M. A. Kastner

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (352)1112.53 Total impact

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    ABSTRACT: We investigate low temperature transport properties of split-gate devices lithographically patterned on a GaAs/AlGaAs heterostructure containing a 2D electron gas with mobility 2000 m^2/Vs in a perpendicular magnetic field. By using quantum point contacts (QPCs) with different lithographic widths and varying the voltage applied on the gates for each QPC, we can control the width of the conduction channel continuously from ˜3000 to ˜100nm. The width of the channel is estimated from the low-field magnetic field dependence of the conductance through the QPC. We find that the spin-splitting of the Landau levels is suppressed in the QPCs compared to the bulk, and we measure the filling factor numax above which spin splitting can no longer be observed. Surprisingly, we find that numax is approximately half the number of quantum channels in the QPC for all widths less than 1200 nm. This work was partially supported by ARO (W911NF-05-1-0062), by the NSEC program of NSF (PHY-0117795), by NSF (DMR-0353209) and by Project Q of Microsoft.
    No preview · Article · Jan 2007
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    ABSTRACT: We measure the relaxation rate $W \equiv T_{1}^{-1}$ of a single electron spin in a quantum dot at magnetic fields from 7 T down to 1.75 T, much lower than previously measured. At 1.75 T we find that $T_{1}$ is 170 ms. We find good agreement between our measurements and theoretical predictions of the relaxation rate caused by the spin-orbit interaction, demonstrating that spin-orbit coupling can account for spin relaxation in quantum dots. Comment: 4 pages, 3 figures
    Preview · Article · Jul 2006
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    Ian J. Gelfand · S. Amasha · M. A. Kastner · C. Kadow · A. C. Gossard
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    ABSTRACT: We demonstrate low leakage surface gating of an indium arsenide heterostructure with the two-dimensional electron gas close to the surface. Gating is made possible by growing an aluminum oxide layer on top of the device. We find that the depletion point can be changed by applying a positive gate voltage and we see hysteresis when the voltage is swept below depletion.
    Preview · Article · Jun 2006 · Applied Physics Letters
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    ABSTRACT: Single-electron transistors (SETs) are attractive candidates for spin qubits. An AlGaAs/GaAs SET consists of a confined two-dimensional droplet of electrons, called an artificial atom or quantum dot, coupled by tunnel barriers to two conducting leads. Controlling the voltages on the lithographic gates that define the quantum dot allows us to confine a single electron in the dot, as well as to adjust the tunnel barriers to the leads. By applying a magnetic field, we can split the spin-up and spin-down states of the electron by an energy |g|µ B B; the goal is to utilize coherent superpositions of these spin states to construct a qubit. We will discuss our attempts to observe electron spin resonance (ESR) in this system by applying magnetic fields at microwave frequencies. Observation of ESR would demonstrate that we can manipulate a single spin and allow us to measure the decoherence time T 2 *.
    Preview · Article · Jun 2006 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We measure the conductance of close-packed films of CdTe nanocrystals in field-effect structures in the dark and in the presence of light. We find that the majority carriers are holes, that they are injected from gold electrodes into the CdTe nanocrystal films, and that the hole density can be modulated with gate voltage. Secondary photocurrents have a photoconductive gain of ∼10 at 106 V∕cm showing that the hole mobility is higher than the electron mobility. A single phenomenological description of the field dependence of the hole mobility can explain the dependence of current on source-drain voltage for both dark and light currents.
    No preview · Article · Apr 2006 · Physical Review B
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    ABSTRACT: Utilizing a current-biased quantum-point-contact charge sensor, we observe electrons hopping on and off a AlGaAs/GaAs single-electron transistor (SET) in real time. An electron tunnels between the extended states in the leads and the lowest-energy state localized in the lateral quantum dot created by nanometer-size surface electrodes. We observe changes in the tunneling rates, caused by the spin splitting in a magnetic field B applied parallel to the 2DEG. We have also observed single-electron photo-ionization of the SET by application of microwave radiation. This work is supported by the ARO (W911NF-05-1-0062), the NSF (DMR-0353209) and in part by the NSEC Program of the NSF (PHY-0117795).
    No preview · Article · Mar 2006
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    ABSTRACT: Measurements of charge fluctuations in an AlGaAs/GaAs single electron transistor (SET) are presented. The SET consists of a lateral quantum dot created by confining a two-dimensional electron gas using nanometer-size surface electrodes. The charge on the quantum dot is detected by changes in conductance of a nearby quantum point contact. We discuss noise and bandwidth characteristics of our charge detection method, which uses commercially available voltage amplifiers. Our real time charge detection capabilities are used to investigate charge dynamics on the SET in a magnetic field parallel to the two-dimensional electron gas. This work is supported by the U.S. Army Research Office under Contract No. W911NF-05-1-0062, by the National Science Foundation under Grant No. DMR-0353209, and in part by the NSEC Program of the National Science Foundation under Award No. PHY-0117795.
    No preview · Article · Mar 2006
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    ABSTRACT: We present measurements of few electron quantum dots formed by lateral depletion of a GaAs/AlGaAs 2D electron gas by surface gates. The two electron regime, on which we focus here, is characterized by singlet and triplet states which are relevant for quantum computation proposals. These two states are revealed in electronic transport through the dot in various ways: sequential tunneling, inelastic cotunneling as well as by an additional mode of transport we ascribe to sequential tunneling activated by inelastic cotunneling. These various signatures provide independent ways to measure the singlet-triplet energy splitting J over large ranges of gate voltages. We present the temperature, magnetic field and tunnel-coupling dependence of these transport features, which are in good agreement with recent theory. Further, we observe signatures of spin-blockade that becomes visible for source-drain voltages exceeding the triplet energy. This work was partially supported by the ARO (W911NF-05-1-0062), by the NSEC program of the NSF (PHY-0117795) and by NSF (DMR-0353209).
    No preview · Article · Mar 2006
  • Marc A. Kastner
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    ABSTRACT: Schemes are examined for implementing quantum computers to solve problems that cannot be solved in polynomial time on classical computers. Special attention is given to the newly proposed adiabatic quantum computation algorithms. We explore the ways in which the latter might be easier to implement than the more conventional approach.
    No preview · Article · Nov 2005 · Proceedings of the IEEE
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    ABSTRACT: We report the fabrication of multi-island single-electron devices made by lithographic contacting of self-assembled alkanethiol-coated gold nanocrystals. The advantages of this method, which bridges the dimensional gap between lithographic and NC sizes, are (1) that all tunnel junctions are defined by self-assembly rather than lithography and (2) that the ratio of gate capacitance to total capacitance is high. The rich electronic behavior of a double-island device, measured at 4.2 K, is predicted in detail by combining finite element and Monte Carlo simulations with the standard theory of Coulomb blockade with very few adjustable parameters.
    Full-text · Article · Sep 2005 · Applied Physics Letters
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    ABSTRACT: An artificial atom with four electrons is driven through a singlet-triplet transition by varying the confining potential. In the triplet, a Kondo peak with a narrow dip at drain-source voltage V_ds=0 is observed. The low energy scale V_ds* characterizing the dip is consistent with predictions for the two-stage Kondo effect. The phenomenon is studied as a function of temperature T and magnetic field B, parallel to the two-dimensional electron gas. The low energy scales T* and B* are extracted from the behavior of the zero-bias conductance and are compared to the low energy scale V_ds* obtained from the differential conductance. Good agreement is found between kT* and |g|muB*, but eV_ds* is larger, perhaps because of nonequilibrium effects. Comment: 7 pages, 7 figures. Added labels on Fig. 3f and one reference
    Preview · Article · May 2005 · Physical Review B
  • Venda Porter · Marc Kastner · Moungi Bawendi
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    ABSTRACT: We present a photocurrent study of CdSe quantum dot films exhibiting unity internal quantum efficiency as a result of post-deposition treatments. While the photocurrent of untreated films is highly voltage dependent at all voltages, the treated films depend strongly on voltage at low voltage, linearly with voltage above a voltage threshold, and finally saturate at high voltage. The voltage dependence of the treated films can be reproduced with a model assuming blocking contacts and a field dependent exciton ionization efficiency that saturates to unity. The increase in exciton ionization efficiency is a result of increased surface passivation and decreased QD spacing.
    No preview · Article · Mar 2005
  • Sami Amasha · Ian J. Gelfand · Marc A. Kastner
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    ABSTRACT: We present a detailed study of the Kondo peak splitting as a function of Kondo temperature TK and magnetic field B parallel to the 2DEG in an AlGaAs/GaAs single-electron transistor. We observe that, at fixed B, the Kondo splitting decreases logarithmically with Kondo temperature, in agreement with theory. However, we find that the magnitude of the prefactor of the logarithm is much larger than predicted. We also find that there exists a critical magnetic field Bc below which the Kondo peak does not split, in qualitative agreement with theory. However, our results indicate that Bc is smaller than predicted. These measurements show that the theory of non-equilibrium Kondo physics is still incomplete.
    No preview · Article · Mar 2005
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    ABSTRACT: We address anomalous transport phenomena in arrays of semiconductor nanocrystals (quantum dots): Transient power-law decay of current as a response to a step in large bias voltage applied across the array, as well as memory effects observed after successive applications of the bias voltage. A novel phenomenological model of transport in such systems is proposed, capable of rationalizing both anomalous transport and memory. The model describes electron transport by a stationary Levy process of transmission events and therefore requires no time dependence of system properties. The long tail in the waiting time distribution gives rise to a nonstationary response in the presence of a voltage pulse. Noise measurements agree well with the predicted non-Poissonian fluctuations in current. We briefly discuss possible microscopic mechanisms that could cause the anomalous statistics in transmission.
    No preview · Article · Jan 2005 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We report the observation of a magnetic-field-induced transition between magnetically disordered and ordered phases in slightly under-doped La(2-x)SrxCuO4 with x=0.144. Static incommensurate spin-density-wave order is induced above a critical field of about 3 T, as measured by elastic neutron scattering. Our results allow us to constrain the location of a quantum critical point on the phase diagram.
    Full-text · Article · Dec 2004 · Physical Review B
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    S. Amasha · I. J. Gelfand · MA Kastner · A. Kogan
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    ABSTRACT: A Kondo peak in the differential conductance of a single-electron transistor is measured as a function of both magnetic field and the Kondo temperature. We observe that the Kondo splitting decreases logarithmically with Kondo temperature and that there exists a critical magnetic field Bc below which the Kondo peak does not split, in qualitative agreement with theory. However, we find that the magnitude of the prefactor of the logarithm is larger than predicted and is independent of B, in contradiction with theory. Our measurements also suggest that the value of Bc is smaller than predicted. Comment: 6 pages, 5 figures. Replaced with version submitted to PRB that includes corrected theoretical predictions, additonal analysis, and other suggested modifications
    Full-text · Article · Nov 2004 · Physical Review B
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    ABSTRACT: We measure the spin splitting in a magnetic field B of localized states in single-electron transistors using a new method, inelastic spin-flip cotunneling. Because it involves only internal excitations, this technique gives the most precise value of the Zeeman energy Delta=/g/mu(B)B. In the same devices we also measure the splitting with B of the Kondo peak in differential conductance. The Kondo splitting appears only above a threshold field as predicted by theory. However, the magnitude of the Kondo splitting at high fields exceeds 2/g/mu(B)B in disagreement with theory.
    Full-text · Article · Nov 2004 · Physical Review Letters
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    ABSTRACT: We present measurements of photoconductivity in CdSe quantum dot films treated with a variety of reagents. While the photocurrent of untreated samples is highly voltage dependent at all voltages, after treatment the photocurrent is much larger, depends strongly on voltage at low voltage, displays a linear region above a voltage threshold, and finally saturates at high voltage. All regions of the current-voltage curves after treatment can be reproduced with a model that requires noninjecting contacts and a field dependent exciton ionization efficiency that saturates to unity. This model is shown to be consistent with the trends observed with different treatments. The changes in photocurrent with treatment are shown to be largely a consequence of increased quantum dot surface passivation and decreased quantum dot spacing, regardless of whether the molecules used for treatment are conjugated or able to cross-link the quantum dots.
    No preview · Article · Nov 2004 · Physical review. B, Condensed matter
  • Andrei Kogan · Sami Amasha · MA Kastner
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    ABSTRACT: We measure the differential conductance of a single-electron transistor (SET) irradiated with microwaves. The spin-entangled many-electron Kondo state produces a zero-bias peak in the dc differential conductance if the quantum dot in the SET contains an unpaired electron. When the photon energy hf is comparable to the energy width of the Kondo peak and to e (the charge on the electron) times the microwave voltage across the dot, satellites appear in the differential conductance shifted in voltage by +/-hf/e from the zero-bias resonance. We also observe an overall suppression of the Kondo features with increasing microwave voltage.
    No preview · Article · Jun 2004 · Science
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    ABSTRACT: High-temperature cuprate superconductors often have dynamic and sometimes static magnetic order, which coexist with superconductivity. Underdoped La_2-xSr_xCuO4 has static magnetic order when x < 0.14. At higher doping, the static magnetic order is destroyed and a spin-gap opens when it is optimally- or slightly over-doped (0.15
    No preview · Article · Jan 2004

Publication Stats

20k Citations
1,112.53 Total Impact Points

Institutions

  • 1974-2015
    • Massachusetts Institute of Technology
      • • Department of Physics
      • • Department of Materials Science and Engineering
      • • Research Laboratory of Electronics
      Cambridge, Massachusetts, United States
  • 2002
    • Columbia University
      • Department of Physics
      New York, New York, United States
  • 2001
    • Tel Aviv University
      • Department of Physics and Astronomy
      Tell Afif, Tel Aviv, Israel
    • Rutgers, The State University of New Jersey
      Нью-Брансуик, New Jersey, United States
  • 1988
    • Nippon Telegraph and Telephone
      Edo, Tōkyō, Japan
    • Boston University
      • Center for Polymer Studies
      Boston, Massachusetts, United States
  • 1970
    • University of Illinois at Chicago
      • Department of Physics
      Chicago, Illinois, United States