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Special Issue "Metal-Insulator Transition"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 June 2017)

Special Issue Editor

Guest Editor
Dr. Horng-Tay Jeng

Department of Physics, National Tsing-Hua University, Taiwan
Website | E-Mail

Special Issue Information

Dear Colleagues,

Metal-insulator transition, characterized by an abrupt change in the electrical conductivity from a metallic to an insulating phase, is an important phenomenon, widely observed in various condensed-matter systems. It is frequently found in transition-metal oxides and semiconductors, though it can also be found in emergent materials, such as two-dimensional and topological materials. Because of the huge resistivity changes, even over tens of orders of magnitude, metal-insulator transition, not only shows great importance in fundamental physics and material research, but also provides great potentials in nanotechnology. These transitions can be manipulated by tuning various ambient parameters, such as pressure, doping, strain, and so on. For two-dimensional layered systems, there are extra degrees of freedom to achieve the metal-insulator transition by controlling the number of layers and/or shaping the layer edges. Intrinsic parameters, such as the strong electron-electron correlation and the spin-orbit coupling strength, play a crucial role in band gap formation in transition-metal oxides and topological materials, respectively. In the former case, the insulating phase, caused by the correlation effects, is categorized as Mott insulators, while, in the latter case, the strong spin-orbit coupling strength may lead to the metallic topological states in topological insulators and semiconductors. As such, this Special Issue is dedicated to achieve a better understanding on the metal-insulator transitions in all kinds of materials and nanotechnology applications.

Prof. Dr. Horng-Tay Jeng
Guest Editor

Manuscript Submission Information

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Keywords

  • Metal-insulator transition
  • transition-metal oxides
  • 2-dimensional materials
  • topological materials
  • strong electron-electron correlation
  • spin-orbit coupling
  • Mott insulators
  • topological insulators
  • topological semiconductors
  • nanotechnology

Published Papers (9 papers)

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Research

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Open AccessFeature PaperArticle Monoclinic 122-Type BaIr2Ge2 with a Channel Framework: A Structural Connection between Clathrate and Layered Compounds
Materials 2017, 10(7), 818; doi:10.3390/ma10070818
Received: 26 June 2017 / Revised: 8 July 2017 / Accepted: 10 July 2017 / Published: 18 July 2017
Cited by 1 | PDF Full-text (2419 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A new 122-type phase, monoclinic BaIr2Ge2 is successfully synthesized by arc melting; X-ray diffraction and scanning electron microscopy are used to purify the phase and determine its crystal structure. BaIr2Ge2 adopts a clathrate-like channel framework structure of
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A new 122-type phase, monoclinic BaIr2Ge2 is successfully synthesized by arc melting; X-ray diffraction and scanning electron microscopy are used to purify the phase and determine its crystal structure. BaIr2Ge2 adopts a clathrate-like channel framework structure of the monoclinic BaRh2Si2-type, with space group P21/c. Structural comparisons of clathrate, ThCr2Si2, CaBe2Ge2, and BaRh2Si2 structure types indicate that BaIr2Ge2 can be considered as an intermediate between clathrate and layered compounds. Magnetic measurements show it to be diamagnetic and non-superconducting down to 1.8 K. Different from many layered or clathrate compounds, monoclinic BaIr2Ge2 displays a metallic resistivity. Electronic structure calculations performed for BaIr2Ge2 support its observed structural stability and physical properties. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Open AccessFeature PaperArticle Generalized GW+Boltzmann Approach for the Description of Ultrafast Electron Dynamics in Topological Insulators
Materials 2017, 10(7), 810; doi:10.3390/ma10070810
Received: 27 June 2017 / Revised: 27 June 2017 / Accepted: 11 July 2017 / Published: 17 July 2017
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Abstract
Quantum-phase transitions between trivial insulators and topological insulators differ from ordinary metal-insulator transitions in that they arise from the inversion of the bulk band structure due to strong spin–orbit coupling. Such topological phase transitions are unique in nature as they lead to the
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Quantum-phase transitions between trivial insulators and topological insulators differ from ordinary metal-insulator transitions in that they arise from the inversion of the bulk band structure due to strong spin–orbit coupling. Such topological phase transitions are unique in nature as they lead to the emergence of topological surface states which are characterized by a peculiar spin texture that is believed to play a central role in the generation and manipulation of dissipationless surface spin currents on ultrafast timescales. Here, we provide a generalized G W +Boltzmann approach for the description of ultrafast dynamics in topological insulators driven by electron–electron and electron–phonon scatterings. Taking the prototypical insulator Bi 2 Te 3 as an example, we test the robustness of our approach by comparing the theoretical prediction to results of time- and angle-resolved photoemission experiments. From this comparison, we are able to demonstrate the crucial role of the excited spin texture in the subpicosecond relaxation of transient electrons, as well as to accurately obtain the magnitude and strength of electron–electron and electron–phonon couplings. Our approach could be used as a generalized theory for three-dimensional topological insulators in the bulk-conducting transport regime, paving the way for the realization of a unified theory of ultrafast dynamics in topological materials. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Open AccessFeature PaperArticle Weak Localization and Antilocalization in Topological Materials with Impurity Spin-Orbit Interactions
Materials 2017, 10(7), 807; doi:10.3390/ma10070807
Received: 14 June 2017 / Revised: 3 July 2017 / Accepted: 10 July 2017 / Published: 15 July 2017
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Abstract
Topological materials have attracted considerable experimental and theoretical attention. They exhibit strong spin-orbit coupling both in the band structure (intrinsic) and in the impurity potentials (extrinsic), although the latter is often neglected. In this work, we discuss weak localization and antilocalization of massless
[...] Read more.
Topological materials have attracted considerable experimental and theoretical attention. They exhibit strong spin-orbit coupling both in the band structure (intrinsic) and in the impurity potentials (extrinsic), although the latter is often neglected. In this work, we discuss weak localization and antilocalization of massless Dirac fermions in topological insulators and massive Dirac fermions in Weyl semimetal thin films, taking into account both intrinsic and extrinsic spin-orbit interactions. The physics is governed by the complex interplay of the chiral spin texture, quasiparticle mass, and scalar and spin-orbit scattering. We demonstrate that terms linear in the extrinsic spin-orbit scattering are generally present in the Bloch and momentum relaxation times in all topological materials, and the correction to the diffusion constant is linear in the strength of the extrinsic spin-orbit. In topological insulators, which have zero quasiparticle mass, the terms linear in the impurity spin-orbit coupling lead to an observable density dependence in the weak antilocalization correction. They produce substantial qualitative modifications to the magnetoconductivity, differing greatly from the conventional Hikami-Larkin-Nagaoka formula traditionally used in experimental fits, which predicts a crossover from weak localization to antilocalization as a function of the extrinsic spin-orbit strength. In contrast, our analysis reveals that topological insulators always exhibit weak antilocalization. In Weyl semimetal thin films having intermediate to large values of the quasiparticle mass, we show that extrinsic spin-orbit scattering strongly affects the boundary of the weak localization to antilocalization transition. We produce a complete phase diagram for this transition as a function of the mass and spin-orbit scattering strength. Throughout the paper, we discuss implications for experimental work, and, at the end, we provide a brief comparison with transition metal dichalcogenides. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Open AccessArticle Anderson Insulators in Self-Assembled Gold Nanoparticles Thin Films: Single Electron Hopping between Charge Puddles Originated from Disorder
Materials 2017, 10(6), 645; doi:10.3390/ma10060645
Received: 26 April 2017 / Revised: 7 June 2017 / Accepted: 8 June 2017 / Published: 12 June 2017
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Abstract
The Anderson insulating states in Au nanoparticle assembly are identified and studied under the application of magnetic fields and gate voltages. When the inter-nanoparticle tunneling resistance is smaller than the quantum resistance, the system showing zero Mott gap can be insulating at very
[...] Read more.
The Anderson insulating states in Au nanoparticle assembly are identified and studied under the application of magnetic fields and gate voltages. When the inter-nanoparticle tunneling resistance is smaller than the quantum resistance, the system showing zero Mott gap can be insulating at very low temperature. In contrast to Mott insulators, Anderson insulators exhibit great negative magnetoresistance, inferring charge delocalization in a strong magnetic field. When probed by the electrodes spaced by ~200 nm, they also exhibit interesting gate-modulated current similar to the multi-dot single electron transistors. These results reveal the formation of charge puddles due to the interplay of disorder and quantum interference at low temperatures. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Open AccessArticle Influence of Discharge Current on Phase Transition Properties of High Quality Polycrystalline VO2 Thin Film Fabricated by HiPIMS
Materials 2017, 10(6), 633; doi:10.3390/ma10060633
Received: 29 April 2017 / Revised: 4 June 2017 / Accepted: 6 June 2017 / Published: 9 June 2017
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Abstract
To fabricate high-quality polycrystalline VO2 thin film with a metal–insulator transition (MIT) temperature less than 50 °C, high-power impulse magnetron sputtering with different discharge currents was employed in this study. The as-deposited VO2 films were characterized by a four-point probe resistivity
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To fabricate high-quality polycrystalline VO2 thin film with a metal–insulator transition (MIT) temperature less than 50 °C, high-power impulse magnetron sputtering with different discharge currents was employed in this study. The as-deposited VO2 films were characterized by a four-point probe resistivity measurement system, visible-near infrared (IR) transmittance spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The resistivity results revealed that all the as-deposited films had a high resistance change in the phase transition process, and the MIT temperature decreased with the increased discharge current, where little deterioration in the phase transition properties, such as the resistance and transmittance changes, could be found. Additionally, XRD patterns at various temperatures exhibited that some reverse deformations that existed in the MIT process of the VO2 film, with a large amount of preferred crystalline orientations. The decrease of the MIT temperature with little deterioration on phase transition properties could be attributed to the reduction of the preferred grain orientations. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Open AccessArticle Switching VO2 Single Crystals and Related Phenomena: Sliding Domains and Crack Formation
Materials 2017, 10(5), 554; doi:10.3390/ma10050554
Received: 24 April 2017 / Revised: 9 May 2017 / Accepted: 11 May 2017 / Published: 19 May 2017
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Abstract
VO2 is the prototype material for insulator–metal transition (IMT). Its transition at TIMT = 340 K is fast and consists of a large resistance jump (up to approximately five orders of magnitude), a large change in its optical properties in the
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VO2 is the prototype material for insulator–metal transition (IMT). Its transition at TIMT = 340 K is fast and consists of a large resistance jump (up to approximately five orders of magnitude), a large change in its optical properties in the visible range, and symmetry change from monoclinic to tetragonal (expansion by 1% along the tetragonal c-axis and 0.5% contraction in the perpendicular direction). It is a candidate for potential applications such as smart windows, fast optoelectronic switches, and field-effect transistors. The change in optical properties at the IMT allows distinguishing between the insulating and the metallic phases in the mixed state. Static or dynamic domain patterns in the mixed-state of self-heated single crystals during electric-field induced switching are in strong contrast with the percolative nature of the mixed state in switching VO2 films. The most impressive effect—so far unique to VO2—is the sliding of narrow semiconducting domains within a metallic background in the positive sense of the electric current. Here we show images from videos obtained using optical microscopy for sliding domains along VO2 needles and confirm a relation suggested in the past for their velocity. We also show images for the disturbing damage induced by the structural changes in switching VO2 crystals obtained for only a few current–voltage cycles. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Open AccessArticle Self-Compliant Bipolar Resistive Switching in SiN-Based Resistive Switching Memory
Materials 2017, 10(5), 459; doi:10.3390/ma10050459
Received: 20 March 2017 / Revised: 22 April 2017 / Accepted: 25 April 2017 / Published: 26 April 2017
Cited by 1 | PDF Full-text (2604 KB) | HTML Full-text | XML Full-text
Abstract
Here, we present evidence of self-compliant and self-rectifying bipolar resistive switching behavior in Ni/SiNx/n+ Si and Ni/SiNx/n++ Si resistive-switching random access memory devices. The Ni/SiNx/n++ Si device’s Si bottom electrode had a higher dopant
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Here, we present evidence of self-compliant and self-rectifying bipolar resistive switching behavior in Ni/SiNx/n+ Si and Ni/SiNx/n++ Si resistive-switching random access memory devices. The Ni/SiNx/n++ Si device’s Si bottom electrode had a higher dopant concentration (As ion > 1019 cm−3) than the Ni/SiNx/n+ Si device; both unipolar and bipolar resistive switching behaviors were observed for the higher dopant concentration device owing to a large current overshoot. Conversely, for the device with the lower dopant concentration (As ion < 1018 cm−3), self-rectification and self-compliance were achieved owing to the series resistance of the Si bottom electrode. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Open AccessArticle VO2 Thermochromic Films on Quartz Glass Substrate Grown by RF-Plasma-Assisted Oxide Molecular Beam Epitaxy
Materials 2017, 10(3), 314; doi:10.3390/ma10030314
Received: 21 January 2017 / Revised: 14 March 2017 / Accepted: 15 March 2017 / Published: 19 March 2017
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Abstract
Vanadium dioxide (VO2) thermochromic thin films with various thicknesses were grown on quartz glass substrates by radio frequency (RF)-plasma assisted oxide molecular beam epitaxy (O-MBE). The crystal structure, morphology and chemical stoichiometry were investigated systemically by X-ray diffraction (XRD), atomic force
[...] Read more.
Vanadium dioxide (VO2) thermochromic thin films with various thicknesses were grown on quartz glass substrates by radio frequency (RF)-plasma assisted oxide molecular beam epitaxy (O-MBE). The crystal structure, morphology and chemical stoichiometry were investigated systemically by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. An excellent reversible metal-to-insulator transition (MIT) characteristics accompanied by an abrupt change in both electrical resistivity and optical infrared (IR) transmittance was observed from the optimized sample. Remarkably, the transition temperature (TMIT) deduced from the resistivity-temperature curve was reasonably consistent with that obtained from the temperature-dependent IR transmittance. Based on Raman measurement and XPS analyses, the observations were interpreted in terms of residual stresses and chemical stoichiometry. This achievement will be of great benefit for practical application of VO2-based smart windows. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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Review

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Open AccessReview A Review on Disorder-Driven Metal–Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials
Materials 2017, 10(8), 862; doi:10.3390/ma10080862
Received: 9 June 2017 / Revised: 23 July 2017 / Accepted: 25 July 2017 / Published: 27 July 2017
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Abstract
Metal–insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the
[...] Read more.
Metal–insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge1Sb2Te4 (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal–insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices. Full article
(This article belongs to the Special Issue Metal-Insulator Transition)
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