title: Persistent order due to transiently enhanced nesting in an electronically excited charge density wave.
abstract: Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time- and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of the dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. Our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order.
authors.affiliation: Fakultät für Physik, Universität Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg, Germany.|Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Rettig
authors.affiliation: Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany.|Abteilung Physikalische Chemie, Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Cortés
authors.affiliation: Geballe Laboratory for Advanced Materials, Department of Applied Physics, Via Pueblo Mall, Stanford, California 94305, USA.|SLAC National Accelerator Laboratory, Stanford Institute for Material and Energy Sciences, Menlo Park, 94025 California, USA.
authors.forename: J-H
authors.initials: JH
authors.lastname: Chu
authors.affiliation: Geballe Laboratory for Advanced Materials, Department of Applied Physics, Via Pueblo Mall, Stanford, California 94305, USA.|SLAC National Accelerator Laboratory, Stanford Institute for Material and Energy Sciences, Menlo Park, 94025 California, USA.
authors.forename: I R
authors.initials: IR
authors.lastname: Fisher
authors.affiliation: Geballe Laboratory for Advanced Materials, Department of Applied Physics, Via Pueblo Mall, Stanford, California 94305, USA.
authors.forename: F
authors.initials: F
authors.lastname: Schmitt
authors.affiliation: SLAC National Accelerator Laboratory, Stanford Institute for Material and Energy Sciences, Menlo Park, 94025 California, USA.
authors.forename: R G
authors.initials: RG
authors.lastname: Moore
authors.affiliation: Geballe Laboratory for Advanced Materials, Department of Applied Physics, Via Pueblo Mall, Stanford, California 94305, USA.|SLAC National Accelerator Laboratory, Stanford Institute for Material and Energy Sciences, Menlo Park, 94025 California, USA.
authors.forename: Z-X
authors.initials: ZX
authors.lastname: Shen
authors.affiliation: SLAC National Accelerator Laboratory, Stanford Institute for Material and Energy Sciences, Menlo Park, 94025 California, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Kirchmann
authors.affiliation: Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany.|Abteilung Physikalische Chemie, Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Wolf
authors.affiliation: Fakultät für Physik, Universität Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg, Germany.|Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Bovensiepen