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Rossokhaty AV, Baum Y, Folk JA, Watson JD, Gardner GC, Manfra MJ. Electron-Hole Asymmetric Chiral Breakdown of Reentrant Quantum Hall States. Phys Rev Lett 2016; 117:166805. [PMID: 27792394 DOI: 10.1103/physrevlett.117.166805] [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: 12/18/2015] [Indexed: 06/06/2023]
Abstract
Reentrant integer quantum Hall (RIQH) states are believed to be correlated electron solid phases, although their microscopic description remains unclear. As bias current increases, longitudinal and Hall resistivities measured for these states exhibit multiple sharp breakdown transitions, a signature unique to RIQH states. A comparison of RIQH breakdown characteristics at multiple voltage probes indicates that these signatures can be ascribed to a phase boundary between broken-down and unbroken regions, spreading chirally from source and drain contacts as a function of bias current and passing voltage probes one by one. The chiral sense of the spreading is not set by the chirality of the edge state itself, instead depending on electron- or holelike character of the RIQH state.
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Affiliation(s)
- A V Rossokhaty
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada
- Department of Radio Engineering and Cybernetics, Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region 141700, Russia
| | - Y Baum
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - J A Folk
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada
| | - J D Watson
- Department of Physics and Astronomy, and Station Q Purdue, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - G C Gardner
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - M J Manfra
- Department of Physics and Astronomy, and Station Q Purdue, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
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Kjaergaard M, Nichele F, Suominen HJ, Nowak MP, Wimmer M, Akhmerov AR, Folk JA, Flensberg K, Shabani J, Palmstrøm CJ, Marcus CM. Quantized conductance doubling and hard gap in a two-dimensional semiconductor-superconductor heterostructure. Nat Commun 2016; 7:12841. [PMID: 27682268 PMCID: PMC5056412 DOI: 10.1038/ncomms12841] [Citation(s) in RCA: 121] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2016] [Accepted: 08/08/2016] [Indexed: 12/11/2022] Open
Abstract
Coupling a two-dimensional (2D) semiconductor heterostructure to a superconductor opens new research and technology opportunities, including fundamental problems in mesoscopic superconductivity, scalable superconducting electronics, and new topological states of matter. One route towards topological matter is by coupling a 2D electron gas with strong spin–orbit interaction to an s-wave superconductor. Previous efforts along these lines have been adversely affected by interface disorder and unstable gating. Here we show measurements on a gateable InGaAs/InAs 2DEG with patterned epitaxial Al, yielding devices with atomically pristine interfaces between semiconductor and superconductor. Using surface gates to form a quantum point contact (QPC), we find a hard superconducting gap in the tunnelling regime. When the QPC is in the open regime, we observe a first conductance plateau at 4e2/h, consistent with theory. The hard-gap semiconductor–superconductor system demonstrated here is amenable to top-down processing and provides a new avenue towards low-dissipation electronics and topological quantum systems. Interface transparency between 2D semiconductors and superconductors is a longstanding problem, seriously hindering potential applications. Here, using a new hybrid system, Kjaergaard et al. report quantized conductance doubling and a hard superconducting gap measured via a quantum point contact, indicating a near pristine interface.
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Affiliation(s)
- M Kjaergaard
- Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - F Nichele
- Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - H J Suominen
- Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - M P Nowak
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 4056, 2600 GA Delft, The Netherlands.,QuTech, Delft University of Technology, PO Box 4056, 2600 GA Delft, The Netherlands.,AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Mickiewicza 30, 30-059 Kraków, Poland
| | - M Wimmer
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 4056, 2600 GA Delft, The Netherlands.,QuTech, Delft University of Technology, PO Box 4056, 2600 GA Delft, The Netherlands
| | - A R Akhmerov
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 4056, 2600 GA Delft, The Netherlands
| | - J A Folk
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z1.,Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z4
| | - K Flensberg
- Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - J Shabani
- California NanoSystems Institute, University of California, Santa Barbara, California 93106, USA
| | - C J Palmstrøm
- California NanoSystems Institute, University of California, Santa Barbara, California 93106, USA
| | - C M Marcus
- Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
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Abstract
A principal motivation to develop graphene for future devices has been its promise for quantum spintronics. Hyperfine and spin-orbit interactions are expected to be negligible in single-layer graphene. Spin transport experiments, on the other hand, show that graphene's spin relaxation is orders of magnitude faster than predicted. We present a quantum interference measurement that disentangles sources of magnetic and nonmagnetic decoherence in graphene. Magnetic defects are shown to be the primary cause of spin relaxation, masking any potential effects of spin-orbit interaction.
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Affiliation(s)
- M B Lundeberg
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z4
| | - R Yang
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z4
| | - J Renard
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z4
| | - J A Folk
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z4
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Renard J, Lundeberg MB, Folk JA, Pennec Y. Real-time imaging of K atoms on graphite: interactions and diffusion. Phys Rev Lett 2011; 106:156101. [PMID: 21568578 DOI: 10.1103/physrevlett.106.156101] [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: 09/30/2010] [Indexed: 05/30/2023]
Abstract
Scanning tunneling microscopy (STM) at liquid helium temperature is used to image potassium adsorbed on graphite at low coverage (≈0.02 monolayer). Single atoms appear as protrusions on STM topographs. A statistical analysis of the position of the atoms demonstrates repulsion between adsorbates, which is quantified by comparison with molecular dynamics simulations. This gives access to the dipole moment of a single adsorbate, found to be 10.5±1 D. Time-lapse imaging shows that long-range order is broken by thermally activated diffusion, with a 30 meV barrier to hopping between graphite lattice sites.
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Affiliation(s)
- J Renard
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T1Z4, Canada.
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Frolov SM, Venkatesan A, Yu W, Folk JA, Wegscheider W. Electrical generation of pure spin currents in a two-dimensional electron gas. Phys Rev Lett 2009; 102:116802. [PMID: 19392226 DOI: 10.1103/physrevlett.102.116802] [Citation(s) in RCA: 2] [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: 10/02/2008] [Indexed: 05/27/2023]
Abstract
Pure spin currents are generated and detected in micron-wide channels of a GaAs two-dimensional electron gas, using quantum point contacts in an in-plane magnetic field as injectors and detectors. The enhanced sensitivity to spin transport offered by a nonlocal measurement geometry enables accurate spin current measurements in this widely studied physical system. The polarization of the contacts is used to extract the quantum point contact g factor and provides a test for spontaneous polarization at 0.7 structure. The spin relaxation length in the channel is 30-50 microm over the magnetic field range 3-10 T, much longer than has been reported in GaAs two-dimensional electron gases but shorter than that expected from Dyakonov-Perel relaxation.
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Affiliation(s)
- S M Frolov
- Department of Physics, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
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Heersche HB, de Groot Z, Folk JA, van der Zant HSJ, Romeike C, Wegewijs MR, Zobbi L, Barreca D, Tondello E, Cornia A. Electron transport through single Mn12 molecular magnets. Phys Rev Lett 2006; 96:206801. [PMID: 16803192 DOI: 10.1103/physrevlett.96.206801] [Citation(s) in RCA: 183] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2005] [Indexed: 05/10/2023]
Abstract
We report transport measurements through a single-molecule magnet, the Mn12 derivative [Mn12O12(O2C-C6H4-SAc)16(H2O)4], in a single-molecule transistor geometry. Thiol groups connect the molecule to gold electrodes that are fabricated by electromigration. Striking observations are regions of complete current suppression and excitations of negative differential conductance on the energy scale of the anisotropy barrier of the molecule. Transport calculations, taking into account the high-spin ground state and magnetic excitations of the molecule, reveal a blocking mechanism of the current involving nondegenerate spin multiplets.
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Affiliation(s)
- H B Heersche
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
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Heersche HB, de Groot Z, Folk JA, Kouwenhoven LP, van der Zant HSJ, Houck AA, Labaziewicz J, Chuang IL. Kondo effect in the presence of magnetic impurities. Phys Rev Lett 2006; 96:017205. [PMID: 16486511 DOI: 10.1103/physrevlett.96.017205] [Citation(s) in RCA: 8] [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: 07/24/2005] [Indexed: 05/06/2023]
Abstract
We measure transport through gold grain quantum dots fabricated using electromigration, with magnetic impurities in the leads. A Kondo interaction is observed between dot and leads, but the presence of magnetic impurities results in a gate-dependent zero-bias conductance peak that is split due to a RKKY interaction between the spin of the dot and the static spins of the impurities. A magnetic field restores the single Kondo peak in the case of an antiferromagnetic RKKY interaction. This system provides a new platform to study Kondo and RKKY interactions in metals at the level of a single spin.
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Affiliation(s)
- H B Heersche
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
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Abstract
We present gate-dependent transport measurements of Kondo impurities in bare gold break junctions, generated with high yield using an electromigration process that is actively controlled. Thirty percent of measured devices show zero-bias conductance peaks. Temperature dependence suggests Kondo temperatures approximately 7 K. The peak splitting in magnetic field is consistent with theoretical predictions for g = 2, though in many devices the splitting is offset from 2g mu(B)B by a fixed energy. The Kondo resonances observed here may be due to atomic-scale metallic grains formed during electromigration.
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Affiliation(s)
- A A Houck
- Center for Bits and Atoms and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Koppens FHL, Folk JA, Elzerman JM, Hanson R, van Beveren LHW, Vink IT, Tranitz HP, Wegscheider W, Kouwenhoven LP, Vandersypen LMK. Control and Detection of Singlet-Triplet Mixing in a Random Nuclear Field. Science 2005; 309:1346-50. [PMID: 16037418 DOI: 10.1126/science.1113719] [Citation(s) in RCA: 477] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We observed mixing between two-electron singlet and triplet states in a double quantum dot, caused by interactions with nuclear spins in the host semiconductor. This mixing was suppressed when we applied a small magnetic field or increased the interdot tunnel coupling and thereby the singlet-triplet splitting. Electron transport involving transitions between triplets and singlets in turn polarized the nuclei, resulting in marked bistabilities. We extract from the fluctuating nuclear field a limitation on the time-averaged spin coherence time T2* of 25 nanoseconds. Control of the electron-nuclear interaction will therefore be crucial for the coherent manipulation of individual electron spins.
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Affiliation(s)
- F H L Koppens
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, Netherlands
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Potok RM, Folk JA, Marcus CM, Umansky V, Hanson M, Gossard AC. Spin and polarized current from Coulomb blockaded quantum dots. Phys Rev Lett 2003; 91:016802. [PMID: 12906563 DOI: 10.1103/physrevlett.91.016802] [Citation(s) in RCA: 8] [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: 03/02/2003] [Indexed: 05/24/2023]
Abstract
We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition.
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Affiliation(s)
- R M Potok
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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Abstract
We demonstrate a quantum coherent electron spin filter by directly measuring the spin polarization of emitted current. The spin filter consists of an open quantum dot in an in-plane magnetic field; the in-plane field gives the two spin directions different Fermi wavelengths resulting in spin-dependent quantum interference of transport through the device. The gate voltage is used to select the preferentially transmitted spin, thus setting the polarity of the filter. This provides a fully electrical method for the creation and detection of spin-polarized currents. Polarizations of emitted current as high as 70% for both spin directions (either aligned or anti-aligned with the external field) are observed.
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Affiliation(s)
- J A Folk
- Department of Physics, Harvard University, Cambridge, MA 02138, USA.
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Potok RM, Folk JA, Marcus CM, Umansky V. Detecting spin-polarized currents in ballistic nanostructures. Phys Rev Lett 2002; 89:266602. [PMID: 12484844 DOI: 10.1103/physrevlett.89.266602] [Citation(s) in RCA: 7] [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: 06/19/2002] [Indexed: 05/24/2023]
Abstract
We demonstrate a mesoscopic spin polarizer/analyzer system that allows the spin polarization of current from a quantum point contact in a large in-plane magnetic field to be measured. A transverse electron focusing geometry is used to couple current from an emitter point contact into a collector point contact. At large in-plane fields, with the point contacts biased to transmit only a single spin (g<e(2)/h), the voltage across the collector depends on the spin polarization of the current incident on it. Spin polarizations of >70% are found for both emitter and collector at 300 mK and 7 T in-plane field.
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Affiliation(s)
- R M Potok
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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Abstract
Decoherence in nearly isolated GaAs quantum dots is investigated using the change in the average Coulomb blockade peak height when time-reversal symmetry is broken. The normalized change in the average peak height approaches the predicted universal value of 1/4 at temperatures well below the single-particle level spacing, T < Delta, but is greatly suppressed for T > Delta, suggesting that inelastic scattering or other dephasing mechanisms dominate in this regime.
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Affiliation(s)
- J A Folk
- Department of Physics, Stanford University, Stanford, California 94305, USA
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Halperin BI, Stern A, Oreg Y, Cremers JN, Folk JA, Marcus CM. Spin-orbit effects in a GaAs quantum dot in a parallel magnetic field. Phys Rev Lett 2001; 86:2106-2109. [PMID: 11289866 DOI: 10.1103/physrevlett.86.2106] [Citation(s) in RCA: 2] [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: 10/05/2000] [Indexed: 05/23/2023]
Abstract
We analyze the effects of spin-orbit coupling on fluctuations of the conductance of a quantum dot fabricated in a GaAs heterostructure. Counterintuitively we argue that spin-orbit effects may become important in the presence of a large parallel magnetic field B( parallel), even if they are negligible for B( parallel) = 0. This should be manifest in the level repulsion of a closed dot, and in reduced conductance fluctuations in dots with a small number of open channels in each lead, for large B( parallel). Our picture is consistent with the experimental observations of Folk et al.
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Affiliation(s)
- B I Halperin
- Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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Folk JA, Patel SR, Birnbaum KM, Marcus CM, Duruöz CI, Harris JS. Spin degeneracy and conductance fluctuations in open quantum dots. Phys Rev Lett 2001; 86:2102-2105. [PMID: 11289865 DOI: 10.1103/physrevlett.86.2102] [Citation(s) in RCA: 5] [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: 05/03/2000] [Indexed: 05/23/2023]
Abstract
The dependence of conductance fluctuations on parallel magnetic field is used as a probe of spin degeneracy in open GaAs quantum dots. The variance of fluctuations at high parallel field is reduced from the low-field variance (with broken time-reversal symmetry) by factors ranging from roughly 2 in a 1 microm (2) dot to greater than 4 in 8 microm (2) dots. The factor of 2 is expected for Zeeman splitting of spin-degenerate channels. A possible explanation for the larger suppression based on field-dependent spin-orbit scattering is proposed.
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Affiliation(s)
- J A Folk
- Department of Physics, Stanford University, Stanford, California 94305, USA
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Saugstad JA, Marino MJ, Folk JA, Hepler JR, Conn PJ. RGS4 inhibits signaling by group I metabotropic glutamate receptors. J Neurosci 1998; 18:905-13. [PMID: 9437012 PMCID: PMC6792754] [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] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Metabotropic glutamate receptors (mGluRs) couple to heterotrimeric G-proteins and regulate cell excitability and synaptic transmission in the CNS. Considerable effort has been focused on understanding the cellular and biochemical mechanisms that underlie regulation of signaling by G-proteins and their linked receptors, including the mGluRs. Recent findings demonstrate that regulators of G-protein signaling (RGS) proteins act as effector antagonists and GTPase-activating proteins for Galpha subunits to inhibit cellular responses by G-protein-coupled receptors. RGS4 blocks Gq activation of phospholipase Cbeta and is expressed broadly in rat brain. The group I mGluRs (mGluRs 1 and 5) couple to Gq pathways to regulate several effectors in the CNS. We examined the capacity of RGS4 to regulate group I mGluR responses. In Xenopus oocytes, purified RGS4 virtually abolishes the mGluR1a- and mGluR5a-mediated but not the inositol trisphospate-mediated activation of a calcium-dependent chloride current. Additionally, RGS4 markedly attenuates the mGluR5-mediated inhibition of potassium currents in hippocampal CA1 neurons. This inhibition is dose-dependent and occurs at concentrations that are virtually identical to those required for inhibition of phospholipase C activity in NG108-15 membranes and reconstituted systems using purified proteins. These findings demonstrate that RGS4 can modulate mGluR responses in neurons, and they highlight a previously unknown mechanism for regulation of G-protein-coupled receptor signaling in the CNS.
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Affiliation(s)
- J A Saugstad
- Department of Pharmacology, Emory University, Atlanta, Georgia 30322, USA
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Folk JA, Patel SR, Godijn SF, Huibers AG, Cronenwett SM, Marcus CM, Campman K, Gossard AC. Statistics and parametric correlations of Coulomb blockade peak fluctuations in quantum dots. Phys Rev Lett 1996; 76:1699-1702. [PMID: 10060495 DOI: 10.1103/physrevlett.76.1699] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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