Special Seminar: Edoardo Baldini, EPFL Lausanne, Switzerland, "Exploring the Nonequilibrium Dynamics of Collective Excitations"

Mon, Jun 6, 2016, 1:30 pm to 2:30 pm
Jadwin A07
One of the distinctive characteristics of strongly interacting and correlated quantum systems is the non-trivial interplay between low- and high-energy degrees of freedom. The origin of this interplay lies in the electron-electron and electron-boson interactions, which spread the optical spectral weight over a wide energy range. To address this phenomenology, we investigate this class of solids by means of ultrafast optical spectroscopy covering a broad spectral range, both in the visible and in the ultraviolet (UV) [1-6]. This approach allows not only to develop realistic nonequilibrium models for the dielectric functions of these systems, but also to monitor the impact of coherent bosonic excitations on the optical properties. In this talk, I will discuss the application of this technique on two prototypical transition metal oxides, i.e. a bilayer cuprate (NdBa2Cu3O6+δ) and anatase titanium dioxide (TiO2). In NdBa2Cu3O6+ δ, by means of a continuum visible probe, we discover several observables associated with a precursor superconducting state above TC; the spectral fingerprint of the precursor state is also disentangled from the response of the pseudogap correlations [5]. In anatase TiO2, the use of ultrafast broadband UV spectroscopy reveals the signature of bound excitonic quasiparticles, retaining an intermediate character between the Frenkel and Wannier-Mott regimes [6]; the coupling between coherent acoustic phonons and these exotic collective charge excitations is also investigated. [1] B. Mansart et al., PNAS USA 110, 4539 (2013) [2] A. Mann et al., Phys. Rev. B 92, 035147 (2015) [3] A. Mann et al., arxiv.org/abs/1602.07924 (submitted) [4] S. Borroni, E. Baldini et al., arxiv.org/abs/1507.07193 (submitted) [5] E. Baldini et al., arxiv.org/abs/1510.00305 (under review in Nature Communications) [6] E. Baldini et al., arxiv.org/abs/1601.01244 (under review in Nature Materials)