Thermal noise of a cryo-cooled silicon cantilever locally heated up to its melting point

TL;DR

This study investigates the thermal noise behavior of a cryo-cooled silicon cantilever heated to its melting point, revealing deviations from classical expectations due to out-of-equilibrium conditions and shared dissipation mechanisms.

Contribution

The paper extends the Fluctuation-Dissipation Theorem to describe thermal fluctuations in a non-equilibrium, laser-heated cantilever, demonstrating lower-than-expected thermal noise.

Findings

Thermal fluctuations are lower than predicted by average temperature.

Dissipation is shared between clamping losses and distributed damping.

Thermal noise increases with heat flux but remains suppressed.

Abstract

The Fluctuation-Dissipation Theorem (FDT) is a powerful tool to estimate the thermal noise of physical systems in equilibrium. In general however, thermal equilibrium is an approximation, or cannot be assumed at all. A more general formulation of the FDT is then needed to describe the behavior of the fluctuations. In our experiment we study a micro-cantilever brought out-ofequilibrium by a strong heat flux generated by the absorption of the light of a laser. While the base is kept at cryogenic temperatures, the tip is heated up to the melting point, thus creating the highest temperature difference the system can sustain. We independently estimate the temperature profile of the cantilever and its mechanical fluctuations, as well as its dissipation. We then demonstrate how the thermal fluctuations of all the observed degrees of freedom, though increasing with the heat flux, are much lower than what is expected from the average temperature of the system. We interpret these results thanks to a minimal extension of the FDT: this dearth of thermal noise arises from a dissipation shared between clamping losses and distributed damping.