1
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Xu Q, Cheung HFH, Cormode DS, Puel TO, Pal S, Yusuf H, Chilcote M, Flatté ME, Johnston‐Halperin E, Fuchs GD. Strong Photon-Magnon Coupling Using a Lithographically Defined Organic Ferrimagnet. Adv Sci (Weinh) 2024; 11:e2310032. [PMID: 38279583 PMCID: PMC11005739 DOI: 10.1002/advs.202310032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Indexed: 01/28/2024]
Abstract
A cavity-magnonic system composed of a superconducting microwave resonator coupled to a magnon mode hosted by the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x) is demonstrated. This work is motivated by the challenge of scalably integrating a low-damping magnetic system with planar superconducting circuits. V[TCNE]x has ultra-low intrinsic damping, can be grown at low processing temperatures on arbitrary substrates, and can be patterned via electron beam lithography. The devices operate in the strong coupling regime, with a cooperativity exceeding 1000 for coupling between the Kittel mode and the resonator mode at T≈0.4 K, suitable for scalable quantum circuit integration. Higher-order magnon modes are also observed with much narrower linewidths than the Kittel mode. This work paves the way for high-cooperativity hybrid quantum devices in which magnonic circuits can be designed and fabricated as easily as electrical wires.
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Affiliation(s)
- Qin Xu
- Department of PhysicsCornell UniversityIthacaNY14853USA
| | | | | | - Tharnier O. Puel
- Department of Physics and AstronomyUniversity of IowaIowa CityIA52242USA
| | - Srishti Pal
- School of Applied and Engineering PhysicsCornell UniversityIthacaNY14853USA
| | - Huma Yusuf
- Department of PhysicsThe Ohio State UniversityColumbusOH43210USA
| | - Michael Chilcote
- School of Applied and Engineering PhysicsCornell UniversityIthacaNY14853USA
| | - Michael E. Flatté
- Department of Physics and AstronomyUniversity of IowaIowa CityIA52242USA
| | | | - Gregory D. Fuchs
- School of Applied and Engineering PhysicsCornell UniversityIthacaNY14853USA
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2
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Fukami M, Marcks JC, Candido DR, Weiss LR, Soloway B, Sullivan SE, Delegan N, Heremans FJ, Flatté ME, Awschalom DD. Magnon-mediated qubit coupling determined via dissipation measurements. Proc Natl Acad Sci U S A 2024; 121:e2313754120. [PMID: 38165926 PMCID: PMC10786302 DOI: 10.1073/pnas.2313754120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 11/14/2023] [Indexed: 01/04/2024] Open
Abstract
Controlled interaction between localized and delocalized solid-state spin systems offers a compelling platform for on-chip quantum information processing with quantum spintronics. Hybrid quantum systems (HQSs) of localized nitrogen-vacancy (NV) centers in diamond and delocalized magnon modes in ferrimagnets-systems with naturally commensurate energies-have recently attracted significant attention, especially for interconnecting isolated spin qubits at length-scales far beyond those set by the dipolar coupling. However, despite extensive theoretical efforts, there is a lack of experimental characterization of the magnon-mediated interaction between NV centers, which is necessary to develop such hybrid quantum architectures. Here, we experimentally determine the magnon-mediated NV-NV coupling from the magnon-induced self-energy of NV centers. Our results are quantitatively consistent with a model in which the NV center is coupled to magnons by dipolar interactions. This work provides a versatile tool to characterize HQSs in the absence of strong coupling, informing future efforts to engineer entangled solid-state systems.
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Affiliation(s)
- Masaya Fukami
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL60637
| | - Jonathan C. Marcks
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL60637
- Center for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, IL60439
| | - Denis R. Candido
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA52242
| | - Leah R. Weiss
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL60637
- Advanced Institute for Materials Research, Tohoku University, Sendai980-8577, Japan
| | - Benjamin Soloway
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL60637
| | - Sean E. Sullivan
- Center for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, IL60439
| | - Nazar Delegan
- Center for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, IL60439
| | - F. Joseph Heremans
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL60637
- Center for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, IL60439
| | - Michael E. Flatté
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA52242
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven5600 MB, Netherlands
| | - David D. Awschalom
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL60637
- Center for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, IL60439
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3
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da Cruz AR, Flatté ME. Dissipationless Circulating Currents and Fringe Magnetic Fields Near a Single Spin Embedded in a Two-Dimensional Electron Gas. Phys Rev Lett 2023; 131:086301. [PMID: 37683147 DOI: 10.1103/physrevlett.131.086301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 02/21/2023] [Accepted: 05/26/2023] [Indexed: 09/10/2023]
Abstract
Theoretical calculations predict the anisotropic dissipationless circulating current induced by a spin defect in a two-dimensional electron gas. The shape and spatial extent of these dissipationless circulating currents depend dramatically on the relative strengths of spin-orbit fields with differing spatial symmetry, offering the potential to use an electric gate to manipulate nanoscale magnetic fields and couple magnetic defects. The spatial structure of the magnetic field produced by this current is calculated and provides a direct way to measure the spin-orbit fields of the host, as well as the defect spin orientation, e.g., through scanning nanoscale magnetometry.
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Affiliation(s)
- Adonai R da Cruz
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven 5612 AZ, The Netherlands
| | - Michael E Flatté
- Department of Applied Physics, Eindhoven University of Technology, Eindhoven 5612 AZ, The Netherlands
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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4
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Park J, Jaramillo DE, Shi Y, Jiang HZH, Yusuf H, Furukawa H, Bloch ED, Cormode DS, Miller JS, Harris TD, Johnston-Halperin E, Flatté ME, Long JR. Permanent Porosity in the Room-Temperature Magnet and Magnonic Material V(TCNE) 2. ACS Cent Sci 2023; 9:777-786. [PMID: 37122461 PMCID: PMC10141614 DOI: 10.1021/acscentsci.3c00053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Indexed: 05/03/2023]
Abstract
Materials that simultaneously exhibit permanent porosity and high-temperature magnetic order could lead to advances in fundamental physics and numerous emerging technologies. Herein, we show that the archetypal molecule-based magnet and magnonic material V(TCNE)2 (TCNE = tetracyanoethylene) can be desolvated to generate a room-temperature microporous magnet. The solution-phase reaction of V(CO)6 with TCNE yields V(TCNE)2·0.95CH2Cl2, for which a characteristic temperature of T* = 646 K is estimated from a Bloch fit to variable-temperature magnetization data. Removal of the solvent under reduced pressure affords the activated compound V(TCNE)2, which exhibits a T* value of 590 K and permanent microporosity (Langmuir surface area of 850 m2/g). The porous structure of V(TCNE)2 is accessible to the small gas molecules H2, N2, O2, CO2, ethane, and ethylene. While V(TCNE)2 exhibits thermally activated electron transfer with O2, all the other studied gases engage in physisorption. The T* value of V(TCNE)2 is slightly modulated upon adsorption of H2 (T* = 583 K) or CO2 (T* = 596 K), while it decreases more significantly upon ethylene insertion (T* = 459 K). These results provide an initial demonstration of microporosity in a room-temperature magnet and highlight the possibility of further incorporation of small-molecule guests, potentially even molecular qubits, toward future applications.
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Affiliation(s)
- Jesse
G. Park
- Department
of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
| | - David E. Jaramillo
- Department
of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
- Materials
Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720, United States
| | - Yueguang Shi
- Department
of Physics and Astronomy, University of
Iowa, Iowa City, Iowa 52242-1479, United States
| | - Henry Z. H. Jiang
- Department
of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
- Materials
Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720, United States
- Institute
for Decarbonization Materials, Berkeley, California 94720, United States
| | - Huma Yusuf
- Department
of Physics, Ohio State University, Columbus, Ohio 43210-1117, United States
| | - Hiroyasu Furukawa
- Department
of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
- Materials
Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720, United States
- Institute
for Decarbonization Materials, Berkeley, California 94720, United States
| | - Eric D. Bloch
- Department
of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
| | - Donley S. Cormode
- Department
of Physics, Ohio State University, Columbus, Ohio 43210-1117, United States
| | - Joel S. Miller
- Department
of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, United States
| | - T. David Harris
- Department
of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
- Institute
for Decarbonization Materials, Berkeley, California 94720, United States
| | | | - Michael E. Flatté
- Department
of Physics and Astronomy, University of
Iowa, Iowa City, Iowa 52242-1479, United States
- Department
of Applied Physics, Eindhoven University
of Technology, Eindhoven 5612 AZ, The Netherlands
| | - Jeffrey R. Long
- Department
of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
- Materials
Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720, United States
- Institute
for Decarbonization Materials, Berkeley, California 94720, United States
- Department
of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, California 94720, United States
- Email
for J.R.L.:
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5
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Thompson SM, Şahin C, Yang S, Flatté ME, Murray CB, Bassett LC, Kagan CR. Red Emission from Copper-Vacancy Color Centers in Zinc Sulfide Colloidal Nanocrystals. ACS Nano 2023; 17:5963-5973. [PMID: 36892080 DOI: 10.1021/acsnano.3c00191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Copper-doped zinc sulfide (ZnS:Cu) exhibits down-conversion luminescence in the UV, visible, and IR regions of the electromagnetic spectrum; the visible red, green, and blue emission is referred to as R-Cu, G-Cu, and B-Cu, respectively. The sub-bandgap emission arises from optical transitions between localized electronic states created by point defects, making ZnS:Cu a prolific phosphor material and an intriguing candidate material for quantum information science, where point defects excel as single-photon sources and spin qubits. Colloidal nanocrystals (NCs) of ZnS:Cu are particularly interesting as hosts for the creation, isolation, and measurement of quantum defects, since their size, composition, and surface chemistry can be precisely tailored for biosensing and optoelectronic applications. Here, we present a method for synthesizing colloidal ZnS:Cu NCs that emit primarily R-Cu, which has been proposed to arise from the CuZn-VS complex, an impurity-vacancy point defect structure analogous to well-known quantum defects in other materials that produce favorable optical and spin dynamics. First-principles calculations confirm the thermodynamic stability and electronic structure of CuZn-VS. Temperature- and time-dependent optical properties of ZnS:Cu NCs show blueshifting luminescence and an anomalous plateau in the intensity dependence as temperature is increased from 19 K to 290 K, for which we propose an empirical dynamical model based on thermally activated coupling between two manifolds of states inside the ZnS bandgap. Understanding of R-Cu emission dynamics, combined with a controlled synthesis method for obtaining R-Cu centers in colloidal NC hosts, will greatly facilitate the development of CuZn-VS and related complexes as quantum point defects in ZnS.
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Affiliation(s)
- Sarah M Thompson
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Cüneyt Şahin
- UNAM - National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent University, Ankara, TR 06800, Turkey
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, United States
| | - Shengsong Yang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Michael E Flatté
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, United States
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - Christopher B Murray
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Lee C Bassett
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Cherie R Kagan
- Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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6
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ter Huurne SE, Da Cruz AR, van Hoof N, Godiksen RH, Elrafei SA, Curto AG, Flatté ME, Rivas JG. High-Frequency Sheet Conductance of Nanolayered WS 2 Crystals for Two-Dimensional Nanodevices. ACS Appl Nano Mater 2022; 5:15557-15562. [PMID: 36338326 PMCID: PMC9623546 DOI: 10.1021/acsanm.2c03517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Accepted: 09/29/2022] [Indexed: 06/16/2023]
Abstract
Time-resolved terahertz (THz) spectroscopy is a powerful technique for the determination of charge transport properties in photoexcited semiconductors. However, the relatively long wavelengths of THz radiation and the diffraction limit imposed by optical imaging systems reduce the applicability of THz spectroscopy to large samples with dimensions in the millimeter to centimeter range. Exploiting THz near-field spectroscopy, we present the first time-resolved THz measurements on a single exfoliated 2D nanolayered crystal of a transition metal dichalcogenide (WS2). The high spatial resolution of THz near-field spectroscopy enables mapping of the sheet conductance for an increasing number of atomic layers. The single-crystalline structure of the nanolayered crystal allows for the direct observation of low-energy phonon modes, which are present in all thicknesses, coupling with free carriers. Density functional theory calculations show that the phonon mode corresponds to the breathing mode between atomic layers in the weakly bonded van der Waals layers, which can be strongly influenced by substrate-induced strain. The non-invasive and high-resolution mapping technique of carrier dynamics in nanolayered crystals by time-resolved THz time domain spectroscopy enables possibilities for the investigation of the relation between phonons and charge transport in nanoscale semiconductors for applications in two-dimensional nanodevices.
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Affiliation(s)
- Stan E.T. ter Huurne
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
| | - Adonai Rodrigues Da Cruz
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
| | - Niels van Hoof
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
| | - Rasmus H. Godiksen
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
| | - Sara A. Elrafei
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
| | - Alberto G. Curto
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
| | - Michael E. Flatté
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
- Department
of Physics and Astronomy, University of
Iowa, Iowa City, Iowa52242, United States
| | - Jaime Gómez Rivas
- Department
of Applied Physics and Eindhoven Hendrik Casimir Institute, Eindhoven University of Technology, P.O. Box 513, Eindhoven5600 MB, The Netherlands
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7
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He B, Şahin C, Boona SR, Sales BC, Pan Y, Felser C, Flatté ME, Heremans JP. Large magnon-induced anomalous Nernst conductivity in single-crystal MnBi. Joule 2021; 5:3057-3067. [PMID: 34841198 PMCID: PMC8604385 DOI: 10.1016/j.joule.2021.08.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 06/14/2021] [Accepted: 08/20/2021] [Indexed: 05/12/2023]
Abstract
Thermoelectric modules are a promising approach to energy harvesting and efficient cooling. In addition to the longitudinal Seebeck effect, transverse devices utilizing the anomalous Nernst effect (ANE) have recently attracted interest. For high conversion efficiency, it is required that the material have a large ANE thermoelectric power and low electrical resistance, which lead to the conductivity of the ANE. ANE is usually explained in terms of intrinsic contributions from Berry curvature. Our observations suggest that extrinsic contributions also matter. Studying single-crystal manganese-bismuth (MnBi), we find a high ANE thermopower (∼10 μV/K) under 0.6 T at 80 K, and a transverse thermoelectric conductivity of over 40 A/Km. With insight from theoretical calculations, we attribute this large ANE predominantly to a new advective magnon contribution arising from magnon-electron spin-angular momentum transfer. We propose that introducing a large spin-orbit coupling into ferromagnetic materials may enhance the ANE through the extrinsic contribution of magnons.
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Affiliation(s)
- Bin He
- Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
- Corresponding author
| | - Cüneyt Şahin
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
- Optical Science and Technology Center and Department of Physics and Astronomy, the University of Iowa, Iowa City, IA 52242, USA
| | - Stephen R. Boona
- Center of Electron Microscopy and Analysis, The Ohio State University, Columbus, OH 43210, USA
| | - Brian C. Sales
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Yu Pan
- Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
| | - Claudia Felser
- Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
| | - Michael E. Flatté
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
- Optical Science and Technology Center and Department of Physics and Astronomy, the University of Iowa, Iowa City, IA 52242, USA
| | - Joseph P. Heremans
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
- Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, USA
- Department of Physics, The Ohio State University, Columbus, OH 43210, USA
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8
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Vu D, Zhang W, Şahin C, Flatté ME, Trivedi N, Heremans JP. Thermal chiral anomaly in the magnetic-field-induced ideal Weyl phase of Bi 1-xSb x. Nat Mater 2021; 20:1525-1531. [PMID: 34099904 DOI: 10.1038/s41563-021-00983-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Accepted: 03/12/2021] [Indexed: 05/12/2023]
Abstract
The chiral anomaly is the predicted breakdown of chiral symmetry in a Weyl semimetal with monopoles of opposite chirality when an electric field is applied parallel to a magnetic field. It occurs because of charge pumping between monopoles of opposite chirality. Experimental observation of this fundamental effect is plagued by concerns about the current pathways. Here we demonstrate the thermal chiral anomaly, energy pumping between monopoles, in topological insulator bismuth-antimony alloys driven into an ideal Weyl semimetal state by a Zeeman field, with the chemical potential pinned at the Weyl points and in the absence of any trivial Fermi surface pockets. The experimental signature is a large enhancement of the thermal conductivity in an applied magnetic field parallel to the thermal gradient. This work demonstrates both pumping of energy and charge between the two Weyl points of opposite chirality and that they are related by the Wiedemann-Franz law.
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Affiliation(s)
- Dung Vu
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH, USA
| | - Wenjuan Zhang
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Cüneyt Şahin
- Optical Science and Technology Center and Department of Physics and Astronomy, The University of Iowa, Iowa City, IA, USA
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, USA
| | - Michael E Flatté
- Optical Science and Technology Center and Department of Physics and Astronomy, The University of Iowa, Iowa City, IA, USA
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, USA
| | - Nandini Trivedi
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Joseph P Heremans
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH, USA.
- Department of Physics, The Ohio State University, Columbus, OH, USA.
- Department of Material Science and Engineering, The Ohio State University, Columbus, OH, USA.
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9
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Mueller SM, Kim D, McMillan SR, Tjung SJ, Repicky JJ, Gant S, Lang E, Bergmann F, Werner K, Chowdhury E, Asthagiri A, Flatté ME, Gupta JA. Tunable tunnel barriers in a semiconductor via ionization of individual atoms. J Phys Condens Matter 2021; 33:275002. [PMID: 33878736 DOI: 10.1088/1361-648x/abf9bd] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 04/20/2021] [Indexed: 06/12/2023]
Abstract
We report scanning tunneling microscopy (STM) studies of individual adatoms deposited on an InSb(110) surface. The adatoms can be reproducibly dropped off from the STM tip by voltage pulses, and impact tunneling into the surface by up to ∼100×. The spatial extent and magnitude of the tunneling effect are widely tunable by imaging conditions such as bias voltage, set current and photoillumination. We attribute the effect to occupation of a (+/0) charge transition level, and switching of the associated adatom-induced band bending. The effect in STM topographic images is well reproduced by transport modeling of filling and emptying rates as a function of the tip position. STM atomic contrast and tunneling spectra are in good agreement with density functional theory calculations for In adatoms. The adatom ionization effect can extend to distances greater than 50 nm away, which we attribute to the low concentration and low binding energy of the residual donors in the undoped InSb crystal. These studies demonstrate how individual atoms can be used to sensitively control current flow in nanoscale devices.
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Affiliation(s)
- Sara M Mueller
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
| | - Dongjoon Kim
- Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, OH 43210, United States of America
| | - Stephen R McMillan
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, United States of America
| | - Steven J Tjung
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
| | - Jacob J Repicky
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
| | - Stephen Gant
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
| | - Evan Lang
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
| | - Fedor Bergmann
- Bergmann Messgeraete Entwicklung KG, Kocheler Strasse 101, 82418 Murnau, Germany
| | - Kevin Werner
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
- BAE Systems, 130 Daniel Webster Hwy., MER15-1813, Merrimack, NH 03054, United States of America
| | - Enam Chowdhury
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
- Department of Material Science and Engineering, Ohio State University, Columbus OH 43210, United States of America
| | - Aravind Asthagiri
- Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, OH 43210, United States of America
| | - Michael E Flatté
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, United States of America
| | - Jay A Gupta
- Department of Physics, Ohio State University, Columbus, OH 43210, United States of America
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10
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McMillan SR, Harmon NJ, Flatté ME. Image of Dynamic Local Exchange Interactions in the dc Magnetoresistance of Spin-Polarized Current through a Dopant. Phys Rev Lett 2020; 125:257203. [PMID: 33416385 DOI: 10.1103/physrevlett.125.257203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Revised: 09/15/2020] [Accepted: 11/10/2020] [Indexed: 06/12/2023]
Abstract
We predict strong, dynamical effects in the dc magnetoresistance of current flowing from a spin-polarized electrical contact through a magnetic dopant in a nonmagnetic host. Using the stochastic Liouville formalism we calculate clearly defined resonances in the dc magnetoresistance when the applied magnetic field matches the exchange interaction with a nearby spin. At these resonances spin precession in the applied magnetic field is canceled by spin evolution in the exchange field, preserving a dynamic bottleneck for spin transport through the dopant. Similar features emerge when the dopant spin is coupled to nearby nuclei through the hyperfine interaction. These features provide a precise means of measuring exchange or hyperfine couplings between localized spins near a surface using spin-polarized scanning tunneling microscopy, without any ac electric or magnetic fields, even when the exchange or hyperfine energy is orders of magnitude smaller than the thermal energy.
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Affiliation(s)
- Stephen R McMillan
- Optical Science and Technology Center, and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Nicholas J Harmon
- Optical Science and Technology Center, and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Michael E Flatté
- Optical Science and Technology Center, and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
- Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
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11
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Atxabal A, McMillan SR, García-Arruabarrena B, Parui S, Llopis R, Casanova F, Flatté ME, Hueso LE. Strain Effects on the Energy-Level Alignment at Metal/Organic Semiconductor Interfaces. ACS Appl Mater Interfaces 2019; 11:12717-12722. [PMID: 30859806 DOI: 10.1021/acsami.8b21531] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Flexible and wearable devices are among the upcoming trends in the opto-electronics market. Nevertheless, bendable devices should ensure the same efficiency and stability as their rigid analogs. It is well-known that the energy barriers between the metal Fermi energy and the molecular levels of organic semiconductors devoted to charge transport are key parameters in the performance of organic-based electronic devices. Therefore, it is paramount to understand how the energy barriers at metal/organic semiconductor interfaces change with bending. In this work, we experimentally measure the interface energy barriers between a metallic contact and small semiconducting molecules. The measurements are performed in operative conditions, while the samples are bent by a controlled applied mechanical strain. We determine that energy barriers are not sensitive to bending of the sample, but we observe that the hopping transport of the charges in flat molecules can be tuned by mechanical strain. The theoretical model developed for this work confirms our experimental observations.
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Affiliation(s)
- Ainhoa Atxabal
- CIC nanoGUNE , 20018 Donostia-San Sebastian , Basque Country, Spain
| | - Stephen R McMillan
- Department of Physics and Astronomy , University of Iowa , 203 Van Allen Hall , Iowa City , Iowa 52242-1479 , United States
| | | | - Subir Parui
- CIC nanoGUNE , 20018 Donostia-San Sebastian , Basque Country, Spain
| | - Roger Llopis
- CIC nanoGUNE , 20018 Donostia-San Sebastian , Basque Country, Spain
| | - Fèlix Casanova
- CIC nanoGUNE , 20018 Donostia-San Sebastian , Basque Country, Spain
- IKERBASQUE, Basque Foundation for Science , 48013 Bilbao , Basque Country, Spain
| | - Michael E Flatté
- Department of Physics and Astronomy , University of Iowa , 203 Van Allen Hall , Iowa City , Iowa 52242-1479 , United States
| | - Luis E Hueso
- CIC nanoGUNE , 20018 Donostia-San Sebastian , Basque Country, Spain
- IKERBASQUE, Basque Foundation for Science , 48013 Bilbao , Basque Country, Spain
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12
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Candido DR, Flatté ME, Egues JC. Blurring the Boundaries Between Topological and Nontopological Phenomena in Dots. Phys Rev Lett 2018; 121:256804. [PMID: 30608841 DOI: 10.1103/physrevlett.121.256804] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Indexed: 06/09/2023]
Abstract
We investigate the electronic and transport properties of topological and nontopological InAs_{0.85}Bi_{0.15} quantum dots (QDs) described by a ∼30 meV gapped Bernevig-Hughes-Zhang (BHZ) model with cylindrical confinement, i.e., "BHZ dots." Via modified Bessel functions, we analytically show that nontopological dots quite unexpectedly have discrete helical edge states, i.e., Kramers pairs with spin-angular-momentum locking similar to topological dots. These unusual nontopological edge states are geometrically protected due to confinement for a wide range of parameters and remarkably contrast with the bulk-edge correspondence in topological insulators, as no bulk topological invariant guarantees their existence. Moreover, for a conduction window with four edge states, we find that the two-terminal conductance G versus the QD radius R and the gate V_{g} controlling its levels shows a double peak at 2e^{2}/h for both topological and trivial BHZ QDs. This is in stark contrast to conductance measurements in 2D quantum spin Hall and trivial insulators. All of these results were also found in HgTe QDs. Bi-based BHZ dots should also prove important as hosts to room temperature edge spin qubits.
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Affiliation(s)
- Denis R Candido
- Instituto de Física de São Carlos, Universidade de São Paulo, 13560-970, São Carlos, São Paulo, Brazil
| | - Michael E Flatté
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA
- International Institute of Physics, Federal University of Rio Grande do Norte, 59078-970, P.O. Box 1613, Natal, Brazil
| | - J Carlos Egues
- Instituto de Física de São Carlos, Universidade de São Paulo, 13560-970, São Carlos, São Paulo, Brazil
- International Institute of Physics, Federal University of Rio Grande do Norte, 59078-970, P.O. Box 1613, Natal, Brazil
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13
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Golovatski EA, Flatté ME. Interaction of two domain walls during spin-torque-induced coherent motion. J Phys Condens Matter 2018; 30:315802. [PMID: 29916815 DOI: 10.1088/1361-648x/aacd84] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We show that the application of a spin-polarized current to a double p domain wall system with a variable distance between the walls results in an interaction between the two domain walls. The transmission spectrum changes from that of a spin-dependent resonant double barrier to one like a [Formula: see text] wall. In addition, the spin torque on each individual wall creates coupled motion in the domain walls. The walls move independently with a fast speed at large separations, but slow considerably at small separations.
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Affiliation(s)
- E A Golovatski
- Department of Physics, Central College, Pella, IA 50129, United States of America. Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, United States of America
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14
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Zhang Y, Park A, Cintora A, McMillan SR, Harmon NJ, Moehle A, Flatté ME, Fuchs GD, Ober CK. Impact of the Synthesis Method on the Solid-State Charge Transport of Radical Polymers. J Mater Chem C Mater 2018; 6:111-118. [PMID: 29430302 PMCID: PMC5800793 DOI: 10.1039/c7tc04645f] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
There are conflicting reports in the literature about the presence of room temperature conductivity in poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA), a redox active polymer with radical groups pendent to an insulating backbone. To understand the variability in the findings across the literature and synthetic methods, we prepared PTMA using three living methods - anionic, ATRP and RAFT polymerization. We find that all three synthetic methods produce PTMA with radical yields of 70 - 80%, controlled molecular weight, and low dispersity. Additionally, we used on-chip EPR to probe the robustness of radical content in solid films under ambient air and light, and found negligible change in the radical content over time. Electrically, we found that PTMA is highly insulating - conductivity in the range 10-11 S/cm - regardless of the synthetic method of preparation. These findings provide greater clarity for potential applications of PTMA in energy storage.
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Affiliation(s)
- Yiren Zhang
- Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
| | - Albert Park
- Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
| | - Alicia Cintora
- Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
| | - Stephen R McMillan
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Nicholas J Harmon
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Austin Moehle
- Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
| | - Michael E Flatté
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Gregory D Fuchs
- Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
| | - Christopher K Ober
- Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
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15
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Singh S, Katoch J, Zhu T, Meng KY, Liu T, Brangham JT, Yang F, Flatté ME, Kawakami RK. Strong Modulation of Spin Currents in Bilayer Graphene by Static and Fluctuating Proximity Exchange Fields. Phys Rev Lett 2017; 118:187201. [PMID: 28524685 DOI: 10.1103/physrevlett.118.187201] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Indexed: 06/07/2023]
Abstract
Two-dimensional materials provide a unique platform to explore the full potential of magnetic proximity-driven phenomena, which can be further used for applications in next-generation spintronic devices. Of particular interest is to understand and control spin currents in graphene by the magnetic exchange field of a nearby ferromagnetic material in graphene-ferromagnetic-insulator (FMI) heterostructures. Here, we present the experimental study showing the strong modulation of spin currents in graphene layers by controlling the direction of the exchange field due to FMI magnetization. Owing to clean interfaces, a strong magnetic exchange coupling leads to the experimental observation of complete spin modulation at low externally applied magnetic fields in short graphene channels. Additionally, we discover that the graphene spin current can be fully dephased by randomly fluctuating exchange fields. This is manifested as an unusually strong temperature dependence of the nonlocal spin signals in graphene, which is due to spin relaxation by thermally induced transverse fluctuations of the FMI magnetization.
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Affiliation(s)
- Simranjeet Singh
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Jyoti Katoch
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Tiancong Zhu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Keng-Yuan Meng
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Tianyu Liu
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Jack T Brangham
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Fengyuan Yang
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Michael E Flatté
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Roland K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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16
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van Bree J, Flatté ME. Atomic-Scale Magnetometry of Dynamic Magnetization. Phys Rev Lett 2017; 118:087601. [PMID: 28282167 DOI: 10.1103/physrevlett.118.087601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Indexed: 06/06/2023]
Abstract
The spatial resolution of imaging magnetometers has benefited from scanning probe techniques. The requirement that the sample perturbs the scanning probe through a magnetic field external to its volume limits magnetometry to samples with pre-existing magnetization. We propose a magnetometer in which the perturbation is reversed: the probe's magnetic field generates a response of the sample, which acts back on the probe and changes its energy. For an NV^{-} spin center in diamond this perturbation changes the fine-structure splitting of the spin ground state. Sensitive measurement techniques using coherent detection schemes then permit detection of the magnetic response of paramagnetic and diamagnetic materials. This technique can measure the thickness of magnetically dead layers with better than 0.1 Å accuracy.
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Affiliation(s)
- J van Bree
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA
| | - M E Flatté
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA
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17
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Jungwirth NR, Calderon B, Ji Y, Spencer MG, Flatté ME, Fuchs GD. Temperature Dependence of Wavelength Selectable Zero-Phonon Emission from Single Defects in Hexagonal Boron Nitride. Nano Lett 2016; 16:6052-6057. [PMID: 27580074 DOI: 10.1021/acs.nanolett.6b01987] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We investigate the distribution and temperature-dependent optical properties of sharp, zero-phonon emission from defect-based single photon sources in multilayer hexagonal boron nitride (h-BN) flakes. We observe sharp emission lines from optically active defects distributed across an energy range that exceeds 500 meV. Spectrally resolved photon-correlation measurements verify single photon emission, even when multiple emission lines are simultaneously excited within the same h-BN flake. We also present a detailed study of the temperature-dependent line width, spectral energy shift, and intensity for two different zero-phonon lines centered at 575 and 682 nm, which reveals a nearly identical temperature dependence despite a large difference in transition energy. Our temperature-dependent results are well described by a lattice vibration model that considers piezoelectric coupling to in-plane phonons. Finally, polarization spectroscopy measurements suggest that whereas the 575 nm emission line is directly excited by 532 nm excitation, the 682 nm line is excited indirectly.
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Affiliation(s)
| | - Brian Calderon
- Cornell University , Ithaca, New York 14853, United States
| | - Yanxin Ji
- Cornell University , Ithaca, New York 14853, United States
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18
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Liu T, Vignale G, Flatté ME. Nonlocal Drag of Magnons in a Ferromagnetic Bilayer. Phys Rev Lett 2016; 116:237202. [PMID: 27341254 DOI: 10.1103/physrevlett.116.237202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Indexed: 06/06/2023]
Abstract
Quantized spin waves, or magnons, in a magnetic insulator are assumed to interact weakly with the surroundings, and to flow with little dissipation or drag, producing exceptionally long diffusion lengths and relaxation times. In analogy to Coulomb drag in bilayer two-dimensional electron gases, in which the contribution of the Coulomb interaction to the electric resistivity is studied by measuring the interlayer resistivity (transresistivity), we predict a nonlocal drag of magnons in a ferromagnetic bilayer structure based on semiclassical Boltzmann equations. Nonlocal magnon drag depends on magnetic dipolar interactions between the layers and manifests in the magnon current transresistivity and the magnon thermal transresistivity, whereby a magnon current in one layer induces a chemical potential gradient and/or a temperature gradient in the other layer. The largest drag effect occurs when the magnon current flows parallel to the magnetization; however, for oblique magnon currents a large transverse current of magnons emerges. We examine the effect for practical parameters, and find that the predicted induced temperature gradient is readily observable.
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Affiliation(s)
- Tianyu Liu
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - G Vignale
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
| | - Michael E Flatté
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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19
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Ou YS, Chiu YH, Harmon NJ, Odenthal P, Sheffield M, Chilcote M, Kawakami RK, Flatté ME, Johnston-Halperin E. Exchange-Driven Spin Relaxation in Ferromagnet-Oxide-Semiconductor Heterostructures. Phys Rev Lett 2016; 116:107201. [PMID: 27015506 DOI: 10.1103/physrevlett.116.107201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Indexed: 06/05/2023]
Abstract
We demonstrate that electron spin relaxation in GaAs in the proximity of a Fe/MgO layer is dominated by interaction with an exchange-driven hyperfine field at temperatures below 60 K. Temperature-dependent spin-resolved optical pump-probe spectroscopy reveals a strong correlation of the electron spin relaxation with carrier freeze-out, in quantitative agreement with a theoretical interpretation that at low temperatures the free-carrier spin lifetime is dominated by inhomogeneity in the local hyperfine field due to carrier localization. As the regime of large nuclear inhomogeneity is accessible in these heterostructures for magnetic fields <3 kG, inferences from this result resolve a long-standing and contentious dispute concerning the origin of spin relaxation in GaAs at low temperature when a magnetic field is present. Further, this improved fundamental understanding clarifies the importance of future experiments probing the time-dependent exchange interaction at a ferromagnet-semiconductor interface and its consequences for spin dissipation and transport during spin pumping.
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Affiliation(s)
- Yu-Sheng Ou
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - Yi-Hsin Chiu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - N J Harmon
- Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242-1479, USA
| | - Patrick Odenthal
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Matthew Sheffield
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - Michael Chilcote
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
| | - R K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - M E Flatté
- Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242-1479, USA
| | - E Johnston-Halperin
- Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
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20
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Pu Y, Odenthal PM, Adur R, Beardsley J, Swartz AG, Pelekhov DV, Flatté ME, Kawakami RK, Pelz J, Hammel PC, Johnston-Halperin E. Ferromagnetic Resonance Spin Pumping and Electrical Spin Injection in Silicon-Based Metal-Oxide-Semiconductor Heterostructures. Phys Rev Lett 2015; 115:246602. [PMID: 26705647 DOI: 10.1103/physrevlett.115.246602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Indexed: 06/05/2023]
Abstract
We present the measurement of ferromagnetic resonance (FMR-)driven spin pumping and three-terminal electrical spin injection within the same silicon-based device. Both effects manifest in a dc spin accumulation voltage V_{s} that is suppressed as an applied field is rotated to the out-of-plane direction, i.e., the oblique Hanle geometry. Comparison of V_{s} between these two spin injection mechanisms reveals an anomalously strong suppression of FMR-driven spin pumping with increasing out-of-plane field H_{app}^{z}. We propose that the presence of the large ac component to the spin current generated by the spin pumping approach, expected to exceed the dc value by 2 orders of magnitude, is the origin of this discrepancy through its influence on the spin dynamics at the oxide-silicon interface. This convolution, wherein the dynamics of both the injector and the interface play a significant role in the spin accumulation, represents a new regime for spin injection that is not well described by existing models of either FMR-driven spin pumping or electrical spin injection.
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Affiliation(s)
- Y Pu
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - P M Odenthal
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - R Adur
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - J Beardsley
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - A G Swartz
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - D V Pelekhov
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - M E Flatté
- Departent of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - R K Kawakami
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - J Pelz
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - P C Hammel
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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21
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Wohlgenannt M, Flatté ME, Harmon NJ, Wang F, Kent AD, Macià F. Singlet-to-triplet interconversion using hyperfine as well as ferromagnetic fringe fields. Philos Trans A Math Phys Eng Sci 2015; 373:rsta.2014.0326. [PMID: 25987575 PMCID: PMC4455723 DOI: 10.1098/rsta.2014.0326] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/01/2015] [Indexed: 06/04/2023]
Abstract
Until recently the important role that spin-physics ('spintronics') plays in organic light-emitting devices and photovoltaic cells was not sufficiently recognized. This attitude has begun to change. We review our recent work that shows that spatially rapidly varying local magnetic fields that may be present in the organic layer dramatically affect electronic transport properties and electroluminescence efficiency. Competition between spin-dynamics due to these spatially varying fields and an applied, spatially homogeneous magnetic field leads to large magnetoresistance, even at room temperature where the thermodynamic influences of the resulting nuclear and electronic Zeeman splittings are negligible. Spatially rapidly varying local magnetic fields are naturally present in many organic materials in the form of nuclear hyperfine fields, but we will also review a second method of controlling the electrical conductivity/electroluminescence, using the spatially varying magnetic fringe fields of a magnetically unsaturated ferromagnet. Fringe-field magnetoresistance has a magnitude of several per cent and is hysteretic and anisotropic. This new method of control is sensitive to even remanent magnetic states, leading to different conductivity/electroluminescence values in the absence of an applied field. We briefly review a model based on fringe-field-induced polaron-pair spin-dynamics that successfully describes several key features of the experimental fringe-field magnetoresistance and magnetoelectroluminescence.
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Affiliation(s)
- M Wohlgenannt
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, IA 52242, USA
| | - M E Flatté
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, IA 52242, USA
| | - N J Harmon
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, IA 52242, USA
| | - F Wang
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, IA 52242, USA
| | - A D Kent
- Department of Physics, New York University, 4 Washington Place, New York, NY 10003, USA
| | - F Macià
- Department of Physics, New York University, 4 Washington Place, New York, NY 10003, USA
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22
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Marinescu M, Kornyshev AA, Flatté ME. Electrical control of Faraday rotation at a liquid-liquid interface. Faraday Discuss 2015; 178:363-70. [PMID: 25774647 DOI: 10.1039/c4fd00210e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A theory is developed for the Faraday rotation of light from a monolayer of charged magnetic nanoparticles at an electrified liquid-liquid interface. The polarization fields of neighboring nanoparticles enhance the Faraday rotation. At such interfaces, and for realistic sizes and charges of nanoparticles, their adsorption-desorption can be controlled with a voltage variation<1 V, providing electrovariable Faraday rotation. A calculation based on the Maxwell-Garnett theory predicts that the corresponding redistribution of 40 nm nanoparticles of yttrium iron garnet can switch a cavity with a quality factor larger than 10(4) for light of wavelength 500 nm at normal incidence.
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Affiliation(s)
- Monica Marinescu
- Department of Mechanical Engineering, Faculty of Engineering, Imperial College, London, SW7 2AZ, UK.
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23
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Şahin C, Flatté ME. Tunable giant spin hall conductivities in a strong spin-orbit semimetal: Bi(1-x) Sb(x). Phys Rev Lett 2015; 114:107201. [PMID: 25815962 DOI: 10.1103/physrevlett.114.107201] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Indexed: 06/04/2023]
Abstract
Intrinsic spin Hall conductivities are calculated for strong spin-orbit Bi(1-x)Sb(x) semimetals, from the Kubo formula and using Berry curvatures evaluated throughout the Brillouin zone from a tight-binding Hamiltonian. Nearly crossing bands with strong spin-orbit interaction generate giant spin Hall conductivities in these materials, ranging from 474 (ℏ/e)(Ω cm)^{-1} for bismuth to 96 (ℏ/e)(Ω cm)^{-1} for antimony; the value for bismuth is more than twice that of platinum. The large spin Hall conductivities persist for alloy compositions corresponding to a three-dimensional topological insulator state, such as Bi(0.83)Sb(0.17). The spin Hall conductivity could be changed by a factor of 5 for doped Bi, or for Bi(0.83)Sb(0.17), by changing the chemical potential by 0.5 eV, suggesting the potential for doping or voltage tuned spin Hall current.
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Affiliation(s)
- Cüneyt Şahin
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Michael E Flatté
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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24
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Zhang X, Liu T, Flatté ME, Tang HX. Electric-field coupling to spin waves in a centrosymmetric ferrite. Phys Rev Lett 2014; 113:037202. [PMID: 25083662 DOI: 10.1103/physrevlett.113.037202] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Indexed: 06/03/2023]
Abstract
We experimentally demonstrate that the spin-orbit interaction can be utilized for direct electric-field tuning of the propagation of spin waves in a single-crystal yttrium iron garnet magnonic waveguide. Magnetoelectric coupling not due to the spin-orbit interaction and, hence, an order of magnitude weaker leads to electric-field modification of the spin-wave velocity for waveguide geometries where the spin-orbit interaction will not contribute. A theory of the phase shift, validated by the experiment data, shows that, in the exchange spin wave regime, this electric tuning can have high efficiency. Our findings point to an important avenue for manipulating spin waves and developing electrically tunable magnonic devices.
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Affiliation(s)
- Xufeng Zhang
- Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511, USA
| | - Tianyu Liu
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Michael E Flatté
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
| | - Hong X Tang
- Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511, USA
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25
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van Bree J, Silov AY, Koenraad PM, Flatté ME. Spin-orbit-induced circulating currents in a semiconductor nanostructure. Phys Rev Lett 2014; 112:187201. [PMID: 24856716 DOI: 10.1103/physrevlett.112.187201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Indexed: 06/03/2023]
Abstract
Circulating orbital currents produced by the spin-orbit interaction for a single electron spin in a quantum dot are explicitly evaluated at zero magnetic field, along with their effect on the total magnetic moment (spin and orbital) of the electron spin. The currents are dominated by coherent superpositions of the conduction and valence envelope functions of the electronic state, are smoothly varying within the quantum dot, and are peaked roughly halfway between the dot center and edge. Thus the spatial structure of the spin contribution to the magnetic moment (which is peaked at the dot center) differs greatly from the spatial structure of the orbital contribution. Even when the spin and orbital magnetic moments cancel (for g=0) the spin can interact strongly with local magnetic fields, e.g., from other spins, which has implications for spin lifetimes and spin manipulation.
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Affiliation(s)
- J van Bree
- PSN, COBRA Research Institute, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
| | - A Yu Silov
- PSN, COBRA Research Institute, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
| | - P M Koenraad
- PSN, COBRA Research Institute, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
| | - M E Flatté
- PSN, COBRA Research Institute, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands and Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA
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26
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Macià F, Wang F, Harmon NJ, Kent AD, Wohlgenannt M, Flatté ME. Organic magnetoelectroluminescence for room temperature transduction between magnetic and optical information. Nat Commun 2014; 5:3609. [DOI: 10.1038/ncomms4609] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 03/10/2014] [Indexed: 11/09/2022] Open
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27
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Magyar A, Hu W, Shanley T, Flatté ME, Hu E, Aharonovich I. Synthesis of luminescent europium defects in diamond. Nat Commun 2014; 5:3523. [DOI: 10.1038/ncomms4523] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 02/27/2014] [Indexed: 11/09/2022] Open
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28
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Affiliation(s)
- Michael E Flatté
- Optical Science and Technology Center and the Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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29
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Abstract
A theory is introduced for spin relaxation and spin diffusion of hopping carriers in a disordered system. For disorder described by a distribution of waiting times between hops (e.g., from multiple traps, site-energy disorder, and/or positional disorder) the dominant spin relaxation mechanisms in organic semiconductors (hyperfine, hopping-induced spin-orbit, and intrasite spin relaxation) each produce different characteristic spin relaxation and spin diffusion dependences on temperature. The resulting unique experimental signatures predicted by the theory for each mechanism in organic semiconductors provide a prescription for determining the dominant spin relaxation mechanism.
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Affiliation(s)
- N J Harmon
- Department of Physics and Astronomy, Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA.
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30
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Harmon NJ, Flatté ME. Spin-flip induced magnetoresistance in positionally disordered organic solids. Phys Rev Lett 2012; 108:186602. [PMID: 22681098 DOI: 10.1103/physrevlett.108.186602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Revised: 03/14/2012] [Indexed: 06/01/2023]
Abstract
A model for magnetoresistance in positionally disordered organic materials is presented and solved using percolation theory. The model describes the effects of spin dynamics on hopping transport by considering changes in the effective density of hopping sites, a key quantity determining the properties of percolative transport. Faster spin-flip transitions open up "spin-blocked" pathways to become viable conduction channels and hence produce magnetoresistance. Features of this percolative magnetoresistance can be found analytically in several regimes, and agree with previous measurements, including the sensitive dependence of the magnetic-field dependence of the magnetoresistance on the ratio of the carrier hopping time to the hyperfine-induced carrier spin precession time. Studies of magnetoresistance in known systems with controllable positional disorder would provide an additional stringent test of this theory.
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Affiliation(s)
- N J Harmon
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA.
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31
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Abstract
The sensitive dependence of a semiconductor's electronic, optical and magnetic properties on dopants has provided an extensive range of tunable phenomena to explore and apply to devices. Recently it has become possible to move past the tunable properties of an ensemble of dopants to identify the effects of a solitary dopant on commercial device performance as well as locally on the fundamental properties of a semiconductor. New applications that require the discrete character of a single dopant, such as single-spin devices in the area of quantum information or single-dopant transistors, demand a further focus on the properties of a specific dopant. This article describes the huge advances in the past decade towards observing, controllably creating and manipulating single dopants, as well as their application in novel devices which allow opening the new field of solotronics (solitary dopant optoelectronics).
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Affiliation(s)
- Paul M Koenraad
- COBRA Inter-University Research Institute, Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
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32
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Berman DH, Flatté ME. Electron-beam formation from spin-orbit interactions in zinc-blende semiconductor quantum wells. Phys Rev Lett 2010; 105:157202. [PMID: 21230935 DOI: 10.1103/physrevlett.105.157202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Indexed: 05/30/2023]
Abstract
We find a dramatic enhancement of electron propagation along a narrow range of real-space angles from an isotropic source in a two-dimensional quantum well made from a zinc-blende semiconductor. This "electron-beam" formation is caused by the interplay between spin-orbit interaction originating from a perpendicular electric field to the quantum well and the intrinsic spin-orbit field of the zinc-blende crystal lattice in a quantum well, in situations where the two fields are different in strength but of the same order of magnitude. Beam formation is associated with caustics and can be described semiclassically using a stationary phase analysis.
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Affiliation(s)
- David H Berman
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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33
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Celebi C, Garleff JK, Silov AY, Yakunin AM, Koenraad PM, Van Roy W, Tang JM, Flatté ME. Surface induced asymmetry of acceptor wave functions. Phys Rev Lett 2010; 104:086404. [PMID: 20366956 DOI: 10.1103/physrevlett.104.086404] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2009] [Indexed: 05/29/2023]
Abstract
Measurements of the local density of states of individual acceptors in III-V semiconductors show that the symmetry of the acceptor states strongly depends on the depth of the atom below a (110) surface. Tight-binding calculations performed for a uniformly strained bulk material demonstrate that strain induced by the surface relaxation is responsible for the observed depth-dependent symmetry breaking of acceptor wave functions. As this effect is strongest for weakly bound acceptors, it explains within a unified approach the commonly observed triangular shapes of shallow acceptors and the crosslike shapes of deeply bound acceptor states in III-V materials.
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Affiliation(s)
- C Celebi
- COBRA Inter-University Research Institute, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands
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34
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Abstract
We analyze the interaction of a nanomagnet (ferromagnetic) with a single photonic mode of a cavity in a fully quantum-mechanical treatment and find that exceptionally large quantum-coherent magnet-photon coupling can be achieved. Coupling terms in excess of several THz are predicted to be achievable in a spherical cavity of approximately 1 mm radius with a nanomagnet of approximately 100 nm radius and ferromagnetic resonance frequency of approximately 200 GHz. Eigenstates of the magnet-photon system correspond to entangled states of spin orientation and photon number, in which over 10{5} values of each quantum number are represented; conversely, initial (coherent) states of definite spin and photon number evolve dynamically to produce large oscillations in the microwave power (and nanomagnet spin orientation), and are characterized by exceptionally long dephasing times.
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Affiliation(s)
- O O Soykal
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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35
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Abstract
An ac electric field applied to a single donor-bound electron in a semiconductor modulates the orbital character of its wave function, which affects the electron's spin dynamics via the spin-orbit interaction. Numerical calculations of the spin dynamics of a single hydrogenic donor (Si) embedded in GaAs, using a real-space multiband k.p formalism, show the high symmetry of the hydrogenic donor state results in strongly nonlinear dependences of the electronic g tensor on applied fields. A nontrivial consequence is that the most rapid Rabi oscillations occur for electric fields modulated at a subharmonic of the Larmor frequency.
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Affiliation(s)
- A De
- Department of Physics and Astronomy and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA
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36
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Tang JM, Flatté ME. Magnetic circular dichroism from the impurity band in III-V diluted magnetic semiconductors. Phys Rev Lett 2008; 101:157203. [PMID: 18999634 DOI: 10.1103/physrevlett.101.157203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Indexed: 05/27/2023]
Abstract
The magnetic circular dichroism of III-V diluted magnetic semiconductors, calculated within a theoretical framework suitable for highly disordered materials, is shown to be dominated by optical transitions between the bulk bands and an impurity band formed from magnetic dopant states. The real-space Green's functions incorporate spatial correlations in the disordered conduction band and valence-band electronic structure, and include extended and localized states on an equal basis. Our findings reconcile unusual trends in the experimental magnetic circular dichroism in III-V diluted magnetic semiconductors with the antiferromagnetic p-d exchange interaction between a magnetic dopant spin and its host.
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Affiliation(s)
- Jian-Ming Tang
- Department of Physics, University of New Hampshire, Durham, New Hampshire 03824-3520, USA
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37
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Myers RC, Mikkelsen MH, Tang JM, Gossard AC, Flatté ME, Awschalom DD. Zero-field optical manipulation of magnetic ions in semiconductors. Nat Mater 2008; 7:203-208. [PMID: 18278049 DOI: 10.1038/nmat2123] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Accepted: 01/17/2008] [Indexed: 05/25/2023]
Abstract
Controlling and monitoring individual spins is desirable for building spin-based devices, as well as implementing quantum information processing schemes. As with trapped ions in cold gases, magnetic ions trapped on a semiconductor lattice have uniform properties and relatively long spin lifetimes. Furthermore, diluted magnetic moments in semiconductors can be strongly coupled to the surrounding host, permitting optical or electrical spin manipulation. Here we describe the zero-field optical manipulation of a few hundred manganese ions in a single gallium arsenide quantum well. Optically created mobile electron spins dynamically generate an energy splitting of the ion spins and enable magnetic moment orientation solely by changing either photon helicity or energy. These polarized manganese spins precess in a transverse field, enabling measurements of the spin lifetimes. As the magnetic ion concentration is reduced and the manganese spin lifetime increases, coherent optical control and readout of single manganese spins in gallium arsenide should be possible.
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Affiliation(s)
- R C Myers
- Center for Spintronics and Quantum Computation, University of California, Santa Barbara, California 93106, USA
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38
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Sheu BL, Myers RC, Tang JM, Samarth N, Awschalom DD, Schiffer P, Flatté ME. Onset of Ferromagnetism in Low-Doped Ga1-xMnxAs. Phys Rev Lett 2007; 99:227205. [PMID: 18233322 DOI: 10.1103/physrevlett.99.227205] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2007] [Indexed: 05/25/2023]
Abstract
We develop a quantitatively predictive theory for impurity-band ferromagnetism in the low-doping regime of Ga1-xMnxAs. We compare it with measurements of a series of samples whose compositions span the transition from paramagnetic insulating to ferromagnetic conducting behavior. The theoretical Curie temperatures depend sensitively on the local fluctuations in the Mn-hole binding energy, which originate from Mn disorder and As antisite defects. The experimentally determined hopping energy is an excellent predictor of the Curie temperature, in agreement with the theory.
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Affiliation(s)
- B L Sheu
- Physics Department and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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39
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Marczinowski F, Wiebe J, Tang JM, Flatté ME, Meier F, Morgenstern M, Wiesendanger R. Local electronic structure near Mn acceptors in InAs: surface-induced symmetry breaking and coupling to host states. Phys Rev Lett 2007; 99:157202. [PMID: 17995207 DOI: 10.1103/physrevlett.99.157202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2007] [Indexed: 05/04/2023]
Abstract
We present low-temperature scanning tunneling spectroscopy measurements on Mn acceptors in InAs in comparison with tight-binding calculations. We find a strong (001)-mirror asymmetry of the bound hole wave function close to the (110) surface. In addition, multiple acceptor-related peaks are observed and are attributed to a spin-orbit splitting of the acceptor level. Because of the p-d exchange interaction the local density of states near the acceptors is enhanced in the valence band and suppressed in the conduction band. We also observe signs of anisotropic scattering of the conduction band states by neutral acceptors.
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Affiliation(s)
- F Marczinowski
- Institute of Applied Physics, Hamburg University, Jungiusstrasse 11, D-20355 Hamburg, Germany
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40
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Yakunin AM, Silov AY, Koenraad PM, Tang JM, Flatté ME, Primus JL, Van Roy W, De Boeck J, Monakhov AM, Romanov KS, Panaiotti IE, Averkiev NS. Warping a single Mn acceptor wavefunction by straining the GaAs host. Nat Mater 2007; 6:512-5. [PMID: 17558428 DOI: 10.1038/nmat1936] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2006] [Accepted: 05/16/2007] [Indexed: 05/15/2023]
Abstract
Transition-metal dopants such as Mn determine the ferromagnetism in dilute magnetic semiconductors such as Ga(1-x)Mn(x)As. Recently, the acceptor states of Mn dopants in GaAs were found to be highly anisotropic owing to the symmetry of the host crystal. Here, we show how the shape of such a state can be modified by local strain. The Mn acceptors near InAs quantum dots are mapped at room temperature by scanning tunnelling microscopy. Dramatic distortions and a reduction in the symmetry of the wavefunction of the hole bound to the Mn acceptor are observed originating from strain induced by quantum dots. Calculations of the acceptor-state wavefunction in the presence of strain, within a tight-binding model and within an effective-mass model, agree with the experimentally observed shape. The magnetic easy axes of strained lightly doped Ga(1-x)Mn(x)As can be explained on the basis of the observed local density of states for the single Mn spin.
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Affiliation(s)
- A M Yakunin
- COBRA Inter-University Research Institute, Eindhoven University of Technology, PO Box 513, NL-5600MB Eindhoven, The Netherlands.
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41
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Hankiewicz EM, Vignale G, Flatté ME. Spin-Hall effect in a [110] GaAs quantum well. Phys Rev Lett 2006; 97:266601. [PMID: 17280444 DOI: 10.1103/physrevlett.97.266601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2006] [Indexed: 05/13/2023]
Abstract
A self-consistent treatment of the spin-Hall effect requires consideration of the spin-orbit coupling and electron-impurity scattering on equal footing. This is done here for the experimentally relevant case of a [110] GaAs quantum well [Sih, Nature Phys. 1, 31 (2005)]. Working within the framework of the exact linear response formalism we calculate the spin-Hall conductivity including the Dresselhaus linear and cubic terms in the band structure, as well as the electron-impurity scattering and electron-electron interaction to all orders. We show that the spin-Hall conductivity naturally separates into two contributions, skew-scattering and side-jump, and we propose an experiment to distinguish between them.
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Affiliation(s)
- E M Hankiewicz
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
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42
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Abstract
We propose a method for all-electrical manipulation of single ion spins substituted into a semiconductor. Mn ions with a bound hole in GaAs form a natural example. Direct electrical manipulation of the ion spin is possible, because electric fields manipulate the orbital wave function of the hole, and through the spin-orbit coupling the spin is reoriented as well. Coupling ion spins can be achieved using gates to control the size of the hole wave function. Coherent manipulation of ionic spins may find applications in high-density storage and in scalable coherent or quantum information processing.
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Affiliation(s)
- Jian-Ming Tang
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242-1479, USA
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43
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Kitchen D, Richardella A, Tang JM, Flatté ME, Yazdani A. Atom-by-atom substitution of Mn in GaAs and visualization of their hole-mediated interactions. Nature 2006; 442:436-9. [PMID: 16871214 DOI: 10.1038/nature04971] [Citation(s) in RCA: 246] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2006] [Accepted: 06/06/2006] [Indexed: 11/09/2022]
Abstract
The discovery of ferromagnetism in Mn-doped GaAs has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices. A major hurdle for realistic applications of Ga(1-x)Mn(x)As, or other dilute magnetic semiconductors, remains that their ferromagnetic transition temperature is below room temperature. Enhancing ferromagnetism in semiconductors requires us to understand the mechanisms for interaction between magnetic dopants, such as Mn, and identify the circumstances in which ferromagnetic interactions are maximized. Here we describe an atom-by-atom substitution technique using a scanning tunnelling microscope (STM) and apply it to perform a controlled study at the atomic scale of the interactions between isolated Mn acceptors, which are mediated by holes in GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn-Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga(1-x)Mn(x)As structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples.
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Affiliation(s)
- Dale Kitchen
- Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544, USA
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44
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Abstract
We show that electron and hole Landé g factors in self-assembled III-V quantum dots have a rich structure intermediate between that of paramagnetic atomic impurities and bulk semiconductors. Strain, dot geometry, and confinement energy modify the effective g factors, yet are insufficient to explain our results. We find that the dot's discrete energy spectrum quenches the orbital angular momentum, pushing the electron g factor towards 2, even when all the materials have negative bulk g factors. The approximate shape of a dot can be determined from measurements of the g factor asymmetry.
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Affiliation(s)
- Craig E Pryor
- Department of Physics, University of Iowa, Iowa City, Iowa 52242, USA
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45
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Abstract
We predict that the flow of unpolarized current in electron-doped GaAs and InP at room temperature is unstable at high electric fields to the dynamic formation of spin-polarized current pulses. Spin-polarized current is spontaneously generated because the conductivity of a spin-polarized electron gas differs from that of an unpolarized electron gas, even in the absence of spin-orbit interaction. Magnetic fields are not required for the generation of these spin-polarized current pulses, although they can help align the polarization of sequential pulses along the same axis.
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Affiliation(s)
- Yunong Qi
- Optical Science and Technology Center and Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA
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46
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Yakunin AM, Silov AY, Koenraad PM, Tang JM, Flatté ME, Van Roy W, De Boeck J, Wolter JH. Spatial structure of Mn-Mn acceptor pairs in GaAs. Phys Rev Lett 2005; 95:256402. [PMID: 16384482 DOI: 10.1103/physrevlett.95.256402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2005] [Indexed: 05/05/2023]
Abstract
The local density of states of Mn-Mn pairs in GaAs is mapped with cross-sectional scanning tunneling microscopy and compared with theoretical calculations based on envelope-function and tight-binding models. These measurements and calculations show that the crosslike shape of the Mn-acceptor wave function in GaAs persists even at very short Mn-Mn spatial separations. The resilience of the Mn-acceptor wave function to high doping levels suggests that ferromagnetism in GaMnAs is strongly influenced by impurity-band formation. The envelope-function and tight-binding models predict similarly anisotropic overlaps of the Mn wave functions for Mn-Mn pairs. This anisotropy implies differing Curie temperatures for Mn delta-doped layers grown on differently oriented substrates.
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Affiliation(s)
- A M Yakunin
- COBRA Inter-University Research Institute, Eindhoven University of Technology, P.O. Box 513, NL-5600MB Eindhoven, The Netherlands
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47
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Leuenberger MN, Flatté ME, Awschalom DD. Teleportation of electronic many-qubit states encoded in the electron spin of quantum dots via single photons. Phys Rev Lett 2005; 94:107401. [PMID: 15783519 DOI: 10.1103/physrevlett.94.107401] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2004] [Indexed: 05/24/2023]
Abstract
We propose a teleportation scheme that relies only on single-photon measurements and Faraday rotation, for teleportation of many-qubit entangled states stored in the electron spins of a quantum dot system. The interaction between a photon and the two electron spins, via Faraday rotation in microcavities, establishes Greenberger-Horne-Zeilinger entanglement in the spin-photon-spin system. The appropriate single-qubit measurements, and the communication of two classical bits, produce teleportation. This scheme provides the essential link between spintronic and photonic quantum information devices by permitting quantum information to be exchanged between them.
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Affiliation(s)
- Michael N Leuenberger
- Department of Physics and Astronomy and OSTC, University of Iowa, Iowa City, Iowa 52242-1479, USA
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48
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Yakunin AM, Silov AY, Koenraad PM, Wolter JH, Van Roy W, De Boeck J, Tang JM, Flatté ME. Spatial structure of an individual Mn acceptor in GaAs. Phys Rev Lett 2004; 92:216806. [PMID: 15245308 DOI: 10.1103/physrevlett.92.216806] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2004] [Indexed: 05/24/2023]
Abstract
The wave function of a hole bound to an individual Mn acceptor in GaAs is spatially mapped by scanning tunneling microscopy at room temperature and an anisotropic, crosslike shape is observed. The spatial structure is compared with that from an envelope-function, effective mass model and from a tight-binding model. This demonstrates that anisotropy arising from the cubic symmetry of the GaAs crystal produces the crosslike shape for the hole wave function. Thus the coupling between Mn dopants in GaMnAs mediated by such holes will be highly anisotropic.
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Affiliation(s)
- A M Yakunin
- COBRA Inter-University, Eindhoven University of Technology, P.O. Box 513, NL-5600MB Eindhoven, The Netherlands
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49
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Abstract
We present the spin and orbitally resolved local density of states (LDOS) for a single Mn impurity and for two nearby Mn impurities in GaAs. The GaAs host is described by a sp(3) tight-binding Hamiltonian, and the Mn impurity is described by a local p-d hybridization and on-site potential. Local spin-polarized resonances within the valence bands significantly enhance the LDOS near the band edge. For two nearby parallel Mn moments the acceptor states hybridize and split in energy. Thus scanning tunneling spectroscopy can directly measure the Mn-Mn interaction as a function of distance.
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Affiliation(s)
- Jian-Ming Tang
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242-1479, USA
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50
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