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Current patterns and orbital magnetism in mesoscopic dc transport.
Michael Walz1, Jan Wilhelm2, Ferdinand Evers1
1Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76344 Eggenstein-Leopoldshafen, Germany and Institut für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology, Campus South, D-76128 Karlsruhe, Germany and Center of Functional Nanostructures, Karlsruhe Institute of Technology, Campus South, D-76131 Karlsruhe, Germany.
Physical Review Letters
|October 11, 2014
Summary
Researchers discovered circulating ring currents in dc-transport measurements, exceeding average currents and generating fluctuating magnetic fields. This orbital magnetism impacts spin relaxation in organic semiconductors.
Area of Science:
- Condensed matter physics
- Quantum chemistry
Background:
- Understanding electron transport in materials is crucial for device applications.
- Orbital magnetism and its influence on spin dynamics are key research areas.
Purpose of the Study:
- To investigate the spatial distribution of local current density in dc-transport measurements.
- To explore the relationship between local current patterns, orbital magnetism, and spin relaxation.
Main Methods:
- Ab initio calculations of local current density (j(r)).
- Analysis of ring current patterns and associated magnetic fields.
Main Results:
- Discovery of pronounced ring current patterns ('eddies') in local current density.
- Ring currents magnitude can exceed average transport current by orders of magnitude.
- Associated magnetic fields exhibit drastic fluctuations with high field gradients (1 T nm⁻¹ V⁻¹).
Conclusions:
- Bias-driven orbital magnetism significantly influences spin relaxation in systems with weak spin-orbit interaction, like organic semiconductors.
- This mechanism competes with hyperfine interaction for spin relaxation, showing comparable strength.
- A proposed NMR-type experiment could detect spatial fluctuations of induced magnetic fields.
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