14 research outputs found
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Direct measurement of Coulomb-laser coupling
The Coulomb interaction between a photoelectron and its parent ion plays an important role in a large range of light-matter interactions. In this paper we obtain a direct insight into the Coulomb interaction and resolve, for the first time, the phase accumulated by the laser-driven electron as it interacts with the Coulomb potential. Applying extreme-ultraviolet interferometry enables us to resolve this phase with attosecond precision over a large energy range. Our findings identify a strong laser-Coulomb coupling, going beyond the standard recollision picture within the strong-field framework. Transformation of the results to the time domain reveals Coulomb-induced delays of the electrons along their trajectories, which vary by tens of attoseconds with the laser field intensity
Direct Observation of Collective Modes of the Charge Density Wave in the Kagome Metal CsVSb
A new group of kagome metals AVSb (A = K, Rb, Cs) exhibit a variety
of intertwined unconventional electronic phases, which emerge from a puzzling
charge density wave phase. Understanding of this parent charge order phase is
crucial for deciphering the entire phase diagram. However, the mechanism of the
charge density wave is still controversial, and its primary source of
fluctuations - the collective modes - have not been experimentally observed.
Here, we use ultrashort laser pulses to melt the charge order in CsVSb
and record the resulting dynamics using femtosecond angle-resolved
photoemission. We resolve the melting time of the charge order and directly
observe its amplitude mode, imposing a fundamental limit for the fastest
possible lattice rearrangement time. These observations together with ab-initio
calculations provide clear evidence for a structural rather than electronic
mechanism of the charge density wave. Our findings pave the way for better
understanding of the unconventional phases hosted on the kagome lattice.Comment: 17 pages, 4 figure
The spontaneous symmetry breaking in TaNiSe is structural in nature
The excitonic insulator is an electronically-driven phase of matter that
emerges upon the spontaneous formation and Bose condensation of excitons.
Detecting this exotic order in candidate materials is a subject of paramount
importance, as the size of the excitonic gap in the band structure establishes
the potential of this collective state for superfluid energy transport.
However, the identification of this phase in real solids is hindered by the
coexistence of a structural order parameter with the same symmetry as the
excitonic order. Only a few materials are currently believed to host a dominant
excitonic phase, TaNiSe being the most promising. Here, we test this
scenario by using an ultrashort laser pulse to quench the broken-symmetry phase
of this transition metal chalcogenide. Tracking the dynamics of the material's
electronic and crystal structure after light excitation reveals surprising
spectroscopic fingerprints that are only compatible with a primary order
parameter of phononic nature. We rationalize our findings through
state-of-the-art calculations, confirming that the structural order accounts
for most of the electronic gap opening. Not only do our results uncover the
long-sought mechanism driving the phase transition of TaNiSe, but they
also conclusively rule out any substantial excitonic character in this
instability
The Role of Electron Trajectories in XUV-Initiated High-Harmonic Generation
High-harmonic generation spectroscopy is a powerful tool for ultrafast spectroscopy with intrinsic attosecond time resolution. Its major limitation—the fact that a strong infrared driving pulse is governing the entire generation process—is lifted by extreme ultraviolet (XUV)-initiated high-harmonic generation (HHG). Tunneling ionization is replaced by XUV photoionization, which decouples ionization from recollision. Here we probe the intensity dependence of XUV-initiated HHG and observe strong spectral frequency shifts of the high harmonics. We are able to tune the shift by controlling the instantaneous intensity of the infrared field. We directly access the reciprocal intensity parameter associated with the electron trajectories and identify short and long trajectories. Our findings are supported and analyzed by ab initio calculations and a semiclassical trajectory model. The ability to isolate and control long trajectories in XUV-initiated HHG increases the range of the intrinsic attosecond clock for spectroscopic applications
Interferometric attosecond lock-in measurement of extreme-ultraviolet circular dichroism
International audienc
Robust enhancement of high harmonic generation via attosecond control of ionization
We demonstrate up to two orders of magnitude enhancements in high harmonic generation efficiency via sub-cycle control and scaling of the ionization rate in a two colour laser field
Robust enhancement of high harmonic generation via attosecond control of ionization
We demonstrate up to two orders of magnitude enhancements in high harmonic generation efficiency via sub-cycle control and scaling of the ionization rate in a two colour laser field
Recommended from our members
The spontaneous symmetry breaking in TaNiSe is structural in nature
The excitonic insulator is an electronically-driven phase of matter that
emerges upon the spontaneous formation and Bose condensation of excitons.
Detecting this exotic order in candidate materials is a subject of paramount
importance, as the size of the excitonic gap in the band structure establishes
the potential of this collective state for superfluid energy transport.
However, the identification of this phase in real solids is hindered by the
coexistence of a structural order parameter with the same symmetry as the
excitonic order. Only a few materials are currently believed to host a dominant
excitonic phase, TaNiSe being the most promising. Here, we test this
scenario by using an ultrashort laser pulse to quench the broken-symmetry phase
of this transition metal chalcogenide. Tracking the dynamics of the material's
electronic and crystal structure after light excitation reveals surprising
spectroscopic fingerprints that are only compatible with a primary order
parameter of phononic nature. We rationalize our findings through
state-of-the-art calculations, confirming that the structural order accounts
for most of the electronic gap opening. Not only do our results uncover the
long-sought mechanism driving the phase transition of TaNiSe, but they
also conclusively rule out any substantial excitonic character in this
instability