Dimitriy A. Sokolov

Аннотация. В статье рассматривается правовой статус лиц, управляющих средствами индивидуальной мобильности в Российской Федерации. С учетом последних изменений, внесенных в Правила дорожного движения Российской Федерации, сравнивается статус лица, управляющего средством индивидуальной мобильности (далее-СИМ) и других участников дорожного движения. На основе анализа правоприменительной практики оценивается сложившаяся

The interplay of electronic and structural degrees of freedom in solids is a topic of intense research. More than 60 years ago, Lifshitz discussed a counterintuitive possibility: lattice softening driven by conduction electrons at topological Fermi surface transitions. The effect that he predicted, however, was small and has not been convincingly observed. Using a piezo-based uniaxial pressure cell to tune the ultraclean metal strontium ruthenate while measuring the stress-strain relationship, we reveal a huge softening of the Young’s modulus at a Lifshitz transition of a two-dimensional Fermi surface and show that it is indeed driven entirely by the conduction electrons of the relevant energy band.

Despite the fruitful achievements in the development of hydrogen production catalysts with record-breaking performances, there is still a lack of durable catalysts that could work under large current densities (>1000 mA cm⁻²). Here, we investigated the catalytic behaviors of Sr₂RuO₄ bulk single crystals. This crystal has demonstrated remarkable activities under the current density of 1000 mA cm⁻², which require overpotentials of 182 and 278 mV in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively. These materials are stable for 56 days of continuous testing at a high current density of above 1000 mA cm⁻² and then under operating temperatures of 70 °C. The in-situ formation of ferromagnetic Ru clusters at the crystal surface is observed, endowing the single-crystal catalyst with low charge transfer resistance and high wettability for rapid gas bubble removal. These experiments exemplify the potential of designing HER catalysts that work under industrial-scale current density.

We perform nuclear magnetic resonance (NMR) measurements of the oxygen-17 Knight shifts for Sr₂RuO₄, while subjected to uniaxial stress applied along [100] direction. The resulting strain is associated with a strong variation of the temperature and magnetic field dependence of the inferred magnetic response. A quasiparticle description based on density-functional theory calculations, supplemented by many-body renormalizations, is found to reproduce our experimental results, and highlights the key role of a van-Hove singularity. The Fermi-liquid coherence scale is shown to be tunable by strain, and driven to low values as the associated Lifshitz transition is approached.

Applying in-plane uniaxial pressure to strongly correlated low-dimensional systems has been shown to tune the electronic structure dramatically. For example, the unconventional superconductor Sr₂RuO₄ can be tuned through a single Van Hove point, resulting in strong enhancement of both T_c and H_c2. Out-of-plane (c axis) uniaxial pressure is expected to tune the quasi-two-dimensional structure even more strongly, by pushing it towards two Van Hove points simultaneously. Here, we achieve a record uniaxial stress of 3.2 GPa along the c axis of Sr₂RuO₄. H_c2 increases, as expected for increasing density of states, but unexpectedly T_c falls. As a first attempt to explain this result, we present three-dimensional calculations in the weak interaction limit. We find that within the weak-coupling framework there is no single order parameter that can account for the contrasting effects of in-plane versus c-axis uniaxial stress, which makes this new result a strong constraint on theories of the superconductivity of Sr₂RuO₄.

One of the main developments in unconventional superconductivity in the past two decades has been the discovery that most unconventional superconductors form phase diagrams that also contain other strongly correlated states. Many systems of interest are therefore close to more than one instability, and tuning between the resultant ordered phases is the subject of intense research¹. In recent years, uniaxial pressure applied using piezoelectric-based devices has been shown to be a particularly versatile new method of tuning^2,3, leading to experiments that have advanced our understanding of the fascinating unconventional superconductor Sr₂RuO₄ (refs. ^4–9). Here we map out its phase diagram using high-precision measurements of the elastocaloric effect in what we believe to be the first such study including both the normal and the superconducting states. We observe a strong entropy quench on entering the superconducting state, in excellent agreement with a model calculation for pairing at the Van Hove point, and obtain a quantitative estimate of the entropy change associated with entry to a magnetic state that is observed in proximity to the superconductivity. The phase diagram is intriguing both for its similarity to those seen in other families of unconventional superconductors and for extra features unique, so far, to Sr₂RuO₄.

Despite the fruitful achievements in the development of hydrogen production catalysts with record-breaking performances, there is still a lack of durable catalysts that could work under large current densities (> 1000 mA cm^− 2). In the context of this need, we investigated the catalytic behaviors of Sr₂RuO₄ (SRO) bulk single crystals with well-defined surface crystal structures, which is a benchmark material to explore exotic metallic states and electronic structures. This single crystal has demonstrated remarkable activities under the current density of 1000 mA cm^− 2, which require overpotentials of 182 and 278 mV in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively, after ohmic correction. These values slightly increased to 272 and 354 mV even without iR correction, exhibiting high potential for industrial-scale hydrogen production. The high performance is also evidenced by the 56 days of continuous testing at a high current density of above 1000 mA cm^− 2 and then under operating temperatures of 70 ℃ for alkaline electrolysis. The in-situ formation of ferromagnetic Ru clusters at the crystal surface is critical for the outstanding catalytic activity, endowing the single-crystal catalyst with low charge transfer resistance and high wettability for rapid gas bubble removal. Density functional theory calculations indicate that SRO gains electrons from the Ru clusters, thus leading to the thermodynamically favorable hydrogen desorption for the rapidly modified catalysts. More generally, our experiment exemplifies the potential of designing novel HER catalysts that work under industrial-scale current density.