The Amplitude of Non-Equilibrium Quantum Interference in Metallic Mesoscopic Systems

– We study the influence of a DC bias voltage V on quantum interference corrections to the measured differential conductance in metallic mesoscopic wires and rings. The amplitude of both universal conductance fluctuations (UCF) and Aharonov-Bohm effect (ABE) is enhanced several times for voltages larger than the Thouless energy. The enhancement persists even in the presence of inelastic electron-electron scattering up to V ∼ 1mV. For larger voltages electronphonon collisions lead to the amplitude decaying as a power law for the UCF and exponentially for the ABE. We obtain good agreement of the experimental data with a model which takes into account the decrease of the electron phase-coherence length due to electron-electron and electron-phonon scattering. If the size of a conductor is of order of the electron phase-coherence length Lφ(T ) the wave character of electrons leads to experimentally observable quantum interference contributions to the conductance G. These are the aperiodic and periodic fluctuations δG of the conductance around its average value. In the former case, called universal conductance fluctuations, the interference pattern is formed as a superposition of contributions from a continuous range of possible interference paths. Averaged over either impurity configuration, magnetic field or energy, the root-mean-square (rms) conductance fluctuation δGrms is of the order ∼ e /h [1]. The periodic fluctuations, known as the Aharonov-Bohm effect [2], are observed if the interference is imposed by geometry of a sample, most commonly in the form of a loop. If the loop is threaded by a magnetic flux φ, δG(φ) exhibits periodic oscillations with a period h/e, and δGrms is again ∼ e /h. Both the UCF [3] and the ABE [4] are suppressed by ensemble averaging if independent phase-coherent units are connected in series. The above behaviour is characteristic of the linear-response regime, i.e. of eV ≪ kBT or eV ≪ Ec, where Ec is the coherence energy (Thouless energy) determined by the size of the conductor. In non-equilibrium (eV ≫ Ec, kBT ) the fluctuations are expected to be remarkably different, as predicted theoretically by Larkin and Khmel’nitskĭı (LK) [5]. If inelastic processes can be () Present address: Department of Physics, Faculty of Science, University of Zagreb, Croatia. () Present address: Institute for Experimental and Applied Physics, University of Regensburg, Germany.