Pump-probe experiment in LaMnO3/SrTiO3 superlattices and thin film (original) (raw)
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Laser-pulse-induced Coherent Oscillations in LaMnO_3/SrTiO_3 Thin Films
New Physics: Sae Mulli, 2013
Coherent oscillation modes in LaMnO3/SrTiO3 thin films were observed by using an ultra-short laser-pulse pump-probe method. The time durations of both the pump and the probe pulses were about 10 femtoseconds. The pulse's center wavelength was about 780 nm which corresponds to about a 1.6-eV photon energy. LaMnO3 is a Mott insulator that is known to be orbitally ordered even at room temperature. A coherent phonon-like oscillation at a higher frequency was expected for the orbital wave response, but signals manifesting the orbital wave was not observed in this experiment. A frequency analysis of the coherent oscillation modes revealed some modes well matched to Raman phonon modes.
Nano letters, 2010
We measure the optical conductivity σ1(ω) of (SrMnO3)n/(LaMnO3)2n superlattices (SL) for n = 1, 3, 5, and 8 and 10 < T < 400 K. Data show a T -dependent insulator to metal transition (IMT) for n ≤ 3, driven by the softening of a polaronic mid-infrared band. At n = 5 that softening is incomplete, while at the largest-period n = 8 compound the MIR band is independent of T and the SL remains insulating. One can thus first observe the IMT in a manganite system in the absence of the disorder due to chemical doping. Unsuccessful reconstruction of the SL optical properties from those of the original bulk materials suggests that (SrMnO3)n/(LaMnO3)2n heterostructures give rise to a novel electronic state.
Electrical and magnetic properties of (SrMnO)∕(LaMnO) superlattices
2008
We report the magnetic and transport properties of superlattices grown by molecular-beam epitaxy on (100) with periodicities, 2, 3, 4, 5, 6, 8, and 16. Although the superlattice constituents, and, are both antiferromagnetic insulators, for small the superlattices behave like the ferromagnetic conductor. As increases, the magnetic properties become dominated by the layers, but the electronic transport properties continue to be controlled by the interfaces.
Electronic Reconstruction at SrMnO3-LaMnO3 Superlattice Interfaces
Physical Review Letters, 2007
We use resonant soft x-ray scattering to study electronic reconstruction at the interface between the Mott insulator LaMnO3 and the "band" insulator SrMnO3. Superlattices of these two insulators were shown previously to have both ferromagnetism and metallic tendencies [Koida et al., Phys. Rev. B 66, 144418 (2002)]. By studying a judiciously chosen superlattice reflection we show that the interface density of states exhibits a pronounced peak at the Fermi level, similar to that predicted by Okamoto et al. [Phys. Rev. B 70, 241104(R) (2004)]. The intensity of this peak correlates with the conductivity and magnetization, suggesting it is the driver of metallic behavior. Our study demonstrates a general strategy for using RSXS to probe the electronic properties of heterostructure interfaces.
Physical Review B, 2010
We report direct evidence of interfacial states at the onset of O K edge confined to a spatial distance of 1 unit-cell full-width at half maximum at the sharp interfaces between epitaxial films of LaMnO 3 and SrMnO 3 from electron energy-loss spectroscopy ͑EELS͒ measurements. The interfacial states are sensitive to interface sharpness; at rough interfaces with interfacial steps of 1-2 unit cells in height, experimental data shows a reduction, or suppression, of the interfacial states. The EELS measurements were performed using a fine electron probe obtained by electron lens aberration correction. By scanning the electron probe across the interface, we are able to map the spatial distribution of the interfacial states across interfaces at high resolution.
Chinese Journal of Physics, 2011
The acoustic phonons in epitaxial ferroelectric (BaTiO 3) n /(SrTiO 3) m superlattices (SLs) are investigated by high-resolution ultraviolet Raman scattering. The temperature dependence of the folded acoustic (FA) phonon Raman intensity through the ferroelectric transition is addressed. A comparison of this behavior between SLs with different number of ferroelectric BaTiO 3 unit cells n and spacer SrTiO 3 unit cells m is presented. A mechanism involving the strain modulation of the spatially varying ferroelectric polarization is introduced to explain the temperature dependence of the FA phonon scattering. The temperature dependence of the polarization can be derived from an analysis of the first-order optical phonon spectra. Using this information, the observed temperature dependence of the whole set of SLs with different n can be consistently accounted for with the presented model. Atomistic shell-model simulations of the spatial pattern of the SL polarization are presented to explain the variation of the FA-spectral intensity for SLs with different m and the experimental fact that no high-order FA-replicas are observed. These results demonstrate the strong coupling between THz hypersound, charge, and light in these multifunctional nanoscale ferroelectrics.
Cooperative Jahn-Teller transition and resonant x-ray scattering in thin film LaMnO 3
Physical Review B, 2002
Epitaxial thin films of stoichiometric LaMnO 3 were grown on SrTiO 3 (110) substrates using the pulsed laser deposition technique. From the high resolution x-ray diffraction measurements, the lattice parameters were determined as a function of temperature and the cooperative Jahn-Teller transition was found to occur at T JT =573.0 K. Also measured was resonant x-ray scattering intensity of the orthorhombic (100) peak of LaMnO 3 near the Mn K edge from low temperatures to above T JT. We demonstrate that the integrated intensity of the (100) peak is proportional to the 3/2 power of the orthorhombic strain at all temperatures, and thus provide an experimental evidence that the resonant scattering near the Mn K edge in LaMnO 3 is largely due to the Jahn-Teller effect.