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Greenberg BL, Robinson ZL, Ayino Y, Held JT, Peterson TA, Mkhoyan KA, Pribiag VS, Aydil ES, Kortshagen UR. Metal-insulator transition in a semiconductor nanocrystal network. SCIENCE ADVANCES 2019; 5:eaaw1462. [PMID: 31467972 PMCID: PMC6707780 DOI: 10.1126/sciadv.aaw1462] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 07/15/2019] [Indexed: 06/01/2023]
Abstract
Many envisioned applications of semiconductor nanocrystals (NCs), such as thermoelectric generators and transparent conductors, require metallic (nonactivated) charge transport across an NC network. Although encouraging signs of metallic or near-metallic transport have been reported, a thorough demonstration of nonzero conductivity, σ, in the 0 K limit has been elusive. Here, we examine the temperature dependence of σ of ZnO NC networks. Attaining both higher σ and lower temperature than in previous studies of ZnO NCs (T as low as 50 mK), we observe a clear transition from the variable-range hopping regime to the metallic regime. The critical point of the transition is distinctly marked by an unusual power law close to σ ∝ T 1/5. We analyze the critical conductivity data within a quantum critical scaling framework and estimate the metal-insulator transition (MIT) criterion in terms of the free electron density, n, and interparticle contact radius, ρ.
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Affiliation(s)
| | - Zachary L. Robinson
- School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
| | - Yilikal Ayino
- School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
| | - Jacob T. Held
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, USA
| | - Timothy A. Peterson
- School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
| | - K. Andre Mkhoyan
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, USA
| | - Vlad S. Pribiag
- School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
| | - Eray S. Aydil
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, USA
| | - Uwe R. Kortshagen
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, USA
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Affiliation(s)
- Arndt Remhof
- Empa, Swiss Federal Laboratories for Materials Testing and Research, Department of Environment, Energy and Mobility, Div. Hydrogen and Energy, Uberlandstrasse 129, CH-8600 Dübendorf, Switzerland.
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Racu AM, Schoenes J. Strong correlations in YH(3-delta) evidenced by Raman spectroscopy. PHYSICAL REVIEW LETTERS 2006; 96:017401. [PMID: 16486512 DOI: 10.1103/physrevlett.96.017401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2005] [Indexed: 05/06/2023]
Abstract
Temperature dependent Raman measurements on insulating YH(3-delta) thin films are reported. With increasing temperature we observe a huge broadening of a line corresponding to an yttrium mode. This particular mode is assigned to a breathing vibration of the yttrium atoms around an octahedral hydrogen position. The line broadening is discussed in terms of a coupling between this breathing mode and the electron excited from an octahedral H vacancy into the 4d conduction band of Y, corroborating the strong correlation models for the electronic structure of YH3.
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Affiliation(s)
- A-M Racu
- Institut für Physik der Kondenbsierten Materie, Technische Universität Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany.
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Durand P, Darling GR, Dubitsky Y, Zaopo A, Rosseinsky MJ. The Mott-Hubbard insulating state and orbital degeneracy in the superconducting C60(3-) fulleride family. NATURE MATERIALS 2003; 2:605-610. [PMID: 12907941 DOI: 10.1038/nmat953] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2003] [Accepted: 07/03/2003] [Indexed: 05/24/2023]
Abstract
Electron correlation controls the properties of important materials such as superconducting and magnetoresistive transition metal oxides and heavy fermion systems. The role of correlation in driving metal-to-insulator transitions assumes further importance because many superconducting materials are located close to such transitions. The nature of the insulating ground state often reveals the dominant interactions in the superconductor, as shown by the importance of the properties of La2CuO4 in understanding the high-temperature-superconducting cuprates. The A3C60 alkali metal fullerides are superconducting systems in which the role of correlation in both the normal state and the superconducting pairing mechanism is controversial, because no magnetic insulator comparable to the superconducting materials has been identified. We describe the first example of a cubic C60(3-) system with degenerate orbitals that adopts the Mott-Hubbard insulating localized electron ground state. Electron repulsion is identified as the interaction that is suppressed on the transition to metallic and superconducting behaviour in the fullerides. This observation is combined with ab initio calculations to demonstrate that it is the orbital degeneracy that allows the superconducting cubic A3C60 fullerides to remain metallic while provoking electron localization in systems with lower symmetry.
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Affiliation(s)
- P Durand
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK
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