regime, which allows to increase the effective carrier temperature while leaving their density unaffected, the phonon coherence time does not display significant fluence-dependent variations. Our results thus reveal a pathway to displacive excitation of coherent phonons, free from additional scattering and dissipation mechanisms typically associated with an increase of the free-carrier density.

cond-mat.mes-hall↗

arXiv2016

Dual nature of magnetic dopants and competing trends in topological insulators

Topological insulators interacting with magnetic impurities have been reported to host several unconventional effects. These phenomena are described within the framework of gapping Dirac quasiparticles due to broken time-reversal symmetry. However, the overwhelming majority of studies demonstrate the presence of a finite density of states near the Dirac point even once Topological insulators become magnetic. Here, we map the response of topological states to magnetic impurities at the atomic scale. We demonstrate that magnetic order and gapless states can coexist. We show how this is the result of the delicate balance between two opposite trends, i.e. gap opening and emergence of a Dirac node impurity band, both induced by the magnetic dopants. Our results evidence a more intricate and rich scenario with respect to the once generally assumed, showing how different electronic and magnetic states may be generated and controlled in this fascinating class of materials.

cond-mat.mes-hall↗

arXiv2015

Systematics of molecular self-assembled networks at topological insulators surfaces

The success of topological insulators (TI) in creating devices with unique functionalities is directly connected to the ability of coupling their helical spin states to well defined perturbations. However, up to now, TI-based heterostructures always resulted in very disordered interfaces, characterized by strong mesoscopic fluctuations of the chemical potential which make the spin-momentum locking ill-defined over length scales of few nanometers or even completely destroy topological states. These limitations call for the ability to control topological interfaces with atomic precision. Here, we demonstrate that molecular self-assembly processes driven by inherent interactions among the constituents offer the opportunity to create well-defined networks at TIs surfaces. Even more remarkably, we show that the symmetry of the overlayer can be finely controlled by appropriate chemical modifications. By analyzing the influence of the molecules on the TI electronic properties, we rationalize our results in terms of the charge redistribution taking place at the interface. Overall, our approach offers a precise and fast way to produce tailor-made nanoscale surface landscapes. In particular, our findings make organic materials ideal TIs counterparts, since they offer the possibility to chemically tune both electronic and magnetic properties within the same family of molecules, thereby bringing us a significant step closer towards an application of this fascinating class of materials.

cond-mat.mes-hall↗