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We present a nematic response function model (NRFM) for fit-free direct extraction of the characteristic time of ultrafast electronic thermalization in iron-based superconductors, materials with electronic nematicity. By combining the NRFM for polarization-dependent pump–probe measurements of electronic nematic response with the two-temperature model (TTM) for sub-picosecond quasiparticle relaxation, we quantify the electronic thermalization timescales and their anisotropy. The nematic response function is modeled as the difference in normalized reflectivity signals, revealing a pronounced sub-picosecond extremum in signal evolution that directly yields the characteristic electronic thermalization time. This method demonstrates that the NRFM is consistent with TTM fits of transient optical response, yielding electronic thermalization time constants on the order of 110–230 fs for the FeSe1−xTex and Ba(Fe0.92Co0.08)2As2 thin films. The proposed approach can be applied to any material that exhibits electronic nematicity, providing a powerful tool for direct mapping of the relaxation time in nematic materials, avoiding complex experimental data-fitting procedures.
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A Case for Dynamic Percolation Underlying Mechanistic Crossovers in the Relaxation of Liquids
Not AvailablOne of the outstanding questions regarding liquid dynamics is the cause of the apparent mechanistic changes in relaxation at the characteristic temperatures TA and TB, where, as the temperature is lowered, α relaxation times become super-Arrhenius, and the βJG relaxation bifurcates from α, respectively. Based on system-averaged picosecond-time scale dynamic signatures in five molecular liquids and a Kob-Andersen (KA) model system, we propose that these mechanistic changes arise from the percolation of distinct dynamic environments in the liquid, where the dynamic environment of a particle is defined by the number of structural excitations in its first solvation shell. Analysis of the KA system trajectories supports this idea and suggests that the most prominent effects can be understood in terms of environments that are mobile or immobile on a picosecond time scale. Further, the existence and percolation of these dynamic environments can account for many of the characteristic dynamic signatures of glass-forming liquids.e
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- Award ID(s):
- 2426182
- PAR ID:
- 10645709
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry B
- Volume:
- 129
- Issue:
- 26
- ISSN:
- 1520-6106
- Page Range / eLocation ID:
- 6620 to 6631
- Subject(s) / Keyword(s):
- liquids glassformers dynamics transport relaxation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acs.jpcb.5c01033
