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 In$_{1-x}$Mn$_{x}$As 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 $1/f$ 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 $L_{\phi}^{\rm WL}$ and $L_{\phi}^{\rm TDUCF}$ 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 $1/f$ to very high frequencies is incorrect. In the latter case, TDUCF in excess of $1/f$ expectations may have implications for decoherence in solid-state qubits.Comment: 8 pages, 9 figures, accepted to PR

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 (Ni$_{0.8}$Fe$_{0.2}$) 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

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

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