C. R. Dean

McGill University, Montréal, Quebec, Canada

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Publications (13)49.66 Total impact

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    ABSTRACT: Applying high magnetic fields parallel to the surface of a high-mobility 2D electron gas, we have recently observed a transition from the fractional quantum Hall liquid to an insulating phase, for filling factors as high as ν = 0.8 [B. A. Piot et al., Nature Phys. doi:10.1038/nphys1094]. This transition can be seen as a continuous distortion of the 2D Wigner crystal into a 'quasi-3D' insulating state. Here, we provide additional arguments confirming that carrier localization cannot be accounted for by disorder effects alone, and instead is most likely due to the stabilization of an electron solid by the strong parallel magnetic field in a 'quasi-3D' geometry.
    International Journal of Modern Physics B 01/2012; 23(12n13). · 0.46 Impact Factor
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    ABSTRACT: Electrically detected nuclear magnetic resonance was studied in detail in a two-dimensional electron gas as a function of current bias and temperature. We show that applying a relatively modest dc-current bias, I_dc ~ 0.5 microAmps, can induce a re-entrant and even enhanced nuclear spin signal compared with the signal obtained under similar thermal equilibrium conditions at zero current bias. Our observations suggest that dynamic nuclear spin polarization by small current flow is possible in a two-dimensional electron gas, allowing for easy manipulation of the nuclear spin by simple switching of a dc current. Comment: 5 pages, 3 figs
    Physical review. B, Condensed matter 04/2009; · 3.77 Impact Factor
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    ABSTRACT: Using a tilted-field geometry, the effect of an in-plane magnetic field on the even denominator nu=5/2 fractional quantum Hall state is studied. The energy gap of the nu=5/2 state is found to collapse linearly with the in-plane magnetic field above approximately 0.5 T. In contrast, a strong enhancement of the gap is observed for the nu=7/3 state. The radically distinct tilted-field behavior between the two states is discussed in terms of Zeeman and magneto-orbital coupling within the context of the proposed Moore-Read Pfaffian wave function for the 5/2 fractional quantum Hall effect.
    Physical Review Letters 11/2008; 101(18):186806. · 7.73 Impact Factor
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    ABSTRACT: When a strong magnetic field is applied perpendicularly (along
    Nature Physics 10/2008; 4(12):936-939. · 19.35 Impact Factor
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    ABSTRACT: The fractional quantum Hall effect is observed at low magnetic field where the cyclotron energy is smaller than the Coulomb interaction energy. The nu=5/2 excitation gap at 2.63 T is measured to be 262+/-15 mK, similar to values obtained in samples with twice the electronic density. Examining the role of disorder on the 5/2 state, we find that a large discrepancy remains between theory and experiment for the intrinsic gap extrapolated from the infinite mobility limit. The observation of a 5/2 state in the low-field regime suggests that inclusion of nonperturbative Landau level mixing may be necessary to fully understand the energetics of half-filled fractional quantum Hall liquids.
    Physical Review Letters 04/2008; 100(14):146803. · 7.73 Impact Factor
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    ABSTRACT: A study of the resistively detected nuclear magnetic resonance (RDNMR) lineshape in the vicinity of nu=1 was performed on a high-mobility 2D electron gas formed in GaAs/AlGaAs. In higher Landau levels, application of an RF field at the nuclear magnetic resonance frequency coincides with an observed minimum in the longitudinal resistance, as predicted by the simple hyperfine interaction picture. Near nu=1 however, an anomalous dispersive lineshape is observed where a resistance peak follows the usual minimum. In an effort to understand the origin of this anomalous peak we have studied the resonance under various RF and sample conditions. Interestingly, we show that the lineshape can be completely inverted by simply applying a DC current. We interpret this as evidence that the minima and maxima in the lineshape originate from two distinct mechanisms.
    Physica E Low-dimensional Systems and Nanostructures 03/2008; 40:990-994. · 1.86 Impact Factor
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    ABSTRACT: We present an investigation into the manipulation of nuclear spins near the nu=1 quantum Hall state of GaAs/AlGaAs using optical pumping methods. For this, we have built a custom-designed polarization controller which allows for arbitrary polarizations of near-infrared laser light to be transmitted through fiber optics onto the sample. Using resistive readout, it is demonstrated that different polarizations of light induce specific changes in the transport properties in the first Landau level of the GaAs/AlGaAs quantum well.
    Physica E Low-dimensional Systems and Nanostructures 01/2008; 40:1252-1254. · 1.86 Impact Factor
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    ABSTRACT: The effect of the substrate surface, structure, and chemistry on the interfacial interaction in Ni(thin film)/SiC was examined, with a focus on the recently discovered formation of a nickel intercalated graphite phase. Very thin Ni films (∼7 nm) were deposited onto heated 6H–SiC(0001) substrates prepared with: (i) an oxide layer, (ii) a surface reconstruction, and (iii) a pristine surface (no oxide and no reconstruction), followed by further annealing. Characterization using x-ray diffraction and atomic force microscopy revealed remarkable differences between the samples in terms of both surface morphology and crystallography. Nickel silicides were present in all samples; however, the phase composition differed depending on sample preparation. Furthermore, the pristine surface was the only one that clearly promoted the growth of the nickel graphite intercalation compound (Ni-GIC).
    Journal of Materials Research. 08/2007; 22(09):2522 - 2530.
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    ABSTRACT: A fiber-optic-based polarization control system that uses a backreflection measurement scheme at low temperatures has been developed. This provides a stringent test of the light polarization state at the output of the fiber, allowing for determination and control of the degree of circular polarization; i.e., it can generate linear, right, or left circular polarization with cryogenic fibers. This polarization controller is paving the way toward the control and manipulation of nuclear spins in semiconductors via the optical Overhauser effect and could be used, for example, for the purpose of quantum information processing with the large nuclear spins of GaAs.
    Optics Letters 07/2007; 32(11):1378-80. · 3.39 Impact Factor
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    ABSTRACT: This article discusses the design and application of a simple eye-safe monitoring assembly of thin film deposition and its advantages over the existent eye protection filters. This assembly prevents users from being exposed to the radiation field caused by lasers or incandescent objects during thin film deposition. Its design is simple, the device being reliable and easy to operate.
    Journal of Laser Applications 01/2006; 18(1). · 0.57 Impact Factor
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    ABSTRACT: Thickness evaluation is a particular challenge encountered in the fabrication of nanosculptured thin films fabricated by glancing angle deposition (GLAD). In this article, we deduce equations which allow for accurate in situ thickness monitoring of GLAD thin films deposited onto substrates tilted with respect to the direction of incoming vapor. Universal equations are derived for the general case of Gaussian vapor flux distribution, off-axis sensors, variable substrate tilt, and nonunity sticking coefficient. The mathematical description leads to an incidence angle dependence of thickness and density, allowing for quantitative prediction of porosity in samples with different morphologies and thickness calibrations. In addition, variation of sticking probability with the incidence angle creates a nonmonotonic variation of the film thickness and porosity with the substrate tilt. We discuss the implications of the substrate type, sensor type, and source geometry in a precise quantitative determination of the thickness of thin films fabricated on tilted substrates. Our equations can be particularized for the case of films fabricated at normal incidence.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2005; · 1.36 Impact Factor
  • Cory Dean, Kevin Robbie
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    ABSTRACT: Graphite Intercalation Compounds (GICs) are an interesting class of hybrid materials that often have surprising and unique chemical and physical properties. Recent studies have demonstrated a new technique for fabricating transition metal GICs using thin film deposition. In the first realization of a pure transition metal-GIC, thin films of Ni were vacuum deposited onto crystalline SiC and annealed to high temperatures, resulting in the formation of small islands. Examination with scanning tunnelling microscopy (STM), scanning electron microscopy (SEM), and Auger electron spectroscopy (AES), revealed these island structures to be composed of Ni atoms intercalated into a graphite matrix. Current investigations have extended our understanding of the Ni-GIC growth process so that islands of increased size and density have been realized, allowing us to probe the crystal structure of these unique materials using x-ray diffraction. A review of the growth and characterization of the first reported pure Ni-GIC structures will be given in addition to new findings from x-ray diffraction, and a discussion of the Ni-GIC growth mechanism.
    01/2004;
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    ABSTRACT: An ultrahigh vacuum apparatus for the deposition of thin films with controlled three-dimensional nanometer-scale structure is described. Our system allows an alternate, faster, cheaper way of obtaining nanoscale structured thin films when compared to traditional procedures of patterning and etching. It also allows creation of porous structures that are unattainable with known techniques. The unique feature of this system is the dynamic modification of the substrate tilt and azimuthal orientation with respect to the vapor source during deposition of a thin film. Atomic-scale geometrical shadowing creates a strong directional dependence in the aggregation of the film, conferring control over the resulting morphological structure on a scale of less than 10 nm. Motion can create pillars, helixes, zig–zags, etc. Significant features of the apparatus include variable substrate temperature, insertion and removal of specimens from atmospheric conditions without venting the deposition system, computer controlled process parameters, and in situ analysis capabilities. The deposition system was successfully employed for the fabrication of a variety of nanostructured thin films with a wide range of potential applications. © 2004 American Institute of Physics.
    Review of Scientific Instruments 01/2004; 75. · 1.60 Impact Factor