Articles de revistahttp://hdl.handle.net/2117/239592024-03-29T07:50:00Z2024-03-29T07:50:00ZUltrafast disordering of vanadium dimers in photoexcited VO2Wall, SimonYang, ShanVidas, LucianaChollet, MatthieuGlownia, MichaelKozina, MichaelKatayama, TetsuoHenighan, ThomasJiang, MasonMiller, Timothy A.Reis, David A.Boatner, Lynn A.Delaire, OlivierTrigo, Marianohttp://hdl.handle.net/2117/1237152022-05-17T11:07:17Z2018-11-07T16:52:23ZUltrafast disordering of vanadium dimers in photoexcited VO2
Wall, Simon; Yang, Shan; Vidas, Luciana; Chollet, Matthieu; Glownia, Michael; Kozina, Michael; Katayama, Tetsuo; Henighan, Thomas; Jiang, Mason; Miller, Timothy A.; Reis, David A.; Boatner, Lynn A.; Delaire, Olivier; Trigo, Mariano
Time-resolved x-ray scattering can be used to investigate the dynamics of materials during the switch from one structural phase to another. So far, methods provide an ensemble average and may miss crucial aspects of the detailed mechanisms at play. Wall et al. used a total-scattering technique to probe the dynamics of the ultrafast insulator-to-metal transition of vanadium dioxide (VO2) (see the Perspective by Cavalleri). Femtosecond x-ray pulses provide access to the time- and momentum-resolved dynamics of the structural transition. Their results show that the photoinduced transition is of the order-disorder type, driven by an ultrafast change in the lattice potential that suddenly unlocks the vanadium atoms and yields large-amplitude uncorrelated motions, rather than occurring through a coherent displacive mechanism.
2018-11-07T16:52:23ZWall, SimonYang, ShanVidas, LucianaChollet, MatthieuGlownia, MichaelKozina, MichaelKatayama, TetsuoHenighan, ThomasJiang, MasonMiller, Timothy A.Reis, David A.Boatner, Lynn A.Delaire, OlivierTrigo, MarianoTime-resolved x-ray scattering can be used to investigate the dynamics of materials during the switch from one structural phase to another. So far, methods provide an ensemble average and may miss crucial aspects of the detailed mechanisms at play. Wall et al. used a total-scattering technique to probe the dynamics of the ultrafast insulator-to-metal transition of vanadium dioxide (VO2) (see the Perspective by Cavalleri). Femtosecond x-ray pulses provide access to the time- and momentum-resolved dynamics of the structural transition. Their results show that the photoinduced transition is of the order-disorder type, driven by an ultrafast change in the lattice potential that suddenly unlocks the vanadium atoms and yields large-amplitude uncorrelated motions, rather than occurring through a coherent displacive mechanism.Imaging Nanometer Phase Coexistence at Defects During the Insulator−Metal Phase Transformation in VO2 Thin Films by Resonant Soft X‑ray HolographyVidas, LucianaGünther, Christian M.Miller, Timothy A.Pfau, BastianPerez-Salinas, DanielMartínez, ElíasSchneider, MichaelGuehers, ErikGargiani, PierluigiValvidares, ManuelMarvel, Robert E.Hallman, Kent A.Haglund, Richard F.Eisebitt, StefanWall, Simonhttp://hdl.handle.net/2117/1174232022-05-17T11:43:18Z2018-05-23T13:22:21ZImaging Nanometer Phase Coexistence at Defects During the Insulator−Metal Phase Transformation in VO2 Thin Films by Resonant Soft X‑ray Holography
Vidas, Luciana; Günther, Christian M.; Miller, Timothy A.; Pfau, Bastian; Perez-Salinas, Daniel; Martínez, Elías; Schneider, Michael; Guehers, Erik; Gargiani, Pierluigi; Valvidares, Manuel; Marvel, Robert E.; Hallman, Kent A.; Haglund, Richard F.; Eisebitt, Stefan; Wall, Simon
We use resonant soft X-ray holography to image the insulator−metal phase transition in vanadium dioxide with element and polarization specificity and nanometer spatial resolution. We observe that nanoscale inhomogeneity in the film results in spatial-dependent transition pathways between the insulating and metallic states. Additional nanoscale phases form in the vicinity of defects which are not apparent in the initial or final states of the system, which would be missed in area-integrated X-ray absorption measurements. These intermediate phases are vital to understand the phase transition in VO2, and our results demonstrate how resonant imaging can be used to understand the electronic properties of phase-separated correlated materials obtained by X-ray absorption.
2018-05-23T13:22:21ZVidas, LucianaGünther, Christian M.Miller, Timothy A.Pfau, BastianPerez-Salinas, DanielMartínez, ElíasSchneider, MichaelGuehers, ErikGargiani, PierluigiValvidares, ManuelMarvel, Robert E.Hallman, Kent A.Haglund, Richard F.Eisebitt, StefanWall, SimonWe use resonant soft X-ray holography to image the insulator−metal phase transition in vanadium dioxide with element and polarization specificity and nanometer spatial resolution. We observe that nanoscale inhomogeneity in the film results in spatial-dependent transition pathways between the insulating and metallic states. Additional nanoscale phases form in the vicinity of defects which are not apparent in the initial or final states of the system, which would be missed in area-integrated X-ray absorption measurements. These intermediate phases are vital to understand the phase transition in VO2, and our results demonstrate how resonant imaging can be used to understand the electronic properties of phase-separated correlated materials obtained by X-ray absorption.Light control of orbital domains: case of the prototypical manganite La0.5Sr1.5MnO4Miller, TimothyGensch, MichaelWall, Simonhttp://hdl.handle.net/2117/1070592022-05-17T10:20:21Z2017-08-04T07:42:23ZLight control of orbital domains: case of the prototypical manganite La0.5Sr1.5MnO4
Miller, Timothy; Gensch, Michael; Wall, Simon
Control of electronic and structural ordering in correlated materials on the ultrafast timescale with light is a new and emerging approach to disentangle the complex interplay of the charge, spin, orbital and structural degree of freedom. In this paper we present an overview of how orbital order and orbital domains can be controlled by near IR and THz radiation in the layered manganite La0.5Sr1.5MnO4. We show how near-IR pumping can efficiently and rapidly melt orbital ordering. However, the nanoscale domain structure recovers unchanged demonstrating the importance of structural defects for the orbital domain formation. On the contrary, we show that pulsed THz fields can be used to effectively orientate the domains. In this case the alignment depends on the in-plane electric field polarisation and is induced by an energy penalty that arises from THz field induced hopping of the localised charges.
2017-08-04T07:42:23ZMiller, TimothyGensch, MichaelWall, SimonControl of electronic and structural ordering in correlated materials on the ultrafast timescale with light is a new and emerging approach to disentangle the complex interplay of the charge, spin, orbital and structural degree of freedom. In this paper we present an overview of how orbital order and orbital domains can be controlled by near IR and THz radiation in the layered manganite La0.5Sr1.5MnO4. We show how near-IR pumping can efficiently and rapidly melt orbital ordering. However, the nanoscale domain structure recovers unchanged demonstrating the importance of structural defects for the orbital domain formation. On the contrary, we show that pulsed THz fields can be used to effectively orientate the domains. In this case the alignment depends on the in-plane electric field polarisation and is induced by an energy penalty that arises from THz field induced hopping of the localised charges.Terahertz field control of in-plane orbital order in La0.5Sr1.5MnO4Miller, Timothy A.Chhajlany, Ravindra W.Tagliacozzo, LucaGreen, BertramKovalev, SergeyPrabhakaran, DharmalingamLewenstein, MaciejGensch, MichaelWall, Simonhttp://hdl.handle.net/2117/791402020-07-22T18:04:20Z2015-11-12T14:43:09ZTerahertz field control of in-plane orbital order in La0.5Sr1.5MnO4
Miller, Timothy A.; Chhajlany, Ravindra W.; Tagliacozzo, Luca; Green, Bertram; Kovalev, Sergey; Prabhakaran, Dharmalingam; Lewenstein, Maciej; Gensch, Michael; Wall, Simon
In-plane anisotropic ground states are ubiquitous in correlated solids such as pnictides, cuprates and manganites. They can arise from doping Mott insulators and compete with phases such as superconductivity; however, their origins are debated. Strong coupling between lattice, charge, orbital and spin degrees of freedom results in simultaneous ordering of multiple parameters, masking the mechanism that drives the transition. Here we demonstrate that the orbital domains in a manganite can be oriented by the polarization of a pulsed THz light field. Through the application of a Hubbard model, we show that domain control can be achieved by enhancing the local Coulomb interactions, which drive domain reorientation. Our results highlight the key role played by the Coulomb interaction in the control and manipulation of orbital order in the manganites and demonstrate a new way to use THz to understand and manipulate anisotropic phases in a potentially broad range of correlated materials.
2015-11-12T14:43:09ZMiller, Timothy A.Chhajlany, Ravindra W.Tagliacozzo, LucaGreen, BertramKovalev, SergeyPrabhakaran, DharmalingamLewenstein, MaciejGensch, MichaelWall, SimonIn-plane anisotropic ground states are ubiquitous in correlated solids such as pnictides, cuprates and manganites. They can arise from doping Mott insulators and compete with phases such as superconductivity; however, their origins are debated. Strong coupling between lattice, charge, orbital and spin degrees of freedom results in simultaneous ordering of multiple parameters, masking the mechanism that drives the transition. Here we demonstrate that the orbital domains in a manganite can be oriented by the polarization of a pulsed THz light field. Through the application of a Hubbard model, we show that domain control can be achieved by enhancing the local Coulomb interactions, which drive domain reorientation. Our results highlight the key role played by the Coulomb interaction in the control and manipulation of orbital order in the manganites and demonstrate a new way to use THz to understand and manipulate anisotropic phases in a potentially broad range of correlated materials.Time-domain separation of optical properties from structural transitions in resonantly bonded materialsWaldecker, LutzMiller, Timothy A.Rudé, MiquelBertoni, RomanOsmond, JohannSimpson, Robert E.Ernstorfer, RalphWall, Simonhttp://hdl.handle.net/2117/789052022-05-17T12:08:08Z2015-11-06T14:05:09ZTime-domain separation of optical properties from structural transitions in resonantly bonded materials
Waldecker, Lutz; Miller, Timothy A.; Rudé, Miquel; Bertoni, Roman; Osmond, Johann; Simpson, Robert E.; Ernstorfer, Ralph; Wall, Simon
The extreme electro-optical contrast between crystalline and amorphous states in phase-change materials is routinely exploited in optical data storage1 and future applications include universal memories2, flexible displays3, reconfigurable optical circuits4, 5, and logic devices6. Optical contrast is believed to arise owing to a change in crystallinity. Here we show that the connection between optical properties and structure can be broken. Using a combination of single-shot femtosecond electron diffraction and optical spectroscopy, we simultaneously follow the lattice dynamics and dielectric function in the phase-change material Ge2Sb2Te5 during an irreversible state transformation. The dielectric function changes by 30% within 100 fs owing to a rapid depletion of electrons from resonantly bonded states. This occurs without perturbing the crystallinity of the lattice, which heats with a 2-ps time constant. The optical changes are an order of magnitude larger than those achievable with silicon and present new routes to manipulate light on an ultrafast timescale without structural changes.
2015-11-06T14:05:09ZWaldecker, LutzMiller, Timothy A.Rudé, MiquelBertoni, RomanOsmond, JohannSimpson, Robert E.Ernstorfer, RalphWall, SimonThe extreme electro-optical contrast between crystalline and amorphous states in phase-change materials is routinely exploited in optical data storage1 and future applications include universal memories2, flexible displays3, reconfigurable optical circuits4, 5, and logic devices6. Optical contrast is believed to arise owing to a change in crystallinity. Here we show that the connection between optical properties and structure can be broken. Using a combination of single-shot femtosecond electron diffraction and optical spectroscopy, we simultaneously follow the lattice dynamics and dielectric function in the phase-change material Ge2Sb2Te5 during an irreversible state transformation. The dielectric function changes by 30% within 100 fs owing to a rapid depletion of electrons from resonantly bonded states. This occurs without perturbing the crystallinity of the lattice, which heats with a 2-ps time constant. The optical changes are an order of magnitude larger than those achievable with silicon and present new routes to manipulate light on an ultrafast timescale without structural changes.