arXiv subjects

A. Yu. Kuntsevich

Publications and source records attributed to A. Yu. Kuntsevich.

At least 19 recordsLinked to original sources

arXiv2026

Large-area CVD Graphene for Photogating-Based Photodetection

Our work explores large-area CVD graphene as a scalable platform for photodetectors. We show that substrate-induced photogating in graphene/SiO$_2$/Si structures enables a photoconductivity signal in mono-, bi-, and trilayer CVD graphene. The devices respond to illumination with photon energies above the Si band gap and do not respond to telecom frequency, suggesting the photoconductivity mechanism through the photogating. Large sample area and gate voltage-dependent resistivity measurements allow us to prove the dominant role of the photogating directly, demonstrating similarity of the capacitive recharging current and the photoresponse. The sensitivity is the highest (995 A/W) for the monolayer graphene. Increasing the number of graphene layers reduces the sensitivity due to screening and parallel conduction, but can improve detectivity by lowering the noise level. The sensitivity of CVD graphene device depends on fabrication route of photolitography: device with metal contacts fabricated before graphene transfer show higher photoresponce. Thus, our work demonstrate the potential of industrially relevant CVD graphene for sensitive photogating-based photodetectors.

cond-mat.mes-hall↗

arXiv2025

3D-printed microscope with illumination for undergraduate wave optics laboratory

We present an educational tool, a microscope with a video camera, that can be fabricated either from a standard microscope or assembled from inexpensive, commercially available components (objectives, beam splitters, LEDs, linear stages) and 3D-printed elements. Usage of interference filters in combination with white light-emitting diode (LED) illumination enables the quantitative study of optical phenomena such as refraction, interference (e.g., Newton's rings), Fresnel and Fraunhofer diffraction. Thus, we propose an instrument that can be used to illustrate the theoretical foundations of an undergraduate optics course and beyond.

physics.optics↗

arXiv2025

High and Magnetic-field-dependent Surface Carriers Mobility in 3D Topological Insulators without Bulk States

By applying the conventional two-liquid model to the magnetoresistivity tensor, we reveal a record-high carrier mobility for surface states in tetradymite topological insulators ($\sim$ 20000 cm$^2$/Vs) in both bulk crystals and thin flakes of Sn-Bi$_{1.1}$Sb$_{0.9}$Te$_2$S. Bulk crystals of this 3D topological insulator exhibit a transition from bulk to surface-dominated conductivity below 100 K, whereas in thin flakes, bulk conductivity is suppressed at even higher temperatures. Our data therefore suggest that a key ingredient for elevated mobility is the absence of bulk carriers at the Fermi level. A fingerprint of the high-mobility carriers, i.e a steep low-field magnetoresistance along with a strong Hall effect nonlinearity below 1 T, signifies the presence of at least two surface-related carrier species, even when bulk states are frozen out. To explain the magnetoresistance and the Hall effect in a wider range of magnetic fields ($>1$ T), one must assume that the carrier mobility drops with the field. The influence of Zeeman splitting on mobility and the contribution of anomalous Hall conductivity provide a much better description of the magnetoresistance and the nonlinearity of the Hall coefficient. Our data call for a revision of the surface state mobility in 3D topological insulators.

cond-mat.mes-hall↗

arXiv2025

Surface acoustic wave enabled all-optical determination of the interlayer elastic constants of van der Waals interface

Understanding the properties of two-dimensional materials interfaces with the substrate is necessary for device applications. Surface acoustic wave propagation through the layered material flake on a substrate could provide unique information on the transverse rigidity of the flake-to-substrate interaction. We generate ultrasonic waves by a focused femtosecond laser pulse at the surface of the model system -- fused silica with h-BN flake transferred above. Using an all-optical spatially resolved pump-probe interferometric technique, we measure the spatial dependencies of the surface vertical velocity profiles. Our measurements reveal the appearance of the surface acoustic wave dispersion in the hBN flake region compared to fused silica surface. Multilayer modeling allows us to gain access to longitudinal and shear elastic coupling constants $c^*_{33}$ and $c^*_{44}$ between hexagonal BN and substrate.

cond-mat.mtrl-sci↗

arXiv2025

Metastable states of 2D-material-on-metal-islands structures revealed by thermal cycling

The integration of 2D materials with artificially textured substrates offers exceptional opportunities for engineering novel functional devices. A straightforward technological route towards such devices is a mechanical dry or wet transfer of 2D layer or heterostructure onto prepared patterned elements with subsequent van der Waals bonding. An issue of van der Waals bond stability is crucial for device operation but is almost unexplored. In our research we address it by studying transport properties of hBN/graphene heterostructures transferred onto metallic island arrays and subjected to thermal cycling. We reveal that heating from cryogenic to room temperature and cooling back leads to irreversible changes in electronic transport properties: the contact between metal and graphene degrades, and signatures of suspended graphene regions transport disappear. These changes are accompanied by slight movement of the flakes and atomic-force-microscope-detected breakdown of van der Waals bonds between the flake and substrate near the metal electrodes. Interestingly, a hot pressing allows to restore the metal-to-graphene contact. We relate the observed metastability to the thermal-expansion-driven flake delamination and argue that it is accompanied by redistribution of the interfacial water or organic residues. Our findings provide useful insights into the topic of interfacial stability in van der Waals heterostructures and establish constraints for low-temperature applications of transferred 2D devices. We also add up an additional control parameter for the experimentalists in the field of 2D materials - degree of quenched disorder.

cond-mat.mes-hall↗

arXiv2025

High-performance amorphous superconducting rhenium films by e-beam evaporation

We present electron beam evaporation of rhenium films on room-temperature substrates. The films are shown to be amorphous and achieve a record-high critical temperature for rhenium - exceeding 7 K at the midpoint of the transition - alongside a high critical current density of 5000 A/mm^2 and critical fields above 10 T. Terahertz spectroscopy reveals a BCS-like character of superconductivity with a zero-temperature energy gap of approximately 2 meV and subgap optical conductivity. Despite being friable, the films are stable and compatible with lift-off processes that opens the capabilities for superconducting device applications.

cond-mat.supr-con↗

arXiv2025

Absence of reflectivity of the phonon-polariton at the SiC surface from the metal mask edge

Surface phonon polariton (SPhP) waves are excited at the silicon carbide ($SiC$) surface under irradiation of light close to the lattice resonance frequency. Metal mask at the surface blocks irradiation of certain areas and thus allows tuning standing or propagating wave pattern and, thus, open opportunities for surface polariton optic devices. In this study we show by means of scanning near-field microscopy that the edge of such a mask reflects SPhP waves negligibly. This condition differs dramatically from numerous recent observations of polariton reflections in 2D materials and makes the metallized $SiC$ platform advantageous in a sense of capability to calculate wavefield using a simple Green function-based approach.

physics.optics↗

arXiv2024

Strain in 2D TMDCs induced by metal-assisted exfoliation from the polyvinilalcohol-covered substrate

We have modified the metal-assisted transfer technique to obtain large-area few-layer flakes from transition metal dichalcogenides bulk crystals by introducing an initial stage - exfoliation of the bulk crystal onto an intermediate substrate, specifically a silicon wafer coated with polyvinyl alcohol. Following this, we thermally evaporate silver onto the sample and transfer the top layers of the crystal along with the silver layer to the target substrate. This technique allows the production of visually non-corrugated single- and few-layer flakes with high yield. A direct comparison of the micro-Raman and micro-photoluminescence spectra of flakes exfoliated using our method with the spectra of those exfoliated from scotch tape reveals differences in their properties. We identify signatures of deformations in the flakes exfoliated from the intermediate substrate, indicating the presence of static friction between the substrate and the flake. Our findings thus suggest a novel method to induce intrinsic deformation in 2D materials.

cond-mat.mtrl-sci↗

arXiv2024

Phonon-polariton Bragg generation at the surface of silicon carbide

Phonon polaritons are known to emerge at the surfaces of solids under IR irradiation at frequencies close to the optical phonon resonance. Metal, patterned on the top of the polariton-active surface, locally blocks the excitation of the surface waves due to plasmonic screening and can be used for the design of wave patterns. We excite the polaritonic waves at the surface of SiC under the irradiation of a CO$_2$ laser ($λ\sim10$ $μ$m) and visualize them using apertureless near-field interference scanning probe microscopy. From the near-field scans in the vicinity of the gold film periodical strip structures, we identify the Bragg scattering (diffraction) outside the lattice with the contribution from separate strips coherently summed up, provided that the wavelength matching condition is fulfilled. The observed phenomena agree with the wavefield calculations. Our observations demonstrate the potential of metal-patterned silicon carbide for the fabrication of on-chip polaritonic IR circuits.

physics.optics↗

arXiv2024

Laser-pump-resistive-probe technique to study nanosecond-scale relaxation processes

Standard optical pump-probe methods analyze a system's temporal response to a laser pulse within sub-femtoseconds to several nanoseconds, constrained by the optical delay line's length. While resistance is a sensitive detector in various fields, its measurements are typically slow (>microseconds) due to stabilization requirements. We suggest here a time-resolved pump-probe technique which combines an optical pump pulse and a rectangular electrical probe pulse through the sample, measuring transmission in a 50 Ohm matched circuit with a digital oscilloscope. This allows electrically-driven delays from nanoseconds to seconds. Demonstrations include studying heat-induced changes in a thin amorphous VO$_x$ film and carrier relaxation in a CdS photoresistor, showcasing potential applications in heat transfer, biochemical reactions, and gradual electronic transformations.

physics.ins-det↗

arXiv2023

Amorphous VO$_x$ films with high temperature coefficient of the resistivity grown by reactive e-beam evaporation of V metal

Amorphous VO$_x$ films without a hysteretic phase transition are stable with respect to thermal cycling and highly demanded as sensitive elements of the resistive thermometers and microbolometers. In this paper we present simple and low-temperature growth of amorphous vanadium oxide films by reactive electron beam evaporation of vanadium metal in $\sim 10^{-4}$ mBar oxygen atmosphere. The temperature coefficient of the resistivity (TCR) of the films is weakly sensitive to substrate material and temperature and could be tuned by oxygen pressure in the growth chamber up to -2.2\% /K. The resistivity value is stable for months. It depends on the substrate material and substrate temperature during the evaporation. Simplicity and controllability of the method should lead to various laboratory and industrial applications.

cond-mat.mtrl-sci↗

arXiv2023

Indication of novel magnetoresistance mechanism in (Bi,Sb)$_2$(Te,Se)$_3$ 3D topological insulator thin films

Electron states with the spin-momentum-locked Dirac dispersion at the surface of a three-dimensional (3D) topological insulator are known to lead to weak antilocalization (WAL), i.e. low temperature and low-magnetic field quantum interference-induced positive magnetoresistance (MR). In this work we report on the MR measurements in (Bi,Sb)$_2$(Te,Se)$_3$ 3D topological insulator thin films epitaxially grown on Si(111), demonstrating an anomalous WAL amplitude. This anomalously high amplitude of WAL can not be explained by parabolic or linear MR and indicates the existence of an additional, MR mechanism. Another supporting observation is not linear in the classically weak magnetic field Hall effect in the same films. The increase of the low-field Hall coefficient, with respect to the higher-field value, reaches 10$\%$. We consistently explain both transport features within a two-liquid model, where the mobility of one of the components drops strongly in a weak magnetic field. We argue that this dependence may arise from the Zeeman field induced gap opening mechanism.

cond-mat.mes-hall↗

arXiv2022

Unveiling the electron-nuclear spin dynamics in an n-doped InGaAs epilayer by spin noise spectroscopy

We discuss the implications of a small indium content (3%) in a GaAs epilayer on the electron- and nuclear-spin relaxation due to enhanced quadrupolar effects induced by the strain. Using the weakly perturbative spin-noise spectroscopy, we study the electron-spin relaxation dynamics without explicit excitation. The observed temperature dependence indicates the presence of localized states, which have an increased interaction with the surrounding nuclear spins. Time-resolved spin-noise spectroscopy is then applied to study the relaxation dynamics of the optically pumped nuclear-spin system. It shows a multi-exponential decay with time components, ranging from several seconds to hundreds of seconds. Further, we provide a measurement of the local magnetic field acting between the nuclear spins and discover a strong contribution of quadrupole effects. Finally, we apply the nuclear spin diffusion model, that allows us to estimate the concentration of the localized carrier states and to determine the nuclear spin diffusion constant characteristic for this system.

cond-mat.mes-hall↗

arXiv2021

Breaking of Ginzburg-Landau description in the temperature dependence of the anisotropy in the nematic superconductor

Nematic superconductors are characterized by an apparent crystal symmetry breaking that results in the anisotropy of the in-plane upper critical magnetic field $H_{c2}$. The symmetry breaking is usually attributed to the strain of the crystal lattice. The nature and the value of the strain are debatable. We perform systematic measurements of the $H_{c2}$ anisotropy in the high-quality Sr$_x$Bi$_2$Se$_3$ single crystals in the temperature range 1.8~K$<T<T_c\approx 2.7$~K using temperature stabilization with an accuracy of 0.0001 K. We observe that in all tested samples the anisotropy is weakly temperature dependent when $T<0.8\,T_c$ and smoothly decreases at higher temperatures without any sign of singularity when $T\rightarrow T_c$. Such a behavior {is in a drastic contradiction with the prediction of} the Ginzburg-Landau theory for the nematic superconductors. We discuss possible reasons for this discrepancy.

cond-mat.supr-con↗

arXiv2021

3D Hypersound Microscopy of Van der Waals Heterostructures

We employ here a picosecond ultrasonic technique to study Van der Waals heterostructures. Temporal variation of the reflection coefficient of the Al film that covers Van der Waals hBN/WSe$_2$/hBN heterostructures on a sapphire substrate after the femtosecond laser pulse excitation is carefully measured using an interferometric technique with spatial resolution. The laser pulse generates a broadband sound wave packet in aluminum film propagating perpendicular to the plane direction and partially reflecting from the heterostructural interfaces. The demonstrated technique has enough sensitivity to resolve a WSe$_2$ monolayer embedded in hBN. We apply a multilayered model of the optical and acoustical response that allows to evaluate the mechanical parameters, in particular, rigidity of interfaces, inaccessible from the other measurements. Mapping of the Fourier spectra of the response clearly visualizes different composition regions and can therefore serve as an acoustic tomography tool. Our findings demonstrate almost zero acoustic phonon dissipation below 150 GHz at the interfaces and in the layers that makes Van der Waals heterostructures perspective for nano-acoustical applications.

cond-mat.mes-hall↗

arXiv2020

Nonexponential photoluminescence dynamics in an inhomogeneous ensemble of excitons in WSe$_2$ monolayers

The spectral and spatiotemporal dynamics of photoluminescence in monolayers of transition metal dichalcogenide WSe$_2$ obtained by mechanical exfoliation on a Si/SiO$_2$ substrate is studied over a wide range of temperatures and excitation powers. It is shown that the dynamics is nonexponential and, for times $t$ exceeding $\sim$50 ps after the excitation pulse, is described by a dependence of the form $1/(t+t_0)$. Photoluminescence decay is accelerated with a decrease in temperature, as well as with a decrease in the energy of emitting states. It is shown that the observed dynamics cannot be described by a bimolecular recombination process, such as exciton--exciton annihilation. A model that describes the nonexponential photoluminescence dynamics by taking into account the spread of radiative recombination times of localized exciton states in a random potential gives good agreement with experimental data.

cond-mat.mes-hall↗

arXiv2020

Link between superconductivity and a Lifshitz transition in intercalated Bi$_2$Se$_3$

Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium or niobium between the quintuple layers of the topological insulator Bi$_2$Se$_3$ increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi$_2$Se$_3$ using angle resolved photoemission spectroscopy (ARPES) and Shubnikov-de Haas (SdH) oscillations. Despite the apparent low Hall number of $\sim2 \times 10 ^{19}$cm$^{-3}$, we show that the Fermi surface is shaped as an open cylinder with a larger carrier density of $\sim 10 ^{20}$cm$^{-3}$. We suggest that superconductivity in intercalated Bi$_2$Se$_3$ emerges with the appearance of a quasi-2D open Fermi surface.

cond-mat.supr-con↗

arXiv2020

Simple mechanism that breaks the Hall effect linearity at low temperatures

Hall resistance $R_{\textrm{xy}}$ is commonly suggested to be linear-in-magnetic-field $B$, provided the field is small. We argue here that at low temperatures this linearity is broken due to weak localization/antilocalization phenomena in inhomogeneous systems, while in a uniform medium these effects do not affect the linear field dependence of $R_{\textrm{xy}}(B)$. We calculate the Hall resistance for different two-component media using a mean-field approach and show that this non-linearity is experimentally observable.

cond-mat.mes-hall↗