Speaker
Description
Strongly interacting Fermi liquids often turn into bad metals at elevated temperature. Here, we use angle resolved photoemission (ARPES) to study the fate of quasiparticles in the model Fermi liquid Sr$_2$RuO$_4$ during this crossover. In contrast to common ARPES folklore, our experiments show that quasiparticles do not disappear via a vanishing residue Z. To the contrary, we find that the residue Z increases with increasing temperature and gradually diminishing coherence. Quasiparticles eventually die not by losing weight but by dissolving via excessive broadening. These findings are in semi-quantitative agreement with dynamical mean field theory calculations.
We further investigate the evolution of the spectral function under uniaxial strain including the regime in which recent transport measurements observed non-Fermi liquid behavior [1]. To this end, we introduce a new method for precision ARPES experiments under continuously varying strain. Our data monitor the tuning the of a van Hove singularity across the chemical potential and show that quasiparticles remain intact in the non-Fermi liquid state at the critical strain. This implies that non-Fermi liquid behavior emerges in Sr$_2$RuO$_4$ from subtle changes in the scattering rate rather than from a breakdown of the concept of quasiparticles.
References
[1]. M. E. Barber, A. S. Gibbs, Y. Maeno, A. P. Mackenzie, and C. W. Hicks, Phys. Rev. Lett. 120, 076602 (2018).
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