Abstract
The absence of mirror symmetry, or chirality, is behind striking natural phenomena found in systems as diverse as DNA and crystalline solids. A remarkable example occurs when chiral semimetals with topologically protected band degeneracies are illuminated with circularly polarized light. Under the right conditions, the part of the generated photocurrent that switches sign upon reversal of the light’s polarization, known as the circular photo-galvanic effect, is predicted to depend only on fundamental constants. The conditions to observe quantization are non-universal, and depend on material parameters and the incident frequency. In this work, we perform terahertz emission spectroscopy with tunable photon energy from 0.2 –1.1 eV in the chiral topological semimetal CoSi. We identify a large longitudinal photocurrent peaked at 0.4 eV reaching ~550 μ A/V2, which is much larger than the photocurrent in any chiral crystal reported in the literature. Using first-principles calculations we establish that the peak originates only from topological band crossings, reaching 3.3 ± 0.3 in units of the quantization constant. Our calculations indicate that the quantized circular photo-galvanic effect is within reach in CoSi upon doping and increase of the hot-carrier lifetime. The large photo-conductivity suggests that topological semimetals could potentially be used as novel mid-infrared detectors.
| Original language | English |
|---|---|
| Article number | 154 |
| Journal | Nature Communications |
| Volume | 12 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 1 2021 |
Funding
We thank C. L. Kane for helpful discussions and N. P. Armitage and J. Stensberg for proof-reading the manuscript. Z.N. and L.W. are supported by the ARO YIP award under the Grant W911NF1910342. X.H. is partially supported by the ARO MURI under the Grant W911NF2020166. The acquisition of the oscillator laser for the SHG experiment is supported by NSF through the University of Pennsylvania Materials Research Science and Engineering Center (MRSEC) (DMR-1720530). E.J.M’s theoretical work is supported by the DOE under grant DE FG02 84ER45118. Research at the University of Maryland was supported by the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant No. GBMF9071, and the Maryland Quantum Materials Center. Y.Z. is currently supported by the DOE Office of Basic Energy Sciences under Award desc0018945 to Liang Fu. F.J. acknowledges funding from the Spanish MCI/AEI through grant No. PGC2018-101988-B-C21. O.P. is supported by an FPU predoctoral contract from MECD No. FPU16/05460 and the Spanish grant PGC2018-099199-BI00 from MCIU/AEI/FEDER. B.X. is supported by the Schweizerische Nationalfonds (SNF) by Grant No. 200020-172611. A.G.G. is supported by the ANR under the grant ANR-18-CE30-0001-01 (TOPODRIVE) and the European Union Horizon 2020 research and innovation programme under grant agreement No. 829044 (SCHINES). Y.Z., K.M., and C.F. acknowledge the financial support from the European Research Council (ERC) Advanced Grant No. 742068 "TOP-MAT”; Deutsche Forschungsgemeinschaft (DFG) through SFB 1143, and the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter-ct.qmat (EXC 2147, Project No. 390858490). The DFT calculations are carried on Draco cluster of MPCDF, Max Planck society.