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Dragan Mihailovic - Dept. of Complex Matter, Jozef Stefan Institute and International Postgraduate School, CENN Nanocenter and University of Ljubljana, Slovenia

Femtosecond trajectories through symmetry-breaking transitions in superconductors and charge-density waves


The study of system trajectories through symmetry breaking phase transitions (SBTs) - whether in condensed matter physics, cosmology or finance - has become a topic of significant interest in recent years. Condensed matter systems as model systems offer a variety of different order parameter symmetries and microscopic interactions, yet can be probed in great detail using new spectroscopy methods. Using new femtosecond spectroscopy techniques we are able to study the
femtosecond evolution of bosonic and fermionic excitations through an electronic charge-ordering transition in charge-density-wave systems1,2 and in the La1.9Sr0.1CuO4 superconductor3 revealing coherent aperiodic undulations of the order parameter, critical slowing down, and creation of the particle-hole gap as the system evolves through the SBT. Of particular interest is the observation of spectro-temporal distortions arising from spontaneous annihilation of topological defects and concurrent emission of ‘Higgs’ waves, analogous to topological excitations discussed by the Kibble-Zurek cosmological model. Modeling based on Ginzburg-Landau theory developed by Brazovskii is used to reproduce the aftermath of the transition in CDWs without free parameters1,2. The two types of system studied highlight the difference between constrained evolution and rapid quench behaviour.
However, comparison of data with predictions of Lu-Dac and Kabanov in the close vicinity of the transition indicates behavior beyond TDGL predictions.

 

[1] R.Yusupov et al., Nature Physics 6, 681 (2010)

[2] R.Yusupov et al, J.Supercond Nov. Magn. 24, 1191 (2011)

[3] P.Kusar et al. (unpublished, 2011)

 

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