Abstract: Temperature is one of the most central concepts of thermal physics with historical roots in the seventeenth century mechanics and nineteenth century thermodynamics. Building up on these early foundations, I will highlight how the understanding of temperature gets increasingly challenging when small systems are away from equilibrium, get scaled to ensemble sizes below classical limits, and when quantum effects become relevant. Today, the apparently simply question of ‘what is the temperature’ is again up for debate, fueled by the miniaturization of technology and the experimental progress to study physical properties and processes down to atomic length and ultrafast time scales. Aiming to clarify questions such as how to measure temperature on the length-scale of nanoscale transistors, how interfaces and contacts influence dissipation processes, and how fundamental heat and charge transport relations may change at the atomic scale, we have recently developed new thermal nanometrology techniques based on scanning probe methods . By demonstrating the real-space quantification of local Joule and Peltier effects at metal-semiconductor contacts , and the first atomic scale validation of the Wiedemann-Franz law at room temperature , I will illustrate the application of theses approaches. Finally, I’ll provide an outlook on our ongoing efforts to open the door for spatio-temporal characterization of thermal phenomena at the transition from the classical to the quantum regime.
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