Attosecond state-resolved carrier motion in quantum materials probed by soft X-ray XANES

TL;DR

This paper demonstrates the use of attosecond soft X-ray spectroscopy to observe element-specific carrier dynamics in quantum materials in real time, revealing how optical fields influence charge carriers at the atomic level.

Contribution

It introduces a novel application of attosecond soft X-ray absorption spectroscopy to directly observe and analyze ultrafast, element-specific electronic dynamics in quantum materials.

Findings

Observation of 3d-state dynamics in TiS2 at the Ti L-edge with attosecond resolution.

Identification of efficient photo-doping of Ti:3d conduction band states.

Detection of coherent intra-band carrier motion across 38% of the Brillouin zone.

Abstract

Recent developments in attosecond technology led to tabletop X-ray spectroscopy in the soft X-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near edge spectroscopy (XANES) to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the element- and state-specificity at the transition metal L-edge of the quantum material allows to unambiguously identify how and where the optical field influences charge carriers. This precision elucidates that the Ti:3d conduction band states are efficiently photo-doped to a density of 1.9 x 10^21 cm^-3 and that the light-field induces coherent motion of intra-band carriers across 38% of the first Brillouin zone. Lastly, we describe the prospects with such unambiguous real-time observation of carrier dynamics in specific bonding or anti-bonding states and speculate that such capability will bring unprecedented opportunities towards an engineered approach for designer materials with pre-defined properties and efficiency. Examples are composites of semiconductors and insulators like Si, Ge, SiO2, GaN, BN, quantum materials like graphene, TMDCs, or high-Tc superconductors like NbN or LaBaCuO. Exiting are prospects to scrutinize canonical questions in multi-body physics such as whether the electrons or lattice trigger phase transitions.