Quantum coherence in a ferromagnetic metal: time-dependent conductance fluctuations

We report on intrinsic time-dependent conductance fluctuations observed in mesoscopic AuFe spin glass wires. These dynamical fluctuations have a 1/f-like spectrum and appear below the measured spin glass freezing temperature of our samples. The dependence of the fluctuation amplitude on temperature, magnetic field, voltage and Fe concentration allows a consistent interpretation in terms of quantum interference effects which are sensitive to the slowly fluctuating spin configu...

We study electron transport through a domain wall in a ferromagnetic nanowire subject to spin-dependent scattering. A scattering matrix formalism is developed to address both coherent and incoherent transport properties. The coherent case corresponds to elastic scattering by static defects, which is dominant at low temperatures, while the incoherent case provides a phenomenological description of the inelastic scattering present in real physical systems at room temperature. I...

This lecture note reviews a variety of transport and thermodynamic measurements of electron decoherence time in low-dimensional conductors at low temperature. The mechanism of dephasing by electron interaction mediated by an arbitrarily small number of magnetic impurities is neither applicable to our linear-response measurements of weak localization, nor is it observed in the recent high-field measurements of the decoherence time in nominally pure quasi-one dimensional gold w...

We present data of transport measurements through a metallic nanobridge exhibiting diffusive electron transport. A logarithmic temperature dependence and a zero-bias anomaly in the differential conductance are observed, independent of magnetic field. The data can be described by a single scaling law. The theory of electron-electron interaction in disordered systems, adapted to the case of finite-size systems in non-equilibrium, yields quantitative agreement with experiment. M...

Quantum interference effects and resulting quantum corrections of the conductivity have been intensively studied in disordered conductors over the last decades. The knowledge of phase coherence lengths and underlying dephasing mechanisms are crucial to understand quantum corrections to the resistivity in the different material systems. Due to the internal magnetic field and the associated breaking of time-reversal symmetry quantum interference effects in ferromagnetic materia...

Quasi-ballistic semiconductor quantum wires are exposed to localized perpendicular magnetic fields, also known as magnetic barriers. Pronounced, reproducible conductance fluctuations as a function of the magnetic barrier amplitude are observed. The fluctuations are strongly temperature dependent and remain visible up to temperatures of about 10 K. Simulations based on recursive Green functions suggest that the conductance fluctuations originate from parametric interferences o...

We present a calculation of the dephasing time of electrons in a ferromagnet relevant for the conductance fluctuations. We focus on the contribution from the interaction with spin waves. Explicit results are presented for a quasi-one-dimensional systems. Going beyond previous calculations, we do not restrict ourselves to the limit of a small exchange splitting compared to the electronic elastic scattering time, nor does our calculation rely on the diffusion approximation to d...

We have measured Universal Conductance Fluctuations in the metallic spin glass Ag:Mn as a function of temperature and magnetic field. From this measurement, we can access the phase coherence time of the electrons in the spin glass. We show that this phase coherence time increases with both the inverse of the temperature and the magnetic field. From this we deduce that decoherence mechanisms are still active even deep in the spin glass phase.

We show that in a magnetic nanowire with double magnetic domain walls, quantum interference results in spin-split quasistationary states localized mainly between the domain walls. Spin-flip-assisted transmission through the domain structure increases strongly when these size-quantized states are tuned on resonance with the Fermi energy, e.g. upon varying the distance between the domain walls which results in resonance-type peaks of the wire conductance. This novel phenomena i...

The observation of coherent quantum transport phenomena in metals and semiconductors is limited by the eventual loss of phase coherence of the conducting electrons. We use the weak localization effect to measure the low-temperature dephasing time in a two-dimensional electron Fermi liquid in GaAs/AlGaAs heterostructures. We use a novel temperature calibration method based on the integer quantum Hall effect in order to directly measure the electrons' temperature. The data are ...