No abstract

No abstract

We describe a mechanism for insulator-to-metal transition triggered by spin-canting following fs laserexcitation of insulating anti-ferromagnetic (AFM) states of colossal magneto-resistive (CMR) manganites. We show that photoexcitation of composite fermion quasi-particles dressed by spin fluctuations results in the population of a broad metallic conduction band due to canting of the AFM background spins via strong electron-spin local correlation. By inducing spin-canting, photoexcitation can increase the quasi-particle energy dispersion and quench the charge excitation energy gap. This increases the critical Jahn-Teller (JT) lattice displacement required to maintain an insulating state. We present fs-resolved pump-probe measurements showing bi-exponential relaxation of the differential reflectivity below the AFM transition temperature. We observe a nonlinear dependence of the ratio of the fs and ps relaxation component amplitudes at the same pump fluence threshold where we observe femtosecond magnetization photoexcitation. We attribute this correlation between nonlinear fs spin and charge dynamics to spin/charge/lattice coupling and population inversion between the polaronic majority carriers and metallic quasi-electron minority carriers as the lattice displacement becomes smaller than the critical value required to maintain an insulating state following laser-induced spin canting.