Document Type


Publication Date



American Institute of Physics Publishing


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.


Copyright © 2018 American Institute of Physics. Reprinted with permission.

Datasets are included as additional files.

supplementaryinformation.pdf (705 kB)
Supplementary Information

Fig2.txt (31 kB)
Fig. 2

Fig3.txt (125 kB)
Fig. 3

Fig4.txt (319 kB)
Fig. 4

FigS1.txt (311 kB)
Fig. S1

FigS2.txt (2764 kB)
Fig. S2

FigS3.txt (127 kB)
Fig. S3

FigS4.txt (14 kB)
Fig. S4

FigS6.txt (4 kB)
Fig. S6

FigS7.txt (28 kB)
Fig. S7

FigS8.txt (10 kB)
Fig. S8

FigS9.txt (7 kB)
Fig. S9

FigS10.txt (6 kB)
Fig. S10



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.