arXiv subjects

M. A. Tarkhov

Publications and source records attributed to M. A. Tarkhov.

13 recordsLinked to original sources

arXiv2026

4-Pixel NbN Hot-Electron Bolometer Integrated in a Si$_3$N$_4$ Planar Optical Waveguide with On-Chip Fiber-Alignment Trench

In this work, we design and characterize a 4-pixel superconducting hot-electron bolometer (HEB) based on niobium nitride (NbN), integrated with individual planar silicon nitride (Si$_3$N$_4$) waveguides. The implemented architecture enables simultaneous detection of an optical signal in four independent channels. To efficiently couple optical radiation under cryogenic conditions, we employ an edge (end-fire) coupling approach using dedicated U-shaped grooves that provide accurate and stable positioning of an optical fiber with respect to the on-chip waveguide facet. The device responsivity is measured as a function of the HEB operating point. The measured voltage responsivity reaches $3800~\mathrm{V/W}$ at a modulation frequency of $3~\mathrm{GHz}$. We demonstrate detection of optically modulated signals in the gigahertz range. The developed fabrication route is promising for compact integrated receiver systems and low-noise cryogenic microwave transducers, including superconducting nanowire single-photon detectors (SNSPDs).

cond-mat.supr-con↗

arXiv2025

Control of thin NbN film superconducting properties by ScN buffer layer

This work investigates the effect of a scandium nitride buffer layer on the superconducting properties of niobium nitride thin films. The use of a ScN buffer layer significantly improves the characteristics of 29 nm thick NbN films: the critical temperature Tc increases from 9 K to 12.5 K, while the resistivity at 20 K decreases from 330 mkOhm*cm to 210 mkOhm*cm compared to films without a buffer layer. These enhancements are attributed to the better lattice matching between NbN and ScN, which results in a higher quality crystal lattice of the NbN film, as confirmed by transmission electron microscopy and X-ray diffraction data.

cond-mat.supr-con↗

arXiv2025

Multiterminal Ballistic Josephson Effect in Monocrystalline Gold

We report on the realization of a planar, quasi-ballistic Josephson junction array using a Au micron-sized single-crystal. The system exhibits a nonlocal, multiterminal Josephson effect, where the supercurrent between any two superconducting leads is governed by the phase coherence across the entire crystal. Key evidence includes a non-monotonic dependence of the critical current on junction length and magnetic interference patterns with periods corresponding to the shared normal-metal area. Nonlocal transport measurements further confirm that the supercurrent between two electrodes depends on the phase configuration of all the others. Our results, supported by a developed theoretical model, establish a platform for exploring complex superconducting phenomena in multiterminal ballistic systems.

cond-mat.supr-con↗

arXiv2025

Practical way to increase nonlinearity of kinetic inductance of superconductor

This work demonstrates that depositing a thin layer of Mo (5-15 nm) onto a 10 nm thick NbN strip leads to a significant increase in the nonlinearity of the kinetic inductance $L_k$. Specifically, the change in $L_k$ with increasing current reached 70% in the NbN/Mo bilayer at liquid helium temperature, whereas in the NbN strip, $L_k$ changed by only 10% in the superconducting state. In addition to altering the nonlinear properties, the Mo layer caused a significant increase in the critical current at low temperatures (up to 2 times in the case of a 5 nm thick Mo layer). The increased nonlinearity of $L_k$ can be explained by two factors: i) a reduction of the critical supervelocity at which the superconducting state becomes unstable with respect to vortex formation when a Mo layer is deposited on NbN, and ii) a higher sensitivity of the induced superconductivity in Mo to supervelocity/supercurrent. Considering the results on the transport properties of SN bilayers with a high ratio of layer resistivities $ρ_S/ρ_N >> 1$, it can be concluded that depositing a thin layer of a relatively low-resistivity metal onto a superconductor with high $ρ$ is a practical method for achieving a large nonlinearity of the superconductor's kinetic inductance.

cond-mat.supr-con↗

arXiv2024

Response of a Cold-Electron Bolometer in a coplanar antenna system

Cold electron bolometers have shown their suitability for use in modern fundamental physical experiments. Fabrication and measurements of the samples with cold-electron bolometers integrated into coplanar antennas are performed in this study. The bolometric layer was made using combined aluminum-hafnium technology to improve quality of aluminum oxide layer and decrease the leakage current. The samples of two types were measured in a dilution cryostat at various temperatures from 20 to 300 mK. The first sample with Ti/Au/Pd antenna shows response in the two frequency bands, at 7--9 GHz with bandwidth of about 20%, and also at 14 GHz with 10% bandwidth. The NEP below 10 aW/Hz^1/2 is reached at 300 mK for 7.7 GHz signal. The second sample with aluminum made antenna shows response in the frequency range 0.5--3 GHz due to the effect of kinetic inductance of superconducting aluminum.

cond-mat.supr-con↗

arXiv2024

Effect of Etching Methods on Dielectric Losses in Transmons

Superconducting qubits are considered as a promising platform for implementing a fault tolerant quantum computing. However, surface defects of superconductors and the substrate leading to qubit state decoherence and fluctuations in qubit parameters constitute a significant problem. The amount and type of defects depend both on the chip materials and fabrication procedure. In this work, transmons produced by two different methods of aluminum etching: wet etching in a solution of weak acids and dry etching using a chlorine-based plasma are experimentally studied. The relaxation and coherence times for dry-etched qubits are more than twice as long as those for wet-etched ones. Additionally, the analysis of time fluctuations of qubit frequencies and relaxation times, which is an effective method to identify the dominant dielectric loss mechanisms, indicates a significantly lower impact of two-level systems in the dry-etched qubits compared to the wet-etched ones.

quant-ph↗

arXiv2024

Technology of fabrication superconducting free-standing structures (FSS)

In this study, a method for fabrication of superconducting microstructures that are partially or completely isolated from the substrate has been proposed. Two configurations of suspended microbridges have been suggested, i. e., the first structure that features a T-shaped etching of the substrate and the second structure which is completely separated from the substrate through periodically positioned supports. The creation of suspended structures is based on the principle of gas-phase etching of amorphous silicon oxide in a mixture of hydrogen fluoride (HF) and ethanol gases. In the course of the experiments, it has been discovered that suspending micro-structures in the configuration of a micro-bridge results in a slight reduction in superconducting characteristics, ranging from 10 to 15% of the initial parameters. It has also been demonstrated that the thermal coupling between the film and the substrate significantly affects the dissipation of thermal energy. The power dissipated into the substrate at room temperature can vary by up to 250 times based on the value of the micro-bridge undercutting.

cond-mat.supr-con↗

arXiv2024

Molybdenum low resistance thin film resistors for cryogenic devices

We present a study of thin-film molybdenum resistors for NbN electronics operating at cryogenic temperatures. The key step is the 0.5-1.5 keV ion cleaning-activation of NbN before Mo deposition which allows to obtain a high-quality Mo/NbN interface which together with additional aluminum bandage layer in the area of contact pads allow to reduce contact resistance below 1 Ohm. The quality of the interfaces is confirmed by transmission electron microscopy and X-ray reflectometry.

cond-mat.supr-con↗

arXiv2024

Influence ScN protective thin layer on the superconducting properties of ultrathin NbN films

The present study delves into exploring the impact of a thin protective layer of scandium nitride (ScN) on the superconductive properties of thin films of niobium nitride (NbN) generated through reactive magnetron deposition. This is the first time such an investigation has been carried out. The article offers a comprehensive investigation of the morphological, microstructural, and electrophysical features of thin films that have undergone high-temperature annealing in an oxygen-rich environment. The dependence of the critical transition temperature of the NbN thin film on the annealing temperature of the samples in an oxygen medium, with and without ScN coating, was determined. According to X-ray reflectometry studies, it has been observed that the ScN film serves as a protective layer, even when exposed to annealing temperatures of approximately 450°C, without significantly affecting the NbN layer density or thickness. It has been shown that adding a ScN coating to a thin NbN film increases its resistance to corrosive media compared to a film without the coating.

cond-mat.supr-con↗

arXiv2021

Enchanced reflectance SiN$_x$ / SiO$_x$ DBR mirror based on TEOS precursor fabricated by PECVD method

In this study, we investigated the influence of silicon oxide roughness produced from the gas precursor monosilane (SiH$_4$) and the silicon-organic precursor tetraethoxysilane (TEOS) on the optical qualities of a distributed Bragg reflector (DBR). A significant influence of the precursors from which SiOx is deposited on the optical qualities of DBR mirrors is demonstrated in this study. It has been shown experimentally that a mirror produced from the TEOS precursor is endowed with better qualities than a mirror produced using SiH4, that is, the reflectivity increased by 20% and optical losses decreased by half. The roughness average (Ra) of the SiN$_x$/SiO$_x$ / (TEOS) mirror surface decreased by a factor of five compared to that of the SiN$_x$/SiO$_x$ / (SiH4) mirror

physics.optics↗

arXiv2021

Investigation of superconducting properties of NbN films deposited by DC magnetron sputtering on high-k dielectric HfO2 buffer layer

The influence of the buffer layer of hafnia dielectric on superconducting properties of niobium nitride films, produced by the technique of the reactive magnetron depositing has been investigated for the first time. This study presents a comprehensive analysis of morphological, microstructural, and electrophysical parameters of thin NbN films.

cond-mat.supr-con↗

arXiv2021

Negative Differential Resistance in Carbon-Based Nanostructures

Nonlinear electrical properties, such as negative differential resistance (NDR), are essential in numerous electrical circuits, including memristors. Several physical origins have been proposed to lead to the NDR phenomena in semiconductor devices in the last more than half a century. Here, we report NDR behavior formation in randomly oriented graphene-like nanostructures up to 37 K and high on-current density up to 10^5 A/cm^2. Our modeling of the current-voltage characteristics, including the self-heating effects, suggests that strong temperature dependence of the low-bias resistance is responsible for the nonlinear electrical behavior. Our findings open opportunities for the practical realization of the on-demand NDR behavior in nanostructures of 2D and 3D material-based devices via heat management in the conducting films and the underlying substrates.

cond-mat.mes-hall↗

arXiv2020

Environmentally friendly method of silicon recycling: synthesis of silica nanoparticles in an aqueous solution

Future decades will experience tons of silicon waste from various sources, with no reliable recycling route. The transformation of bulk silicon into SiO2 nanoparticles is environmentally significant because it provides a way to recycle residual silicon waste. To address the needs of silicon recycling, we develop a top-down approach that achieves 100% conversion of bulk silicon to silica nanoparticles with outcome sizes of 8-50 nm. In addition to upcycling the potential of silica, our method also possesses several advantages, such as simplicity, scalability and controllable particle size distribution. Many fields of science and manufacturing, such as optics, photonics, medical, and mechanical applications, require size-controllable fabrication of silica nanoparticles. We demonstrate that control over temperature and hydrolysis time has a significant impact on the average particle size and distribution shape. Additionally, we unravel the process of nanoparticle formation using a theoretical nucleation model and quantum density functional theory calculations. Our results provide a theoretical and experimental basis for silica nanoparticle fabrication and pave the way for further silicon conservation research.

cond-mat.mtrl-sci↗