Low temperature dissipation scenarios in palladium nano-mechanical resonators

TL;DR

This paper investigates low-temperature energy loss mechanisms in palladium nano-mechanical resonators, revealing how hydrogen adsorption and induced stress influence dissipation, TLS behavior, and phonon interactions.

Contribution

It demonstrates how hydrogen-induced stress modifies TLS dissipation and phonon coupling in Pd nano-resonators, providing new insights into tunable dissipation mechanisms at low temperatures.

Findings

Dissipation follows a T^{0.4} power law at low temperatures.

Hydrogen reduces the characteristic temperature T_{co} from 1K to 700mK.

Saturation in dissipation suggests possible super-radiant TLS-phonon interactions.

Abstract

We study dissipation in Pd nano-mechanical resonators at low temperatures in the linear response regime. Metallic resonators have shown characteristic features of dissipation due to tunneling two level systems (TLS). This system offers a unique tunability of the dissipation scenario by adsorbing hydrogen ($H_2$) which induces a compressive stress. The intrinsic stress is expected to alter TLS behaviour. We find a sub-linear power law $\sim T^{0.4}$ in dissipation. As seen in TLS dissipation scenarios we find a logarithmic increase of frequency characteristic from the lowest temperatures till a characteristic temperature $T_{co}$ is reached. In samples without $H_2$ the $T_{co} \sim 1K$ whereas with $H_2$ it is clearly reduced to $\sim 700 mK$. Based on standard TLS phenomena we attribute this to enhanced phonon-TLS coupling in samples with compressive strain. We also find with $H_2$ there is a saturation in low temperature dissipation which may possibly be due to super-radiant interaction between TLS and phonons. We discuss the data in the scope of TLS phenomena and similar data for other systems.