arXiv subjects

A. P. Shapovalov

Publications and source records attributed to A. P. Shapovalov.

5 recordsLinked to original sources

arXiv2026

Nonequilibrium Quasiparticle Dynamics in a MoRe-Based Superconducting Resonator under IR Excitation

The response of a MoRe-based superconducting resonator operating near 5 K to pulsed infrared irradiation is investigated, and the underlying physical mechanisms are analyzed. The device exhibits a pronounced nonlinear response dominated by nonequilibrium quasiparticle dynamics rather than uniform thermal heating. Infrared pulses produce strong distortions of the resonance curve and a transient decrease in the resonance frequency, consistent with increased kinetic inductance caused by quasiparticle generation. The frequency shift scales approximately linearly with absorbed power, whereas the dissipation response saturates at higher powers, indicating the formation of a nonequilibrium steady-state quasiparticle population. These observations demonstrate a transition from a linear pair-breaking regime to a saturated dissipation regime, likely associated with a quasiparticle relaxation bottleneck or partial suppression of the smaller superconducting gap in MoRe. The results highlight the relevance of nonequilibrium processes in MoRe and confirm its potential for microwave kinetic-inductance detector applications.

cond-mat.supr-con↗

arXiv2025

Control of the effective value of the critical current of the RF SQUID by the high-frequency electromagnetic field

An analysis of the influence of the high-frequency electromagnetic field on the amplitude-frequency and signal characteristics of RF SQUID and experimental verification are carried out. At low parameter , the RF SQUID behavior is well described analytically by the theoretical model. In experiment, basic operation scheme is used in which the interferometer is inductively connected to a resonant tank circuit driven by RF current at a frequency close to the resonance frequency of the tank. It is shown that parameter , which distinguishes between hysteretic and non-hysteretic regimes, can be effectively adjusted to a desired value by applying the high-frequency field of a certain amplitude and frequency much higher than tank resonant frequency. A significant increase in the conversion factor and sensitivity of the RF SQUID during this adjustment is discussed.

cond-mat.supr-con↗

arXiv2023

Design of deeply cooled ultra-low dissipation amplifier and measuring cell for quantum measurements with a microwave single-photon counter

The requirements and details of designing a measuring cell and low-back-action deeply-cooled amplifier for quantum measurements at 10 mK are discussed. This equipment is a part of a microwave single-photon counter based on a superconducting flux qubit. The high electron mobility transistors (HEMTs) in the amplifier operate in unsaturated microcurrent regime and dissipate only 1 microwatt of dc power per transistor. Simulated amplifier gain is 15 dB at 450 MHz with a high-impedance (~5 kOhm signal source and standard 50-Ohm output.

quant-ph↗

arXiv2009

Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines

Materials of the Y-Ba-Cu-O (melt-textured YBa2Cu3O7-d-based materials or MT-YBCO) and Mg-B-O (MgB2-based materials) systems with high superconducting performance, which can be attained due to the formation of regularly distributed nanostructural defects and inhomogenities in their structure can be effectively used in cryogenic technique, in particular in fault current limiters and electrical machines (electromotors, generators, pumps for liquid gases, etc.). The developed processes of high-temperature (900-800 oC) oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2 GPa) synthesis of MgB2-based materials allowed us to attain high SC (critical current densities, upper critical fields, fields of irreversibility, trapped magnetic fields) and mechanical (hardness, fracture toughness, Young modulus) characteristics. It has been shown that the effect of materials properties improvement in the case of MT-YBCO was attained due to the formation of high twin density (20-22 micron-1), prevention of macrockracking and reduction (by a factor of 4.5) of microcrack density, and in the case of MgB2-based materials due to the formation of oxygen-enriched as compared to the matrix phase fine-dispersed Mg-B-O inhomogenities as well as inclusions of higher borides with near-MgB12 stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain sizes). The possibility is shown to obtain the rather high Tc (37 K) and critical current densities in materials with MgB12 matrix (with 95 percent of shielding fraction as calculated from the resistant curve).

cond-mat.supr-con↗

arXiv2009

Effect of higher borides and inhomogeneity of oxygen distribution on critical current density of undoped and doped magnesium diboride

The effect of doping with Ti, Ta, SiC in complex with synthesis temperature on the amount and distribution of structural inhomogeneities in MgB2 matrix of high-pressuresynthesized-materials (2 GPa) which can influence pining: higher borides (MgB12) and oxygen-enriched Mg-B-O inclusions, was established and a mechanism of doping effect on jc increase different from the generally accepted was proposed. Near theoretically dense SiC-doped material exhibited jc= 1000000 A/sq. cm in 1T field and Hirr =8.5 T at 20 K. The highest jc in fields above 9, 6, and 4 T at 10, 20, and 25 K, respectively, was demonstrated by materials synthesized at 2 GPa, 600 oC from Mg and B without additions (at 20 K jc= 100 A/sq. cm in 10 T field). Materials synthesized from Mg and B taken up to 1:20 ratio were superconductive. The highest jc (60000 A/sq. cm at 20 K in zero field, Hirr= 5 T) and the amount of SC phase (95.3 percents of shielding fraction), Tc being 37 K were demonstrated by materials having near MgB12 composition of the matrix. The materials with MgB12 matrix had a doubled microhardness of that with MgB2 matrix (25 GPa and 13.08 GPa, at a load of 4.9 N, respectively).

cond-mat.supr-con↗