Directly photoexcited Dirac and Weyl fermions in ZrSiS and NbAs

Weber, C. P.; Schoop, L. M.; Parkin, S.; Newby, R.; Nateprov, A.; Lotsch, B. V.; Mariserla, B.; Kim, J.; Dani, K.; Bechtel, H.; Arushanov, E.; Ali, M.

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Directly photoexcited Dirac and Weyl fermions in ZrSiS and NbAs

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Lotsch, B. V.
Department Nanochemistry (Bettina V. Lotsch), Max Planck Institute for Solid State Research, Max Planck Society;

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Citation

Weber, C. P., Schoop, L. M., Parkin, S., Newby, R., Nateprov, A., Lotsch, B. V., et al. (2018). Directly photoexcited Dirac and Weyl fermions in ZrSiS and NbAs. Physical Review Letters, 113(22): 221906.

Cite as: https://hdl.handle.net/21.11116/0000-000E-DB14-5

Abstract

We report ultrafast optical measurements of the Dirac line-node semimetal ZrSiS and the Weyl semimetal NbAs, using mid-infrared pump photons from 86 meV to 500 meV to directly excite Dirac and Weyl fermions within the linearly dispersing bands. In NbAs, the photoexcited Weyl fermions initially form a non-thermal distribution, signified by a brief spike in the differential reflectivity whose sign is controlled by the relative energy of the pump and probe photons. In ZrSiS, electron-electron scattering rapidly thermalizes the electrons, and the spike is not observed. Subsequently, hot carriers in both materials cool within a few picoseconds. This cooling, as seen in the two materials' differential reflectivity, differs in sign, shape, and timescale. Nonetheless, we find that it may be described in a simple model of thermal electrons, without free parameters. The electronic cooling in ZrSiS is particularly fast, which may make the material useful for optoelectronic applications. Published by AIP Publishing.