arXiv subjects

Vasil A. Saroka

Publications and source records attributed to Vasil A. Saroka.

7 recordsLinked to original sources

arXiv2026

Optical properties of hydrogenated graphene superlattices

We investigate with first principles theoretical methods optical response accounting for excitonic effects of quasi-one dimensional monolithic arrays of graphene nanostripes -- two-dimensional graphene superlattices, where quasi-metallic and dielectric regions alternate by selective hydrogenation of graphene. It is shown that chemical engineering of the graphene surface can lead to strong and well-isolated absorption peaks in the far-infrared and possibly even terahertz frequencies. The band gap scaling suggests no excitonic insulators.

cond-mat.mes-hall↗

arXiv2026

On flat band engineering and graphene magnonics

Graph-theoretic topological frustration is a peculiar situation on a finite piece of the honeycomb lattice that prevents a full pairwise coupling of the lattice sites via nearest neighbor links, even when the total number of sites is an even number and the structure possesses no sublattice imbalance. This type of frustration is inherent for organic molecules that are classified as concealed non-Kekulean hydrocarbons, representing peculiar diradicals. Here we show that this topological frustration persists in two-dimensional systems based on the honeycomb lattice. Such systems exhibit fully flat electronic energy bands located at the Fermi level. Therefore, two-dimensional ultimately flat bands can be systematically and predictably constructed for graphene monolayer nanomeshes. These systems are prone to antiferromagnetic ordering and hybrid spin-wave excitations mixing weak ferromagnetic and strong antiferromagnetic features, which could pave the way towards low-power, compact, and ultrafast organic spintronics with near room-temperature operation.

cond-mat.mes-hall↗

arXiv2025

Topological junction states in graphene nanoribbons: A route to topological chemistry

Two-dimensional topological insulators with propagating topological edge states are promising for dissipationless transport, while their one-dimensional analogs are capable of hosting localized topological junction states that are mainly envisaged for quantum computing and spintronics. Here, in contrast, we propose to use the localized nature of topological junction states for sensing applications. We report a systematic topological classification of a wide class of graphene nanoribbons represented by already synthesized extended chevron species. Using this classification, we theoretically model a double junction transport that shows an enhanced interaction with the NO$_2$ molecule. Our results show that topological junction states of nanoribbons can open an avenue for topological sensing and junction-assisted chemistry applications.

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arXiv2024

On a Solution to the Dirac Equation with a Triangular Potential Well

Chiral anomalies resulting from the breaking of classical symmetries at the quantum level are fundamental to quantum field theory and gaining ever-growing importance in the description of topological materials in condensed matter physics. Here we present analytical solutions of the Dirac equation for massless 3+1 fermions confined to an infinite stripe and placed into a background gauge field forming a triangular potential well across the width of the stripe. Such an effective 1+1 system hosts zero-energy modes resulting in the gauge field-dependent chiral anomaly structure. This problem has a direct relation to a half-bearded graphene nanoribbon placed into an in-plane external electric field and offers it an exact solution in terms of new special functions that are similar but not reducible to Airy functions.

cond-mat.mes-hall↗

arXiv2024

Tunable chiral anomalies and coherent transport on a honeycomb lattice

The search for energy efficient materials is urged not only by the needs of modern electronics but also by emerging applications in neuromorphic computing and artificial intelligence. Currently, there exist two mechanisms for achieving dissipationless transport: superconductivity and the quantum Hall effect. Here we reveal that dissipationless transport is theoretically achievable on a honeycomb lattice by rational design of chiral anomalies tunable without any magnetic fields. Breaking the usual assumption of commensurability and applying an external electric field lead to electronic modes exhibiting chiral anomalies capable of dissipationless transport in the material bulk, rather than on the edge. As the electric field increases, the system reaches a cubic-like dispersion material phase. While providing performance comparable to other known honeycomb lattice-based ballistic conductors such as an armchair nanotube, zigzag nanoribbon and hypothetical cumulenic carbyne, this scheme provides routes to a strongly correlated localization due to flat band dispersion and to exotic cubic dispersion material featuring a pitchfork bifurcation and a critical slowing down phenomena. These results open a new research avenue for the design of energy efficient information processing and higher-order dispersion materials.

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arXiv2019

Strong Light-Matter Coupling in Carbon Nanotubes as a Route to Exciton Brightening

We show that strong light-matter coupling can be used to overcome a long standing problem that has prevented efficient optical emission from carbon nanotubes. The luminescence from the nominally bright exciton states of carbon nanotubes is quenched due to the fast nonradiative scattering to the dark exciton state having a lower energy. We present a theoretical analysis to show that by placing carbon nanotubes in an optical microcavity the bright exctonic state may be split into two hybrid exciton-polariton states, while the dark state remains unaltered. For sufficiently strong coupling between the bright exciton and the cavity, we show that the energy of the lower polariton may be pushed below that of the dark exciton. This overturning of the relative energies of the bright and dark excitons prevents the dark exciton from quenching the emission. Our resutls pave the way for a new approach to band-engineering the properties of the nanoscale optoelectronic devices.

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arXiv2018

Phosphorene quantum dot electronic properties and gas sensing

Density functional theory calculations are performed on phosphorene quantum dots having different shapes and edge terminations to investigate their structure stability, electronic properties, and gas sensing ability. All the selected phosphorene dots, namely hexagonal and triangular flakes with armchair and zigzag terminations, have positive binding energies which insure their stability even though the bond lengths are much longer than those in the infinite phosphorene layer. It is found that all the selected hydrogen passivated quantum dots have a wide energy gap. In contrast, the partial passivation with sulfur decreases the gap. Moreover, it transforms the system from antiferromagnetic to ferromagnetic state. The energy gap of hexagonal zigzag cluster can be additionally tuned by electric field: narrowed by about 1.7 eV for hydrogenated or broadened by 0.25 eV for partially sulfurated edges. It is shown that phosphorene quantum dots successfully adsorb H2S, CH4, CO, NH3 gas molecules either on their edge or surface. The highest adsorption energy is obtained for NH3 molecule, when it is placed over the surface. This adsorption is alleviated by in-plane electric field and hindered by perpendicular field.

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