DQMP Seminar - Intrinsic Aharonov-Bohm oscillations in layered metals: A novel signature of phase coherent transport

29.01.2019 13:00 – 14:30

Intrinsic Aharonov-Bohm oscillations in layered metals: A novel signature of phase coherent transport

Despite the wave-like nature of electrons, their transport in metals is usually very successfully described by classical pictures. Quantum mechanics sets the stage for the electronic system, such as providing a dispersion relation E(k) in the crystal that differs from that of free electrons, or the notion of a Fermi surface. Yet beyond that, a semi-classical picture using a Boltzmann transport model well captures the transport properties of metals, even in the presence of strong magnetic fields. To detect the wave-like nature of electrons, metals have been shaped into mesoscopic interferometers resembled by small rings. The conductance of such rings is periodically modulated upon applying a magnetic field, as each additional magnetic flux quantum threading the ring restores constructive interference. These oscillations resemble the Aharonov-Bohm effect, and are among the strongest direct experimental signatures of the phase of the electron in the solid.
In this seminar, I will present a surprising recent discovery of related phase physics in bulk crystals of PdCoO2. This strongly layered material is electronically 2D, which reflects in its sizable transport anisotropy c/a~3000. The conduction occurs exclusively in single-atomic layers of hexagonally distributed Pd atoms. The ultra-clean metal is characterized by an unusually long mean-free-path for an oxide conductor exceeding 20m at low temperatures. We use Focused Ion Beam machining to fabricate bar-shaped samples perpendicular to the Pd layers, to probe the out-of-plane conductivity.
Intriguingly, when the magnetic field is applied parallel to the layers, a pronounced oscillatory magnetoresistance is observed. Unlike Shubnikov-de Haas oscillations, these oscillations are linearly periodic in magnetic field. These oscillations are Aharonov-Bohm oscillations in the single crystal structure. The period of the oscillations is perfectly described by a magnetic flux quantum threading a box spanned by the physical width of the bar and two adjacent atomic layers of Pd. This currently unexplained quantum phenomenon resembles the smallest Aharonov-Bohm interferometer ever observed, with an atomic separation of only 0.6nm between the interferometric paths. The effect is remarkably robust, as we observe quantum coherence already at high temperatures of 50K over distances of 10m. These results highlight unexplored quantum physics in ultrapure layered metals as well as showcase the feasibility of novel applications, such as phase-coherent magnetometers with atomic resolution.

Lieu

Bâtiment: Ecole de Physique

Auditoire Stuckelberg

Organisé par

Département de physique de la matière quantique

Intervenants

Philip Moll, Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)

entrée libre

Classement

Catégorie: Séminaire