Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

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.

Electron-polaron dichotomy of charge carriers in perovskite oxides

“…1b. The calculations confirm that the spin ground state of CMO adopts the G-type AFM order 18,19,26 . The calculated density of states, projected on the orbital contribution of Mn for the two sublattices ( Fig.…”

“…CaMnO 3 belongs to a vast class of perovskite oxides, which are insulating due to strong electronic Coulomb repulsion. It relaxes into an orthorhombically distorted structure due to the strain induced by the different ionic radii of the Ca and Mn cations, consistently with its tolerance factor t = (r Ca + r O )/2(r Mn + r O ) = 0.74 in the range of orthorhombic distortions 17 , while electronspin coupling stabilizes a G-type antiferromagnetic (AFM) order 18,19 . Unlike in many perovskite oxides 15,18,20 , minute doping of CaMnO 3 can induce a sharp transition to a metallic state.…”

Light-control of materials via nonlinear phononics

“…Recent mid-IR pump experiments have observed long-lived metastable ferroelectricity in SrTiO 3 [27] and ferromagnetism in DyFeO 3 [41] and CoF 2 [42], but the precise mechanisms for these phenomena need to be clarified with further experimental studies. Other theoretical predictions based on the nonlinear phonon couplings that await experimental confirmations include indirect-to-direct band gap switching [43], phono-magnetic analogs of opto-magnetic effects [44], cavity control of nonlinear phonon interactions [45], and excitation of an optically silent mode in InMnO 3 [46].…”

Optical amplification in a CDW-phase of a quasi-two dimensional material

“…[60,61] Research about the ultrafast response of two dimensional materials like TMDC in connection with their rich electronic phase diagrams, e.g., superconductivity [62,63] or CDW phases, may well be important for understanding the basic physics for the design of future ultrafast (optoelectronic or optospintronic) devices. [64,65] In this context a lot of current research around the optical excitation and melting of CDW phases was done. [66][67][68][69][70][71][72] Furthermore, spin-selective excitations, [73] strain effects on CDWs [74] and also T iT e 2 /T iSe 2 Moire Bilayer [48] were investigated and T iSe 2 was suggested as a saturable absorber.…”