[論文レビュー] Electrical and Thermal Transport at the Planckian Bound of Dissipation in the Hydrodynamic Electron Fluid of WP2

Johannes Gooth, Fabian Menges+8 more|arXiv (Cornell University)|Jun 19, 2017

Quantum and electron transport phenomena参考文献 40被引用数 69

ひとこと要約

この論文は WP2 における流体力学的電子流を報告し、運動量と熱エネルギーの散逸に対する Planckian-limited 散逸を示し、Wiedemann–Franz law の Weyl semimetal における違反を示す。

ABSTRACT

Materials with strongly-correlated electrons exhibit interesting phenomena such as metal-insulator transitions and high-temperature superconductivity. In stark contrast to ordinary metals, electron transport in these materials is thought to resemble the flow of viscous fluids. Despite their differences, it is predicted that transport in both, conventional and correlated materials, is fundamentally limited by the uncertainty principle applied to energy dissipation. Here we discover hydrodynamic electron flow in the Weyl-semimetal tungsten phosphide (WP2). Using thermal and magneto-electric transport experiments, we observe 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 the observation of a strong violation of the Wiedemann-Franz law. From magneto-hydrodynamic experiments and complementary Hall measurements, the relaxation times for momentum and thermal energy dissipating processes are extracted. Following the uncertainty principle, both are limited by the Planckian bound of dissipation, independent of the underlying transport regime.

研究の動機と目的

• Motivate and identify hydrodynamic electron flow in a strongly correlated, Weyl semimetal material (WP2).
• Characterize the transition from conventional metallic transport to hydrodynamic transport below ~20 K using thermal and magneto-electric measurements.
• Extract momentum- and thermal-energy dissipation relaxation times and test their relation to the Planckian bound.
• Demonstrate how viscosity and hydrodynamics modify electrical and thermal transport properties.

提案手法

• Perform thermal and magneto-electric transport experiments on WP2 across a range of temperatures.
• Analyze channel-width dependence of electrical resistivity to identify viscosity-induced effects.
• Measure Wiedemann–Franz relation to detect violations in the hydrodynamic regime.
• Use magneto-hydrodynamic and Hall measurements to extract relaxation times for momentum and thermal dissipation.
• Compare relaxation times to the Planckian bound of dissipation as a benchmark for dissipation limits.

実験結果

リサーチクエスチョン

• RQ1 Does WP2 exhibit hydrodynamic electron flow as temperature decreases below ~20 K?
• RQ2 How do viscosity and hydrodynamic effects modify electrical resistivity and channel-width scaling?
• RQ3 Are momentum and thermal-energy dissipation times bounded by the Planckian limit independent of transport regime?
• RQ4 To what extent is Wiedemann–Franz law violated in the hydrodynamic regime?

主な発見

• Identification of a hydrodynamic electron fluid in WP2 below ~20 K.
• Observation of viscosity-induced resistivity dependence on the square of channel width.
• Strong violation of the Wiedemann–Franz law in the hydrodynamic regime.
• Extraction of momentum and thermal dissipation relaxation times from magneto-hydrodynamic and Hall data.
• Evidence that both relaxation times are limited by the Planckian bound of dissipation, consistent with the uncertainty principle.
• Results link hydrodynamic transport to fundamental dissipation limits across transport regimes.