arXiv subjects

Ilya A. Eliseyev

Publications and source records attributed to Ilya A. Eliseyev.

6 recordsLinked to original sources

arXiv2025

Epitaxial graphene integrated with a monolayer magnet

Imprinting magnetism into graphene makes an important step to its applications in spintronics. An actively explored approach is proximity coupling of graphene to a 2D magnet. In these endeavors, the use of epitaxial graphene may bring significant advantages due to its superiority over the exfoliated counterpart and natural integration with the substrate but the problem of attaining magnetism persists. Here, we report synthesis and analysis of a heterostructure coupling epitaxial graphene with a regular lattice of magnetic atoms formed by Eu intercalation. The magnetization measurements reveal easy-plane 2D magnetism in the material, with the transition temperature controlled by low magnetic fields. The emerging negative magnetoresistance and anomalous Hall effect point at spin polarization of the carriers in graphene. In the paramagnetic phase, the magnetoresistance in graphene exhibits critical exponential behavior of the induced magnetic state. The intercalation does not compromise the parental electronic structure - quantum oscillations in the resistivity manifest low-mass carriers in graphene. The results are set against those for an isostructural material based on intercalated nonmagnetic Sr. Overall, the study expands the family of 2D magnets and establishes a prospective material for graphene-based spintronics.

cond-mat.mes-hall↗

arXiv2023

Indirect-to-direct bandgap transition in few-layer $β$-InSe as probed by photoluminescence spectroscopy

InSe is a promising material for a next-generation of two-dimensional electronic and optical devices, characteristics of which are largely determined by the type of band structure, direct or indirect. In general, different methods can be sensitive to different peculiarities of the electronic structure leading to different results. In this work, we will focus on the luminescent properties of few-layer $β$-InSe with a thickness of 6 to 75 monolayers (ML). Low-temperature micro-photoluminescence ($mu$-PL) studies show a sharp increase in PL intensity in the range of thicknesses from 16 to 20 monolayers, where, in addition, there is a singularity in the dependence of the work function on the thickness. Time-resolved photoluminescence spectroscopy (TRPL) reveals three characteristic PL decay times that differ from each other by about an order of magnitude. We associate the processes underlying the two faster decays with the recombination of electrons and holes between the band extrema, either directly or through the interband relaxation of holes. Their contributions to the total PL intensity increase significantly in the same thickness range, 16-20 MLs. On the contrary, the slowest contribution, which we attribute mainly to the defect-assisted recombination, prevails at a smaller number of monolayers and then noticeably decreases. These results indicate the indirect-to-direct bandgap transition near 16-20 MLs, which determines the range of applicability of a few-layer $β$-InSe for efficient light emitters.

cond-mat.mes-hall↗

arXiv2022

Twisted Nanotubes of Transition Metal Dichalcogenides with Split Optical Modes for Tunable Radiated Light Resonators

Synthesized micro- and nanotubes composed of transition metal dichalcogenides (TMDCs) such as MoS$_2$ are promising for many applications in nanophotonics, because they combine the abilities to emit strong exciton luminescence and to act as whispering gallery microcavities even at room temperature. In addition to tubes in the form of hollow cylinders, there is an insufficiently-studied class of twisted tubes, the flattened cross section of which rotates along the tube axis. As shown by theoretical analysis, in such nanotubes the interaction of electromagnetic waves excited at opposite sides of the cross section can cause splitting of the whispering gallery modes. By studying micro-photoluminescence spectra measured along individual MoS$_2$ tubes, it has been established that the splitting value, which controls the energies of the split modes, depends exponentially on the aspect ratio of the cross section, which varies in "breathing" tubes, while the relative intensity of the modes in a pair is determined by the angle of rotation of the cross section. These results open up the possibility of creating multifunctional tubular TMDC nanodevices that provide resonant amplification of self-emitting light at adjustable frequencies.

physics.optics↗

arXiv2022

Strong photoluminescence enhancement in indirect bandgap MoSe$_2$ nanophotonic resonator

Transition metal dichalcogenides (TMDs) is a promising platform for new generation optoelectronics and nanophotonics due to their unique optical properties. However, in contrast to direct bandgap TMDs monolayers, bulk samples have an indirect bandgap that restricts their application as light emitters. On the other hand, the high refractive index of these materials seems ideal for creating high-quality nanophotonic resonators with a strong Purcell effect. In this work, we fabricate Whispering-gallery mode (WGM) resonators from bulk (i.e., indirect bandgap) MoSe$_2$ using resistless scanning probe lithography and study their optical properties. Micro-photoluminescence($μ$-PL) investigation revealed WGM spectra of resonators with an enhancement factor of 100 compared to pristine flake. Scattering experiments and modeling also confirm the WGM nature of spectra observed. Temperature dependence of PL revealed two components of photoluminescence. The first one quenches with decreasing temperature, the second one does not and becomes dominant. Therefore, this suggests that resonators amplify both direct and temperature-activated indirect PL. Thus, here we demonstrated the novel approach to fabricating nanophotonic resonators from bulk TMDs and obtaining PL from indirect bandgap materials. We believe that the suggested approach and structures have great prospects in nanophotonics.

cond-mat.mes-hall↗

arXiv2021

MoS$_2$ flake as a van der Waals homostructure: luminescence properties and optical anisotropy

We investigated multilayer plates made by exfoliation from a high-quality MoS$_2$ crystal and reveal that they represent a new object - van der Waals homostructure consisting of a bulk core and a few detached monolayers on its surface. This architecture comprising elements with different electron band structure leads to specific luminescence, when the broad emission band from the core is cut by the absorption peaks of strong exciton resonances in the surface monolayers. The exfoliated flakes exhibit strong optical anisotropy. We have observed a conversion of normally incident light polarization to $15\%$ in transmission geometry. This background effect is due to fluctuations of the c axis relative to the normal, whereas the pronounced resonance contribution is explained by the polarization anisotropy of excitons localized in the stripes of dissected surface monolayers.

cond-mat.mes-hall↗

arXiv2021

Photoluminescence kinetics of dark and bright excitons in atomically thin MoS$_2$

The fine structure of the exciton spectrum, containing optically allowed (bright) and forbidden (dark) exciton states, determines the radiation efficiency in nanostructures. We study time-resolved micro-photoluminescence in MoS$_2$ monolayers and bilayers, both unstrained and compressively strained, in a wide temperature range (10-300 K) to distinguish between exciton states optically allowed and forbidden, both in spin and momentum, as well as to estimate their characteristic decay times and contributions to the total radiation intensity. The decay times were found to either increase or decrease with increasing temperature, indicating the lowest bright or lowest dark state, respectively. Our results unambiguously show that, in an unstrained monolayer, the spin-allowed state is the lowest for a series of A excitons (1.9 eV) with the dark state being < 2 meV higher, and that the splitting energy can increase several times at compression. In contrast, in the indirect exciton series in bilayers (1.5 eV), the spin-forbidden state is the lowest, being about 3 meV below the bright one. The strong effect of strain on the exciton spectrum can explain the large scatter among the published data and must be taken into account to realize the desired optical properties of 2D MoS$_2$.

cond-mat.mes-hall↗