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Nanotechnology, IEEE Transactions on

Issue 1 • Date Jan. 2005

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Displaying Results 1 - 25 of 32
  • Table of contents

    Page(s): c1 - c4
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    Freely Available from IEEE
  • IEEE Transactions on Nanotechnology publication information

    Page(s): c2
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    Freely Available from IEEE
  • Foreword

    Page(s): 1
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  • Spin relaxation in the channel of a spin field-effect transistor

    Page(s): 2 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    We examine the major spin relaxation mechanism (D'yakonov-Perel') in the channel of a spin field-effect transistor (SPINFET) and show analytically that it can be completely eliminated if the channel is a quantum wire and transport is strictly single moded (only the lowest subband is occupied). Single-moded transport also produces the largest "on" to "off" conductance ratio and the largest transconductance of the transistor. View full abstract»

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  • Wave-packet scattering without kinematic entanglement: convergence of expectation values

    Page(s): 8 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    The wave packet spread of a particle in a collection of different mass particles, all with Gaussian wave functions, evolves to a value that is inversely proportional to the mass of the particle. The assumptions underlying this result and its derivation are reviewed. A mathematical demonstration of the convergence of an iteration central to this assertion is presented. Finally, the question of in-principle measurement of wave packet spread is taken up. View full abstract»

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  • Modeling and simulations of a single-spin measurement using MRFM

    Page(s): 14 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    We review the quantum theory of a single-spin magnetic resonance force microscopy (MRFM). We concentrate on the novel technique called oscillating cantilever-driven adiabatic reversals (OSCARs), which has been used for a single-spin detection. First we describe the quantum dynamics of the cantilever-spin system using simple estimates in the spirit of the mean field approximation. Then we present the results of our computer simulations of the Schrödinger equation for the wave function of the cantilever-spin system and of the master equation for the density matrix of the system. We demonstrate that the cantilever behaves like a quasi-classical measurement device which detects the spin projection along the effective magnetic field. We show that the OSCAR technique provides continuous monitoring of the single spin, which could be used to detect the mysterious quantum collapses of the wave function of the cantilever-spin system. View full abstract»

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  • Electron dynamics in a coupled quantum-point contact structure with a local magnetic moment

    Page(s): 21 - 26
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB) |  | HTML iconHTML  

    We develop a theoretical model for the description of electron dynamics in coupled quantum wires when the local magnetic moment is formed in one of the wires. We employ a single-particle Hamiltonian that takes account of the specific geometry of potentials defining the structure as well as electron scattering on the local magnetic moment. The equations for the wave functions in both wires are derived and the approach for their solution is discussed. We determine the transmission coefficient and conductance of the wire having the local magnetic moment and show that our description reproduces the experimentally observed features. View full abstract»

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  • Spin characterization and control over the regime of radiation-induced zero-resistance states

    Page(s): 27 - 34
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    Over the regime of the radiation-induced zero-resistance states and associated oscillatory magnetoresistance, we propose a low-magnetic-field analog of quantum-Hall-limit techniques for the electrical detection of electron spin and nuclear magnetic resonance, dynamical nuclear polarization via electron spin resonance, and electrical characterization of the nuclear spin polarization via the Overhauser shift. In addition, beats observed in the radiation-induced oscillatory magnetoresistance are developed into a method to measure and control the zero-field spin splitting due to the Bychkov-Rashba and bulk inversion asymmetry terms in the high-mobility GaAs-AlGaAs system. View full abstract»

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  • Decoherence of nuclear spin quantum memory in a quantum dot

    Page(s): 35 - 39
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    Recently, an ensemble of nuclear spins in a quantum dot have been proposed as a long-lived quantum memory. A quantum state of an electron spin in the dot can be faithfully transfered into nuclear spins through controlled hyperfine coupling. Here we study the decoherence of this memory due to nuclear spin dipolar coupling and inhomogeneous hyperfine interaction during the storage period. We calculated the maximum fidelity of writing, storing, and reading operations. Our results show that nuclear spin dynamics can severely limit the performance of the proposed device for quantum information processing and storage based on nuclear spins. View full abstract»

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  • Spin injection in spin FETs using a step-doping profile

    Page(s): 40 - 44
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    We investigate the effect of a step-doping profile on the spin injection from a ferromagnetic metal contact into a semiconductor quantum well in spin field-effect transistors using a Monte Carlo model. The considered scheme uses a heavily doped layer at the metal-semiconductor interface to vary the Schottky barrier shape and enhance the tunneling current. It is found that spin flux (spin current density) is enhanced proportionally to the total current, and the variation of current spin polarization does not exceed 20%. View full abstract»

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  • Quantum interference in resonant tunneling and single spin measurements

    Page(s): 45 - 51
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    We consider the resonant tunneling through a multilevel system. It is demonstrated that the resonant current displays quantum interference effects due to a possibility of tunneling through different levels. We show that the interference effects are strongly modulated by a relative phase of states carrying the current. This makes it possible to use these effects for measuring the phase difference between resonant states in quantum dots. We extend our model for a description of magnetotransport through the Zeeman doublets. It is shown that, due to spin-flip transitions, the quantum interference effects generate a distinct peak in the shot-noise power spectrum at the frequency of Zeeman splitting. This mechanism explains modulation in the tunneling current at the Larmor frequency observed in scanning tunneling microscope experiments and can be utilized for a single spin measurement. View full abstract»

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  • Resonant spikes of the nuclear spin qubits relaxation rate in quantum-Hall systems with magnetic impurities

    Page(s): 52 - 56
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    The magnetic field dependence of the local phononassisted nuclear spin qubit relaxation rate in 2DES with magnetic impurities is studied theoretically. For weak and strong scattering limits under a strong magnetic field, we show that the magnetic field dependence of T1-1 exhibits giant spikes, due to the energy matching of the electron Zeeman splitting with the energy spacing between the vibrational mode energies. The localized mode is created by the lattice distortion around the impurity. This resonance phenomenon could be used as a local probe for studying the localized vibrational modes and their coupling to electrons and for the resonant manipulation of the nuclear spin qubits. View full abstract»

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  • Analysis of electron energy States in a thin quantum well in a parallel magnetic field

    Page(s): 57 - 58
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    We carry out a preliminary investigation of electron dynamics in a quantum well subject to a uniform magnetic field applied parallel to its walls. To achieve exact expressions for the Green's function and associated dispersion relation, we study the narrow limit of a delta-function well profile. The Dyson equation is solved and the dispersion relation is examined for weak and strong (quantizing) magnetic fields. View full abstract»

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  • Probing magnetic anisotropy and spin polarization in spintronic materials

    Page(s): 59 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    Magnetic anisotropy and spin polarization are fundamental parameters in ferromagnetic materials that have use in spintronic device applications. As the need for screening properties of new magnetic materials rises, it is important to have measurement probes for quantities such as anisotropy and spin polarization. We have developed two unconventional yet powerful techniques to study these parameters. A resonant RF transverse susceptibility method is used to map the characteristic anisotropy and switching fields over a wide range in temperature and magnetic fields. For studies of spin polarization, the phenomenon of Andreev reflection across ferromagnet-superconductor junctions is used to extract values of the transport spin polarization. The effectiveness of these approaches is demonstrated in candidate spintronic materials such as half-metallic CrO2 thin films and arrays of monodisperse, single-domain Fe nanoparticles. View full abstract»

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  • Study of temperature dependence of electron-phonon relaxation and dephasing in semiconductor double-dot nanostructures

    Page(s): 65 - 70
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    This paper examines mechanisms of relaxation and dephasing of electrons in double-dot nanostructures due to interaction with acoustic phonon modes. The effect of temperature of phonon bath on decay on electron quantum evolution is obtained. Our results set the temperature ranges outside of which the quantum dynamics of electrons will be significantly suppressed. View full abstract»

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  • Shot noise in resonant tunneling through an interacting quantum dot with intradot spin-flip scattering

    Page(s): 71 - 76
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    We present theoretical investigation of the zero-frequency shot-noise spectra in electron tunneling through an interacting quantum dot connected to two ferromagnetic leads with the possibility of spin-flip scattering between the two spin states by means of the recently developed bias-voltage and temperature-dependent quantum rate equations. For this purpose, a generalization of the traditional generation-recombination approach is made for properly taking into account the coherent superposition of electronic states, i.e., the nondiagonal density matrix elements. Our numerical calculations find that the Fano factor increases with increasing the polarization of the two leads, but decreases with increasing the intradot spin-flip scattering. View full abstract»

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  • Decoherence in quantum systems

    Page(s): 77 - 82
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    We discuss various definitions of decoherence and how it can be measured. We compare and contrast decoherence in quantum systems with an infinite number of eigenstates (such as the free particle and the oscillator) and spin systems. In the former case, we point out the essential difference between assuming "entanglement at all times" and entanglement with the reservoir occuring at some initial time. We also discuss optimum calculational techniques in both arenas. View full abstract»

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  • Nuclear spin-lattice relaxation in superlattices

    Page(s): 83 - 89
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    The nuclear spin-lattice relaxation rate in a superlattice subjected to a strong magnetic field H parallel to its axis is studied theoretically. The energy conservation law allows flip-flop spin-reversal processes due to the hyperfine interaction between the nuclear and electron spins only in some intervals of H. In particular, the width of the highest occupied superlattice subband Δ must exceed the spin splitting of Landau levels, which results in the relaxation offset at some critical magnetic field H2. At H2 and low temperatures, the relaxation rate T1-1 versus H dependence has giant oscillations depending on the Fermi level position. The behavior of T1 can be changed by the tilting of the magnetic field, decreasing the Landau level separation at a constant spin-splitting. At some critical tilt angle, these two quantities become equal and inter-Landau-level processes come into action which drastically increases the relaxation rate. View full abstract»

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  • Effects of strong correlations in single electron traps in field-effect transistors

    Page(s): 90 - 95
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    We study effects of strong electron-electron and electron-phonon correlations in single electron traps in metal-oxide-semiconductor field effect transistors (FETs). In order to explain the strong suppression of single electron tunneling in the trap, we introduce a model in which the excess charge of the trap couples to a local lattice deformation. By using nonperturbative techniques, we derive an effective low-energy action for the system. The behavior of the system is characterized by simultaneous polaron tunneling (corresponding to the charging and discharging of the trap) and Kondo screening of the trap spin in the singly occupied state. Hence, the obtained state of the system is a hybrid between the Kondo regime, typically associated with single electron occupancy, and the mixed valence regime, associated with large charge fluctuations. In the presence of a strong magnetic field, we demonstrate that the system is equivalent to a two-level system coupled to an Ohmic bath, with a bias controlled by the applied magnetic field. Due to the Kondo screening, the effect of the magnetic field is significantly suppressed in the singly occupied state. We claim that this suppression can be responsible for the experimentally observed anomalous magnetic field dependence of the average trap occupancy in Si-Si02 FETs. View full abstract»

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  • Relaxation of a nuclear spin placed on a biased nanomechanical oscillator

    Page(s): 96 - 99
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    We propose a mechanism to decrease the time needed to initialize nuclear spin qubits by resonant coupling of the nuclear spins to a heat bath composed of nanomechanical degrees of freedom. To achieve this, we suggest that the nuclear spins be attached to the tip of a cantilever oscillating in a nonuniform magnetic field. The gradient of the magnetic field couples the spin and mechanical degrees of freedom, inducing an additional spin-relaxation mechanism. The nanomechanical oscillator can also serve as one of the contacts of a tunnel junction, facilitating a voltage control of the nuclear spin-relaxation time. We derive an explicit microscopic expression for the relaxation rate of nuclear spins and analyze its voltage and temperature dependencies. View full abstract»

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  • Magnetoresistively detected electron spin resonance in low-density two-dimensional electron gas in GaAs-AlGaAs single quantum wells

    Page(s): 100 - 105
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    Electron spin resonance (ESR) is a natural candidate for quantum bit manipulation, provided that the confinement of a small number of electrons in a sufficiently small volume can be achieved. An important step is the development of low carrier density materials and structures in which the electron spins are isolated and can be controlled by ESR. We report on the realization of three low-density (n1=1.77×1010, n2=4.5×1010, and n3=9×1010 cm-2 without the help of a gate to deplete the channel) two-dimensional electron systems in GaAs-AlGaAs single quantum wells (QWs) and on the magnetoresistively detected electron spin resonance (MDESR) measurements in these samples. The MDESR has been characterized at ν=1 and ν=3 and the current intensity, microwave power, and temperature dependence have been studied. The structures that have been investigated represent the lowest density single QW samples in which MDESR has been detected. The implications of detection of the MDESR at such low electron density to coupled quantum-dot spin device technology will be presented. View full abstract»

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  • Cd1-xMnxTe semimagnetic semiconductors for ultrafast spintronics and magnetooptics

    Page(s): 106 - 112
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    We present ultrafast optical characterization of Cd1-xMnxTe single crystals with high (x>0.5-Mn) concentration, studied by magnetooptical sampling and time-resolved magnetization modulation spectroscopy. We have demonstrated that the dynamics of both Mn spins and carrier spins in Cd1-xMnxTe is extremely fast (in the subpicosecond range), making the nanostructures based on this material very promising for applications in spintronics and magnetooptics. View full abstract»

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  • Nanofabrication aspects of silicon-based spin quantum gates

    Page(s): 113 - 115
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    Electronic and nuclear spins of shallow donors in silicon are particularly attractive among the solid-state systems considered for quantum information storage and processing. Shallow donor exchange gates are frequently invoked to preform two-qubit operations for these spin qubits. Careful analysis of the feasibility of such operations demands realistic descriptions of the underlying electronic structure in Si. Intervalley interference between the conduction-band-edge states of Si leads to oscillatory behavior in the donor-pair exchange J. We calculate the exchange coupling for two donors within the Heitler-London approach and show that, if the donors can be placed at substitutional sites precisely along the [100] crystal direction, the oscillatory behavior of J may be essentially ignored in practice. However, small uncertainties in the relative positioning-between 1-5 nm-with respect to this ideal direction lead to a broad distribution of J values peaked at J∼0, posing severe limitations in the nanofabrication of shallow donor arrays and exchange gates in Si. View full abstract»

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  • Theory of dynamical control of qubit decay and decoherence

    Page(s): 116 - 123
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    We derive and investigate an expression for the dynamically modified decay of states coupled to an arbitrary continuum. This expression is universally valid for weak temporal perturbations. The resulting insights can serve as useful recipes for optimized control of decay and decoherence. View full abstract»

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  • Microwave absorption/reflection and magneto-transport experiments on high-mobility electron gas

    Page(s): 124 - 131
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    We have performed simultaneous measurements of microwave absorption/reflection and magneto-transport characteristics of a high-mobility two-dimensional electrons in GaAs-AlGaAs heterostructure in the regime of microwave-induced resistance oscillations (MIROs). It is shown that the electrodynamic aspect of the problem is important in these experiments. In the absorption experiments, a broad cyclotron resonance line was observed due to a large reflection from the highly conductive electron gas. There were no additional features observed related to absorption at harmonics of the cyclotron resonance. In near-field reflection experiments, a very different oscillation pattern was revealed when compared to MIROs. The oscillation pattern observed in the reflection experiments is probably due to plasma effects occurring in a finite-size sample. The whole microscopic picture of MIROs is more complicated than simply a resonant absorption at harmonics of the cyclotron resonance. Nevertheless, the experimental observations are in good agreement with the model by Ryzhii et al. involving the photo-assisted scattering in the presence of a crossed magnetic field and dc bias. The observed damping factor of MIROs may be attributed to a change in the electron mobility as a function of temperature. View full abstract»

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Aims & Scope

The IEEE Transactions on Nanotechnology is devoted to the publication of manuscripts of archival value in the general area of nanotechnology, which is rapidly emerging as one of the fastest growing and most promising new technological developments for the next generation and beyond.

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Editor-in-Chief
Kang L. Wang
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