Ultrafast Jahn–Teller polaron dynamics in a bi‐layered manganite single crystal

Abstract

We report the photoinduced ultrafast quasiparticle recombination dynamics of colossal magnetoresistance single crystal La1.2Sr1.8Mn2O7 by using femtosecond time‐resolved reflection spectroscopy in a wide range of temperatures. Here, we find the transient reflectivity change ΔR exhibits a competition process of a fast negative component (∼ sub‐picosecond) against a slow positive component (∼ nanosecond), as the sample goes from paramagnetic (PM) to ferromagnetic (FM) state with decreasing the temperature. The very fast initial decay of the photoinduced ΔR corresponds to the photoionization of the Jahn–Teller polaronic response, which is unambiguously sensitive to the coupling between electron and lattice in the PM and FM phases in La1.2Sr1.8Mn2O7 single crystal. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Observation of Small Polaron and Acoustic Phonon Coupling in Ultrathin La0.7Sr0.3MnO3/SrTiO3 Structures

“…This is caused by the liberation of the small polarons due to the optical hopping. The negative sign in Δ R / R induced by the small polaron absorption has also been reported by other groups . Since the second pump excitation at Δ t = 10 ps, Δ R / R 14 ps represents indeed the reflectivity dynamics at Δ t = 4 ps.…”

“…Above T C , the high resistance arises from the partial localization of the e g electrons trapped by lattice distortions due to the Jahn–Teller (JT) effect that takes place on the Mn 3+ sites . The relaxation of JT distortion and its self‐trapping effect usually takes effect within several picoseconds after photoexcitation at high temperature . Therefore, the combination of double exchange interaction and the JT polarons plays a crucial role in determining the magnetic and electrical properties of these manganites.…”