Directional ballistic transport in the two-dimensional metal PdCoO2
Maja D Bachmann1,2, Aaron L Sharpe3,4, Graham Baker5
1Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.
Nature Physics
|July 18, 2022
Summary
In palladium cobaltate (PdCoO2) microstructures, researchers observed resistivity anisotropy and transverse voltage, phenomena forbidden by crystal symmetry. This shape-induced effect arises from ballistic charge carriers colliding with channel walls.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Solid-State Physics
Background:
- Material properties in infinite crystals are dictated by unit cell symmetries.
- Finite crystal shapes break point-group symmetry, an effect usually unobservable in macroscopic metals.
- Observing shape-induced symmetry lowering requires long-lived bulk states from anisotropic Fermi surfaces.
Purpose of the Study:
- To investigate shape-induced symmetry lowering in metals.
- To demonstrate symmetry-forbidden transport signatures in microstructured PdCoO2.
- To link observed phenomena to Fermi surface characteristics and microstructure geometry.
Main Methods:
- Fabrication of bar-shaped transport devices from single crystals using focused ion beam milling.
- Measurement of in-plane resistivity anisotropy and transverse voltage in zero magnetic field.
- Utilizing ballistic Monte Carlo simulations and Boltzmann equation solutions.
Main Results:
- Observed in-plane resistivity anisotropy exceeding a factor of 2 in PdCoO2 microstructures.
- Detected a transverse voltage in zero magnetic field, a symmetry-forbidden transport signature.
- Identified the orientation of the narrow channel as the source of symmetry breaking.
Conclusions:
- Microstructured PdCoO2 exhibits transport properties forbidden by the hexagonal lattice symmetry.
- The interplay between a facetted Fermi surface and a long quasiparticle mean free path is crucial.
- Ballistic charge carrier behavior in confined geometries can reveal subtle symmetry-breaking effects.
Keywords:
Electronic properties and materials
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