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

We review recent experimental progress on the saturation problem in metallic quantum wires. In particular, we address the influence of magnetic impurities on the electron phase coherence time. We also present new measurements of the phase coherence time in ultra-clean gold and silver wires and analyse the saturation of \tauphi in these samples, cognizant of the role of magnetic scattering. For the cleanest samples, Kondo temperatures below 1 mK and extremely-small magnetic-im...

In this article we investigate the time dependence of the gap mode of copper nitrate at various temperatures. We combine state-of-the-art theoretical calculations with high precision neutron resonance spin-echo measurements to understand the anomalous decoherence effects found previously in this material. It is shown that the time domain offers a complementary view on this phenomenon, which allows us to directly compare experimental data and theoretical predictions without th...

This lecture is a tutorial introduction to coherent effects in disordered electronic systems. Avoiding technicalities as most as possible, I present some personal points of view to describe well-known signatures of phase coherence like weak localization correction or universal conductance fluctuations. I show how these physical properties of phase coherent conductors can be simply related to the classical return probability for a diffusive particle. The diffusion equation is ...

We show a dramatic deviation from ergodicity for the conductance fluctuations in graphene. In marked contrast to the ergodicity of dirty metals, fluctuations generated by varying magnetic field are shown to be much smaller than those obtained when sweeping Fermi energy. They also exhibit a strongly anisotropic response to the symmetry-breaking effects of a magnetic field, when applied perpendicular or parallel to the graphene plane. These results reveal a complex picture of q...

We study the effect of the domain wall on electronic transport properties in wire of ferromagnetic 3$d$ transition metals based on the linear response theory. We considered the exchange interaction between the conduction electron and the magnetization, taking into account the scattering by impurities as well. The effective electron-wall interaction is derived by use of a local gauge transformation in the spin space. This interaction is treated perturbatively to the second ord...

We present a circuit model to describe the electron transport through a domain wall in a ferromagnetic nanowire. The domain wall is treated as a coherent 4-terminal device with incoming and outgoing channels of spin up and down and the spin-dependent scattering in the vicinity of the wall is modelled using classical resistances. We derive the conductance of the circuit in terms of general conductance parameters for a domain wall. We then calculate these conductance parameters...

High energy resolution spectroscopic studies of quantum magnets have proven to be extremely valuable in directly accessing magnetodynamics quantities, such as energy barriers, magnetic interactions, lifetime of excited states and fluctuations at the most fundamental level. Here, we explore the existence of a new flavor of low-energy spin-excitations for quantum spins coupled to an electron bath. In sharp contrast to the usual tunneling signature of two steps symmetrically cen...

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 fini...

We have studied the quantum oscillations of the conductance for arrays of connected mesoscopic metallic rings, in the presence of an external magnetic field. Several geometries have been considered: a linear array of rings connected with short or long wires compared to the phase coherence length, square networks and hollow cylinders. Compared to the well-known case of the isolated ring, we show that for connected rings, the winding of the Brownian trajectories around the ring...

We present measurements of the magnetoresistance of long and narrow quasi one-dimensional gold wires containing magnetic iron impurities. The electron phase coherence time extracted from the weak antilocalisation shows a pronounced plateau in a temperature region of 300 mK - 800 mK, associated with the phase breaking due to the Kondo effect. Below the Kondo temperature, the phase coherence time increases, as expected in the framework of Kondo physics. At much lower temperatur...