# Ion-crystal demonstration of structural phase transition induced solely by temperature

## TL;DR

This paper reports the first experimental observation of a temperature-induced linear-zigzag phase transition in ion crystals, highlighting thermal fluctuations' role in atomic thermodynamics.

## Contribution

It demonstrates a novel temperature-driven phase transition in ion crystals, distinct from mechanically induced transitions, emphasizing thermal fluctuations' influence.

## Key findings

- Temperature-controlled phase transition observed in ion crystals.
- Classical Langevin equation explains the transition.
- Thermal fluctuations significantly impact atomic thermodynamics.

## Abstract

We demonstrate for the first time a linear-zigzag phase transition induced solely by temperature of the $^{40}$Ca$^{+}$ ion crystals in a surface-electrode trap. In contrast to the previously observed counterparts based on change of the mechanical equilibrium conditions of the ions, our presented structural phase transition occurs due to controllable influence of thermal fluctuation. The ions' temperature is well controlled by tuning the cooling laser and the experimental observation could be fully understood by classical Langevin equation in addition to the effects from thermal fluctuation. Our experimental investigation indicates the fantastic role of thermal fluctuation played in the thermodynamic process at atomic level, which might bridge the thermodynamics from the macroscopic domain to the quantum regime.