2D Weyl Fermi gas model of Superconductivity in the Surface state of a Topological Insulator at High Magnetic fields

The Nambu-Gorkov Green's function approach is applied to strongly type-II superconductivity in a 2D spin-momentum locked (Weyl) Fermi gas model at high perpendicular magnetic fields. When the chemical potential is sufficiently close to the branching (Dirac) point, such that the cyclotron effective mass, $m^{\ast }$, is a very small fraction of the free electron mass, $m_{e}$, relatively large portion of the $H-T$ phase diagram is exposed to magneto-quantum oscillation effects. This model system is realized in the 2D superconducting state, observed recently on the surface of the topological insulator Sb$_{2}$Te$_{3}$, for which high field measurements were reported at low carrier densities with $m^{\ast}=0.065m_{e}$. Calculations of the pairing condensation energy in such a system, as a function of $H$ and $T$, using both the Weyl model and a reference standard model, that exploits a simple quadratic dispersion law, are found to yield indistinguishable results in comparison with the experimental data. Significant deviations from the predictions of the standard model are found only for very small carrier densities, when the cyclotron energy becomes very large, the Landau level filling factors are smaller than unity, and the Fermi energy shrinks below the cutoff energy.Comment: 10 page

Self-consistent Bogoliubov de Gennes theory of the vortex lattice state in a two-dimensional strong type-II superconductor at high magnetic fields

A self-consistent Bogoliubov deGennes theory of the vortex lattice state in a 2D strong type-II superconductor at high magnetic fields reveals a novel quantum mixed state around the semiclassical Hc2, characterized by a well-defined Landau--Bloch band structure in the quasi-particle spectrum and suppressed order-parameter amplitude, which sharply crossover into the well-known semiclassical (Helfand-Werthamer) results upon decreasing magnetic field. Application to the 2D superconducting state observed recently on the surface of the topological insulator Sb2Te3, accounts well for the experimental data, revealing a strong type-II superconductor, with unusually low carrier density and very small cyclotron mass, which can be realized only in the strong coupling superconductor limit.Comment: 5 pages, 3 figure

Spin-fluctuation mechanism of anomalous temperature dependence of magnetocrystalline anisotropy in itinerant magnets

The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe$_{1-x}$Co$_{x}$)$_{2}$B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit "hot spots" by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models.Comment: 9 pages, 10 figures (including supplemental material

Field-Induced Boson Insulating States in a 2D Superconducting Electron Gas with Strong Spin-Orbit Scatterings

The phenomenon of field-induced superconductor-to-insulator transitions observed experimentally in electron-doped SrTiO$_{3}$/LaAlO$_{3}$ interfaces, analyzed recently by means of 2D superconducting fluctuations theory (Phys. Rev. B \textbf{104}, 054503 (2021)), is revisited with new insights associating it with the appearance at low temperatures of field-induced boson insulating states. Within the framework of the time-dependent Ginzburg-Landau functional approach, we pinpoint the origin of these states in field-induced extreme softening of fluctuation modes over a large region in momentum space, upon diminishing temperature, which drives Cooper-pair fluctuations to condense into mesoscopic puddles in real space. Dynamical quantum tunneling of Cooper-pair fluctuations out of these puddles, introduced within a phenomenological approach, which break into mobile single-electron states, contains the high-field resistance onset predicted by the exclusive boson theory.Comment: arXiv admin note: substantial text overlap with arXiv:2201.0115

Computer modeling when assessing the impact of road factors on performance of quarry vehicles

Relevance. The need to optimize the parameters of mining systems at the level of modern scientific and methodological capabilities, which leads to development of a methodological approach to their description taking into account transients. When optimizing the life cycle of quarry transport systems, mainly structural transients should be taken into account. At the level of its individual elements or optimization of quarry transport systems during their operation, special attention should be paid to parametric transients. Aim. To study the capabilities of the software "Quarry Transport System"; to develop approaches to assessing the impact of road factors on performance of quarry vehicles by simulation; to study the regularity of the influence of restrictions associated with the mutual influence of dump trucks on the rhythm of traffic on auto roads; to study the impact of road factors on the performance of dump trucks. Objects. Quarry with a depth of 380 m with a capacity of 125 million tons/year, with a fleet of dump trucks in the amount of 88 units. Dump trucks have a lifting capacity of 136–220 tons, excavators with a bucket capacity of 15–35 m3. Methods. Computer simulation of quarry transport system functioning; the computer program "Quarry Transport System" developed at the Institute of Mining of the Ural Branch of the Russian Academy of Sciences. Results. The "Quarry Transport System" software allows solving specific problems in the field of career transport, including those related to the assessment of the impact of road factors on technical and economic indicators of career vehicles. The authors have developed the approaches to assessing the impact of road factors on performance of career vehicles. They established the regularity of the influence of restrictions associated with the mutual influence of dump trucks on the rhythm of traffic on auto roads and the influence of road factors on performance of dump trucks

Dilatometric characteristics of weakly sintered ceramics

Thermal expansion of refractory ceramics CaZrO3, MgAl2O4, La2Zr2O7 and YSZ-12 was studied. The samples of the complex oxides were synthesized by solution combustion synthesis with glycine; the fuel:oxidant ratio was varied depending on the character of redox reaction. The linear thermal expansion coefficient (LTEC) of ceramics was measured on the samples with an initial density 23–52%. The maximal sinterability of 89–92% after 6 h annealing at 1550 °С was demonstrated by La2Zr2O7 and YSZ-12, and the minimal values (78–82%) – by CaZrO3 and MgAl2O4. All materials have close LTEC values, from 9.0 to 9.6·10–6 K–1