Zuerch Lab
ULTRAFAST MATERIALS CHEMISTRY AT BERKELEY
Zuerch Lab
ULTRAFAST MATERIALS CHEMISTRY AT BERKELEY

Attosecond X-Ray Spectroscopy
Scheme of attosecond pump-probe spectroscopy detecting X-ray diffraction and X-ray absorption spectra (top panel). Center panels show typical attosecond pulse spectra in the XUV and soft X-ray range and a few material absorption edges indicated. The lower panel shows how nearest-neighbor interactions in condensed phase systems imprint unique spectral signatures onto the X-ray absorption spectra which enable elucidating material properties, which can be in case of pump-probe experiments done dynamically. See [1] for more details and figure credits.

With an optical parametric amplification (OPA) system and hollow-core fiber compressor following an 800 nm Ti:Sapphire laser, we generate few-femtosecond, carrier-envelope phase (CEP) stabilized laser pulses throughout the visible and infrared regions in order to subsequently make high-harmonic generated (HHG) attosecond x-ray pulses spanning 20-600 eV. Combinations of such pulses are employed to perform core-level pump-probe experiments with high spatio-temporal resolution and atom-specificity where samples can remain under ultrahigh vacuum and ultracold temperature conditions. In our approach we combine methods of attosecond spectroscopy with coherent diffraction imaging. The use of XUV and X-ray photon energies enables us to study materials with element-specificity and we typically reach a time resolution better than ~2 fs using pump-probe, which enables us to study light-matter interaction in realtime, faster than typically relaxation processes set in. The short wavelength of XUV/X-rays enables studying spatial properties of materials and superlattices with a resolution if better than 30 nm.

Giauque Hall DG30 attosecond apparatus in operation.

We are specifically interested in studying and controlling charge carrier and spin dynamics in novel superlattice structures. In that context we explore different types of superlattices, for example, formed by twisting atomically thin van der waals materials forming so-called moiré lattices or superlattices formed by anisotropies in layered ferroelectrica. These platforms are of high interest because they provide a highly-ordered, tunable, and periodic platform for localized excitons, spins, and charged particles. Such materials are of interest for quantum information, spintronics, and optoelectronics applications, as well as for the study of canonical models of phase transitions, symmetry-breaking, and electron correlations in condensed matter and many-body physics. Together with colleagues in the College of Chemistry and at the Lawrence Berkeley National Laboratory we further explore the possibilities of using these superlattices as scaffold for novel types of 2D magnets and spin-qubits.

We actively collaborate with materials scientists, theorists, and FEL facilities around the world to answer questions like, what is the influence of the superlattice on the band structure and optoelectronic properties? Can we manipulate the spatiotemporal dynamics of quasiparticles in the superlattice structures in real time? What kinds of couplings exist between the spin, orbit, charge, and lattice degrees of freedom? Can we control how long these couplings persist before decoherence sets in?

References on time-resolved X-ray/attosecond spectroscopy and diffraction imaging

[1] B. Buades, et al., “Attosecond state-resolved carrier motion in quantum materials probed by soft X-ray XANES”, Applied Physics Reviews 8, 011408 (2021) // AIP Feature Article.doi: https://doi.org/10.1063/5.0020649

[2] S. K. Cushing, et al., “Differentiating Photoexcited Carrier and Phonon Dynamics in the Δ, L, and Γ Valleys of Si(100) with Transient Extreme Ultraviolet Spectroscopy”, Journal of Physical Chemistry C 123, 3343–3352 (2019)doi: https://doi.org/10.1021/acs.jpcc.8b10887

[3] P. M. Kraus, M. Zürch, S. K. Cushing, D. M. Neumark, S. R. Leone, “The Ultrafast X-ray Spectrocopic Revolution in Chemical Dynamics” Nature Reviews Chemistry 2, 82-94 (2018)doi: https://doi.org/10.1038/s41570-018-0008-8

[4] T. Helk, M. Zürch , and C. Spielmann, “Towards single shot timeresolved microscopy using short wavelength table-top light sources”, Structural Dynamics 6, 010902 (2019)doi: https://doi.org/10.1063/1.5082686

[5] M. Zürch, et al., “Spatial Coherence Limited Coherence Diffraction Imaging using a Molybdenum Soft X-ray Laser Pumped at Moderate Pump Energies”, Nature Scientific Reports 7:5314, 1-10 (2017)doi: https://doi.org/10.1038/s41598-017-05789-w

[6] M. Zürch, et al., “Direct and Simultaneous Observation of Ultrafast Electron and Hole Dynamics in Germanium”, Nature Communications 8:15734, 1-11 (2017)doi: https://doi.org/10.1038/ncomms15734

[7] M. Zürch, et al., “Carrier Thermalization and Trapping in Silicon-Germanium Alloy Probed by Attosecond XUV Transient Absorption Spectroscopy”, Structural Dynamics 4 (4), 044029 (2017)doi: https://doi.org/10.1063/1.4985056

[8] M. Zürch, et al., “Real-time and Sub-wavelength Ultrafast Coherent Diffraction Imaging in the Extreme Ultraviolet”, Nature Scientific Reports 4 (7356), 1-5 (2014)doi: https://doi.org/10.1038/srep07356

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