Abstract-Terahertz spectroscopy of low-energy excitations in E u 0.42 S r 0.58 Mn O 3

L. S. Kadyrov, E. S. Zhukova, V. I. Torgashev, T. Zhang, Z. V. Gagkaeva, M. Dressel, and B. P. Gorshunov

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.245120

The origin of low-energy excitations in the polycrystalline $E{u}_{0.42}S{r}_{0.58}\mathrm{Mn}{O}_3$ manganite is explored by terahertz and infrared spectroscopies. The transition from the charge and/or orbital to antiferromagnetic order ($T_N=130-140K$) is seen as smooth (spread over a temperature range from 50 to 100 K) decrease of free-carrier conductivity with the activation energy change from 86 meV (high temperatures) to 0.52 meV (low temperatures). A broad relaxation is observed at around $10c{m}^{-1}$ which we associate with the dynamics of free charge carriers in the presence of random localizing potential. We discover an absorption resonance at $\approx 50c{m}^{-1}$ below $T_N$ that is assigned to the formation of hybridized “acoustic phonon-magnon” quasiparticles.

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Abstract-Doubly dressed bosons: Exciton-polaritons in a strong terahertz field

B. Piętka, N. Bobrovska, D. Stephan, M. Teich, M. Król, S. Winnerl, A. Pashkin, R. Mirek, K. Lekenta, F. Morier-Genoud, H. Schneider, B. Deveaud, M. Helm, M. Matuszewski, and J. Szczytko

https://journals.aps.org/prl/accepted/c907bY09Q031096c935669a975ce3e5d3c82b8c69

We demonstrate the existence of a novel quasiparticle: an exciton in a semiconductor doubly dressed with two photons of different wavelengths: near infrared cavity photon and terahertz (THz) photon, with the THz coupling strength approaching the ultra-strong coupling regime. This quasiparticle is composed of three different bosons, being a mixture of a matter-light quasiparticle. Our observations are confirmed by a detailed theoretical analysis, treating quantum mechanically all three bosonic fields. The doubly dressed quasiparticles retain the bosonic nature of their constituents, but their internal quantum structure strongly depends on the intensity of the applied terahertz field.