Photoinduced Charge and Spin Dynamics in Strongly Correlated Electron Systems

Abstract

Motivated by photoinduced phase transition in manganese oxides, charge and spin dynamics induced by photoirradiation are examined. We calculate the transient optical absorption spectra of the extended double-exchange model by the density matrix renormalization group (DMRG) method. A charge-ordered insulating (COI) state becomes metallic just after photoirradiation, and the system tends to recover the initial COI state. The recovery is accompanied with remarkable suppression of an antiferromagnetic correlation in the COI state. The DMRG results are consistent with recent pump-probe spectroscopy data. PACS numbers: 78.20.Bh, 78.47.+p, 75.47.Lx Competition among multiple phases is a key issue to understand electronic states in strongly correlated electron systems. Nature of the phases is characterized by internal degrees of freedom of electrons, namely spin, charge, and orbital [1]. Low-lying fluctuations of these degrees of freedom grow up toward the phase boundary. Then, tiny amounts of external perturbations can dramatically change the electronic states. Prototypical examples are perovskite manganese oxides where a ferromagnetic metallic (FM) phase competes with a chargeordered insulating (COI) phase associated with antiferromagnetic (AF) and orbital orders [2]. In the COI phase, electric resistivity drastically decreases by magnetic field, pressure, impurity, and so on.Photoirradiation is known to be a powerful tool to induce such dramatic response. This is called photoinduced phase transition (PIPT) [3]. Ultrafast manipulation of femtosecond pulse laser is characteristic of the PIPT, and provides a striking difference between the PIPT and the other phase transitions. At early stages of the PIPT, only electronic part of the systems is strongly affected, and the spin, charge, and orbital degrees of freedom play major roles on relaxation dynamics. This is in contrast to the other phase transitions where structual deformation sometimes occurs. Thus, we expect novel relaxation processes of the PIPT and electronic structures that can not be created in equillibrium conditions.The manganese oxides provide good playgrounds for elucidating effects of the multiple degrees of freedom on the PIPT [4,5,6,7,8,10]. In particular, the photoirradiation into the COI phase strongly influences transport, magnetic, and optical properties. Remarkable decrease of electric resistivity has been observed in Pr 0.7 Ca 0.3 MnO 3 after the photoirradiation [4,5,6]. Metallic behavior has been also observed in pump-probe reflection spectroscopy measurements on Nd 0.5 Ca 0.5 MnO 3 [7]: spectral weight of optical conductivity above the COI gap is transfered into lower-energy region within 400 fs after the photoirradiation. Magneto-optical Kerr spectroscopy measurements performed on Nd 0.5 Sr 0.5 MnO 3 and Gd 0.55 Sr 0.45 MnO 3 suggest that a FM component is induced by the photoirradiation [8,9].The purpose of this Letter is to examine microscopic processes of the PIPT in a system where the charge and spin degrees of freedom strongly couple ...

Numerical study of photoinduced dynamics in a double-exchange model

“…In order to analyze the photo-excited states in the generalized DE model, the ED method based on the Lanczos algorithm and the DMRG method [25][26][27][28][29] are applied into one-dimensional finite-size clusters.…”

“…We chose the parameters M 2 = 20 and δτ = 0.1/t in Eq. (29), and the truncation number m = 600 − 800. In Eq.…”

Photoinduced magnetic bound state in an itinerant correlated electron system with a spin-state degree of freedom

“…This is termed photo-induced phase transition (PIPT) phenomena. 2 Nowadays, a number of experimental and theoretical studies have been done in PIPT phenomena in transition-metal oxides, [3][4][5][6][7] low-dimensional organic salts, [8][9][10][11] and others. Among the multi-degrees of freedom, spin-state degree of freedom has attracted much attention from view point of optical manipulation of magnetism.…”

Search for the Photo-Induced Hidden Phase in Inorganic and Organic Systems

“…It clearly shows that the photo-induced state can never be attributed to the one similar to thermally induced M phase and strongly suggest the appearance of a hidden phase. To make clear the electronic origin of this transient state, theoretical study of the transient spectra by solving the time-dependent Schrödinger equation for the one-dimensional quarter-filled Peierls-Holstein--extended-Hubbard model has been developed [12]. As a result of it, we reached the conclusion that the photo-excitation of charge transfer from (1001) to (2000) creates the non-equilibrium (1010) charge order state due to the Coulomb interaction competing with electron-phonon coupling as schematically shown in Fig.…”