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.
Highlights
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
Such ultrafast suppression in 2D has been widely observed in previous experiments employing femtosecond time- and angle-resolved photoemission spectroscopy after femtosecond laser excitation[5,6,20] in agreement with the theory[21], which emphasizes the impact of optically induced fluctuations on the interaction leading to Charge density waves (CDWs) formation
We begin by analyzing the electronic structure of HoTe3 in thermal equilibrium using high-resolution laserARPES at hn 1⁄4 7 eV, which is representative for the series of rareearth tritellurides
Summary
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. Coherent lattice dynamics may drive the system towards a high-symmetry state and decrease the lattice distortion, further reducing the CDW modulation and 2D Such ultrafast suppression in 2D has been widely observed in previous experiments employing femtosecond time- and angle-resolved photoemission spectroscopy (trARPES) after femtosecond laser excitation[5,6,20] in agreement with the theory[21], which emphasizes the impact of optically induced fluctuations on the interaction leading to CDW formation. This improved nesting increases the interactions underlying CDW formation which compete with incoherent fluctuations induced by the excitation This surprising observation suggests a pathway to control material properties under non-equilibrium conditions relevant for a wide range of material classes with broken symmetry ground states
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