Том 192, № 7 (2022)
Reviews of topical problems
The SMEFT formalism: the basis for finding deviations from the Standard Model
Аннотация
The search for manifestations of physics beyond the Standard Model (SM) is one of the main directions of research at the LHC and future colliders under discussion. The effects caused by the new physics can consist in the direct detection of new particles if their masses are less than the characteristic energies available at colliders and their interactions with the SM particles are strong enough. But if the masses of new particles are too large, or the interactions with SM particles are too weak, then new particles cannot be detected directly. In this case, the new physics can lead to a modification of the interactions of SM particles, to subthreshold effects. We present„ the current status of an approach or formalism called the Standard Model Effective Field Theory (SMEFT), which allows„ us to describe and model deviations from the SM predictions in a theoretically consistent manner. The advantages of and serious problems with this approach are discussed.
Uspehi fizičeskih nauk. 2022;192(7):697-721
697-721
Instruments and methods of investigation
Gas-dynamic sources of cluster ions for basic and applied research
Аннотация
State of the art in the development and application of gas cluster ion sources is considered. The mechanisms of neutral cluster formation, the techniques applied to study their flows and regularities of ionization and the principles of mass separation of ion beams are discussed. Design features of some cluster ion beam sources intended for various applied and academic studies are considered. Use of such sources for controlled modification of surface topography, ultra-shallow ion implantation, development of analytical techniques, and stimulation of surface chemical reactions is analyzed.
Uspehi fizičeskih nauk. 2022;192(7):722-753
722-753
Approaches to determining curvature of wafers by their topography
Аннотация
We discuss peculiarities of the curvature analysis of’wafers considering the heterogeneity of their topography for a quantitative estimation and localization of irregularity, or for subsequent calculations of mechanical stresses. We analyze three approaches to calculating surface curvatures from digital elevation models. The first one is based on the analysis of wafer surface profiles using polynomial approximation; the calculation is based on the curvature radius determination of a curved line; mechanical stresses are calculated using the Stoney method. The second approach uses the second partial derivatives of an elevation function in the Cartesian or cylindrical coordinate systems to analyze irregular topography and then to calculate mechanical stresses. The third considers the entire wafer topography as a two-dimensional elevation matrix and uses the mathematical apparatus of differential geometry and the experience of geomorphometry to determine convex and concave areas of the surface as well as to perform a complete analysis of the surface curvature system. We demonstrate the implementation of these approaches on a wafer like a segment of a sphere and on a complex-shaped wafer.
Uspehi fizičeskih nauk. 2022;192(7):754-771
754-771
Conferences and symposia
Room temperature superconductivity: from dream to reality (Scientific session of the Physical Sciences Division of the Russian Academy of Sciences, 12 May 2021)
Аннотация
On May 12, 2021, the scientific session of the Physical Sciences Division of the Russian Academy of Sciences on the topic “Room-temperature superconductivity: from dream to reality” was held online.The agenda of the meeting, announced on the website of the Physical Sciences Division of the Russian Academy of Sciences, included the following reports:(1) Sadovskii M V (Institute for Electrophysics, Russian Academy of Sciences, Ural Branch, Ekaterinburg, Russia) “Limits of Eliashberg theory and bounds for superconducting transition temperature.”(2) Struzhkin V I (Center for High Pressure Science and Technology Advanced Research, Shanghai, China) “Magnetic susceptibility studies in new hydride superconductors.”(3) Troyan I A (Federal Research Center Crystallography and Photonics, Russian Academy of Sciences, Moscow, Russia) “Superconductivity in yttrium and lanthanum superhydrides.”(4) Pudalov V M (Lebedev Physical Institute, Russian Academy of Sciences (LPI RAS), Moscow, Russia) “The mystery of the existence of superconductivity and magnetism in $ {RbEuFe_4As_4}$.”Published further in this issue are articles written on the basis of reports 1, 3, and 4.
Uspehi fizičeskih nauk. 2022;192(7):772-772
772-772
Limits of Eliashberg theory and bounds for superconducting transition temperature
Аннотация
The discovery of record-breaking values of superconducting transition temperature $T_c$ in quite a number of hydrides under high pressure was an impressive demonstration of the capabilities of the electron–phonon mechanism of Cooper pairing. This led to increased interest in the foundations and limitations of the Eliashberg–McMillan theory as the main theory describing superconductivity in a system of electrons and phonons. Below, we shall consider both the elementary basics of this theory and a number of new results derived only recently. We shall discuss limitations on the value of the coupling constant related to lattice instability and a phase transition to another phase (CDW, bipolarons). Within the stable metallic phase, the effective pairing constant may acquire arbitrary values. We consider extensions beyond the traditional adiabatic approximation. It is shown that the Eliashberg–McMillan theory is also applicable in the strong antiadiabatic limit. The limit of very strong coupling, being the most relevant one for the physics of hydrides, is analyzed in detail. We also discuss the bounds for $T_c$ appearing in this limit.
Uspehi fizičeskih nauk. 2022;192(7):773-789
773-789
Novel magnetic stoichiometric superconductor compound EuRbFe$_4$As$_4$
Аннотация
In the new stoichiometric high-temperature iron-based superconductor EuRbFe$_4$As$_4$, superconductivity coexists with a peculiar long-range magnetic order of the Eu 4f states; their coexistence is an enigma and a challenge for both experiment and theory. Using angle-resolved photoemission spectroscopy (ARPES), resonant photoemission spectroscopy (ResPES), Andreev reflection spectroscopy, scanning tunneling spectroscopy, and DFT band structure calculations, we have made significant progress in solving this puzzle. Our results unambiguously indicate a separation between the electronic states of Fe (superconductivity) and Eu (magnetism) and demonstrate the existence of superconducting and long-range magnetic orders almost independently of each other.
Uspehi fizičeskih nauk. 2022;192(7):790-798
790-798
High-temperature superconductivity in hydrides
Аннотация
Over the past six years (2015–2021), many superconducting hydrides with critical temperatures $T_c$ up to $+15^{\circ }$C, which are currently record high, have been discovered. Now, we can already say that a special field of superconductivity has developed: hydride superconductivity at ultrahigh pressures. For the most part, the properties of superhydrides are well described by the Migdal–Eliashberg theory of strong electron–phonon interactions, especially when the anharmonicity of phonons is taken into account. We investigate the isotope effect, the effect of a magnetic field (up to 60–70 T) on the critical temperature and critical current in the hydride samples, and the dependence of $T_c$ on the pressure and the degree of doping. The divergences between the theory and experiment are of interest, especially in the regions of phase stability and in the behavior of the upper critical magnetic fields at low temperatures. We present a retrospective analysis of data from 2015–2021 and describe promising directions for future research on hydride superconductivity.
Uspehi fizičeskih nauk. 2022;192(7):799-813
799-813
Physics news on the Internet (based on electronic preprints)
Uspehi fizičeskih nauk. 2022;192(7):814-814
814-814
Personalia
Marat Ravil'evich Gil'fanov (on his 60th birthday)
Uspehi fizičeskih nauk. 2022;192(7):815-816
815-816