Abstract
We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.
Highlights
Light-matter interactions can be utilized to induce ultrafast phenomena in correlated electron materials[1] for realizing functionalities that can neither be observed in bulk equilibrium[2,3,4,5] nor by means of static perturbations to the structure, including chemical substitution, mechanical strain, or digital heterostructures
In collinear G-type AFM insulating oxides with the perovskite ABO3 structure, the B cations are located within corner-connected BO6 octahedra and the B-site transition metal ions form a three-dimensional simple cubic lattice with dn spin up and spin down electrons alternating from site to site
We examine a nonequilibrium LaTiO3 structure with varying amplitude of the first-order Jahn-Teller distortion (FOJT) mode with the assumption this such a local structural geometry is experimentally accessible as a quasi-static configuration
Summary
Light-matter interactions can be utilized to induce ultrafast phenomena in correlated electron materials[1] for realizing functionalities that can neither be observed in bulk equilibrium[2,3,4,5] nor by means of static perturbations to the structure, including chemical substitution, mechanical strain, or digital heterostructures. Inducing nonequilibrium phonon modulations are of particular recent interest owing to their direct[6] and indirect[7,8,9,10] accessibility with high intensity femtosecond laser pulses ranging from the mid-infrared (IR) to terahertz regimes[11]. Ionic Raman scattering (IRS) has been used to dynamically activate Raman modes by leveraging anharmonic interactions with a pumped IR mode leading to in-plane buckling of the lattice planes in bi-layer cuprates and enhanced superconducting transport[15,16]
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