Static strain in heterostructures has been extensively used to engineer electronic and magnetic properties of complex oxides at equilibrium. In the same spirit, modifying the atomic structure of the substrate with light holds promise to control phase transitions across heterointerfaces dynamically. These dynamics follow distinctly new physical pathways when the substrate lattice, instead of the functional film itself, is optically excited. Magnetic and electronic phase transitions are then initiated at the buried interface and may propagate into the film at speeds even above that of sound. This protocol may be beneficial for novel applications in optomagnetic devices, where the functionality is spatially separated from the optically perturbed volume.

Key publications

Time-spliced X-ray diffraction imaging of magnetism dynamics in a NdNiO3 thin film
K. R. Beyerlein
PNAS, 115, 2044-2048 (2018)


Diffraction imaging of nonequilibrium dynamics at atomic resolution is becoming possible with X-ray free-electron lasers. However, there are unresolved problems with applying this method to objects that are confined in only one dimension. Here I show that reliable onedimensional coherent diffraction imaging is possible by splicing together images recovered from different time delays in an optical pump X-ray probe experiment. The time and space evolution of antiferromagnetic order in a vibrationally excited complex oxide heterostructure is recovered from time-resolved measurements of a resonant soft X-ray diffraction peak. Midinfrared excitation of the substrate is shown to lead to a demagnetization front that propagates at a velocity exceeding the speed of sound, a critical observation for the understanding of driven phase transitions in complex condensed matter.

Multiple supersonic phase fronts launched at a complex-oxide hetero-interface
M. Först, K.R. Beyerlein, R. Mankowsky, W. Hu, G. Mattoni, S. Catalano, M. Gibert, O. Yefanov, J.N. Clark, A. Frano, J.M. Glownia, M. Chollet, H. Lemke, B. Moser, S.P. Collins, S.S. Dhesi, A.D. Caviglia, J.-M. Triscone, and A. Cavalleri
Physical Review Letters, 118, 027401 (2017)

Selective optical excitation of a substrate lattice can drive phase changes across heterointerfaces. Thisphenomenon is a nonequilibrium analogue of static strain control in heterostructures and may lead to newapplications in optically controlled phase change devices. Here, we make use of time-resolved nonresonantand resonant x-ray diffraction to clarify the underlying physics and to separate different microscopicdegrees of freedom in space and time. We measure the dynamics of the lattice and that of the chargedisproportionation in NdNiO3, when an insulator-metal transition is driven by coherent lattice distortions inthe LaAlO3 substrate.We find that charge redistribution propagates at supersonic speeds from the interfaceinto the NdNiO3 film, followed by a sonic lattice wave. When combined with measurements of magneticdisordering and of the metal-insulator transition, these results establish a hierarchy of events for ultrafastcontrol at complex-oxide heterointerfaces.

Spatially resolved ultrafast magnetic dynamics launched at a complex-oxide hetero-interface
M. Först, A.D. Caviglia, R. Scherwitzl, R. Mankowsky, P. Zubko, V. Khanna, H. Bromberger, S.B. Wilkins, Y.-D. Chuang, W.S. Lee, W.F. Schlotter, J.J. Turner, G.L. Dakovski, M.P. Minitti, J. Robinson, S.R. Clark, D. Jaksch, J.-M. Triscone, J.P. Hill, S.S. Dhesi, A. Cavalleri
Nature Materials, 14, 883-888 (2015)

Static strain in complex oxide heterostructures has beenextensively used to engineer electronic and magnetic propertiesat equilibrium. In the same spirit, deformations of thecrystal lattice with light may be used to achieve functionalcontrol across heterointerfaces dynamically. Here, by excitinglarge-amplitude infrared-active vibrations in a LaAlO3 substratewe induce magnetic order melting in a NdNiO3 filmacross a heterointerface. Femtosecond resonant soft X-raydiffraction is used to determine the spatiotemporal evolutionof the magnetic disordering.We observe a magnetic melt frontthat propagates from the substrate interface into the film, at aspeed that suggests electronically driven motion. Light controland ultrafast phase front propagation at heterointerfaces maylead to new opportunities in optomagnetism, for example bydriving domain wall motion to transport information acrosssuitably designed devices.

Ultrafast Strain Engineering in Complex Oxide Heterostructures
A. D. Caviglia, R. Scherwitzl, P. Popovich, W. Hu, H. Bromberger, R. Singla, M. Mitrano, M. C. Hoffmann, S. Kaiser, P. Zubko, S. Gariglio, J.-M. Triscone, M. Först, and A. Cavalleri
Physical Review Letters, 108, 136801 (2012)


We report on ultrafast optical experiments in which femtosecond midinfrared radiation is used to excite the lattice of complex oxide heterostructures. By tuning the excitation energy to a vibrational mode of the substrate, a long-lived five-order-of-magnitude increase of the electrical conductivity of NdNiO3 epitaxial thin films is observed as a structural distortion propagates across the interface. Vibrational excitation, extended here to a wide class of heterostructures and interfaces, may be conducive to new strategies for electronic phase control at THz repetition rates.

More publications

Probing photo-induced rearrangements in the NdNiO3 magnetic spiral with polarization-sensitive ultrafast resonant soft x-ray scattering
K.R. Beyerlein, A.S. Disa, M. Först, M. Henstridge, T. Gebert, T. Forrest, A. Fitzpatrick, C. Dominguez, J. Fowlie, M. Gibert, J.-M. Triscone, S.S. Dhesi and A. Cavalleri
Physical Review B 102, 014311 (2020)

Photoinduced melting of magnetic order in the correlated electron insulator NdNiO3
A. D. Caviglia, M. Först, R. Scherwitzl, V. Khanna, H. Bromberger, R. Mankowsky, R. Singla, Y.-D. Chuang, W. S. Lee, O. Krupin, W. F. Schlotter, J. J. Turner, G. L. Dakovski, M. P. Minitti, J. Robinson, V. Scagnoli, S. B.Wilkins, S. A. Cavill,, M. Gibert, S. Gariglio, P. Zubko, J.-M. Triscone, J. P. Hill, S. S. Dhesi, and A. Cavalleri
Physical Review B, 88, 220401(R) (2013)

Broadband THz spectroscopy of the insulator-metal transition driven by coherent lattice deformation at the SmNiO3/LaAlO3 interface
W. Hu, S. Catalano, M. Gibert, J.-M. Triscone, A. Cavalleri
Physical Review B, 93, 161107(R) (2016)