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Lotfizadeh N, McCulley DR, Senger MJ, Fu H, Minot ED, Skinner B, Deshpande VV. Band-Gap-Dependent Electronic Compressibility of Carbon Nanotubes in the Wigner Crystal Regime. PHYSICAL REVIEW LETTERS 2019; 123:197701. [PMID: 31765201 DOI: 10.1103/physrevlett.123.197701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Indexed: 06/10/2023]
Abstract
Electronic compressibility, the second derivative of ground-state energy with respect to total electron number, is a measurable quantity that reveals the interaction strength of a system and can be used to characterize the orderly crystalline lattice of electrons known as the Wigner crystal. Here, we measure the electronic compressibility of individual suspended ultraclean carbon nanotubes in the low-density Wigner crystal regime. Using low-temperature quantum transport measurements, we determine the compressibility as a function of carrier number in nanotubes with varying band gaps. We observe two qualitatively different trends in compressibility versus carrier number, both of which can be explained using a theoretical model of a Wigner crystal that accounts for both the band gap and the confining potential experienced by charge carriers. We extract the interaction strength as a function of carrier number for individual nanotubes and show that the compressibility can be used to distinguish between strongly and weakly interacting regimes.
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Affiliation(s)
- Neda Lotfizadeh
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
| | - Daniel R McCulley
- Department of Physics, Oregon State University, Corvallis, Oregon 97331, USA
| | - Mitchell J Senger
- Department of Physics, Oregon State University, Corvallis, Oregon 97331, USA
| | - Han Fu
- James Franck Institute, University of Chicago, Chicago, Illinois 60637, USA
| | - Ethan D Minot
- Department of Physics, Oregon State University, Corvallis, Oregon 97331, USA
| | - Brian Skinner
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Physics, Ohio State University, Columbus, Ohio 43210, USA
| | - Vikram V Deshpande
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
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2
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Li L, Richter C, Paetel S, Kopp T, Mannhart J, Ashoori RC. Very large capacitance enhancement in a two-dimensional electron system. Science 2011; 332:825-8. [PMID: 21566188 DOI: 10.1126/science.1204168] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Increases in the gate capacitance of field-effect transistor structures allow the production of lower-power devices that are compatible with higher clock rates, driving the race for developing high-κ dielectrics. However, many-body effects in an electronic system can also enhance capacitance. Onto the electron system that forms at the LaAlO(3)/SrTiO(3) interface, we fabricated top-gate electrodes that can fully deplete the interface of all mobile electrons. Near depletion, we found a greater than 40% enhancement of the gate capacitance. Using an electric-field penetration measurement method, we show that this capacitance originates from a negative compressibility of the interface electron system. Capacitance enhancement exists at room temperature and arises at low electron densities, in which disorder is strong and the in-plane conductance is much smaller than the quantum conductance.
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Affiliation(s)
- Lu Li
- Department of Physics, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA
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Hwang EH, Hu BYK, Das Sarma S. Density dependent exchange contribution to partial differential mu/ partial differential n and compressibility in graphene. PHYSICAL REVIEW LETTERS 2007; 99:226801. [PMID: 18233311 DOI: 10.1103/physrevlett.99.226801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2007] [Indexed: 05/25/2023]
Abstract
We calculate partial differentialmu/ partial differentialn (where mu=chemical potential and n=electron density), which is associated with the compressibility, in graphene as a function of n, within the Hartree-Fock approximation. The exchange-driven Dirac-point logarithmic singularity in the quasiparticle velocity of intrinsic graphene disappears in the extrinsic case. The calculated renormalized partial differentialmu/ partial differentialn in extrinsic graphene on SiO2 has the same n;{-(1/2)} density dependence but is 20% larger than the inverse bare density of states, a relatively weak effect compared to the corresponding parabolic-band case. We predict that the renormalization effect can be enhanced to about 50% by changing the graphene substrate.
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Affiliation(s)
- E H Hwang
- Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
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4
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Lüscher S, Moore LS, Rejec T, Meir Y, Shtrikman H, Goldhaber-Gordon D. Charge rearrangement and screening in a quantum point contact. PHYSICAL REVIEW LETTERS 2007; 98:196805. [PMID: 17677648 DOI: 10.1103/physrevlett.98.196805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2006] [Indexed: 05/16/2023]
Abstract
Compressibility measurements are performed on a quantum point contact (QPC). Screening due to mobile charges in the QPC is measured quantitatively, using a second point contact. These measurements are performed from pinch-off through the opening of the first few modes in the QPC. While the measured signal closely matches a Thomas-Fermi-Poisson prediction, deviations from the classical behavior are apparent near the openings of the different modes. Density functional calculations attribute the deviations to a combination of a diverging density of states at the opening of each one-dimensional mode and exchange interaction, which is strongest for the first mode.
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Affiliation(s)
- S Lüscher
- Department of Physics, Stanford University, Stanford, CA 94305, USA
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Golden KI, Mahassen H, Senatore G, Rapisarda F. Transverse dielectric matrix and shear mode dispersion in strongly coupled electronic bilayer liquids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 74:056405. [PMID: 17279999 DOI: 10.1103/physreve.74.056405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2006] [Revised: 09/18/2006] [Indexed: 05/13/2023]
Abstract
The authors develop a transverse dielectric matrix and from it they calculate the shear mode dispersion in strongly coupled charged-particle bilayer liquids in the T=0 quantum domain. The formulation is based on the classical quasilocalized charge approximation (QLCA) and extends the QLCA formalism into the quantum domain. Its development parallels and complements the development of a similarly extended longitudinal dielectric matrix formalism reported in a recent companion work [K. I. Golden, H. Mahassen, G. J. Kalman, G. Senatore, and F. Rapisarda, Phys. Rev. E 71, 036401 (2005)]. Using pair correlation function data generated from diffusion Monte Carlo simulations, the authors calculate the dispersion of the in-phase and out-of-phase shear modes over a wide range of high-r(s) values and layer separations. Over the coupling range 10< or =r(s)< or =30 and for layer separations 0.2/sqrt[pi(n)]< or =d< or =0.5/sqrt[pi(n)] , the present study predicts the existence of a robust out-of-phase gapped shear mode dispersion in the domain of the q,omega -plane above the left boundary of the RPA single-pair excitation region; under these conditions, the out-of-phase collective excitation is entirely immune to Landau damping and can be safely considered to be mostly unaffected by diffusive-migrational damping.
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Affiliation(s)
- Kenneth I Golden
- Department of Mathematics and Statistics, College of Engineering and Mathematical Sciences, University of Vermont, Burlington, VT 05401-1455, USA
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Allison G, Galaktionov EA, Savchenko AK, Safonov SS, Fogler MM, Simmons MY, Ritchie DA. Thermodynamic density of states of two-dimensional GaAs systems near the apparent metal-insulator transition. PHYSICAL REVIEW LETTERS 2006; 96:216407. [PMID: 16803263 DOI: 10.1103/physrevlett.96.216407] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2005] [Indexed: 05/10/2023]
Abstract
We perform combined resistivity and compressibility studies of two-dimensional hole and electron systems which show the apparent metal-insulator transition--a crossover in the sign of deltaR/deltaT with changing density. No thermodynamic anomalies have been detected in the crossover region. Instead, despite a tenfold difference in r(s), the compressibility of both electrons and holes is well described by the theory of nonlinear screening of the random potential. We show that the resistivity exhibits a scaling behavior near the percolation threshold found from analysis of the compressibility. Notably, the percolation transition occurs at a much lower density than the crossover.
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Affiliation(s)
- G Allison
- School of Physics, University of Exeter, Exeter EX4 4QL, United Kingdom
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Lu W, Xiang J, Timko BP, Wu Y, Lieber CM. One-dimensional hole gas in germanium/silicon nanowire heterostructures. Proc Natl Acad Sci U S A 2005; 102:10046-51. [PMID: 16006507 PMCID: PMC1174925 DOI: 10.1073/pnas.0504581102] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two-dimensional electron and hole gas systems, enabled through band structure design and epitaxial growth on planar substrates, have served as key platforms for fundamental condensed matter research and high-performance devices. The analogous development of one-dimensional (1D) electron or hole gas systems through controlled growth on 1D nanostructure substrates, which could open up opportunities beyond existing carbon nanotube and nanowire systems, has not been realized. Here, we report the synthesis and transport studies of a 1D hole gas system based on a free-standing germanium/silicon (Ge/Si) core/shell nanowire heterostructure. Room temperature electrical transport measurements clearly show hole accumulation in undoped Ge/Si nanowire heterostructures, in contrast to control experiments on single-component nanowires. Low-temperature studies show well-controlled Coulomb blockade oscillations when the Si shell serves as a tunnel barrier to the hole gas in the Ge channel. Transparent contacts to the hole gas also have been reproducibly achieved by thermal annealing. In such devices, we observe conductance quantization at low temperatures, corresponding to ballistic transport through 1D subbands, where the measured subband energy spacings agree with calculations for a cylindrical confinement potential. In addition, we observe a "0.7 structure," which has been attributed to spontaneous spin polarization, suggesting the universality of this phenomenon in interacting 1D systems. Lastly, the conductance exhibits little temperature dependence, consistent with our calculation of reduced backscattering in this 1D system, and suggests that transport is ballistic even at room temperature.
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Affiliation(s)
- Wei Lu
- Department of Chemistry and Chemical Biology and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
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Golden KI, Kalman GJ. Dynamical structure functions for charged particle bilayers and superlattices. ACTA ACUST UNITED AC 2003. [DOI: 10.1088/0305-4470/36/22/306] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Das MP, Golden KI, Green F. Dynamical theory of strongly coupled two-dimensional Coulomb fluids in the weakly degenerate quantum domain. PHYSICAL REVIEW E 2001; 64:046125. [PMID: 11690108 DOI: 10.1103/physreve.64.046125] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2001] [Indexed: 11/07/2022]
Abstract
We study the problem of dynamical response and plasma mode dispersion in strongly coupled two-dimensional Coulomb fluids (2DCFs) in the weakly degenerate quantum domain. Adapting the nonlinear response function approach of Golden and Kalman [Phys. Rev. A 19, 2112 (1979)] to the 2DCF, we construct a self-consistent approximation scheme for the calculation of the density response functions and plasma mode dispersion at long wavelengths. The basic ingredients in the construction are (i). the first kinetic equation in the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, (ii). the velocity-average-approximation (VAA) hypothesis, (iii.) the quadratic fluctuation-dissipation theorem, and (iv). the dynamical superposition approximation (DSA) closure hypothesis. The reliability of the VAA-DSA theory can be assessed by observing that the principal coupling correction to the 2D temperature-dependent Lindhard function is identified as being precisely the part of the third-frequency-moment sum-rule coefficient proportional to the potential energy.
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Affiliation(s)
- M P Das
- Department of Theoretical Physics, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia
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Donkó Z, Kalman GJ. Molecular dynamics studies of strongly coupled charged particle bilayers at finite temperatures. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:061504. [PMID: 11415107 DOI: 10.1103/physreve.63.061504] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2000] [Indexed: 05/23/2023]
Abstract
The structure of strongly coupled charged particle bilayers was investigated using molecular dynamics simulation, in a wide range of the plasma coupling parameter Gamma=20-100. The simulations showed the existence of a series of structural transformations, controlled by the separation of the layers. At high values of Gamma a pronounced long-range order was found to develop at intermediate layer separations, with staggered square lattice configuration. The results show a fair agreement with those obtained by hypernetted chain calculations, in terms of intralayer and interlayer pair correlation functions and structure functions.
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Affiliation(s)
- Z Donkó
- Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary
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Ilani S, Yacoby A, Mahalu D, Shtrikman H. Microscopic Structure of the Metal-Insulator Transition in Two Dimensions. Science 2001; 292:1354-7. [PMID: 11359006 DOI: 10.1126/science.1058645] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
A single electron transistor is used as a local electrostatic probe to study the underlying spatial structure of the metal-insulator transition in two dimensions. The measurements show that as we approach the transition from the metallic side, a new phase emerges that consists of weakly coupled fragments of the two-dimensional system. These fragments consist of localized charge that coexists with the surrounding metallic phase. As the density is lowered into the insulating phase, the number of fragments increases on account of the disappearing metallic phase. The measurements reveal that the metal-insulator transition is a result of the microscopic restructuring that occurs in the system.
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Affiliation(s)
- S Ilani
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
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Dultz SC, Jiang HW. Thermodynamic signature of a two-dimensional metal-insulator transition. PHYSICAL REVIEW LETTERS 2000; 84:4689-4692. [PMID: 10990772 DOI: 10.1103/physrevlett.84.4689] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/1999] [Indexed: 05/23/2023]
Abstract
We present a study of the compressibility kappa of a two-dimensional hole system which exhibits a metal-insulator phase transition at zero magnetic field. It has been observed that dkappa/dp changes sign at the critical density for the metal-insulator transition. Measurements also indicate that the insulating phase is incompressible for all values of B. Finally, we show how the phase transition evolves as the magnetic field is varied and construct a phase diagram in the density-magnetic field plane for this system.
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Affiliation(s)
- SC Dultz
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California 90095, USA
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Ilani S, Yacoby A, Mahalu D, Shtrikman H. Unexpected behavior of the local compressibility near the B = 0 metal-insulator transition. PHYSICAL REVIEW LETTERS 2000; 84:3133-3136. [PMID: 11019030 DOI: 10.1103/physrevlett.84.3133] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/1999] [Indexed: 05/23/2023]
Abstract
We have measured the local electronic compressibility of a two-dimensional hole gas as it crosses the B = 0 metal-insulator transition. In the metallic phase, the compressibility follows the mean-field Hartree-Fock (HF) theory and is found to be spatially homogeneous. In the insulating phase it deviates by more than an order of magnitude from the HF predictions and is spatially inhomogeneous. The crossover density between the two types of behavior agrees quantitatively with the transport critical density, suggesting that the system undergoes a thermodynamic change at the transition.
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Affiliation(s)
- S Ilani
- Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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Independently contacted electron–hole gas heterostructures fabricated with focused ion beam doping during molecular beam epitaxial growth. ACTA ACUST UNITED AC 1999. [DOI: 10.1116/1.590986] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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