Nonlinear nanoelectrodynamics of a Weyl metal

Journal Article · 24 November 2021 · Proceedings of the National Academy of Sciences

DOI: https://doi.org/10.1073/pnas.2116366118 · OSTI ID:1832500

Shao, Yinming  ^[1]; Jing, Ran ^[1]; Chae, Sang Hoon ^[1]; Wang, Chong ^[2]; Sun, Zhiyuan ^[1]; Emmanouilidou, Eve  ^[3]; Xu, Suheng ^[1]; Halbertal, Dorri  ^[1]; Li, Baichang  ^[1]; Rajendran, Anjaly ^[1]; Ruta, Francesco L. ^[1]; Xiong, Lin ^[1]; Dong, Yinan ^[1]; McLeod, Alexander S. ^[1]; Sunku, Sai S. ^[1]; Hone, James C. ^[1]; Moore, Joel ^[4]; Orenstein, Joe  ^[5]; Analytis, James G. ^[4]; Millis, Andrew J. ^[1] ; Ni, Ni ^[3]; Xiao, Di ^[2]; Basov, D. N. ^[1]

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1. Columbia University, New York, NY (United States)
2. Carnegie Mellon University, Pittsburgh, PA (United States)
3. University of California, Los Angeles, CA (United States)
4. University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Materials Sciences Division
5. University of California, Berkeley, CA (United States)

Chiral Weyl fermions with linear energy-momentum dispersion in the bulk accompanied by Fermi-arc states on the surfaces prompt a host of enticing optical effects. While new Weyl semimetal materials keep emerging, the available optical probes are limited. In particular, isolating bulk and surface electrodynamics in Weyl conductors remains a challenge. We devised an approach to the problem based on near-field photocurrent imaging at the nanoscale and applied this technique to a prototypical Weyl semimetal TaIrTe₄. As a first step, we visualized nano-photocurrent patterns in real space and demonstrated their connection to bulk nonlinear conductivity tensors through extensive modeling augmented with density functional theory calculations. Notably, our nanoscale probe gives access to not only the in-plane but also the out-of-plane electric fields so that it is feasible to interrogate all allowed nonlinear tensors including those that remained dormant in conventional far-field optics. Surface- and bulk-related nonlinear contributions are distinguished through their “symmetry fingerprints” in the photocurrent maps. Robust photocurrents also appear at mirror-symmetry breaking edges of TaIrTe₄ single crystals that we assign to nonlinear conductivity tensors forbidden in the bulk. Here, nano-photocurrent spectroscopy at the boundary reveals a strong resonance structure absent in the interior of the sample, providing evidence for elusive surface states.

• Research Organization: Columbia University, New York, NY (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: Gordon and Betty Moore Foundation; Gordon and Betty Moore Foundation’s EPiQS Initiative; Simons Foundation; USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE)
• Grant/Contract Number: AC02-05CH11231; SC0019443; SC0021117
• OSTI ID: 1832500
• Journal Information: Proceedings of the National Academy of Sciences, Journal Name: Proceedings of the National Academy of Sciences Journal Issue: 48 Vol. 118; ISSN 1091-6490; ISSN 0027-8424
• Publisher: Proceedings of the National Academy of SciencesCopyright Statement
• Country of Publication: United States
• Language: English