Interplay of chemical disorder and electronic inhomogeneity in unconventional superconductors

Many of today's forefront materials, such as high-Tc superconductors, doped semiconductors, and colossal magnetoresistance materials, are structurally, chemically and/or electronically inhomogeneous at the nanoscale. Although inhomogeneity can degrade the utility of some materials, defects can also be advantageous. Quite generally, defects can serve as nanoscale probes and facilitate quasiparticle scattering used to extract otherwise inaccessible electronic properties. In superconductors, non-stoichiometric dopants are typically necessary to achieve a high transition temperature, while both structural and chemical defects are used to pin vortices and increase critical current. Scanning tunneling microscopy (STM) has proven to be an ideal technique for studying these processes at the atomic scale. In this perspective, we present an overview of STM studies on chemical disorder in unconventional superconductors, and discuss how dopants, impurities and adatoms may be used to probe, pin or enhance the intrinsic electronic properties of these materials.Physic

Visualizing the Interplay of Structural and Electronic Disorders in High-Temperature Superconductors Using Scanning Tunneling Microscopy

The discovery of high-$T_c$ superconductivity in 1986 generated tremendous excitement. However, despite over 25 years of intense research efforts, many properties of these complex materials are still poorly understood. For example, the cuprate phase diagram is dominated by a mysterious "pseudogap" state, a depletion in the Fermi level density of states which persists above the superconducting critical temperature $T_c$. Furthermore, these materials are typically electronically inhomogeneous at the atomic scale, but to what extent the intrinsic chemical or structural disorder is responsible for electronic inhomogeneity, and whether the inhomogeneity is relevant to pseudogap or superconductivity, are unresolved questions. In this thesis, I will describe scanning tunneling microscopy experiments which probe the interplay of structural, chemical and electronic disorder in high-$T_c$ superconductors. First, I will present the imaging of a picoscale orthorhombic structural distortion in Bi-based cuprates. Based on insensitivity of this structural distortion to temperature, magnetic field, and doping level we conclude that it is an omnipresent background not related to the pseudogap state. I will also present the discovery of three types of oxygen disorder in the high-$T_c$ superconductor $Bi_2Sr_2CaCu_2O_{8+x}$ two different interstitials as well as vacancies at the apical oxygen site. We find a strong correlation between the positions of these defects and the nanoscale inhomogeneity in the pseudogap phase, which highlights the importance of chemical disorder in these compounds. Furthermore, I will show the determination of the exact intra-unit-cell positions of these dopants and the effect of different types of intrinsic strain on their placement. I will also describe the identification of chemical disorder in another cuprate $Y_{1−x}Ca_xBa_2Cu_3O_{7−x}$, and the first observation of electronic inhomogeneity of the spectral gap in this material. Finally, I will present definitive identification of the cleavage surfaces in $Pr_xCa_{1−x}Fe_2As_2$, and imaging of Pr dopants which exhibit lack of clustering, thus ruling out Pr inhomogeneity as the likely source of the high-$T_c$ volume fraction. To achieve the aforementioned results, we employ novel analytical and experimental tools such as an average supercell algorithm, high-bias dI/dV dopant mapping, and local barrier height mapping.Physic

Printing Process Parameters Identification System

The paper presents the research aimed at setting up and developing a software system for the printing process parameters identification based on modern computer and software systems, algorithmic principles, principles of expert systems construction and advanced learning. Thus, the possibilities of application of contemporary software tools were investigated, which facilitates the process and forms the program structure of the model that uses programming languages based on the expert systems construction principles and tools for the development of system model based on the principles of modern learning. For complex model development, concepts of process knowledge bases with influential process parameters of printing technique have been developed through modelling and construction based on the logic of expert systems with the presentation, use and involvement of experts knowledge in decision making with the evaluation of the impact of individual parameters. In addition to this approach, a module was developed using modern software tools based on an algorithmic principle and a module for identifying printing process parameters using modern platforms based on advanced learning. Sophisticated software model has been made through the research and developed with databases of process parameter identification systems based on modern software tools. This tool enables a significant expedition of the solution resolving, thus improving the graphical production process and the processes of acquiring and expanding knowledge. The model is based on integrative modules: a printing process parameters identification system based on algorithmic program structure systems, a printing process parameters identification system based on expert system building principles, and a printing process parameter identification system based on modern learning systems

Programming of 3-Axis Hybrid Kinematics CNC Machine for Rapid Prototyping Using Subtractive and Additive Processes

The paper presents the programming and program verification on a 3-axis hybrid kinematics CNC machine for rapid prototyping using subtractive and additive processes. The original hybrid (parallel-serial) 3-axis O-X glide mechanism developed to build a rapid prototyping machine and multifunctional machine tools is presented. The paper analyzes the available programming software, which can be one of the standard CAD/CAM systems or a specialized CAM system, for subtractive processes, i.e. desktop milling. For the additive processes, the software for generating G code based on the STL file as well as the possibility of simulating the machine when working is considered. To verify the program, the simulation of material removal for subtractive processes as well as the simulation of material addition for additive processes were considered. The paper presents the prototype of a hybrid kinematics CNC machine and some of the results of testing with an open control system based on the LinuxCNC

Comparison of different mathematical models for prediction of self-excited vibrations occurance in milling process

In modern production, despite the existence of other production methods, metal cutting still plays an important role. The performance of machine tools has a decisive role in terms of productivity and quality of production increase. Undoubtedly, productivity and quality of production are two mail requirements which are key elements to stay on top in a competitive market. One of the most influencing factor that affect the machine tools are vibrations. The most unwanted vibrations that can appear during metal cutting process are self-excited vibrations, which are one of the three kinds of mechanical vibration, free vibration, forced vibration, and self-excited vibration. When it comes to improving the performance of machine tools, the analysis of the appearance of self-excited vibrations and their isolation occupy a significant place. The aim of this paper derives from trends and limitations exists in metal production. The way to isolate the self-excited vibrations is to predict their occurrence by defining the stability lobe diagram. The paper presents two popular analytical methods for identifying stability lobe diagrams in milling, which shows the boundary between stable and unstable zone of machining operations, depending on the number of revolutions of the spindle and cutting depth. First considered method is Fourier series approach and second one id average tooth angle approach. Lather, both stability lobe diagrams were compared with results obtained experimentally

Nanoscale visualization of the thermally-driven evolution of antiferromagnetic domains in FeTe thin films

Antiferromagnetic order, being a ground state of a number of exotic quantum materials, is of immense interest both from the fundamental physics perspective and for driving potential technological applications. For a complete understanding of antiferromagnetism in materials, nanoscale visualization of antiferromagnetic domains, domain walls and their robustness to external perturbations is highly desirable. Here, we synthesize antiferromagnetic FeTe thin films using molecular beam epitaxy. We visualize local antiferromagnetic ordering and domain formation using spin-polarized scanning tunneling microscopy. From the atomically-resolved scanning tunneling microscopy topographs, we calculate local structural distortions to find a high correlation with the distribution of the antiferromagnetic order. This is consistent with the monoclinic structure in the antiferromagnetic state. Interestingly, we observe a substantial domain wall change by small temperature variations, unexpected for the low temperature changes used compared to the much higher antiferromagnetic ordering temperature of FeTe. This is in contrast to electronic nematic domains in the cousin FeSe multilayer films, where we find no electronic or structural change within the same temperature range. Our experiments provide the first atomic-scale imaging of perturbation-driven magnetic domain evolution simultaneous with the ensuing structural response of the system. The results reveal surprising thermally-driven modulations of antiferromagnetic domains in FeTe thin films well below the Neel temperature

Observation of early social interactions in sibling dyads: a systematic review

Sibling relationships provide unique social experiences that can vary across the lifespan. Early sibling social interactions (ESSI) have been associated with children’s own relationship and developmental outcomes, highlighting the essential role that sibling encounters play, even from a young age. Understanding how these social exchanges occur and unfold and the range of opportunities they provide can shed light on critical aspects of early childhood development and family life. However, the methodological approach used in studying ESSI can infuence our understanding of these early experiences. This systematic review aims to delineate the methodological framework adopted in observational studies of ESSI. Through a systematic search of psychology and domain-general databases until March 2023, we focused on studies that addressed bidirectional naturalistic interactions in young sibling dyads (at least one child aged 0-36 months). Of the 713 articles screened, only 63 met the inclusion criteria. Findings regarding three main issues are examined, including sample characteristics, study designs and procedures, and sibling interactive behaviours targeted. Previous research has focused on a diverse range of sibling behavioral exchanges, including cues of children's social skills and relationship quality within mainly ecological contexts. However, limitations in representativeness and standardization have been identifed. Future studies should incorporate sequential analyses to fully comprehend the interactive nature of early sibling social encountersThis research received support from the Ministry of Science and Innovation of Spain (Grant number PID2020-117087GB-I00). Additionally, the Autonomous University of Madrid provided funding for the predoctoral contract, which contributed to the successful completion of this wor

Atomic-Scale Strain Manipulation of a Charge Density Wave

A charge density wave (CDW) is one of the fundamental instabilities of the Fermi surface occurring in a wide range of quantum materials. In dimensions higher than one, where Fermi surface nesting can play only a limited role, the selection of the particular wave vector and geometry of an emerging CDW should in principle be susceptible to controllable manipulation. In this work, we implement a simple method for straining materials compatible with low-temperature scanning tunneling microscopy/spectroscopy (STM/S), and use it to strain-engineer new CDWs in 2H-NbSe2. Our STM/S measurements combined with theory reveal how small strain-induced changes in the electronic band structure and phonon dispersion lead to dramatic changes in the CDW ordering wave vector and geometry. Our work unveils the microscopic mechanism of a CDW formation in this system, and can serve as a general tool compatible with a range of spectroscopic techniques to engineer novel electronic states in any material where local strain or lattice symmetry breaking plays a role.Comment: to appear in PNAS (2018