C. J. Palmstrøm

University of California, Santa Barbara, Santa Barbara, California, United States

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Publications (276)513.82 Total impact

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    ABSTRACT: Control of zero-field spin splitting is realized in a dual-gated high-quality InAs-AlSb two-dimensional electron gas. Magnetotransport experiments showed clean Shubnikov–de Haas oscillations down to low magnetic fields, and the gate-tuned electron mobility exceeded 700000cm2/Vs. A clear beating effect was observed in magnetoresistance oscillations at large potential asymmetry between gates. Beat patterns due to zero-field spin splitting and other classes of transverse magnetoresistance oscillations were distinguished by temperature-dependent magnetoresistance measurements. Analysis of the magnetoresistance oscillations indicated that the zero-field spin splitting could be tuned via the Rashba effect while keeping the two-dimensional electron gas charge density constant.
    No preview · Article · Feb 2016
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    ABSTRACT: A distinguishing feature of spin accumulation in ferromagnet–semiconductor devices is its precession in a magnetic field. This is the basis for detection techniques such as the Hanle effect, but these approaches become ineffective as the spin lifetime in the semiconductor decreases. For this reason, no electrical Hanle measurement has been demonstrated in GaAs at room temperature. We show here that by forcing the magnetization in the ferromagnet to precess at resonance instead of relying only on the Larmor precession of the spin accumulation in the semiconductor, an electrically generated spin accumulation can be detected up to 300 K. The injection bias and temperature dependence of the measured spin signal agree with those obtained using traditional methods. We further show that this approach enables a measurement of short spin lifetimes (< 100 ps), a regime that is not accessible in semiconductors using traditional Hanle techniques.
    Full-text · Article · Jan 2016 · Nature Communications
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    Full-text · Dataset · Jan 2016
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    ABSTRACT: This work presents the surface reconstructions and transport properties of the topological insulator PtLuSb grown on Al0.1In0.9Sb/GaAs (001). Two stable surface reconstructions, (1x3) and c(2x2), were observed on PtLuSb (001) surfaces. Antimony-dimerization was determined to be the nature of the (1x3) surface reconstruction as evidenced by chemical binding energy shifts in the antimony 4d core-level for surface bonding components. The two surface reconstructions were studied as a function of Sb4 overpressure and substrate temperature to create a reconstruction phase diagram. From this reconstruction phase diagram, a growth window from 320 {\deg}C to 380 {\deg}C using an antimony overpressure was identified. Within this window, the highest quality films were grown at a growth temperature of 380 {\deg}C. These films exhibited lower p-type carrier concentrations as well as relatively high hole mobilities.
    Full-text · Article · Nov 2015 · Journal of Crystal Growth
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    ABSTRACT: The discovery of topological insulators (TIs), materials with bulk band gaps and protected cross-gap surface states, in compounds such as Bi2Se3 has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theory calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally-identical but electronically-varied nature of Heusler compounds. Here, we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin and angle-resolved photoemission spectroscopy (ARPES), complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of TI behavior is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronics devices.
    Full-text · Article · Nov 2015
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    ABSTRACT: Progress in the emergent field of topological superconductivity relies on synthesis of new material combinations, combining superconductivity, low density, and spin-orbit coupling (SOC). For example, theory [1-4] indicates that the interface between a one-dimensional (1D) semiconductor (Sm) with strong SOC and a superconductor (S) hosts Majorana modes with nontrivial topological properties [5-8]. Recently, epitaxial growth of Al on InAs nanowires was shown to yield a high quality S-Sm system with uniformly transparent interfaces [9] and a hard induced gap, indicted by strongly suppressed sub gap tunneling conductance [10]. Here we report the realization of a two-dimensional (2D) InAs/InGaAs heterostructure with epitaxial Al, yielding a planar S-Sm system with structural and transport characteristics as good as the epitaxial wires. The realization of 2D epitaxial S-Sm systems represent a significant advance over wires, allowing extended networks via top-down processing. Among numerous potential applications, this new material system can serve as a platform for complex networks of topological superconductors with gate-controlled Majorana zero modes [1-4]. We demonstrate gateable Josephson junctions and a highly transparent 2D S-Sm interface based on the product of excess current and normal state resistance.
    Full-text · Article · Nov 2015
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    ABSTRACT: We investigate the dynamically polarized nuclear spin system in Fe/n-GaAs heterostructures using the response of the electron-spin system to nuclear magnetic resonance (NMR) in lateral spin-valve devices. The hyperfine interaction is known to act more strongly on donor-bound electron states than on those in the conduction band. We provide a quantitative model of the temperature dependence of the occupation of donor sites. With this model we calculate the ratios of the hyperfine and quadrupolar nuclear relaxation rates of each isotope. For all temperatures measured, quadrupolar relaxation limits the spatial extent of nuclear spin polarization to within a Bohr radius of the donor sites and is directly responsible for the isotope dependence of the measured NMR signal amplitude. The hyperfine interaction is also responsible for the 2kHz Knight shift of the nuclear resonance frequency that is measured as a function of the electron-spin accumulation. The Knight shift is shown to provide a measurement of the electron-spin polarization that agrees qualitatively with standard spin transport measurements.
    No preview · Article · Oct 2015 · Physical Review B
  • S N Gilbert Corder · J K Kawasaki · C J Palmstrøm · H T Krzy˙ · N H Tolk
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    ABSTRACT: Semiconducting GaAs is widely used in microwave and millimeter integrated circuits, infrared LEDs, lasers, and solar cells. Introducing semi-metallic ErAs nanoparticles provides a way to con-trollably tune the optical and electronic properties of GaAs. We show for high volume fractions (0.5-10%) of ErAs nanoparticles embedded in GaAs, the relaxation dynamics indicate ErAs forms discrete states in the GaAs bandgap. For specific carrier momentum conditions, the localized Schot-tky states may be occupied, exhibit carrier trapping, or inject carriers into the GaAs conduction band. Carrier occupation and scattering from the Schottky states has not previously been reported in optical studies of this system. The scattering mechanism is observed to be active above an occupation threshold where the excited carrier density exceeds the trap density. The array of nanoparticle densities and the characterization of the relaxation pathways at multiple carrier excitation energies represents the most complete fundamental investigation of these systems to date.
    No preview · Article · Sep 2015
  • S N Gilbert Corder · J K Kawasaki · C J Palmstrøm · H T Krzy˙ · N H Tolk
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    ABSTRACT: Semiconducting GaAs is widely used in microwave and millimeter integrated circuits, infrared LEDs, lasers, and solar cells. Introducing semi-metallic ErAs nanoparticles provides a way to con-trollably tune the optical and electronic properties of GaAs. We show for high volume fractions (0.5-10%) of ErAs nanoparticles embedded in GaAs, the relaxation dynamics indicate ErAs forms discrete states in the GaAs bandgap. For specific carrier momentum conditions, the localized Schot-tky states may be occupied, exhibit carrier trapping, or inject carriers into the GaAs conduction band. Carrier occupation and scattering from the Schottky states has not previously been reported in optical studies of this system. The scattering mechanism is observed to be active above an occupation threshold where the excited carrier density exceeds the trap density. The array of nanoparticle densities and the characterization of the relaxation pathways at multiple carrier excitation energies represents the most complete fundamental investigation of these systems to date.
    No preview · Article · Sep 2015 · Physical Review B
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    ABSTRACT: The hyperfine field from dynamically polarized nuclei in n-GaAs is very spatially inhomogeneous, as the nu- clear polarization process is most efficient near the randomly-distributed donors. Electrons with polarized spins traversing the bulk semiconductor will experience this inhomogeneous hyperfine field as an effective fluctuating spin precession rate, and thus the spin polarization of an electron ensemble will relax. A theory of spin relaxation based on the theory of random walks is applied to such an ensemble precessing in an oblique magnetic field, and the precise form of the (unequal) longitudinal and transverse spin relaxation analytically derived. To investigate this mechanism, electrical three-terminal Hanle measurements were performed on epitaxially grown Co$_2$MnSi/$n$-GaAs heterostructures fabricated into electrical spin injection devices. The proposed anisotropic spin relaxation mechanism is required to satisfactorily describe the Hanle lineshapes when the applied field is oriented at large oblique angles.
    Full-text · Article · Aug 2015 · Physical Review B
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    ABSTRACT: An understanding of the growth of (110) quantum wells (QWs) is of great importance to spin systems due to the observed long spin relaxation times. In this article, we report on the metamorphic growth and characterization of high mobility undoped InAs (110) QWs on GaAs (110) substrates. A low-temperature nucleation layer reduces dislocation density, results in tilting of the subsequent buffer layer and increases the electron mobility of the QW structure. The mobility varies widely and systematically (4000–16 000 cm2/Vs at room temperature) with deposition temperature and layer thicknesses. Low-temperature transport measurements exhibit Shubnikov de-Haas oscillations and quantized plateaus in the quantum Hall regime.
    No preview · Article · Jun 2015 · Journal of Applied Physics
  • B. Shojaei · A. McFadden · J. Shabani · B. D. Schultz · C. J. Palmstrøm
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    ABSTRACT: A study of scattering mechanisms in gate tunable two dimensional electron gases confined to InAs/(Al,Ga)Sb heterostructures with varying interface roughness and dislocation density is presented. By integrating an insulated gate structure the evolution of the low temperature electron mobility and single-particle lifetime was determined for a previously unexplored density regime, 1011–1012 cm−2, in this system. Existing theoretical models were used to analyze the density dependence of the electron mobility and single particle lifetime in InAs quantum wells. Scattering was found to be dominated by charged dislocations and interface roughness. It was demonstrated that the growth of InAs quantum wells on nearly lattice matched GaSb substrate results in fewer dislocations, lower interface roughness, and improved low temperature transport properties compared to growth on lattice mismatched GaAs substrates.
    No preview · Article · Jun 2015 · Applied Physics Letters
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    ABSTRACT: Semiconducting GaAs is widely used in microwave and millimeter integrated circuits, infrared LEDs, lasers, and solar cells. Introducing semimetallic ErAs nanoparticles provides a way to controllably tune the optical and electronic properties of GaAs. We show that for high volume fractions (0.5%–10%) of ErAs nanoparticles embedded in GaAs, the relaxation dynamics indicates that ErAs forms discrete states in the GaAs band gap. For specific carrier momentum conditions, the localized Schottky states may be occupied, exhibit carrier trapping, or inject carriers into the GaAs conduction band. Carrier occupation and scattering from the Schottky states has not previously been reported in optical studies of this system. The scattering mechanism is observed to be active above an occupation threshold where the excited carrier density exceeds the trap density. The array of nanoparticle densities and the characterization of the relaxation pathways at multiple carrier excitation energies represents the most complete fundamental investigation of these systems to date
    Full-text · Article · Jan 2015 · Physical Review B
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    ABSTRACT: We demonstrate fast universal electrical spin manipulation with inhomogeneous magnetic fields. With fast Rabi frequency up to 127 MHz, we leave the conventional regime of strong nuclear-spin influence and observe a spin-flip fidelity > 96%, a distinct chevron Rabi pattern in the spectral-time domain, and spin resonance linewidth limited by the Rabi frequency, not by the dephasing rate. In addition, we establish fast z-rotations up to 54 MHz by directly controlling the spin phase. Our findings will significantly facilitate tomography and error correction with electron spins in quantum dots.
    Full-text · Article · Nov 2014 · Physical Review Letters

  • No preview · Conference Paper · Sep 2014
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    ABSTRACT: The recent rapid progress in the field of spintronics requires extensive studies of carrier and spin relaxation dynamics in semiconductors. In this work, we employed time and spin resolved differential transmission measurements in order to probe carrier and spin relaxation times in several InAsP ternary alloys. In addition, the dynamics of the excitonic radiative transitions of InAs0.13P0.87 epitaxial layer were studied through the time-resolved photoluminescence spectroscopy.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: We observe a dc voltage peak at ferromagnetic resonance (FMR) in samples consisting of a single ferromagnetic (FM) layer grown epitaxially on the n-GaAs (001) surface. The FMR peak is detected as an interfacial voltage with a symmetric line shape and is present in samples based on various FM/n-GaAs heterostructures, including Co2MnSi/n-GaAs, Co2FeSi/n-GaAs, and Fe/n-GaAs. We show that the interface bias voltage dependence of the FMR signal is identical to that of the tunneling anisotropic magnetoresistance (TAMR) over most of the bias range. Furthermore, we show how the precessing magnetization yields a dc FMR signal through the TAMR effect and how the TAMR phenomenon can be used to predict the angular dependence of the FMR signal. This TAMR-induced FMR peak can be observed under conditions where no spin accumulation is present and no spin-polarized current flows in the semiconductor.
    Full-text · Article · Aug 2014 · Applied Physics Letters
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    J. Shabani · A. P. McFadden · B. Shojaei · C. J. Palmstrøm
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    ABSTRACT: We investigate the performance of gate-defined devices fabricated on high mobility InAs heterostructures. The magnetotransport properties of these structures strongly depend on the surface states. Heterostructures terminated in In$_{0.75}$Ga$_{0.25}$As are found to host a conductive sheet of electrons depending on details of epitaxial growth or deposition of the dielectric material and limit the performance of gate-defined devices. However, In$_{0.75}$Al$_{0.25}$As capped heterostructures show a robust gating behavior suitable for fabrication of gate-defined mesoscopic devices.
    Preview · Article · Aug 2014 · Applied Physics Letters
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    ABSTRACT: Spin-orbit coupling in solids describes an interaction between an electron's spin, an internal quantum-mechanical degree of freedom, with its linear momentum, an external property. Spin-orbit interaction, due to its relativistic nature, is typically small in solids, and is often taken into account perturbatively. It has been recently realized, however, that materials with strong spin-orbit coupling can lead to novel states of matter such as topological insulators and superconductors. This exciting development might lead to a number of useful applications ranging from spintronics to quantum computing. In particular, theory predicts that narrow band gap semiconductors with strong spin-obit coupling are a suitable platform for the realization of Majorana zero-energy modes, predicted to obey exotic non-Abelian braiding statistics. The pursuit for realizing Majorana modes in condensed matter systems and investigating their exotic properties has been a subject of intensive experimental research recently. Here, we demonstrate the first realization of gate-defined wires where one-dimensional confinement is created using electrostatic potentials, on large area InAs two dimensional electron systems (2DESs). The electronic properties of the parent 2DES are fully characterized in the region that wires are formed. The strength of the spin-orbit interaction has been measured and tuned while the high mobility of the 2DES is maintained in the wire. We show that this scheme could provide new prospective solutions for scalable and complex wire networks.
    Preview · Article · Aug 2014
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    J. Shabani · S. Das Sarma · C. J. Palmstrøm
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    ABSTRACT: We report on the first experimental observation of an apparent metal insulator transition in a 2D electron gas confined in an InAs quantum well. At high densities we find that the carrier mobility is limited by background charged impurities and the temperature dependence of the resistivity shows a metallic behavior with resistivity increasing with increasing temperature. At low densities we find an insulating behavior below a critical density of $n_{c} = 3.5 \times 10^{10}$ cm$^{-2}$ with the resistivity decreasing with increasing temperature. We analyze this transition using a percolation model arising from the failure of screening in random background charged impurities. We also examine the percolation transition experimentally by introducing remote ionized impurities at the surface. Using a bias during cool-down, we modify the screening charge at the surface which strongly affects the critical density. Our study shows that transition from a metallic to an insulating phase in our system is due to percolation transition.
    Full-text · Article · Jul 2014 · Physical Review B

Publication Stats

4k Citations
513.82 Total Impact Points

Institutions

  • 1996-2016
    • University of California, Santa Barbara
      • Department of Electrical and Computer Engineering
      Santa Barbara, California, United States
    • Texas A&M University
      • Department of Electrical and Computer Engineering
      College Station, TX, United States
    • Arizona State University
      Phoenix, Arizona, United States
  • 1992-2011
    • University of Minnesota Duluth
      • • Department of Chemical Engineering
      • • Department of Mechanical and Industrial Engineering
      Duluth, Minnesota, United States
  • 1983-2011
    • Cornell University
      • Department of Materials Science and Engineering
      Итак, New York, United States
  • 2006
    • National High Magnetic Field Laboratory
      Tallahassee, Florida, United States
  • 1995
    • Office of Naval Research
      Arlington, Virginia, United States
  • 1993
    • University of Oslo
      • Department of Physics
      Kristiania (historical), Oslo, Norway
    • Princeton University
      • Department of Electrical Engineering
      Princeton, NJ, United States