University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Wednesday, March 9th 2016
1:25 pm:
Speaker: Yuan Li, International Center for Quantum Materials, Peking University
Subject: Story of Electrons Told by Phonons

Intriguing phase behaviors of correlated electrons have been a subject of major research interest over the past half a century, and they are all realized in a framework in which the electrons constantly interact with their hosting crystal lattice. As a result, not only does electrons’ footprint on the lattice help us on the detection of various electronic phases, but the explicit consideration of electron-phonon interactions may be necessary in order for us to thoroughly understand the collective behavior of the electrons.

In this talk, I will present a series of studies aiming to elucidate the role of electron-phonon interactions in electron correlations, using Raman scattering as the primary tool in conjunction with complementary techniques. I will first discuss how electron-phonon interactions, primarily in the form of dynamic magnetoelastic coupling, can be utilized to elucidate the genuine phase boundary and physical origin of the electronic nematic phase in iron-based superconductors. Then I will take a detour to a conventional charge-density-wave material and show that the momentum dependence of electron-phonon interactions is crucial for a quantitative understanding of charge ordering behavior even in the simplest case. This brings up the idea whether it is possible to enhance the interactions between conduction electrons and phonons in particularly important momentum regions, if the material also possesses local-moment magnetism on the back side of the same coin from the Fermi-liquid quasiparticles. Indeed we have found that in a structurally simple spiral magnet, the interaction between phonons and local-moment magnetism gives rise to hybrid magnetoelastic excitations, or “magnetophonons”, at the dispersion intersections between phonons and magnons. How such emerging excitations might affect conduction electrons or even mediate Cooper pairing in unconventional superconductors will be discussed.

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