Higgs-like stiffness and fractons on the verge of phase transitions

TL;DR

This paper introduces the concept of Higgs-like stiffness (HLS) near phase transitions, supported by theoretical modeling and experimental dielectric data, and explores the emergence of fractons related to molecular rotations.

Contribution

It proposes the universal concept of Higgs-like stiffness (HLS) near phase transitions and demonstrates its detection through dielectric response analysis, supported by experimental data.

Findings

HLS appears near classical and quantum phase transitions.

Dielectric measurements reveal signatures of HLS.

Fractons are linked to molecular rotational degrees of freedom.

Abstract

In condensed matter Physics, massive longitudinal Higgs modes emerge from fluctuations of the order parameter. A few years ago, the Higgs mode was \emph{caught} experimentally in the vicinity of an insulator-to-superconductor quantum phase transition [Nat. Phys. $\textbf{11}$, 188 (2015)]. Here, we propose, in analogy to the Higgs mode, the concept of Higgs-like stiffness (HLS), which emerges close to both classical and quantum phase transitions as a universal manifestation of matter. We build up a Landau free energy for the dielectric response function to demonstrate that \emph{any} complex physical quantity can be used to infer the presence of the HLS. Our analysis is corroborated by experimental results of the quasi-static dielectric constant for the (TMTTF)$_2$SbF$_6$ Fabre salt. Yet, we discuss the appearance of fractons in connection with the locking of particular molecular rotational degrees of freedom.