$T$-duality simplifies bulk-boundary correspondence: the parametrised case

We are glad to introduce you that the 2022 International Conference on Semiconductors, Electromagnetics and Condensed Matter Physics (SECMP 2022) was successfully held from February 25-27, 2022. Considering worldwide travel restriction and the impact of COVID-19, SECMP 2022 was carried out in the form of virtual conference to avoid personnel gatherings. Because most participants were still highly enthusiastic about participating in this conference, we chose to carry out SECMP 2022 via online platform according to the original schedule instead of postponing it.SECMP 2022 is organized by AEIC Academic Exchange Information Center. The conference is the premier event for showcasing your work on Semiconductors, Electromagnetics and Condensed Matter Physics. Open to industry and academia, it provides the opportunity to hear from distinguished plenary speakers, discuss ideas with other delegates and initiate new collaborations.This scientific event brings together more than 100 national and international researchers in Semiconductors, Electromagnetics and Condensed Matter Physics. On top of the local participants coming from different national universities, international participants are also registered from different countries, namely UK, Egypt, Malaysia, USA. During the conference, the conference model was divided into three sessions, including oral presentations, keynote speeches, and online Q&A discussion. In the first part, some scholars, whose submissions were selected as the excellent papers, were given about 5-10 minutes to perform their oral presentations one by one. Then in the second part, keynote speakers were each allocated 30-45 minutes to hold their speeches.In the second part, we invited four professors as our keynote speakers. Prof. Zhiyuan Zhu, Southwest University, our first keynote speaker. And then we had Prof. Lexian Yang, Tsinghua University, China. He presented an insightful speech: Evolution of the electronic structure of intrinsic magnetic topological insulator MnBi2Te4 film and bulk. His research interest focuses on the investigation of the electronic structures and novel properties of quantum materials using angle-resolved photoemission spectroscopy (ARPES), including the topological quantum materials, strongly correlated materials, low-dimensional materials, and advanced functional materials. Our third keynote speaker, Prof. Ming Yan, from Shanghai university, China. Prof. Bin Zhu, our finale keynote speaker, from Jiangsu Provincial Key Laboratory of Solar Energy Science and Technology/Energy Storage Joint Research Center, Southeast University, China/Loughborough University, UK, performed a speech: Semiconductor-based superionic conductors for new generation fuel cell applications. Their insightful speeches had triggered heated discussion in the third session of the conference. Every participant praised this conference for disseminating useful and insightful knowledge.The proceedings are a compilation of the accepted papers and represent an interesting outcome of the conference. Topics include but are not limited to the following areas: Semiconductors, Electromagnetics, Condensed Matter Physics and more related topics. All the papers have been through rigorous review and process to meet the requirements of International publication standard.We would like to acknowledge all of those who supported SECMP 2022. The help and contribution of each individual and institution was instrumental in the success of the conference. In particular, we would like to thank the organizing committee for its valuable inputs in shaping the conference program and reviewing the submitted papers.The Committee of SECMP 2022Committee member are available in the pdf

Phenomena include the Kosterlitz-Thouless phase transition, fractional quantum Hall effect, and high-temperature superconductivity have driven advances in condensed matter physics, offering a foundation for the investigation of superconductivity and the quantum Hall effect, as well as aiding in the comprehension of the behavior of strongly correlated electrons. The discovery of topological insulators and the preparation of graphene triggered important breakthroughs 20 years ago, leading to novel phenomena include topological superconductivity, the quantum anomalous Hall effect, corner graphene, and quantum spin liquids, which opened new directions in quantum materials research. Through the study of topological superconductors and flat band effects, this paper elucidates the role of topological energy band theory in describing Majorana fermions and their non-abelian statistical properties and reveals the phenomena of superconductivity and Mott's insulating state due to strong electronic interactions in magic-angle cornering graphene. The results show that the theory of topological energy bands and flat band effects can explain the strongly correlated electronic effects, providing theoretical support for understanding the phase transition from Mott insulating states to superconducting states and the Majorana zero mode in quantum computation. This paper emphasizes the importance of topological and two-dimensional materials in the study of strongly correlated electrons, providing guidance for future research.

The statistical mechanics of random surfaces has proven to be of growing importance in quantum field theory (string theory, random surface representations of gauge theory) and condensed matter physics (domain walls and interfaces, incommensurate phases, spin glasses, crystal surfaces, surface phenomena such as wetting, etc.). During the past three years, the author has been actively involved in developping a suitable mathematical framework for a statistical mechanics of random surfaces. Various applications to quantum field theory and condensed matter physics have been outlined. This work has been carried out in collaboration with M. Aizenman, D. Brydges, J. and L. Chayes, B. Durhuus, T. Jonsson, and T. Spencer. Research in various directions of random surface physics is presently continuing. Several original papers and reviews have appeared in print. Therefore, and because of other obligations, the author has found himself unable to write a detailed account of his lectures. May the following references be useful.

This graduate-level textbook is the first pedagogical synthesis of the field of topological insulators and superconductors, one of the most exciting areas of research in condensed matter physics. Presenting the latest developments, while providing all the calculations necessary for a self-contained and complete description of the discipline, it is ideal for graduate students and researchers preparing to work in this area, and it will be an essential reference both within and outside the classroom. The book begins with simple concepts such as Berry phases, Dirac fermions, Hall conductance and its link to topology, and the Hofstadter problem of lattice electrons in a magnetic field. It moves on to explain topological phases of matter such as Chern insulators, two- and three-dimensional topological insulators, and Majorana p-wave wires. Additionally, the book covers zero modes on vortices in topological superconductors, time-reversal topological superconductors, and topological responses/field theory and topological indices. The book also analyzes recent topics in condensed matter theory and concludes by surveying active subfields of research such as insulators with point-group symmetries and the stability of topological semimetals. Problems at the end of each chapter offer opportunities to test knowledge and engage with frontier research issues. Topological Insulators and Topological Superconductors will provide graduate students and researchers with the physical understanding and mathematical tools needed to embark on research in this rapidly evolving field.

The importance of global band topology is unequivocally recognized in condensed matter physics, and new states of matter, such as topological insulators, have been discovered. Owing to their bulk band topology, 3D topological insulators possess a massless Dirac dispersion with spin–momentum locking at the surface. Although 3D topological insulators were originally proposed in time-reversal invariant systems, the onset of a spontaneous magnetization or, equivalently, a broken time-reversal symmetry leads to the formation of an exchange gap in the Dirac band dispersion. In such magnetic topological insulators, tuning of the Fermi level in the exchange gap results in the emergence of a quantum Hall effect at zero magnetic field, that is, of a quantum anomalous Hall effect. Here, we review the basic concepts of magnetic topological insulators and their experimental realization, together with the discovery and verification of their emergent properties. In particular, we discuss how the development of tailored materials through heterostructure engineering has made it possible to access the quantum anomalous Hall effect, the topological magnetoelectric effect, the physics related to the chiral edge states that appear in these materials and various spintronic phenomena. Further theoretical and experimental research on magnetic topological insulators will provide fertile ground for the development of new concepts for next-generation electronic devices for applications such as spintronics with low energy consumption, dissipationless topological electronics and topological quantum computation. Magnetic topological insulators enable the investigation of the interplay between magnetism and topological electronic states. This Review summarizes the basic notions of magnetic topological insulators and the progress in the experimental realization of exotic topological phenomena.

Half-Heusler d0-d gapless semiconductors as strong Z2 topological insulators

Topological Insulators (TI) have been the subject of intense research by condensed matter physicists over the last decade for many reasons. One of which is the existence of helical edge modes, which can occur even when wave propagation through the bulk of the material is impossible. Eager to engineer devices that support these helical modes, researchers have invented classical systems analogous to the quantum mechanical TI. However, the path to miniaturization for most of these systems for practical devices is not always clear. Here, I propose a classical TI which can be realized with piezoelectric resonators. By using piezoelectric resonators, one may take advantage of the high linearity, compact design, and established micro-fabrication techniques.

Axion is a hypothetical elementary particle which was initially postulated to solve the charge conjugation-parity problem in particle physics. Interestingly, the axion state has emerged in effective theory of topological insulators and has attracted extensive attention in condensed matter physics. Time-reversal or inversion symmetry constrains the axion field $\theta$ to be quantized. When both the time-reversal and inversion symmetries are broken by, say, an antiferromagnetic order, the axion field $\theta$ could become unquantized and dynamical along with magnetic fluctuations, which is termed the dynamical axion field. Here, we reveal that a wide class of topological-insulator-based dynamical axion states could be distinguished from the normal-insulator-based ones by a hidden quantity derived from the pseudospin Chern number. Motivated by recent research on MnBi$_{2}$Te$_{4}$-family materials, we further show that such topological-insulator-based dynamical axion states can be hopefully achieved in MnBi$_{2}$Te$_{4}$-based heterostructures, which should greatly facilitate the study of axion electrodynamics in condensed matter physics.

Topological insulators (TIs) in condensed matter physics have been rapidly developed in acoustic fields and have enabled the controlling of acoustic waves in brand new ways recently. The current acoustic analogs of electronic TIs are mainly based on sonic crystal Bragg scattering. The practical applications of these TIs were restricted by a non-adjustable geometric structure, a wavelength equivalent scale, and a high and fixed frequency response. Here, we propose subwavelength acoustic TIs on the basis of negative metamaterials, which utilize local resonance different from Bragg scattering to design topologically protected acoustic propagation. We demonstrate the existence of band inversion by altering the ratio of the distance of the meta-atoms to the lattice constant. More importantly, the dispersion and edge states of the Dirac cones can offer tunability within a wide frequency range under a fixed lattice constant by adjusting the structural parameters of the meta-atoms. Theoretical analysis, numerical simulations, and experimental measurement verify the edge states of the acoustic TIs. The proposed acoustic topological metamaterials provide a flexible way of manipulating sound propagation.

Exploration of topology is central in condensed matter physics and applications to fault-tolerant quantum information. The bulk-boundary correspondence and tenfold classification determine the topological state compared to a vacuum. Contrary to this belief, we demonstrate that topological zero-energy domain-wall states can emerge for all forbidden 1D classes of the tenfold classification table. The guiding principle is that the difference in the topological quantities of two trivial domains can be quantized, and hence, a topologically protected state can emerge at the domain wall. Such nontrivial domain-wall states are demonstrated using generalized Su-Schrieffeer-Heeger and generalized Kitaev models, which manifest quantized polarization and Majorana fermions, respectively. The quantized Berry phase difference between the domains protects the non-trivial nature of the domain-wall states, extending the bulk-boundary correspondence, also confirmed by the tight-binding and Jackiw-Rebbi methods. Furthermore, we show that the seemingly trivial electronic and superconducting models can be transformed into their topological counterparts in the framework of the topological Fermi-liquid theory. Finally, we propose potential systems where our results may be realized, spanning from electronic and superconducting to optical systems.

<p indent="0mm">The design of metamaterials plays an essential role in effectively controlling acoustic waves, which has led to many fascinating effects, such as acoustic cloaking, negative refraction and extraordinary transmission. Inspired by topological states discovered in condensed matter physics, a new perspective has emerged in considering the band topology of acoustic metamaterials, i.e., topological acoustics. The hallmark of topological states is bulk-boundary correspondence, lower dimensional boundary states protected by bulk topology. Recently, researchers have found that the bulk topology can also correspond to boundary states with two and three dimensions lower than the bulk, such as one-dimensional hinge states or zero-dimensional corner states in three-dimensional systems. This kind of topological state is the so-called higher-order topology. To date, various higher-order topological states have been successfully achieved in both two- and three-dimensional acoustic systems. However, these previous studies focused mainly on periodic systems. The quasi-periodic systems, which break the translational symmetry due to unique rotational symmetries, are rarely studied, especially in experiments. In this work, we experimentally investigate the higher-order topological states in acoustic two-dimensional Penrose quasicrystals possessing five-fold rotational symmetry. The Penrose patterns are constructed using inflation and deflation methods, starting with a decagon as the initial pattern. Since the centers of rotation are different for odd and even iterations, we choose the third and fourth iterations as two typical patterns. After placing uniform acoustic scatters on the vertices of the patterns, two acoustic quasicrystals are created, named G3 (Generation-3) and G4 (Generation-4). The size is controlled by the radius of the acoustic rods (<italic>r</italic>) and the length (<italic>l</italic>). Due to the long-range order and self-similarity characteristics of quasicrystals, the wavefunctions tend to be distributed in a repeating local patch. As the contrast ratio <italic>r</italic>/<italic>l</italic> increases, they also tend to split in the energy spectrum, making higher-order topological states possible. Here, we fix <italic>l</italic><sc>=10 cm</sc> and <italic>r</italic>/<italic>l</italic>=0.15, and focus on the states of frequency window ranging from 3 to <sc>5 kHz.</sc> These states can be divided into three series according to their different sound pressure distributions in two different local patches, i.e., <italic>d_xy</italic>- and <italic>d</italic>_{<italic>x</italic>2-<italic>y</italic>2}-like field distributions in local patch A and <italic>p_x</italic>-like in local patch B. For models G3 and G4 associated with their pentagon versions G3P and G4P, we find localized states at five corners of G3, G4, and G4P, and also appearing at the middle of the edges in G3P. Their topological properties are further analyzed by calculating the fractional corner charge density through the local density of states, which indicates that those in G3P are trivial while others are topological. Both trivial and topological localized states are experimentally observed via response spectra measurement. G3 and G4 models have similar topological properties, possessing topological corner states protected by five-fold rotational symmetry. Because of the different rotation centers, if the boundary conditions were changed (cut into regular pentagons), the topological corner states of G3P could disappear, while they still exist in G4P for the non-vanishing local patch A at the corners. Our results can be conveniently extended to G5 and G6 or even more complicated quasicrystal models, enriching acoustic topological states in quasi-periodic systems. Such unique five-fold rotational symmetry-protected topological corner states may also contribute to developing novel acoustic functional devices, facilitating acoustic wave localization and energy harvesting.

The past decades have witnessed an explosion of interest in topological materials, and a lot of mathematical concepts have been introduced in condensed matter physics. Among them, the bulk-boundary correspondence is the central topic in topological physics, which has inspired researchers to focus on boundary physics. Recently, the concepts of topological phases have been extended to non-Hermitian Hamiltonians, whose eigenvalues can be complex. Besides the topology, non-Hermiticity can also cause a boundary phenomenon called the non-Hermitian skin effect, which is an extreme sensitivity of the spectrum to the boundary condition. In this article, we review developments in non-Hermitian topological physics by focusing mainly on the boundary problem. As well as the competition between non-Hermitian and topological boundary phenomena, we discuss the topological nature inherent in non-Hermiticity itself.

I discuss the impact of gauge-gravity duality on our understanding of two classes of systems: conformal quantum matter and compressible quantum matter.The first conformal class includes systems, such as the boson Hubbard model in two spatial dimensions, which display quantum critical points described by conformal field theories. Questions associated with nonzero temperature dynamics and transport are difficult to answer using conventional field-theoretic methods. I argue that many of these can be addressed systematically using gauge-gravity duality and discuss the prospects for reliable computation of low-frequency correlations.Compressible quantum matter is characterized by the smooth dependence of the charge density, associated with a global U(1) symmetry, upon a chemical potential. Familiar examples are solids, superfluids, and Fermi liquids, but there are more exotic possibilities involving deconfined phases of gauge fields in the presence of Fermi surfaces. I survey the compressible systems studied using gauge-gravity duality and discuss their relationship to the condensed matter classification of such states. The gravity methods offer hope of a deeper understanding of exotic and strongly coupled compressible quantum states.

The Bi2Te3/FeTe heterostructure intersects several phenomena and key classes of materials in condensed matter physics: topological insulators, superconductivity, magnetism, and the physics of interfaces. While neither the topological insulator (Bi2Te3) nor the iron chalcogenide (FeTe) are themselves superconductors, superconductivity forms in a thin 7nm interfacial layer between the two. The restricted dimensionality and the extraordinarily conductive normal state, possibly sourced by the topologically protected surface states, have led to the observation of novel phenomena such as the Likharev vortex explosion and transitions in behavior resulting from the interplay between current induced depairing and the Berezinski-Kosterlitz-Thouless regime. Bi2Te3/FeTe also displays the anomalous oscillatory magnetoresistance phenomenon, which we had previously observed in cuprates. © 2017 Author(s).

The deconfined quantum critical point of a two-dimensional $SU(N)$ antiferromagnet is governed by an Abelian Higgs model in $d=2+1$ spacetime dimensions featuring $N$ complex scalar fields. In this context, we derive for $2\ensuremath{\le}d\ensuremath{\le}4$ an exact formula for the central charge of the $U(1)$ current in terms of the gauge coupling at quantum criticality and compare it with the corresponding result obtained using gauge-gravity duality. There is a remarkable similarity precisely for $d=2+1$. In this case the amplitude of the current correlation function has the same form as predicted by the gauge-gravity duality. We also compare finite temperature results for the charge susceptibility in the large $N$ limit with the result predicted by the gauge-gravity duality. Our results suggest that condensed matter systems at quantum criticality may provide interesting quantitative tests of the gauge-gravity duality even in the absence of supersymmetry.