R. S. Deacon

RIKEN, Вако, Saitama, Japan

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Publications (15)100.15 Total impact

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    ABSTRACT: Three-dimensional anisotropy of the Lande g-factor and its electrical modulation are studied for single uncapped InAs self-assembled quantum dots (QDs). The g-factor is evaluated from measurement of inelastic cotunneling via Zeeman substates in the QD for various magnetic field directions. We find that the value and anisotropy of the g-factor depends on the type of orbital state which arises from the three-dimensional confinement anisotropy of the QD potential. Furthermore, the g-factor and its anisotropy are electrically tuned by a side-gate which modulates the confining potential.
    Physical review. B, Condensed matter 03/2013; 87(16). DOI:10.1103/PhysRevB.87.161302 · 3.66 Impact Factor
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    ABSTRACT: We use a superconducting quantum interference device (SQUID) to detect the phase of an InAs quantum dot Josephson junction (QDJJ) in the Kondo regime. The QDJJ phase is derived from the measurement of superconducting interference. The π-junction behavior is observed for a QD with an odd electron number and the phase transition from π to 0 is observed by changing the parity of the electron number. In the Kondo regimes, we find that the QDJJ becomes a 0-junction even though the electron number is odd.
    Journal of Physics Conference Series 12/2012; 400(4):2027-. DOI:10.1088/1742-6596/400/4/042027
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    ABSTRACT: We study supercurrent in a single InAs self-assembled quantum dot contacted with superconducting leads and demonstrate that for regions where energy level spacing and charging energy are smaller than tunnel coupling, the supercurrent may be controlled by the degree of overlaps between energy levels, which is tunable using a side-gate electrode. In such regions, we find strong correlation between the supercurrent and the normal state conductance when the device parameters are tuned. In a Kondo regime with low Kondo temperature, we find that the scaling of the supercurrent and normal state conductance varies when the side-gate voltage is changed.
    Applied Physics Letters 05/2012; 100(20):202109. DOI:10.1063/1.4719072 · 3.52 Impact Factor
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    ABSTRACT: Electrical control over electron spin is a prerequisite for spintronics spin-based quantum information processing. In particular, control over the interaction between the orbital motion and the spin state of electrons would be valuable, because this interaction influences spin relaxation and dephasing. Electric fields have been used to tune the strength of the spin-orbit interaction in two-dimensional electron gases, but not, so far, in quantum dots. Here, we demonstrate that electrical gating can be used to vary the energy of the spin-orbit interaction in the range 50-150 µeV while maintaining the electron occupation of a single self-assembled InAs quantum dot. We determine the spin-orbit interaction energy by observing the splitting of Kondo effect features at high magnetic fields.
    Nature Nanotechnology 12/2011; 7(1):75. DOI:10.1038/nnano.2011.228 · 33.27 Impact Factor
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    ABSTRACT: Electrical control over electron spin is a prerequisite for spintronics spin-based quantum information processing. In particular, control over the interaction between the orbital motion and the spin state of electrons would be valuable, because this interaction influences spin relaxation and dephasing. Electric fields have been used to tune the strength of the spin-orbit interaction in two-dimensional electron gases, but not, so far, in quantum dots. Here, we demonstrate that electrical gating can be used to vary the energy of the spin-orbit interaction in the range 50-150 µeV while maintaining the electron occupation of a single self-assembled InAs quantum dot. We determine the spin-orbit interaction energy by observing the splitting of Kondo effect features at high magnetic fields.
    Nature Nanotechnology 07/2011; 6(8):511-6. DOI:10.1038/nnano.2011.103 · 33.27 Impact Factor
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    ABSTRACT: We investigate the all-electrical tuning of the Landé g tensor in a single uncapped InAs quantum dot contacted with a nanogap electrode technique and electrically gated with both back- and side-gate electrodes. Magnetotransport measurements allow extraction of the g tensor components from measurements of the Zeeman energy for magnetic fields applied in the plane of the sample. The side-gate electrode allows tuning of the anisotropy of the in-plane g tensor components and is suitable for the manipulation of the quantum-dot spin states using g factor modulation resonance schemes.
    Physical Review B 07/2011; 84(4):041302. DOI:10.1103/PhysRevB.84.041302 · 3.66 Impact Factor
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    ABSTRACT: We demonstrate the detection of spin-orbit interaction and evaluation of spin-orbit interaction energy using the Kondo effect in self-assembled InAs quantum dots with large tunnel coupling.
    AIP Conference Proceedings 01/2011; 1399:355. DOI:10.1063/1.3666400
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    ABSTRACT: We measure the non-dissipative supercurrent in a single InAs self-assembled quantum dot (QD) coupled to superconducting leads. The QD occupation is both tuned by a back-gate electrode and lateral side-gate. The geometry of the side-gate allows tuning of the QD-lead tunnel coupling in a region of constant electron number with appropriate orbital state. Using the side-gate effect we study the competition between Kondo correlations and superconducting pairing on the QD, observing a decrease in the supercurrent when the Kondo temperature is reduced below the superconducting energy gap in qualitative agreement with theoretical predictions.
    Physical Review B 08/2010; 82:054512. DOI:10.1103/PhysRevB.82.054512 · 3.66 Impact Factor
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    ABSTRACT: The anisotropy of the spin-orbit interaction (SOI) is studied for a single uncapped InAs self-assembled quantum dot holding just a few electrons. The SOI energy is evaluated from anticrossing or SOI-induced hybridization between the ground and excited states with opposite spins. The magnetic angular dependence of the SOI energy falls on an absolute cosine function for azimuthal rotation, and a cosinelike function for tilting rotation. Furthermore, the SOI energy is quenched for a specific magnetic field vector. The angular dependence of SOI is found to compare well with calculation of Rashba SOI in a two-dimensional harmonic potential.
    Physical Review Letters 06/2010; 104(24):246801. DOI:10.1103/PhysRevLett.104.246801 · 7.73 Impact Factor
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    ABSTRACT: We study transport in self-assembled InAs quantum dots contacted with one superconducting and one normal-metal electrode. Low bias transport is dominated by Andreev processes which are sensitive to local correlations such as electron-electron interaction and the Kondo effect. We identify that, for appropriate tunnel coupling with normal and superconducting leads, Andreev transport is enhanced by the Kondo effect and that the Kondo temperature is reduced relative to the normal state due to lack of low-energy excitations with the superconducting lead.
    Physical Review B 03/2010; 81(12):121308R. DOI:10.1103/PhysRevB.81.121308 · 3.66 Impact Factor
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    ABSTRACT: The coupling of a quantum dot with a BCS-type superconducting reservoir results in an intriguing system where low energy physics is governed by the interplay of two distinct phases, singlet and doublet. In this Letter we show that the spectrum of Andreev energy levels, which capture the properties of the two phases, can be detected in transport measurements with a quantum dot strongly coupled to a superconducting lead and weakly coupled to a normal metal lead. We observe phase transitions between BCS singlet and degenerate magnetic doublet states when the quantum dot chemical potential is tuned with an electrostatic gate, in good qualitative agreement with numerical renormalization group calculations.
    Physical Review Letters 02/2010; 104(7):076805. DOI:10.1103/PhysRevLett.104.076805 · 7.73 Impact Factor
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    ABSTRACT: We present measurements of proximity supercurrent in single self assembled InAs quantum dots contacted with superconducting Aluminium electrodes. The magnitude of the switching current displays strong even-odd parity as singlet-like correlation impedes the proximity effect.
    AIP Conference Proceedings 01/2010; 1199:275. DOI:10.1063/1.3295406
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    ABSTRACT: We study the transport properties of a single InAs self-assembled quantum dot contacted with superconducting leads. The charging energy Ec of the quantum dot is much larger than the superconducting gap energy Delta. For the dot whose tunnel coupling Gamma to the lead is much larger than Delta but smaller than Ec, we observe enhancement of first-order Andreev reflections by the Kondo effect. We find that the zero-bias conductance measured for various Delta's and Kondo temperature TK's collapses onto a single curve with Delta/TK as the only relevant energy scale, providing experimental evidence for universal scaling in this system. On the other hand, for the dot with Gamma comparable to Ec we observe a supercurrent flowing through the dot, reflecting the charge fluctuation sufficiently greater that one.
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    ABSTRACT: We report a first direct observation of proximity supercurrent in a single InAs self-assembled quantum dot coupled to superconducting electrodes. We utilize large SAQDs with strong dot-lead coupling allowing sufficient overlap of quantized state that charge fluctuation in the dot may exceed one electron. Although the charging energy is larger than the superconductivity gap, Δ, the voltage characteristic measured in the current-driven four-terminal geometry signifies a supercurrent flow though the dot. The observed critical current is of the order of 10 pA, and much smaller than expected from theory. This current also shows the parity effect with the number of electrons in the dot, suggesting that the singlet correlation impedes the Cooper pair tunneling.
    Journal of Physics Conference Series 03/2009; 150(2):022032. DOI:10.1088/1742-6596/150/2/022032
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    ABSTRACT: Influence of spin-orbit interaction (SOI) on the energy spectrum is studied for single uncapped InAs self-assembled quantum dots (SAQDs) holding just a few electrons. We measure Coulomb oscillations with magnetic field, and identify lifting of spin doublets in the low field range and transitions in the ground states with keeping the total angular momentum in the high field range. Both of these features are induced by large Zeeman splitting in the present SAQDs. For the ground state transitions, anti-crossing due to the SOI hybridization between the ground and excited states with opposite spins is observed in the excitation spectra, and the SOI energy of about 0.1 meV is evaluated from the anti-crossing size. This energy is comparable to that of previous report on InAs nanowires, and reproduced by simple calculation using the g-factor also derived in the excitation spectra.
    Journal of Physics Conference Series 03/2009; 150(2):022084. DOI:10.1088/1742-6596/150/2/022084