36 research outputs found
Mesoscopic conductance effects in InMnAs structures
Quantum corrections to the electrical conduction of magnetic semiconductors
are comparatively unexplored. We report measurements of time-dependent
universal conductance fluctuations (TDUCF) and magnetic field dependent
universal conductance fluctuations (MFUCF) in micron-scale structures
fabricated from two different InMnAs thin films. TDUCF and MFUCF
increasing in magnitude with decreasing temperature are observed. At 4 K and
below, TDUCF are suppressed at finite magnetic fields independent of field
orientation.Comment: 5 pages, 3+2 figures, 1 table; Appl. Phys. Lett. (in press
Time-dependent universal conductance fluctuations in mesoscopic Au wires: implications
In cold, mesoscopic conductors, two-level fluctuators lead to time-dependent
universal conductance fluctuations (TDUCF) manifested as noise. In Au
nanowires, we measure the magnetic field dependence of TDUCF, weak localization
(WL), and magnetic field-driven (MF) UCF before and after treatments that alter
magnetic scattering and passivate surface fluctuators. Inconsistencies between
and strongly suggest either that the
theory of these mesoscopic phenomena in weakly disordered, highly pure Au is
incomplete, or that the assumption that the TDUCF frequency dependence remains
to very high frequencies is incorrect. In the latter case, TDUCF in
excess of expectations may have implications for decoherence in
solid-state qubits.Comment: 8 pages, 9 figures, accepted to PR
Electronic coherence in metals: comparing weak localization and time-dependent conductance fluctuations
Quantum corrections to the conductivity allow experimental assessment of
electronic coherence in metals. We consider whether independent measurements of
different corrections are quantitatively consistent, particularly in systems
with spin-orbit or magnetic impurity scattering. We report weak localization
and time-dependent universal conductance fluctuation data in quasi-one- and
two-dimensional AuPd wires between 2 K and 20 K. The data inferred from both
methods are in excellent quantitative agreement, implying that precisely the
same coherence length is relevant to both corrections.Comment: 5 pages, 4 figures. Scheduled to appear in PRB 70, 041304 (2004
Quantum coherence in a ferromagnetic metal: time-dependent conductance fluctuations
Quantum coherence of electrons in ferromagnetic metals is difficult to assess
experimentally. We report the first measurements of time-dependent universal
conductance fluctuations in ferromagnetic metal (NiFe)
nanostructures as a function of temperature and magnetic field strength and
orientation. We find that the cooperon contribution to this quantum correction
is suppressed, and that domain wall motion can be a source of
coherence-enhanced conductance fluctuations. The fluctuations are more strongly
temperature dependent than those in normal metals, hinting that an unusual
dephasing mechanism may be at work.Comment: 5 pages, 4 figure
Low-temperature electron dephasing time in AuPd revisited
Ever since the first discoveries of the quantum-interference transport in
mesoscopic systems, the electron dephasing times, , in the
concentrated AuPd alloys have been extensively measured. The samples were made
from different sources with different compositions, prepared by different
deposition methods, and various geometries (1D narrow wires, 2D thin films, and
3D thickfilms) were studied. Surprisingly, the low-temperature behavior of
inferred by different groups over two decades reveals a systematic
correlation with the level of disorder of the sample. At low temperatures,
where is (nearly) independent of temperature, a scaling
is found, where
is the maximum value of measured in the experiment, is the
electron diffusion constant, and the exponent is close to or slightly
larger than 1. We address this nontrivial scaling behavior and suggest that the
most possible origin for this unusual dephasing is due to dynamical structure
defects, while other theoretical explanations may not be totally ruled out.Comment: to appear in Physica E, Proceedings for the International Seminar and
Workshop "Quantum Coherence, Noise, and Decoherence in Nanostructures", 15-26
May 2006, Dresde
Enhanced electrical properties of vertically aligned carbon nanotube-epoxy nanocomposites with high packing density
A Method for the Quantification of Nanoparticle Dispersion in Nanocomposites Based on Fractal Dimension
Dispersion quantification provides critical insight and towards understanding and improving the influence of nanoparticle dispersion on the behaviour of the nanocomposite at macro and nanoscale level. This study was precipitated by the limitations of most methods for quantifying dispersion to sufficiently handle issues regarding scalability, complexity, consistency and versatility. A quantity (D 0 ) based on the variance of the fractal dimension was used to quantify dispersion successfully. The concept was validated using real microscopy images. The approach is simple and versatile to implement
Electron phase coherence in mesoscopic normal metal wires
Corrections to the classically predicted electrical conductivity in normal metals arise due to the quantum mechanical properties of the conduction electrons. These corrections provide multiple experimental tests of the conduction electrons' quantum phase coherence. I consider if independent measurements of the phase coherence via different corrections are quantitatively consistent, particularly in systems with spin-orbit or magnetic impurity scattering. More precisely, do independent quantum corrections to the classically predicted conductivity depend identically on the ubiquitous dephasing mechanisms in normal metals? I have inferred the coherence lengths from the weak localization magnetoresistance, magnetic field-dependence of time-dependent universal conductance fluctuations, and magnetic field-dependent universal conductance fluctuations, three observable quantum corrections, in quasi one- and two-dimensional AuPd wires and quasi-1D Ag and Au wires between 2 and 20 K. While the coherence lengths inferred from weak localization and time-dependent universal conductance fluctuations are in excellent quantitative agreement in AuPd, the strong quantitative agreement is apparently lost below a critical temperature in both Ag and Au. Such a disagreement is inconsistent with current theory and must be explained. I developed a hypothesis attributing the coherence length discrepancy seen in Ag and Au to a crossover from the saturated to unsaturated time-dependent conductance fluctuation regime. Two experimental tests were then employed to test this hypothesis. One test examined the effects of a changing spin-flip scattering rate in Au while the second examined how passivation of the two level systems responsible for time-dependent conductance fluctuations at the surface of a Au nanowire affects the inferred coherence lengths. The results of the two tests strongly indicate that the observed disagreement in Au (and likely Ag) is indeed due to a crossover from saturated to unsaturated time-dependent conductance fluctuations
Augustini Triumphi Anconitani ... Summa de potestate ecclesiastica edita anno Dñi. MCCCXX
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