Materials & devices
Transport at the Planckian bound of dissipation
We observed signatures of hydrodynamic electron flow in the Weyl semimetal tungsten diphosphide (WP2). Using thermal and magneto-electric transport experiments, we find indications of the transition from a conventional metallic state at higher temperatures to a hydrodynamic electron fluid below 20 K. The hydrodynamic regime is characterized by a viscosity-induced dependence of the electrical resistivity on the square of the channel width and by a strong violation of the Wiedemann–Franz law. From magneto-hydrodynamic experiments and complementary Hall measurements, the relaxation times for momentum relaxing and conserving processes are extracted. Following the uncertainty principle, both electrical and thermal transport are limited by the Planckian bound of dissipation, independent of the underlying transport regime.
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Local thermometry of self-heated nanoscale devices
Hot spots with dimensions of only a few nanometers form in numerous nanoelectronic devices. Based on recent advances in spatial resolution, these hotspots can now be studied by means of Scanning Thermal Microscopy (SThM). Here, we discuss SThM for nanoscale thermometry in comparison with other established thermometry techniques. In situ measurements of semiconductor channels for logic, and phase change memory devices are used to demonstrate today’s measurement capabilities. Temperature fields characterize not only energy dissipation in intact devices but can also serve to identify device failure and fabrication issues.
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