The flow of the Berry curvature vector field

The concept of Berry phase and Berry curvature has become ubiquitous in solid state physics as it relates to variety of phenomena, such as topological insulators, polarization, and various Hall effects. It is well known that large Berry curvatures arise from close proximity of hybridizing bands, however, the vectorial nature of the Berry curvature is not utilized in current research. On bulk bcc Fe, we demonstrate the flow of the Berry curvature vector field which features not only monopoles but also higher dimensional structures with its own topological features. They can provide a novel unique view on the electronic structure in all three dimensions. This knowledge is also used to quantify particular contributions to the intrinsic anomalous Hall effect in a simple analytical form.

The role of scale factor in the formation of prod-uct properties under the action of surface modifi-cation

Based on theoretical and experimental research in the fields of solid-state physics and physical materials science, it is proved that the surface layer of a solid body, which is deformed, is an independent functional subsystem and radically affects large-scale levels of plastic flow and destruction of the product as a whole. As is known, the most effective method of improving the performance of products is the grinding of grain, because it is the grain boundary (substructural) mechanism of strengthening which provides an increase in the structural strength of the product. In this regard, special attention is paid to submicro- and nano-structuring of the surface. Goal. The aim of the work is to study the process of structure formation of the surface layer under the action of ion bombardment (IB) and its effect on the properties of products taking into account the scale factor. To achieve this goal, the following tasks were set: to evaluate the characteristics of the surface microstructure after IB and to study its tensile behavior in cylindrical and flat samples of low-carbon steel in order to take into account the scale factor in changing their properties. The submicro-structuring of the surface by ion bombardment is carried out in the work and its influence on the behavior of products during tensile deformation is investigated. It is established that the presence of a thin modified layer (with a constant core) significantly changes the properties of the product under force. The decisive role belongs to the contribution of the surface layer (scale factor) – the ratio of the area of the modified layer to the volume of the product: if it is <1 the effect of hardening is better realized while maintaining plasticity, and if ˃ 1, it is a significant effect of plasticization which maintains (or even increases) hardening.

Highlighting non-parabolic bands in semiconductors

The parabolic approximation to the dispersion relation is a simplification that has often been adopted for the electronic band structure of most semiconductors near the edges of the fundamental bandgap. A non-parabolic approximation can be justified which will better describe the properties of semiconductors of narrow bandgaps for which a reduction to a quadratic form is not accurate enough, nor always warranted. It also stands for a better approximation in III–V compounds and for more complex thermoelectric materials. Some of the consequences of adopting non-parabolic bands will be highlighted, as well as approximate expressions for statistical properties. It is emphasized that many properties of semiconductors are not difficult to calculate with non-parabolic bands, which may have a wider range of applications in actual materials. These calculations can then be introduced in solid state physics and statistical physics courses through projects and homework problem sets. Specific examples are discussed designed to clarify basic physics concepts in semiconductors.

In memoriam. Orlando Zelaya-Angel’s contributions in Superficies y Vacío

Professor Orlando Zelaya Angel was an outstanding member of the research community on Solid State Physics. He served as President to the Sociedad Mexicana de Ciencia de Superficies y Vacío (SMCSyV; currently Sociedad Mexicana de Ciencia y Tecnología de Superficies y Materiales – SMCTSM), for the period 1995-1996. Professor Zelaya formed many researchers in Mexico, who continue developing research, either in Mexico, in their countries of origin, or abroad. Throughout the evolution of Superficies y Vacío, Professor Zelaya, contributed with sixteen articles on subjects ranging from thin films for optoelectronic applications, through hard coatings and studies on the process for production of Tortillas; covering most of his research areas of interest. Here is a subject-chronological compilation of the abstracts to his articles in Superficies y Vacío, after a year of his departure.

Response to Comment on “Investigation on Anomalous Thermal Quenching of Mn4+ Luminescence in A2XF6:Mn4+” [ECS J. Solid State Sci. Technol. 10 076007 (2021)]

Yan argued that an abnormal negative thermal quenching (TQ) of the A2XF6:Mn4+ fluoride phosphors was a pitfall caused by the diminishment in optical path lengths of the spectrofluorometer originating from the increasing volume of the phosphor (namely, thermal expansion) at elevated temperatures [S. Yan, J. Solid State Sci. Technol., 9, 106004 (2020)], but not from any intrinsic effects that can be rigidly modeled based on the solid state physics. We disagree with this comment and explain in more detail that abnormal negative TQ is surely explained by the intrinsic properties of the Mn4+-activated fluoride phosphors with denying his/her previous work.

State of the Art in Crystallization of LiNbO3 and Their Applications

Lithium niobate (LiNbO3) crystals are important dielectric and ferroelectric materials, which are widely used in acoustics, optic, and optoelectrical devices. The physical and chemical properties of LiNbO3 are dependent on microstructures, defects, compositions, and dimensions. In this review, we first discussed the crystal and defect structures of LiNbO3, then the crystallization of LiNbO3 single crystal, and the measuring methods of Li content were introduced to reveal reason of growing congruent LiNbO3 and variable Li/Nb ratios. Afterwards, this review provides a summary about traditional and non-traditional applications of LiNbO3 crystals. The development of rare earth doped LiNbO3 used in illumination, and fluorescence temperature sensing was reviewed. In addition to radio-frequency applications, surface acoustic wave devices applied in high temperature sensor and solid-state physics were discussed. Thanks to its properties of spontaneous ferroelectric polarization, and high chemical stability, LiNbO3 crystals showed enhanced performances in photoelectric detection, electrocatalysis, and battery. Furthermore, domain engineering, memristors, sensors, and harvesters with the use of LiNbO3 crystals were formulated. The review is concluded with an outlook of challenges and potential payoff for finding novel LiNbO3 applications.

Single-shot measurement of the photonic band structure in a fiber-based Floquet-Bloch lattice

Floquet-Bloch lattices are systems in which wave packets are subjet to periodic modulations both in time and space, showing rich dynamics. While this type of lattice is difficult to implement in solid-state physics, optical systems have provided excellent platforms to probe their physics: among other effects, they have revealed genuine phenomena such as the anomalous Floquet topological insulator and the funnelling of light into localised interface modes. Despite the crucial importance of the band dispersion in the photon dynamics and the topological properties of the lattice, the direct experimental measurement of the Floquet-Bloch bands has remained elusive. Here we report the direct measurement of the Floquet-Bloch bands of a photonic lattice with a single shot method. We use a system of two coupled fibre rings that implements a time-multiplexed Floquet-Bloch lattice. By Fourier transforming the impulse response of the lattice we obtain the band structure together with an accurate characterization of the lattice eigenmodes, i. e. the amplitudes and the phases of the Floquet-Bloch eigenvectors over the entire Brillouin zone. Our results open promising perspectives for the observation of topological effects in the linear and nonlinear regime in Floquet systems.

High Temperature Superconductors Through the Van Hove Singularity

<p>The antibonding VHS of the high temperature superconductor Bi-2212 appears in the extreme overdoped regime, a part of the cuprate phase diagram little studied to date. Observation of this VHS motivated taking a fresh look at the cuprates using fundamentals of electronics as the foundation for understanding the physics involved in the superconductivity of these materials. In the study of the high temperature superconductors it appears important questions have been overlooked, notably the possible contribution of the gapped state and whether these materials are better considered as doped semiconductors rather than as 'poor' metals. We also find the question of the contribution of oxygen, a substance with a strong magnetic signature, to data of the oxygen-doped cuprates has been neglected. Comparison with non-oxygen doping is supportive of the view the oxygen dopant contributes noticeably to magnetic data. Through magnetic susceptibility measurements the antibonding VHS location, predicted by use of Fermi liquid theory, is well confirmed in polycrystals of the lead-doped cuprate Bi-2212. It was found that the peak in the DOS at the VHS produces no corresponding local peak in the critical temperature versus doping. Instead, the VHS appears associated with the disappearance of the superconductivity, rather than with the maximum critical temperature. We find the metal-insulator transition plays an important role. There are two of these in the cuprates, a horizontal doping dependent one and a vertical temperature dependent one. They affect each other. Noting the consequences of doping an insulator until a metallic state is reached enables a connection to be made between doping and pressure. Three requirements are identified for superconductivity to occur: 1. screening 2. pairing 3. charge mobility Each requirement may be separately satisfied in a manner whereby each can vary differently as a function of the same variable. The superconductivity of the cuprates is found to arise out of an underlying non-metallic state. As such, BCS theory, being formulated to explain superconductivity arising from metallic conduction, cannot be directly applicable. However, although HTS materials are a rich repository of both novel and familiar solid state physics, evidence does not appear to support the notion that superconductivity in the cuprates is caused by "exotic" physics. We also find cause for optimism regarding the development of new or improved superconducting materials.</p>

High Temperature Superconductors Through the Van Hove Singularity

<p>The antibonding VHS of the high temperature superconductor Bi-2212 appears in the extreme overdoped regime, a part of the cuprate phase diagram little studied to date. Observation of this VHS motivated taking a fresh look at the cuprates using fundamentals of electronics as the foundation for understanding the physics involved in the superconductivity of these materials. In the study of the high temperature superconductors it appears important questions have been overlooked, notably the possible contribution of the gapped state and whether these materials are better considered as doped semiconductors rather than as 'poor' metals. We also find the question of the contribution of oxygen, a substance with a strong magnetic signature, to data of the oxygen-doped cuprates has been neglected. Comparison with non-oxygen doping is supportive of the view the oxygen dopant contributes noticeably to magnetic data. Through magnetic susceptibility measurements the antibonding VHS location, predicted by use of Fermi liquid theory, is well confirmed in polycrystals of the lead-doped cuprate Bi-2212. It was found that the peak in the DOS at the VHS produces no corresponding local peak in the critical temperature versus doping. Instead, the VHS appears associated with the disappearance of the superconductivity, rather than with the maximum critical temperature. We find the metal-insulator transition plays an important role. There are two of these in the cuprates, a horizontal doping dependent one and a vertical temperature dependent one. They affect each other. Noting the consequences of doping an insulator until a metallic state is reached enables a connection to be made between doping and pressure. Three requirements are identified for superconductivity to occur: 1. screening 2. pairing 3. charge mobility Each requirement may be separately satisfied in a manner whereby each can vary differently as a function of the same variable. The superconductivity of the cuprates is found to arise out of an underlying non-metallic state. As such, BCS theory, being formulated to explain superconductivity arising from metallic conduction, cannot be directly applicable. However, although HTS materials are a rich repository of both novel and familiar solid state physics, evidence does not appear to support the notion that superconductivity in the cuprates is caused by "exotic" physics. We also find cause for optimism regarding the development of new or improved superconducting materials.</p>