Pub Date : 2021-04-03DOI: 10.1080/00018732.2022.2084006
R. Dittmann, S. Menzel, R. Waser
This review addresses resistive switching devices operating according to the bipolar valence change mechanism (VCM), which has become a major trend in electronic materials and devices over the last decade due to its high potential for non-volatile memories and future neuromorphic computing. We will provide detailed insights into the status of understanding of these devices as a fundament for their use in the different fields of application. The review covers the microscopic physics of memristive states and the switching kinetics of VCM devices. It is shown that the switching of all variants of VCM cells relies on the movement of mobile donor ions, which are typically oxygen vacancies or cation interstitials. VCM cells consist of three parts: an electronically active electrode (AE), often a metal with a high work function, in front of which the switching occurs, a mixed ionic-electronic conducting (MIEC) layer consisting of a nanometer-scale metal oxide or a stack of different metal oxides, and an ohmic counter electrode (OE). After an introduction to definitions and classification, the fundamentals of solid-state physics and chemistry associated with VCM cells are described, including redox processes and the role of electrodes. The microscopic changes induced by electroforming, a process often required prior to resistive switching, are described in terms of electronic initialization and subsequent changes in chemistry, structure, and conductivity. The switching process is discussed in terms of switching polarity, geometry of the switching region, and spectroscopic detection of the valence changes. Emphasis is placed on the extreme nonlinearity of switching kinetics described by physics-based multiscale modeling, ranging from ab initio methods to kinetic Monte Carlo and finite element models to compact models that can be used in circuit simulators. The review concludes with a treatment of the highly relevant reliability issues and a description of the failure mechanisms, including mutual trade-offs.
{"title":"Nanoionic memristive phenomena in metal oxides: the valence change mechanism","authors":"R. Dittmann, S. Menzel, R. Waser","doi":"10.1080/00018732.2022.2084006","DOIUrl":"https://doi.org/10.1080/00018732.2022.2084006","url":null,"abstract":"This review addresses resistive switching devices operating according to the bipolar valence change mechanism (VCM), which has become a major trend in electronic materials and devices over the last decade due to its high potential for non-volatile memories and future neuromorphic computing. We will provide detailed insights into the status of understanding of these devices as a fundament for their use in the different fields of application. The review covers the microscopic physics of memristive states and the switching kinetics of VCM devices. It is shown that the switching of all variants of VCM cells relies on the movement of mobile donor ions, which are typically oxygen vacancies or cation interstitials. VCM cells consist of three parts: an electronically active electrode (AE), often a metal with a high work function, in front of which the switching occurs, a mixed ionic-electronic conducting (MIEC) layer consisting of a nanometer-scale metal oxide or a stack of different metal oxides, and an ohmic counter electrode (OE). After an introduction to definitions and classification, the fundamentals of solid-state physics and chemistry associated with VCM cells are described, including redox processes and the role of electrodes. The microscopic changes induced by electroforming, a process often required prior to resistive switching, are described in terms of electronic initialization and subsequent changes in chemistry, structure, and conductivity. The switching process is discussed in terms of switching polarity, geometry of the switching region, and spectroscopic detection of the valence changes. Emphasis is placed on the extreme nonlinearity of switching kinetics described by physics-based multiscale modeling, ranging from ab initio methods to kinetic Monte Carlo and finite element models to compact models that can be used in circuit simulators. The review concludes with a treatment of the highly relevant reliability issues and a description of the failure mechanisms, including mutual trade-offs.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"70 1","pages":"155 - 349"},"PeriodicalIF":0.0,"publicationDate":"2021-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47793533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-02DOI: 10.1080/00018732.2021.1969727
F. Mivehvar, F. Piazza, T. Donner, H. Ritsch
We review the recent developments and the current status in the field of quantum-gas cavity QED. Since the first experimental demonstration of atomic self-ordering in a system composed of a Bose–Einstein condensate coupled to a quantized electromagnetic mode of a high-Q optical cavity, the field has rapidly evolved over the past decade. The composite quantum-gas-cavity systems offer the opportunity to implement, simulate, and experimentally test fundamental solid-state Hamiltonians, as well as to realize non-equilibrium many-body phenomena beyond conventional condensed-matter scenarios. This hinges on the unique possibility to design and control in open quantum environments photon-induced tunable-range interaction potentials for the atoms using tailored pump lasers and dynamic cavity fields. Notable examples range from Hubbard-like models with long-range interactions exhibiting a lattice-supersolid phase, over emergent magnetic orderings and quasicrystalline symmetries, to the appearance of dynamic gauge potentials and non-equilibrium topological phases. Experiments have managed to load spin-polarized as well as spinful quantum gases into various cavity geometries and engineer versatile tunable-range atomic interactions. This led to the experimental observation of spontaneous discrete and continuous symmetry breaking with the appearance of soft-modes as well as supersolidity, density and spin self-ordering, dynamic spin-orbit coupling, and non-equilibrium dynamical self-ordered phases among others. In addition, quantum-gas-cavity setups offer new platforms for quantum-enhanced measurements. In this review, starting from an introduction to basic models, we pedagogically summarize a broad range of theoretical developments and put them in perspective with the current and near future state-of-art experiments.
{"title":"Cavity QED with quantum gases: new paradigms in many-body physics","authors":"F. Mivehvar, F. Piazza, T. Donner, H. Ritsch","doi":"10.1080/00018732.2021.1969727","DOIUrl":"https://doi.org/10.1080/00018732.2021.1969727","url":null,"abstract":"We review the recent developments and the current status in the field of quantum-gas cavity QED. Since the first experimental demonstration of atomic self-ordering in a system composed of a Bose–Einstein condensate coupled to a quantized electromagnetic mode of a high-Q optical cavity, the field has rapidly evolved over the past decade. The composite quantum-gas-cavity systems offer the opportunity to implement, simulate, and experimentally test fundamental solid-state Hamiltonians, as well as to realize non-equilibrium many-body phenomena beyond conventional condensed-matter scenarios. This hinges on the unique possibility to design and control in open quantum environments photon-induced tunable-range interaction potentials for the atoms using tailored pump lasers and dynamic cavity fields. Notable examples range from Hubbard-like models with long-range interactions exhibiting a lattice-supersolid phase, over emergent magnetic orderings and quasicrystalline symmetries, to the appearance of dynamic gauge potentials and non-equilibrium topological phases. Experiments have managed to load spin-polarized as well as spinful quantum gases into various cavity geometries and engineer versatile tunable-range atomic interactions. This led to the experimental observation of spontaneous discrete and continuous symmetry breaking with the appearance of soft-modes as well as supersolidity, density and spin self-ordering, dynamic spin-orbit coupling, and non-equilibrium dynamical self-ordered phases among others. In addition, quantum-gas-cavity setups offer new platforms for quantum-enhanced measurements. In this review, starting from an introduction to basic models, we pedagogically summarize a broad range of theoretical developments and put them in perspective with the current and near future state-of-art experiments.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"70 1","pages":"1 - 153"},"PeriodicalIF":0.0,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46791454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-01DOI: 10.1080/00018732.2021.1935698
J. Tranquada
Understanding the electron pairing in hole-doped cuprate superconductors has been a challenge, in particular because the “normal” state from which it evolves is unprecedented. Now, after three and a half decades of research, involving a wide range of experimental characterizations, it is possible to delineate a clear and consistent cuprate story. It starts with doping holes into a charge-transfer insulator, resulting in in-gap states. These states exhibit a pseudogap resulting from the competition between antiferromagnetic superexchange J between nearest-neighbor Cu atoms (a real-space interaction) and the kinetic energy of the doped holes, which, in the absence of interactions, would lead to extended Bloch-wave states whose occupancy is characterized in reciprocal space. To develop some degree of coherence on cooling, the spin and charge correlations must self-organize in a cooperative fashion. A specific example of resulting emergent order is that of spin and charge stripes, as observed in La Ba CuO . While stripe order frustrates bulk superconductivity, it nevertheless develops pairing and superconducting order of an unusual character. The antiphase order of the spin stripes decouples them from the charge stripes, which can be viewed as hole-doped, two-leg, spin- ladders. Established theory tells us that the pairing scale is comparable to the singlet-triplet excitation energy, , on the ladders. To achieve superconducting order, the pair correlations in neighboring ladders must develop phase order. In the presence of spin stripe order, antiphase Josephson coupling can lead to pair-density-wave superconductivity. Alternatively, in-phase superconductivity requires that the spin stripes have an energy gap, which empirically limits the coherent superconducting gap. Hence, superconducting order in the cuprates involves a compromise between the pairing scale, which is maximized at , and phase coherence, which is optimized at . To understand further experimental details, it is necessary to take account of the local variation in hole density resulting from dopant disorder and poor screening of long-range Coulomb interactions. At large hole doping, kinetic energy wins out over J, the regions of intertwined spin and charge correlations become sparse, and the superconductivity disappears. While there are a few experimental mysteries that remain to be resolved, I believe that this story captures the essence of the cuprates.
理解空穴掺杂的铜酸盐超导体中的电子配对一直是一个挑战，特别是因为它进化的“正常”状态是前所未有的。现在，经过三十年半的研究，包括广泛的实验表征，有可能描绘出一个清晰一致的铜酸盐故事。它首先将空穴掺杂到电荷转移绝缘体中，从而产生间隙状态。这些态表现出由最近邻Cu原子之间的反铁磁超交换J（真实空间相互作用）和掺杂空穴的动能之间的竞争所产生的伪间隙，在没有相互作用的情况下，这将导致扩展的布洛赫波态，其占据特征在倒易空间中。为了在冷却过程中形成一定程度的相干性，自旋和电荷相关性必须以协作的方式自组织。由此产生的出射秩序的一个具体例子是在La Ba CuO中观察到的自旋和电荷条纹。虽然条带有序性阻碍了体超导性，但它仍然发展出一种不同寻常的配对和超导有序性。自旋条纹的反相顺序使它们与电荷条纹解耦，电荷条纹可以被视为空穴掺杂的双腿自旋梯。已有的理论告诉我们，在阶梯上，配对尺度与单重激发能相当。为了实现超导有序，相邻阶梯中的对相关性必须发展为相序。在存在自旋条纹序的情况下，反相位约瑟夫逊耦合可以导致对密度波超导性。或者，同相超导性要求自旋条纹具有能隙，这在经验上限制了相干超导间隙。因此，铜酸盐中的超导顺序涉及在配对尺度和相位相干性之间的折衷，配对尺度在时最大化，相位相干性在时优化。为了进一步了解实验细节，有必要考虑由掺杂无序和长程库仑相互作用的不良屏蔽引起的空穴密度的局部变化。在大空穴掺杂时，动能战胜J，自旋和电荷相互交织的区域变得稀疏，超导性消失。虽然还有一些实验谜团有待解决，但我相信这个故事抓住了铜酸盐的本质。
{"title":"Cuprate superconductors as viewed through a striped lens","authors":"J. Tranquada","doi":"10.1080/00018732.2021.1935698","DOIUrl":"https://doi.org/10.1080/00018732.2021.1935698","url":null,"abstract":"Understanding the electron pairing in hole-doped cuprate superconductors has been a challenge, in particular because the “normal” state from which it evolves is unprecedented. Now, after three and a half decades of research, involving a wide range of experimental characterizations, it is possible to delineate a clear and consistent cuprate story. It starts with doping holes into a charge-transfer insulator, resulting in in-gap states. These states exhibit a pseudogap resulting from the competition between antiferromagnetic superexchange J between nearest-neighbor Cu atoms (a real-space interaction) and the kinetic energy of the doped holes, which, in the absence of interactions, would lead to extended Bloch-wave states whose occupancy is characterized in reciprocal space. To develop some degree of coherence on cooling, the spin and charge correlations must self-organize in a cooperative fashion. A specific example of resulting emergent order is that of spin and charge stripes, as observed in La Ba CuO . While stripe order frustrates bulk superconductivity, it nevertheless develops pairing and superconducting order of an unusual character. The antiphase order of the spin stripes decouples them from the charge stripes, which can be viewed as hole-doped, two-leg, spin- ladders. Established theory tells us that the pairing scale is comparable to the singlet-triplet excitation energy, , on the ladders. To achieve superconducting order, the pair correlations in neighboring ladders must develop phase order. In the presence of spin stripe order, antiphase Josephson coupling can lead to pair-density-wave superconductivity. Alternatively, in-phase superconductivity requires that the spin stripes have an energy gap, which empirically limits the coherent superconducting gap. Hence, superconducting order in the cuprates involves a compromise between the pairing scale, which is maximized at , and phase coherence, which is optimized at . To understand further experimental details, it is necessary to take account of the local variation in hole density resulting from dopant disorder and poor screening of long-range Coulomb interactions. At large hole doping, kinetic energy wins out over J, the regions of intertwined spin and charge correlations become sparse, and the superconductivity disappears. While there are a few experimental mysteries that remain to be resolved, I believe that this story captures the essence of the cuprates.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"69 1","pages":"437 - 509"},"PeriodicalIF":0.0,"publicationDate":"2020-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/00018732.2021.1935698","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47042105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-02DOI: 10.1080/00018732.2021.1876991
Yuto Ashida, Z. Gong, Masahito Ueda
A review is given on the foundations and applications of non-Hermitian classical and quantum physics. First, key theorems and central concepts in non-Hermitian linear algebra, including Jordan normal form, biorthogonality, exceptional points, pseudo-Hermiticity, and parity-time symmetry, are delineated in a pedagogical and mathematically coherent manner. Building on these, we provide an overview of how diverse classical systems, ranging from photonics, mechanics, electrical circuits, and acoustics to active matter, can be used to simulate non-Hermitian wave physics. In particular, we discuss rich and unique phenomena found therein, such as unidirectional invisibility, enhanced sensitivity, topological energy transfer, coherent perfect absorption, single-mode lasing, and robust biological transport. We then explain in detail how non-Hermitian operators emerge as an effective description of open quantum systems on the basis of the Feshbach projection approach and the quantum trajectory approach. We discuss their applications to physical systems relevant to a variety of fields, including atomic, molecular and optical physics, mesoscopic physics, and nuclear physics with emphasis on prominent phenomena and subjects in quantum regimes, such as quantum resonances, superradiance, the continuous quantum Zeno effect, quantum critical phenomena, Dirac spectra in quantum chromodynamics, and nonunitary conformal field theories. Finally, we introduce the notion of band topology in complex spectra of non-Hermitian systems and present their classifications by providing the proof, first given by this review in a complete manner, as well as a number of instructive examples. Other topics related to non-Hermitian physics, including nonreciprocal transport, speed limits, nonunitary quantum walk, are also reviewed.
{"title":"Non-Hermitian physics","authors":"Yuto Ashida, Z. Gong, Masahito Ueda","doi":"10.1080/00018732.2021.1876991","DOIUrl":"https://doi.org/10.1080/00018732.2021.1876991","url":null,"abstract":"A review is given on the foundations and applications of non-Hermitian classical and quantum physics. First, key theorems and central concepts in non-Hermitian linear algebra, including Jordan normal form, biorthogonality, exceptional points, pseudo-Hermiticity, and parity-time symmetry, are delineated in a pedagogical and mathematically coherent manner. Building on these, we provide an overview of how diverse classical systems, ranging from photonics, mechanics, electrical circuits, and acoustics to active matter, can be used to simulate non-Hermitian wave physics. In particular, we discuss rich and unique phenomena found therein, such as unidirectional invisibility, enhanced sensitivity, topological energy transfer, coherent perfect absorption, single-mode lasing, and robust biological transport. We then explain in detail how non-Hermitian operators emerge as an effective description of open quantum systems on the basis of the Feshbach projection approach and the quantum trajectory approach. We discuss their applications to physical systems relevant to a variety of fields, including atomic, molecular and optical physics, mesoscopic physics, and nuclear physics with emphasis on prominent phenomena and subjects in quantum regimes, such as quantum resonances, superradiance, the continuous quantum Zeno effect, quantum critical phenomena, Dirac spectra in quantum chromodynamics, and nonunitary conformal field theories. Finally, we introduce the notion of band topology in complex spectra of non-Hermitian systems and present their classifications by providing the proof, first given by this review in a complete manner, as well as a number of instructive examples. Other topics related to non-Hermitian physics, including nonreciprocal transport, speed limits, nonunitary quantum walk, are also reviewed.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"69 1","pages":"249 - 435"},"PeriodicalIF":0.0,"publicationDate":"2020-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/00018732.2021.1876991","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44599615","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-04-02DOI: 10.1080/00018732.2020.1854965
M. te Vrugt, H. Löwen, R. Wittkowski
Classical dynamical density functional theory (DDFT) is one of the cornerstones of modern statistical mechanics. It is an extension of the highly successful method of classical density functional theory (DFT) to nonequilibrium systems. Originally developed for the treatment of simple and complex fluids, DDFT is now applied in fields as diverse as hydrodynamics, materials science, chemistry, biology, and plasma physics. In this review, we give a broad overview over classical DDFT. We explain its theoretical foundations and the ways in which it can be derived. The relations between the different forms of deterministic and stochastic DDFT as well as between DDFT and related theories, such as quantum-mechanical time-dependent DFT, mode coupling theory, and phase field crystal models, are clarified. Moreover, we discuss the wide spectrum of extensions of DDFT, which covers methods with additional order parameters (like extended DDFT), exact approaches (like power functional theory), and systems with more complex dynamics (like active matter). Finally, the large variety of applications, ranging from fluid mechanics and polymer physics to solidification, pattern formation, biophysics, and electrochemistry, is presented.
{"title":"Classical dynamical density functional theory: from fundamentals to applications","authors":"M. te Vrugt, H. Löwen, R. Wittkowski","doi":"10.1080/00018732.2020.1854965","DOIUrl":"https://doi.org/10.1080/00018732.2020.1854965","url":null,"abstract":"Classical dynamical density functional theory (DDFT) is one of the cornerstones of modern statistical mechanics. It is an extension of the highly successful method of classical density functional theory (DFT) to nonequilibrium systems. Originally developed for the treatment of simple and complex fluids, DDFT is now applied in fields as diverse as hydrodynamics, materials science, chemistry, biology, and plasma physics. In this review, we give a broad overview over classical DDFT. We explain its theoretical foundations and the ways in which it can be derived. The relations between the different forms of deterministic and stochastic DDFT as well as between DDFT and related theories, such as quantum-mechanical time-dependent DFT, mode coupling theory, and phase field crystal models, are clarified. Moreover, we discuss the wide spectrum of extensions of DDFT, which covers methods with additional order parameters (like extended DDFT), exact approaches (like power functional theory), and systems with more complex dynamics (like active matter). Finally, the large variety of applications, ranging from fluid mechanics and polymer physics to solidification, pattern formation, biophysics, and electrochemistry, is presented.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"69 1","pages":"121 - 247"},"PeriodicalIF":0.0,"publicationDate":"2020-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/00018732.2020.1854965","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43101280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-04DOI: 10.1080/00018732.2023.2190730
J. Langer
The thermodynamic dislocation theory (TDT) is based on two fundamental but unconventional assumptions: first, that the dislocations in a persistently deforming crystalline solid must obey the second law of thermodynamics and thus be described by an effective temperature; and second, that the controlling time scale for deformation of these systems is the inverse of the thermally activated rate at which entangled dislocation lines become unpinned from each other. By use of these first-principles concepts and comparisons with experimental data, I show that this theory achieves new, usefully predictive understandings of strain hardening, yield stresses, shear banding, and brittle and ductile fracture. I argue that it opens new directions for research.
{"title":"Statistical thermodynamics of dislocations in solids","authors":"J. Langer","doi":"10.1080/00018732.2023.2190730","DOIUrl":"https://doi.org/10.1080/00018732.2023.2190730","url":null,"abstract":"The thermodynamic dislocation theory (TDT) is based on two fundamental but unconventional assumptions: first, that the dislocations in a persistently deforming crystalline solid must obey the second law of thermodynamics and thus be described by an effective temperature; and second, that the controlling time scale for deformation of these systems is the inverse of the thermally activated rate at which entangled dislocation lines become unpinned from each other. By use of these first-principles concepts and comparisons with experimental data, I show that this theory achieves new, usefully predictive understandings of strain hardening, yield stresses, shear banding, and brittle and ductile fracture. I argue that it opens new directions for research.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"70 1","pages":"445 - 467"},"PeriodicalIF":0.0,"publicationDate":"2020-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42691892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-02DOI: 10.1080/00018732.2020.1837833
M. Dressel, S. Tomi'c
This review provides a perspective on recent developments and their implications for our understanding of novel quantum phenomena in the physics of two-dimensional organic solids. We concentrate on the phase transitions and collective response in the charge sector, the importance of coupling of electronic and lattice degrees of freedom and stress an intriguing role of disorder. After a brief introduction to low-dimensional organic solids and their crystallographic structures, we focus on the dimensionality and interactions and emergent quantum phenomena. Important topics of current research in organic matter with sizeable electronic correlations are Mott metal-insulator phase transitions, charge order and ferroelectricity. Highly frustrated two-dimensional systems are established model compounds for studying the quantum spin liquid state and the competition with magnetic long-range order. There are also unique examples of quantum disordered state of magnetic and electric dipoles. Representative experimental results are complemented by current theoretical approaches.
{"title":"Molecular quantum materials: electronic phases and charge dynamics in two-dimensional organic solids","authors":"M. Dressel, S. Tomi'c","doi":"10.1080/00018732.2020.1837833","DOIUrl":"https://doi.org/10.1080/00018732.2020.1837833","url":null,"abstract":"This review provides a perspective on recent developments and their implications for our understanding of novel quantum phenomena in the physics of two-dimensional organic solids. We concentrate on the phase transitions and collective response in the charge sector, the importance of coupling of electronic and lattice degrees of freedom and stress an intriguing role of disorder. After a brief introduction to low-dimensional organic solids and their crystallographic structures, we focus on the dimensionality and interactions and emergent quantum phenomena. Important topics of current research in organic matter with sizeable electronic correlations are Mott metal-insulator phase transitions, charge order and ferroelectricity. Highly frustrated two-dimensional systems are established model compounds for studying the quantum spin liquid state and the competition with magnetic long-range order. There are also unique examples of quantum disordered state of magnetic and electric dipoles. Representative experimental results are complemented by current theoretical approaches.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"69 1","pages":"1 - 120"},"PeriodicalIF":0.0,"publicationDate":"2020-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/00018732.2020.1837833","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48099038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-03DOI: 10.1080/00018732.2019.1650450
R. D’Souza, J. G'omez-Gardenes, J. Nagler, A. Arenas
The emergence of large-scale connectivity and synchronization are crucial to the structure, function and failure of many complex socio-technical networks. Thus, there is great interest in analyzing phase transitions to large-scale connectivity and to global synchronization, including how to enhance or delay the onset. These phenomena are traditionally studied as second-order phase transitions where, at the critical threshold, the order parameter increases rapidly but continuously. In 2009, an extremely abrupt transition was found for a network growth process where links compete for addition in an attempt to delay percolation. This observation of ‘explosive percolation’ was ultimately revealed to be a continuous transition in the thermodynamic limit, yet with very atypical finite-size scaling, and it started a surge of work on explosive phenomena and their consequences. Many related models are now shown to yield discontinuous percolation transitions and even hybrid transitions. Explosive percolation enables many other features such as multiple giant components, modular structures, discrete scale invariance and non-self-averaging, relating to properties found in many real phenomena such as explosive epidemics, electric breakdowns and the emergence of molecular life. Models of explosive synchronization provide an analytic framework for the dynamics of abrupt transitions and reveal the interplay between the distribution in natural frequencies and the network structure, with applications ranging from epileptic seizures to waking from anesthesia. Here we review the vast literature on explosive phenomena in networked systems and synthesize the fundamental connections between models and survey the application areas. We attempt to classify explosive phenomena based on underlying mechanisms and to provide a coherent overview and perspective for future research to address the many vital questions that remained unanswered.
{"title":"Explosive phenomena in complex networks","authors":"R. D’Souza, J. G'omez-Gardenes, J. Nagler, A. Arenas","doi":"10.1080/00018732.2019.1650450","DOIUrl":"https://doi.org/10.1080/00018732.2019.1650450","url":null,"abstract":"The emergence of large-scale connectivity and synchronization are crucial to the structure, function and failure of many complex socio-technical networks. Thus, there is great interest in analyzing phase transitions to large-scale connectivity and to global synchronization, including how to enhance or delay the onset. These phenomena are traditionally studied as second-order phase transitions where, at the critical threshold, the order parameter increases rapidly but continuously. In 2009, an extremely abrupt transition was found for a network growth process where links compete for addition in an attempt to delay percolation. This observation of ‘explosive percolation’ was ultimately revealed to be a continuous transition in the thermodynamic limit, yet with very atypical finite-size scaling, and it started a surge of work on explosive phenomena and their consequences. Many related models are now shown to yield discontinuous percolation transitions and even hybrid transitions. Explosive percolation enables many other features such as multiple giant components, modular structures, discrete scale invariance and non-self-averaging, relating to properties found in many real phenomena such as explosive epidemics, electric breakdowns and the emergence of molecular life. Models of explosive synchronization provide an analytic framework for the dynamics of abrupt transitions and reveal the interplay between the distribution in natural frequencies and the network structure, with applications ranging from epileptic seizures to waking from anesthesia. Here we review the vast literature on explosive phenomena in networked systems and synthesize the fundamental connections between models and survey the application areas. We attempt to classify explosive phenomena based on underlying mechanisms and to provide a coherent overview and perspective for future research to address the many vital questions that remained unanswered.","PeriodicalId":7373,"journal":{"name":"Advances in Physics","volume":"68 1","pages":"123 - 223"},"PeriodicalIF":0.0,"publicationDate":"2019-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/00018732.2019.1650450","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49153517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-04-03DOI: 10.1080/00018732.2019.1590295
Hengxing Xu, Miaosheng Wang, Zhi-Gang Yu, Kai Wang, Bin Hu
Magnetic field can influence photoluminescence, electroluminescence, photocurrent, injection current, and dielectric constant in organic materials, organic–inorganic hybrids, and nanoparticles at room temperature by re-distributing spin populations, generating emerging phenomena including magneto-photoluminescence, magneto-electroluminescence, magneto-photocurrent, magneto-electrical current, and magneto-dielectrics. These so-called intrinsic magnetic field effects (MFEs) can be observed in linear and non-linear regimes under one-photon and two-photon excitations in both low- and high-orbital materials. On the other hand, spin injection can be realized to influence spin-dependent excited states and electrical conduction via organic/ferromagnetic hybrid interface, leading to extrinsic MFEs. In last decades, MFEs have been serving as a unique experimental tool to reveal spin-dependent processes in excited states, electrical transport, and polarization in light-emitting diodes, solar cells, memories, field-effect transistors, and lasing devices. Very recently, they provide critical understanding on the operating mechanisms in advanced organic optoelectronic materials such as thermally activated delayed fluorescence light-emitting materials, non-fullerene photovoltaic bulk-heterojunctions, and organic–inorganic hybrid perovskites. While MFEs were initially realized by operating spin states in organic semiconducting materials with delocalized π electrons under negligible orbital momentum, recent studies indicate that MFEs can also be achieved under strong orbital momentum and Rashba effect in light emission, photovoltaics, and dielectric polarization. The transition of MFEs from the spin regime to the orbital regime creates new opportunities to versatilely control light-emitting, photovoltaic, lasing, and dielectric properties by using long-range Coulomb and short-range spin–spin interactions between orbitals. This article reviews recent progress on MFEs with the focus on elucidating fundamental mechanisms to control optical, electrical, optoelectronic, and polarization behaviors via spin-dependent excited states, electrical transport, and dielectric polarization. In this article both representative experimental results and mainstream theoretical models are presented to understand MFEs in the spin and orbital regimes for organic materials, nanoparticles, and organic–inorganic hybrids under linear and non-linear excitation regimes with emphasis on underlying spin-dependent processes.
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