Coherent dynamics of macroscopic electronic order through a symmetry-breaking transition

TL;DR

This study uses high-time-resolution femtosecond spectroscopy to observe the coherent dynamics of electronic order parameters during a symmetry-breaking phase transition, revealing new insights into collective excitations and topological defect dynamics.

Contribution

It introduces a novel three-pulse femtosecond spectroscopy technique to directly observe the evolution of electronic order through a phase transition in a condensed matter system.

Findings

Detection of coherent aperiodic undulations of the order parameter

Observation of critical slowing down of collective modes

Identification of particle-hole gap evolution via Peierls-BCS mechanism

Abstract

The temporal evolution of systems undergoing symmetry breaking phase transitions (SBTs) is of great fundamental interest not only in condensed matter physics, but extends from cosmology to brain function and finance \cite{topology,Kibble,Eltsov,Finance}. However, the study of such transitions is often hindered by the fact that they are difficult to repeat, or they occur very rapidly. Here we report for the first time on a high-time-resolution study of the evolution of both bosonic and fermionic excitations through a second order electronic charge-ordering SBT in a condensed matter system. Using a new three-pulse femtosecond spectroscopy technique, we periodically quench our model system into the high-symmetry state, detecting hitherto unrecorded coherent aperiodic undulations of the order parameter (OP), critical slowing down of the collective mode, and evolution of the particle-hole gap appearing through the Peierls-BCS mechanism as the system evolves through the transition. Numerical modeling based on Ginzburg-Landau theory is used to reproduce the observations without free parameters. The close analogy with other Higgs potentials in particle physics\cite{Higgs} gives new insight into hitherto unexplored dynamics of both single particle and collective excitations through a SBT. Of particular interest is the observation of spectro-temporal distortions caused by disturbances of the field arising from spontaneous annihilation of topological defects, similar to those discussed by the Kibble-Zurek cosmological model.