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Journal ArticleDOI

Superconductivity induced by Se-doping in layered charge-density-wave system 1T-TaS2−xSex

14 May 2013-Applied Physics Letters (American Institute of Physics)-Vol. 102, Iss: 19, pp 192602
TL;DR: In this paper, the appearance of a series of electronic states: the Mott phase melts into a nearly commensurate charge-density-wave (CDW) phase, superconductivity in a wide x range develops within the nearly-comensurate CDW state, and finally, the corresponding CDW phase reproduces for heavy Se content.
Abstract: Layered 1T-TaS2–xSex (0≤x≤2) single crystals have been systematically fabricated by a chemical vapor transport technique. Surprisingly, the superconductivity is induced by the Se doping. We demonstrate the appearance of a series of electronic states: the Mott phase melts into a nearly commensurate charge-density-wave (CDW) phase, superconductivity in a wide x range develops within the nearly commensurate CDW state, and finally commensurate CDW phase reproduces for heavy Se content. The rich phase diagram provides an ideal platform to investigate the interplay between electron correlation, CDW, and superconductivity, as well as the potential applications in electronic devices.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors provide a holistic overview of the different synthesis and characterization techniques, electronic and photonic device characteristics, and catalytic properties of transition metal dichalcogenides and their heterostructures, and comment on the challenges that need to be overcome for full-scale commercial implementation of this novel class of layered materials.
Abstract: Interest in 2D materials and van der Waals solids is growing exponentially across various scientific and engineering disciplines owing to their fascinating electrical, optical, chemical, and thermal properties. Whereas the micromechanical exfoliation technique has been adopted for rapid material characterization and demonstration of innovative device ideas based on these 2D systems, significant advances have recently been made in large-scale homogeneous and heterogeneous growth of these materials. This review reflects recent progress and outlines future prospects of these novel 2D materials. We provide a holistic overview of the different synthesis and characterization techniques, electronic and photonic device characteristics, and catalytic properties of transition metal dichalcogenides and their heterostructures. We also comment on the challenges that need to be overcome for full-scale commercial implementation of this novel class of layered materials.

551 citations

Journal ArticleDOI
TL;DR: The structures of metallic transition metal dichalcogenides and their synthetic approaches for not only high-quality wafer-scale samples using conventional methods but also local small areas by a modification of the materials using Li intercalation, electron beam irradiation, light illumination, pressures, and strains are presented.
Abstract: Transition metal dichalcogenides are layered materials which are composed of transition metals and chalcogens of the group VIA in a 1:2 ratio. These layered materials have been extensively investigated over synthesis and optical and electrical properties for several decades. It can be insulators, semiconductors, or metals revealing all types of condensed matter properties from a magnetic lattice distorted to superconducting characteristics. Some of these also feature the topological manner. Instead of covering the semiconducting properties of transition metal dichalcogenides, which have been extensively revisited and reviewed elsewhere, here we present the structures of metallic transition metal dichalcogenides and their synthetic approaches for not only high-quality wafer-scale samples using conventional methods (e.g., chemical vapor transport, chemical vapor deposition) but also local small areas by a modification of the materials using Li intercalation, electron beam irradiation, light illumination, pr...

275 citations

Journal ArticleDOI
TL;DR: It is demonstrated that the intrinsic properties of atomically thin flakes are preserved by encapsulation with hexagonal boron nitride in inert atmosphere and this facile assembly method is used together with transmission electron microscopy and transport measurements to probe the nature of the 2D state and show that its conductance is dominated by discommensurations.
Abstract: The layered transition metal dichalcogenides host a rich collection of charge density wave phases in which both the conduction electrons and the atomic structure display translational symmetry breaking. Manipulating these complex states by purely electronic methods has been a long-sought scientific and technological goal. Here, we show how this can be achieved in 1T-TaS2 in the 2D limit. We first demonstrate that the intrinsic properties of atomically thin flakes are preserved by encapsulation with hexagonal boron nitride in inert atmosphere. We use this facile assembly method together with transmission electron microscopy and transport measurements to probe the nature of the 2D state and show that its conductance is dominated by discommensurations. The discommensuration structure can be precisely tuned in few-layer samples by an in-plane electric current, allowing continuous electrical control over the discommensuration-melting transition in 2D.

209 citations

Journal ArticleDOI
TL;DR: In this paper, a review of all synthetic methods to 2D transition metal dichalcogenides (TMDCs) is presented by considering the quality and characteristics of the nanosheets produced.

165 citations

Journal ArticleDOI
TL;DR: A survey of the mechanisms underlying strong electron correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions, is presented, focusing on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity.
Abstract: Strong electron correlations are at the heart of many physical phenomena of current interest to the condensed matter community. Here we present a survey of the mechanisms underlying such correlations in charge density wave (CDW) systems, including the current theoretical understanding and experimental evidence for CDW transitions. The focus is on emergent phenomena that result as CDWs interact with other charge or spin states, such as magnetism and superconductivity. In addition to reviewing the CDW mechanisms in 1D, 2D, and 3D systems, we pay particular attention to the prevalence of this state in two particular classes of compounds, the high temperature superconductors (cuprates) and the layered transition metal dichalcogenides. The possibilities for quantum criticality resulting from the competition between magnetic fluctuations and electronic instabilities (CDW, unconventional superconductivity) are also discussed.

116 citations

References
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Journal ArticleDOI
TL;DR: This Review describes how the tunable electronic structure of TMDs makes them attractive for a variety of applications, as well as electrically active materials in opto-electronics.
Abstract: Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.

7,903 citations

Journal ArticleDOI
04 Feb 2011-Science
TL;DR: It is shown that WS2 and MoS2 effectively reinforce polymers, whereas WS2/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.
Abstract: If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, and Bi2Te3 can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS2 and MoS2 effectively reinforce polymers, whereas WS2/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.

6,043 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that charge-density waves and their concomitant periodic structural distortions occur in all the 4d1/5d1 dichalcogenides and related the observed periodicities of these CDW states to the theoretical form of the parent Fermi surfaces.
Abstract: The d1 layer metals TaS2, TaSe2, NbSe2, in all their various polytypic modifications, acquire, below some appropriate temperature, phase conditions that their electromagnetic properties have previously revealed as ‘anomalous’. Our present electron-microscope studies indicate that this anomalous behaviour usually includes the adoption, at some stage, of a superlattice. The size of superlattice adopted often is forecast in the pattern of satellite spotting and strong diffuse scattering found above the transition. Our conclusions are that charge-density waves and their concomitant periodic structural distortions occur in all these 4d1/5d1 dichalcogenides. We have related the observed periodicities of these CDW states to the theoretical form of the parent Fermi surfaces. Particularly for the 1T octahedrally coordinated polytypes the Fermi surface is very simple and markedly two-dimensional in character, with large near-parallel walls. Such a situation is known theoretically to favour the formation of...

1,648 citations

Journal ArticleDOI
06 Mar 2003-Nature
TL;DR: There is a marked resemblance in superconducting properties between the present material and high-Tc copper oxides, suggesting that the two systems have similar underlying physics.
Abstract: Since the discovery of high-transition-temperature (high-T(c)) superconductivity in layered copper oxides, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that Na(x)CoO2*yH2O (x approximately 0.35, y approximately 1.3) is a superconductor with a T(c) of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-T(c) copper oxides, suggesting that the two systems have similar underlying physics.

1,495 citations

Journal ArticleDOI
TL;DR: Using first-principles structure optimization and phonon calculations based on density functional theory, this paper predicted that, out of 88 different combinations of MX2 compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures.
Abstract: Recent studies have revealed that single-layer transition-metal oxides and dichalcogenides (MX2) might offer properties superior to those of graphene. So far, only very few MX2 compounds have been synthesized as suspended single layers, and some of them have been exfoliated as thin sheets. Using first-principles structure optimization and phonon calculations based on density functional theory, we predict that, out of 88 different combinations of MX2 compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures. These materials have two-dimensional hexagonal lattices and have top-view appearances as if they consisted of either honeycombs or centered honeycombs. However, their bonding is different from that of graphene; they can be viewed as a positively charged plane of transition-metal atoms sandwiched between two planes of negatively charged oxygen or chalcogen atoms. Electron correlation in transition-metal oxides was treated by including Coulomb repulsion through LDA...

1,152 citations