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ABSTRACT: We show a dramatic deviation from ergodicity for the conductance fluctuations in graphene. In marked contrast to the ergodicity of dirty metals, fluctuations generated by varying magnetic field are shown to be much smaller than those obtained when sweeping Fermi energy. They also exhibit a strongly anisotropic response to the symmetry-breaking effects of a magnetic field, when applied perpendicular or parallel to the graphene plane. These results reveal a complex picture of quantum interference in graphene, whose description appears more challenging than for conventional mesoscopic systems.
Physical Review B (Rapid Communications). 10/2012;
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ABSTRACT: The temperature dependence of the mesoscopic conductance fluctuations is investigated for
disordered graphene. The fluctuations are generated by varying either magnetic field or carrier
density (via a back-gate). Very different temperature cut-offs are found for these two types of
fluctuations, with the density-induced features persisting to much higher temperatures (beyond
100 K, even) than those observed when sweeping magnetic field. The robust character of the
density-dependent fluctuations may cause them to play an important role in determining the
operation of future graphene nanodevices, particularly as device sizes are reduced to the nanoscale.
Applied Physics Letters 08/2012; · 3.84 Impact Factor
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ABSTRACT: Background Immediate-type skin allergic reactions, such as passive cutaneous anaphylactic reaction, are associated with circadian rhythm, but the role of circadian mechanisms on delayed-type skin allergic reactions, such as contact hypersensitivity (CHS), remains uncertain. In mice, CHS, a T cell-mediated immune response, is a classic model of human allergic contact dermatitis. Objectives We investigated whether biological clock dysfunction affects CHS pathogenesis in Clock mutant mice compared with wild-type (WT) mice. Methods Mice were treated with 2,4,6-trinitro-1-chlorobenzene (TNCB) on the abdominal skin on day 0 (sensitisation) and then treated with TNCB on the ears on day 5 (challenge). Results We found that biological clock dysfunction resulted in severe inflammation. Ear swelling, serum IgE level, and mast cell number were significantly increased in Clock mutant mice compared with WT mice. These results provide evidence that Clock mutation promotes the T helper type (Th)2 immune response and exacerbates CHS. Corticosterone has a protective effect on CHS. The serum corticosterone level lost rhythmicity and showed a decreased daily level in Clock mutant mice compared with WT mice, supporting the exacerbating effect of Clock mutation on CHS. Adrenalectomy markedly worsened TNCB-induced CHS in WT mice but not in Clock mutant mice. In addition, dramatic dexamethasone-induced protection of CHS was observed in Clock mutant mice compared with WT mice. Conclusions The present results suggest that circadian rhythm might be an important factor in the regulation of CHS via corticosterone rhythmicity and/or level.
British Journal of Dermatology 07/2012; · 3.67 Impact Factor
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ABSTRACT: We use scanning gate microscopy to probe the ballistic motion of electrons within an open GaAs/AlGaAs quantum dot. Conductance maps are recorded by scanning a biased tip over the open quantum dot while a magnetic field is applied. We show that, for specific magnetic fields, the measured conductance images resemble the classical transmitted and backscattered trajectories and their quantum mechanical analogue. In addition, we prove experimentally, with this direct measurement technique, the existence of pointer states. The demonstrated direct imaging technique is essential for the fundamental understanding of wave function scarring and quantum decoherence theory.
Physical Review Letters 03/2012; 108(13):136804. · 7.37 Impact Factor
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ABSTRACT: Ion irradiation of electronic-type-separated single wall carbon nanotubes: A model for radiation effects in nanostructured carbon J. Appl. Phys. 112, 034314 (2012) Resistive switching and activity-dependent modifications in Ni-doped graphene oxide thin films Appl. Phys. Lett. 101, 063104 (2012) Photoinduced molecular desorption from graphene films Appl. Phys. Lett. 101, 053107 (2012) Giant Goos-Hänchen shift in graphene double-barrier structures Appl. Phys. Lett. 100, 253116 (2012) Observation of the quantum Hall effect in epitaxial graphene on SiC(0001) with oxygen adsorption Appl.
Applied Physics Letters 01/2012; · 3.84 Impact Factor
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ABSTRACT: We demonstrate a fully-tunable multi-state Fano system in which
remotely-implemented quantum states interfere with each other through their
coupling to a mutual continuum. On tuning these resonances near coincidence a
robust avoided crossing is observed, with a distinctive character that confirms
the continuum as the source of the coupling. While the continuum often serves
as a source of decoherence, our work therefore shows how its presence can
instead also be essential to mediate the interaction of quantum states, a
result that could allow new approaches to engineer the collective states of
nanostructures.
11/2009;
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ABSTRACT: Quasi-periodic conductance fluctuations are observed in the low-temperature magneto-conductance of a bilayer graphene sample. The quasi-periodic nature of the fluctuations is confirmed by their Fourier power spectrum, which consists of just a small number of dominant frequency components. From an experimental study of these features, which are highly reminiscent of those reported previously for ballistic semiconductor quantum dots, we suggest that they are associated with the formation of an open quantum dot in the submicron graphene sample.
Journal of Physics Condensed Matter 09/2009; 21(38):382202. · 2.55 Impact Factor
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ABSTRACT: Low temperature transport of a well-defined open-quantum dot has been studied via scanning gate microscopy (SGM). The open dot was fabricated on AlGaAs/GaAs heterostructure using trenches defined via electron beam lithography and a wet etching. The active size of the quantum cavity is approximately 1 μm × 1 μm. The SGM observation was performed at low temperature with a conductive piezolever, which is lifted up 50 nm above the surface with applied a negative voltage. During the scan of the tip, resistance across the dot is measured in a four-probe configuration and stored in a SPM controller synchronized with the position of the tip. The SGM response at zero-magnetic field shows a high resistance when the tip situates onto a line along the inlet and the outlet of the dot. The image could be understood as that the tip induced potential disturbs the current flow in the dot and it results in the increase of resistance. Such an image can be obtained even at more than 8 K, therefore this image would correspond to a classical transport. On the other hand, the image obtained at less than 2 K shows almost similar image as that observed at higher temperature. However, after subtracting the high temperature image as the back ground structure, which is achieved by a high pass filtering, conductance fluctuations are visualized in the low temperature image. These fluctuations would be attributed to a change of quantum interference condition as well as a manipulation of the wave-function confined in the open quantum dot.
Journal of Physics Conference Series 03/2009; 150(2):022002.
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ABSTRACT: Bound-state (BS) formation in quantum point contacts (QPCs) may offer a convenient way to localize and probe single spins. In this letter, we investigate how such BSs are affected by monitoring them with a second QPC, which is coupled to the BS via wavefunction overlap. We show that this coupling leads to a unique detector backaction, in which the BS is weakened by increasing its proximity to the detector. We also show, however, that this interaction between the QPCs can be regulated at will, by using an additional gate to control their wavefunction overlap.
09/2008;
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ABSTRACT: Summary form only given. Recently, there are many interests on electronics nano-device applications based on carbon nano-tubes (CNT). We have studied the low temperature transport properties due to the crossing of two multi walled carbon nano-tubes (MWNTs). Especially, there exists a peak structure in the zero bias anomalies of the I-V characteristics of the crossing and this is found to be very sensitive to change of temperature, magnetic field and source drain voltage. Fano resonance like behavior has been observed in the central structure of the zero bias anomaly. [1,2] With radio wave irradiations in the microwave-region, the central part of the anomaly is found to respond strongly. It can be connected to new CNT applications for extremely small sized microwave detection. Also, we have observed quantum coherent transport in MWNT and hybrid devices using MWNT and single walled carbon nano-tube (SWNT). In such nano-scaled electronic devices, there exist crossing points as a quantum dot or quantum point contact. The origin of the sensitivity in the crossing may be associated with the quantum nature in the transport through localized or conductive states in the CNT. However, such sensitiveness is unstable, it may also be sensitive to the thermal cycling in the low temperature transport measurements. Since it must be originated to the nano-scaled structure changes in CNT, we must carefully clarify on the nature of the structural defects in the CNT. In the quantum device applications, such as microwave detection and so on, it should be noted that there exist certain degradations preventing the coherent properties in low temperature transports which is strongly related to the device performance. The details of the results of recent experiments in MWNT and SWNT, will be discussed based on quantum transport device performances.
Electron Devices and Solid-State Circuits, 2007. EDSSC 2007. IEEE Conference on; 01/2008
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ABSTRACT: Using an approach that allows us to probe the electronic structure of strongly pinched-off quantum point contacts (QPCs), we provide evidence for the formation of self-consistently realized bound states (BSs) in these structures. Our approach exploits the resonant interaction between closely coupled QPCs, and demonstrates that the BSs may give rise to a robust confinement of single spins, which show clear Zeeman splitting in a magnetic field.
Physical Review Letters 10/2007; 99(13):136805. · 7.37 Impact Factor
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ABSTRACT: We report on a remarkable resonance in the differential conductance of long quantum point contacts (QPCs) that is observed as a precursor to regular quantized transport. This effect is increasingly pronounced in longer QPCs, in which the differential conductance may resonantly exceed 2e2/h. From a study of the experimental characteristics of this feature, we suggest that it may be associated with the formation of a well-resolved energy gap that opens dynamically as a result of enhanced many-body interactions in long QPCs.
Physical Review Letters 10/2006; 97(9):096801. · 7.37 Impact Factor
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ABSTRACT: Much attention has been given to sub-1G<sub>0</sub> (=2e<sup>2</sup>/h) features in the transmission curve of a quantum point contact (e.g.: 0.5G<sub>0</sub>, 0.7G<sub>0</sub>). Explanations for this phenomenon have been attributed to many-body interactions such as the Kondo effect or the formation of spin polarized currents. We have used scanning gate microscopy to directly observe the local features of the transport associated with sub-1G<sub>0</sub> structures. Images taken with this technique reveal striking features such as weak localization induced within the constriction as well as the formation of self-consistent potentials in the QPC.
Nanotechnology, 2005. 5th IEEE Conference on; 08/2005
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ABSTRACT: We demonstrate the presence of a resonant interaction between a pair of coupled quantum wires, which are formed in the ultrahigh mobility two-dimensional electron gas of a GaAs/AlGaAs quantum well. The coupled-wire system is realized by an extension of the split-gate technique, in which bias voltages are applied to Schottky gates on the semiconductor surface, to vary the width of the two quantum wires, as well as the strength of the coupling between them. The key observation of interest here is one in which the gate voltages used to define one of the wires are first fixed, after which the conductance of this wire is measured as the gate voltage used to form the other wire is swept. Over the range of gate voltage where the swept wire pinches off, we observe a resonant peak in the conductance of the fixed wire that is correlated precisely to this pinchoff condition. In this paper, we present new results on the current- and temperature-dependence of this conductance resonance, which we suggest is related to the formation of a local moment in the swept wire as its conductance is reduced below 2e<sup>2</sup>/h.
IEEE Transactions on Nanotechnology 04/2004; · 2.29 Impact Factor
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ABSTRACT: We study the transport in a system of coupled quantum wires and show evidence for a resonant interaction that occurs whenever one of them is biased close to pinch off. Measuring the conductance of one of the wires, as the width of the other is varied, we observe a resonant peak in the conductance that is correlated to the point at which the other wire pinches off. The origin of this interaction remains undetermined at present, although its characteristics appear consistent with predictions that a correlated many-body state should form in narrow wires as their conductance vanishes. © 2003 American Institute of Physics.
Applied Physics Letters 06/2003; 82(22):3952-3954. · 3.84 Impact Factor
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ABSTRACT: We study the characteristics of the fluctuations, observed in the low-temperature magnetoconductance of an open quantum-dot molecule formed from a pair of split-gate quantum dots. The evolution of these fluctuations suggests a decrease in the typical area for coherent interference with decreasing dot-coupling strength. We discuss this behavior in terms of a transition from multi- to single-dot interference as a function of the interdot coupling. © 2002 American Institute of Physics.
Applied Physics Letters 04/2002; 80(16):2970-2972. · 3.84 Impact Factor
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ABSTRACT: The details of electron interference in quantum-dot systems coupled via quantum point contacts (QPCs) is studied via simulation and experiment. In both open and closed coupled systems, one sees transitions from multi- to single-dot behavior, even when the QPCs support several modes. The results also reveal a non-trivial scaling of the conductance fluctuations in quantum-dot arrays, arising from the influence of the inter-dot coupling on energy hybridization.
Nanotechnology, 2002. IEEE-NANO 2002. Proceedings of the 2002 2nd IEEE Conference on; 02/2002
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A. Shailos,
C. Prasad,
M. Elhassan,
R. Akis,
D. K. Ferry,
J. P. Bird, N. Aoki,
L.-H. Lin,
Y. Ochiai,
K. Ishibashi,
Y. Aoyagi
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ABSTRACT: Temperature-dependent studies of the resistance of open quantum-dot arrays reveal a regime of intermediate temperature (∼1–5 K), over which the resistance increases exponentially with decreasing temperature. In this Brief Report, we explore the origins of this unexpected localization by studying its correlation to the temperature-dependent variation of the magnetoconductance. Based on these studies, we suggest that the exponential regime corresponds to that over which we transition from strongly broadened to energetically resolved levels in the dots. In order to provide further support for this interpretation, we perform numerical studies of temperature-dependent transport through the quantum dots, and discuss the role that many-body effects may play in giving rise to the behavior found in experiment.
Phys. Rev. B. 10/2001; 64(19).
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M. Elhassan,
J. P. Bird,
A. Shailos,
C. Prasad,
R. Akis,
D. K. Ferry,
Y. Takagaki,
L.-H. Lin, N. Aoki,
Y. Ochiai,
K. Ishibashi,
Y. Aoyagi
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ABSTRACT: The details of electron interference in open quantum-dot arrays are studied in experiment and numerical simulations. Reproducible fluctuations are observed in their low-temperature magnetoconductance and the characteristics of these are suggested to be consistent with a transition from multiple to single-dot interference, which occurs as the strength of the interdot coupling is varied. These results therefore reveal a nontrivial scaling of the conductance fluctuations in quantum-dot arrays, which is thought to arise due to the influence of the interdot coupling on energy hybridization.
Phys. Rev. B. 08/2001; 64(8).
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ABSTRACT: We study both the phase-breaking and the energy-relaxation times as a function of both temperature and bias current in arrays of coupled, open quantum dots. These times show a saturation at low temperature, and a decay at higher temperatures. Importantly, the variations of sample resistance as a function of temperature and current cannot be used to infer the electron temperature at a given bias current, which suggests that the energy relaxation process is likely to be phonon based.
Phys. Rev. B. 12/2000; 62(23).
