title: A time-dependent order parameter for ultrafast photoinduced phase transitions.
abstract: Strongly correlated electron systems often exhibit very strong interactions between structural and electronic degrees of freedom that lead to complex and interesting phase diagrams. For technological applications of these materials it is important to learn how to drive transitions from one phase to another. A key question here is the ultimate speed of such phase transitions, and to understand how a phase transition evolves in the time domain. Here we apply time-resolved X-ray diffraction to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite. We find that although the actual change in crystal symmetry associated with this transition occurs over different timescales characteristic of the many electronic and vibrational coordinates of the system, the dynamics of the phase transformation can be well described using a single time-dependent 'order parameter' that depends exclusively on the electronic excitation.
authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland [2] SwissFEL, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Beaud
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Caviezel
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
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authors.affiliation: Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
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authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland [2] SwissFEL, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
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authors.lastname: Ingold
authors.affiliation: Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland.
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authors.affiliation: Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
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authors.affiliation: Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
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authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland [2] SwissFEL, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Radovic
authors.affiliation: Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Huber
authors.affiliation: Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Kubacka
authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland [2] Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Ferrer
authors.affiliation: LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: H T
authors.initials: HT
authors.lastname: Lemke
authors.affiliation: LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: M
authors.initials: M
authors.lastname: Chollet
authors.affiliation: LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: D
authors.initials: D
authors.lastname: Zhu
authors.affiliation: LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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authors.initials: JM
authors.lastname: Glownia
authors.affiliation: LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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authors.initials: M
authors.lastname: Sikorski
authors.affiliation: LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: A
authors.initials: A
authors.lastname: Robert
authors.affiliation: 1] Department of Applied Physics and Quantum-Phase Electronics Center, University of Tokyo, Hongo, Tokyo 113-8656, Japan [2] Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Chiba 277-8581, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Wadati
authors.affiliation: RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: 1] Department of Applied Physics and Quantum-Phase Electronics Center, University of Tokyo, Hongo, Tokyo 113-8656, Japan [2] RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kawasaki
authors.affiliation: 1] Department of Applied Physics and Quantum-Phase Electronics Center, University of Tokyo, Hongo, Tokyo 113-8656, Japan [2] RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Tokura
authors.affiliation: Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland.
authors.forename: S L
authors.initials: SL
authors.lastname: Johnson
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: U
authors.initials: U
authors.lastname: Staub
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