Metal-Insulator Transitions

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Applied Physics General".

Deadline for manuscript submissions: closed (30 November 2018) | Viewed by 34132

Special Issue Editors

Physics Department, Northeastern University, Boston, MA 02115, USA
Interests: metal-insulator transitions; condensed matter experiment
Institute of Solid State Physics, Russian Academy of Sciences Chernogolovka, Moscow District, 2 Academician Ossipyan str., 142432 Moscow, Russia
Interests: quantum transport; two-dimensional electron systems; electron-electron interactions; phase transitions; nanostructures

Special Issue Information

Dear Colleagues,

The distinction between metals and insulators seemed simple: If the chemical potential lies within the conduction band, the system is a metal; if it lies between the conduction and the valence bands, the system is an insulator. However, after Anderson and Mott's concepts of localization, it turned out that the situation is not that simple, and that the strong disorder can cause localization, even in three-dimensional metals. Especially intriguing is the situation in disordered two-dimensional (2D) electron systems. According to the scaling theory of localization, the ever-present randomness causes noninteracting 2D electrons to always be localized in the limit of zero temperature. However, new evidence has emerged within the past two decades indicating a transition from insulating to metallic phase in two-dimensional systems of strongly interacting electrons.

The aim of this Special Issue is to attract world-leading researchers in the area of metal-insulator transitions to highlight the latest exciting developments as well as to discuss the underlying physics. The accepted contributions will include experimental results and theoretical considerations.

Prof. Sergey Kravchenko
Prof. Alexander Shashkin
Guest Editors

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Keywords

  • disorder
  • randomness
  • electron-electron interactions
  • scaling theory
  • Anderson transition
  • Mott transition

Published Papers (8 papers)

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Research

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14 pages, 2717 KiB  
Article
Magnetic Shell Structure of 2D-Trapped Fermi Gases in the Flat-Band Lieb Lattices
by Joo-Hyeok Jeong, Hyunjoon Park, Dongkyu Kim and Dong-Hee Kim
Appl. Sci. 2019, 9(3), 365; https://doi.org/10.3390/app9030365 - 22 Jan 2019
Cited by 2 | Viewed by 2872
Abstract
We investigate the magnetic shell structure of repulsively interacting two-component Fermi gases trapped in a two-dimensional harmonic potential and loaded on the optical Lieb lattices. We employ the real-space dynamical mean-field theory (R-DMFT) to explicitly consider the trap potential in a self-consistent way. [...] Read more.
We investigate the magnetic shell structure of repulsively interacting two-component Fermi gases trapped in a two-dimensional harmonic potential and loaded on the optical Lieb lattices. We employ the real-space dynamical mean-field theory (R-DMFT) to explicitly consider the trap potential in a self-consistent way. Computing the profiles of particle density and local magnetization across the lattice sites in the trap, we find that the incompressible core with ferrimagnetic ordering appears with the density plateau at the trap center, which is surrounded by the shell of the normal metallic phase. We examine the incompressibility of the core by adding more particles and creating the higher spin-population imbalance. While the core area expands from the outer shell with added particles and increased polarization, the excess particles are prohibited from going inside the core, and thus the density plateau is unchanged at the half-filling with the same magnetic ordering. In addition, we find that the feature of the phase separation differs with the sublattices, where the interstitial sites causing the flat band dispersion shows the signature of the abrupt transition in the density and magnetization at the boundary between the core and surrounding shells. Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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11 pages, 2491 KiB  
Article
Strain Induced Metal–Insulator Transition of Magnetic SrRuO3 Single Layer in SrRuO3/SrTiO3 Superlattice
by Angus Huang, Sheng-Hsiung Hung and Horng-Tay Jeng
Appl. Sci. 2018, 8(11), 2151; https://doi.org/10.3390/app8112151 - 03 Nov 2018
Cited by 5 | Viewed by 3839
Abstract
Ferromagnetic phase in a two-dimensional system plays an important role not only in applications but also in studies of phase transition theory. Among numerous ferromagnetic materials, Sr Ru O 3 is famous for its half-metallicity, itinerant ferromagnetism and non-Fermi liquid metalicity. Single layer [...] Read more.
Ferromagnetic phase in a two-dimensional system plays an important role not only in applications but also in studies of phase transition theory. Among numerous ferromagnetic materials, Sr Ru O 3 is famous for its half-metallicity, itinerant ferromagnetism and non-Fermi liquid metalicity. Single layer Sr Ru O 3 in Sr Ru O 3 / Sr Ti O 3 (SRO/STO) superlattice has been predicted as a two-dimensional half-metallic ferromagnetic system based on density functional theory (DFT). However, experiments show that metal–insulator transition associated with ferro–antiferromagnetism (FM–AFM) transition occurs when the thickness of SRO is less than 4 u.c. Combining DFT calculations with Monte Carlo simulations, we demonstrate in this work that the bulk ferromagnetic metallicity can be realized in single layer SRO in SRO/STO superlattice by manipulating the strain effect to trigger the metal–insulator transition, achieving two-dimensional (2D) half-metallic SRO thin film beyond the experimental observation of AFM insulator.Our results pave a new route to fulfill the ultrathin spin-polarized-2D electron gas (SP-2DEG). Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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11 pages, 1763 KiB  
Article
Enhanced Thermochromic Properties of Vanadium Dioxide (VO2)/Glass Heterostructure by Inserting a Zr-Based Thin Film Metallic Glasses (Cu50Zr50) Buffer Layer
by Chaoyang Kang, Cong Zhang, Yingxue Yao, Yuanjun Yang, Haitao Zong, Liwei Zhang and Ming Li
Appl. Sci. 2018, 8(10), 1751; https://doi.org/10.3390/app8101751 - 28 Sep 2018
Cited by 15 | Viewed by 3725
Abstract
Vanadium dioxide (VO2) with reversible metal–insulator transition (MIT) is one of the most promising energy-efficient materials. Especially for VO2-based smart windows, the visible transmittance and solar modulation ability are the most critical parameters. However, VO2 thin films that [...] Read more.
Vanadium dioxide (VO2) with reversible metal–insulator transition (MIT) is one of the most promising energy-efficient materials. Especially for VO2-based smart windows, the visible transmittance and solar modulation ability are the most critical parameters. However, VO2 thin films that are directly deposited onto glass substrates are of poor crystallinity and MIT performance, limiting the practical applications of VO2/glass heterostructures. In this paper, a buffer layer of Cu50Zr50 was introduced to build a novel Zr-based thin film metallic glass (VO2/Cu50Zr50/glass) with multilayer structures for thermochromic applications. It is observed that the insertion of a Cu50Zr50 buffer layer with appropriate thickness results in a clear enhancement of crystalline quality and MIT performance in the VO2/Cu50Zr50/glass thin films, compared with the single-layer VO2/glass thin films. Moreover, the VO2/Cu50Zr50/glass bi-layer films exhibit better optical performance with enhanced solar modulation ability (ΔTsol = 14.3%) and a high visible transmittance (Tvis = 52.3%), which represents a good balance between ΔTsol and Tvis for smart window applications. Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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Review

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13 pages, 1350 KiB  
Review
Recent Developments in the Field of the Metal-Insulator Transition in Two Dimensions
by Alexander A. Shashkin and Sergey V. Kravchenko
Appl. Sci. 2019, 9(6), 1169; https://doi.org/10.3390/app9061169 - 19 Mar 2019
Cited by 26 | Viewed by 4003
Abstract
We review the latest developments in the field of the metal-insulator transition in strongly-correlated two-dimensional electron systems. Particular attention is given to recent discoveries of a sliding quantum electron solid and interaction-induced spectrum flattening at the Fermi level in high-quality silicon-based structures. Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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13 pages, 383 KiB  
Review
Hidden Charge Orders in Low-Dimensional Mott Insulators
by Serena Fazzini and Arianna Montorsi
Appl. Sci. 2019, 9(4), 784; https://doi.org/10.3390/app9040784 - 22 Feb 2019
Cited by 1 | Viewed by 3010
Abstract
The opening of a charge gap driven by interaction is a fingerprint of the transition to a Mott insulating phase. In strongly correlated low-dimensional quantum systems, it can be associated to the ordering of hidden non-local operators. For Fermionic 1D models, in the [...] Read more.
The opening of a charge gap driven by interaction is a fingerprint of the transition to a Mott insulating phase. In strongly correlated low-dimensional quantum systems, it can be associated to the ordering of hidden non-local operators. For Fermionic 1D models, in the presence of spin–charge separation and short-ranged interaction, a bosonization analysis proves that such operators are the parity and/or string charge operators. In fact, a finite fractional non-local parity charge order is also capable of characterizing some two-dimensional Mott insulators, in both the Fermionic and the bosonic cases. When string charge order takes place in 1D, degenerate edge modes with fractional charge appear, peculiar of a topological insulator. In this article, we review the above framework, and we test it to investigate through density-matrix-renormalization-group (DMRG) numerical analysis the robustness of both hidden orders at half-filling in the 1D Fermionic Hubbard model extended with long range density-density interaction. The preliminary results obtained at finite size including several neighbors in the case of dipolar, screened and unscreened repulsive Coulomb interactions, confirm the phase diagram of the standard extended Hubbard model. Besides the trivial Mott phase, the bond ordered and charge density wave insulating phases are also not destroyed by longer ranged interaction, and still manifest hidden non-local orders. Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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20 pages, 14871 KiB  
Review
Metal-to-Insulator Transition in Ultrathin Manganite Heterostructures
by Zhaoliang Liao and Jiandi Zhang
Appl. Sci. 2019, 9(1), 144; https://doi.org/10.3390/app9010144 - 03 Jan 2019
Cited by 23 | Viewed by 8792
Abstract
Thickness-driven phase transitions have been widely observed in many correlated transition metal oxides materials. One of the important topics is the thickness-driven metal to insulator transition in half-metal La2/3Sr1/3MnO3 (LSMO) thin films, which has attracted great attention in [...] Read more.
Thickness-driven phase transitions have been widely observed in many correlated transition metal oxides materials. One of the important topics is the thickness-driven metal to insulator transition in half-metal La2/3Sr1/3MnO3 (LSMO) thin films, which has attracted great attention in the past few decades. In this article, we review research on the nature of the metal-to-insulator (MIT) transition in LSMO ultrathin films. We discuss in detail the proposed mechanisms, the progress made up to date, and the key issues existing in understanding the related MIT. We also discuss MIT in other correlated oxide materials as a comparison that also has some implications for understanding the origin of MIT. Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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74 pages, 3586 KiB  
Review
Systematic Quantum Cluster Typical Medium Method for the Study of Localization in Strongly Disordered Electronic Systems
by Hanna Terletska, Yi Zhang, Ka-Ming Tam, Tom Berlijn, Liviu Chioncel, N. S. Vidhyadhiraja and Mark Jarrell
Appl. Sci. 2018, 8(12), 2401; https://doi.org/10.3390/app8122401 - 26 Nov 2018
Cited by 19 | Viewed by 4419
Abstract
Great progress has been made in recent years towards understanding the properties of disordered electronic systems. In part, this is made possible by recent advances in quantum effective medium methods which enable the study of disorder and electron-electronic interactions on equal footing. They [...] Read more.
Great progress has been made in recent years towards understanding the properties of disordered electronic systems. In part, this is made possible by recent advances in quantum effective medium methods which enable the study of disorder and electron-electronic interactions on equal footing. They include dynamical mean-field theory and the Coherent Potential Approximation, and their cluster extension, the dynamical cluster approximation. Despite their successes, these methods do not enable the first-principles study of the strongly disordered regime, including the effects of electronic localization. The main focus of this review is the recently developed typical medium dynamical cluster approximation for disordered electronic systems. This method has been constructed to capture disorder-induced localization and is based on a mapping of a lattice onto a quantum cluster embedded in an effective typical medium, which is determined self-consistently. Unlike the average effective medium-based methods mentioned above, typical medium-based methods properly capture the states localized by disorder. The typical medium dynamical cluster approximation not only provides the proper order parameter for Anderson localized states, but it can also incorporate the full complexity of Density-Functional Theory (DFT)-derived potentials into the analysis, including the effect of multiple bands, non-local disorder, and electron-electron interactions. After a brief historical review of other numerical methods for disordered systems, we discuss coarse-graining as a unifying principle for the development of translationally invariant quantum cluster methods. Together, the Coherent Potential Approximation, the Dynamical Mean-Field Theory and the Dynamical Cluster Approximation may be viewed as a single class of approximations with a much-needed small parameter of the inverse cluster size which may be used to control the approximation. We then present an overview of various recent applications of the typical medium dynamical cluster approximation to a variety of models and systems, including single and multiband Anderson model, and models with local and off-diagonal disorder. We then present the application of the method to realistic systems in the framework of the DFT and demonstrate that the resulting method can provide a systematic first-principles method validated by experiment and capable of making experimentally relevant predictions. We also discuss the application of the typical medium dynamical cluster approximation to systems with disorder and electron-electron interactions. Most significantly, we show that in the limits of strong disorder and weak interactions treated perturbatively, that the phenomena of 3D localization, including a mobility edge, remains intact. However, the metal-insulator transition is pushed to larger disorder values by the local interactions. We also study the limits of strong disorder and strong interactions capable of producing moment formation and screening, with a non-perturbative local approximation. Here, we find that the Anderson localization quantum phase transition is accompanied by a quantum-critical fan in the energy-disorder phase diagram. Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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10 pages, 4281 KiB  
Review
New Reentrant Insulating Phases in Strongly Interacting 2D Systems with Low Disorder
by Richard L. J. Qiu, Chieh-Wen Liu, Shuhao Liu and Xuan P. A. Gao
Appl. Sci. 2018, 8(10), 1909; https://doi.org/10.3390/app8101909 - 14 Oct 2018
Cited by 4 | Viewed by 2859
Abstract
The metal-insulator transition (MIT) in two-dimension (2D) was discovered by Kravchenko et al. more than two decades ago in strongly interacting 2D electrons residing in a Si-metal-oxide-semiconductor field-effect transistor (Si-MOSFET). Its origin remains unresolved. Recently, low magnetic field reentrant insulating phases (RIPs), which [...] Read more.
The metal-insulator transition (MIT) in two-dimension (2D) was discovered by Kravchenko et al. more than two decades ago in strongly interacting 2D electrons residing in a Si-metal-oxide-semiconductor field-effect transistor (Si-MOSFET). Its origin remains unresolved. Recently, low magnetic field reentrant insulating phases (RIPs), which dwell between the zero-field (B = 0) metallic state and the integer quantum Hall (QH) states where the Landau-level filling factor υ > 1, have been observed in strongly correlated 2D GaAs hole systems with a large interaction parameter, rs, (~20–40) and a high purity. A new complex phase diagram was proposed, which includes zero-field MIT, low magnetic field RIPs, integer QH states, fractional QH states, high field RIPs and insulating phases (HFIPs) with υ < 1 in which the insulating phases are explained by the formation of a Wigner crystal. Furthermore, evidence of new intermediate phases was reported. This review article serves the purpose of summarizing those recent experimental findings and theoretical endeavors to foster future research efforts. Full article
(This article belongs to the Special Issue Metal-Insulator Transitions)
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