• Hervé, Marius
• Godin, Nicolas
• Privault, Gaël
• Ohkoshi, Shin-Ichi
• Akagi, Shintaro
• Tokoro, Hiroko
• Bertoni, Roman
• Collet, Eric
• Lorenc, Maciej
• Kubicki, Jacek

Abstract

International audience ; We study by femtosecond infrared spectroscopy the ultrafast and persistent photoinduced phase transition of the RbMnCo[Fe(CN)] ⋅ 0.2HO material, induced at room temperature by a single laser shot. This system exhibits a charge-transfer based phase transition with a 75 K wide thermal hysteresis, centred at room temperature, from the low temperature Mn-N-C-Fe tetragonal phase to the high temperature Mn-N-C-Fe cubic phase. At room temperature, the photoinduced phase transition is persistent. However, the out-of-equilibrium dynamics leading to this phase is multi-scale. Femtosecond infrared spectroscopy, particularly sensitive to local reorganizations through the evolution of the frequency of the N-C vibration modes with the different characteristic electronic states, reveals that at low laser fluence and on short time scale, the photoexcitation of the Mn-N-C-Fe phase creates small charge-transfer polarons [Mn-N-C-Fe]* within ≃250 fs. The local trapping of photoinduced intermetallic charge-transfer is characterized by the appearance of a polaronic infrared band, due to the surrounding Mn-N-C-Fe species. Above a threshold fluence, when a critical fraction of small CT-polarons is reached, the macroscopic phase transition to the persistent Mn-N-C-Fe cubic phase occurs within ≃ 100 ps. This non-linear photo-response results from elastic cooperativity, intrinsic to a switchable lattice and reminiscent of a feedback mechanism.

Topics

• impedance spectroscopy
• phase
• phase transition
• intermetallic
• infrared spectroscopy