Chiral terahertz wave emission from the Weyl semimetal TaAs

Gao, Yuan; Kaushik, Sahal; Philip, Evan John; Li, Z.; Qin, Yuchang; Liu, Y. P.; Zhang, W. L.; Su, Yu-Hsin; Chen, Xinzhong; Weng, Hongming; Kharzeev, Dmitri E.; Liu, M. K.; Qi, J.

doi:10.1038/s41467-020-14463-1

Cited by 138 publications

(116 citation statements)

References 53 publications

(104 reference statements)

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“…Numerous theoretical and experimental studies have revealed that the chiral fermions can host rich fascinating physical phenomena, such as the chiral zero sound [39,40], colossal chiral ultrafast photocurrents [41], and photoinduced anomalous Hall effects [42]. Our discovery introduces a new degree of freedom to study the chiral fermions, which would facilitate uncovering more exotic behaviour associated with the chiral fermions in materials.…”

Section: Discussionmentioning

confidence: 86%

Chiral fermion reversal in chiral crystals

Li¹,

Xu²,

Rao³

et al. 2019

Nat Commun

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In materials chiral fermions such as Weyl fermions are characterized by nonzero chiral charges, which are singular points of Berry curvature in momentum space. Recently, new types of chiral fermions beyond Weyl fermions have been discovered in structurally chiral crystals CoSi, RhSi and PtAl. Here, we have synthesized RhSn single crystals, which have opposite structural chirality to the CoSi crystals we previously studied. Using angle-resolved photoemission spectroscopy, we show that the bulk electronic structures of RhSn are consistent with the band calculations and observe evident surface Fermi arcs and helical surface bands, confirming the existence of chiral fermions in RhSn. It is noteworthy that the helical surface bands of the RhSn and CoSi crystals have opposite handedness, meaning that the chiral fermions are reversed in the crystals of opposite structural chirality. Our discovery establishes a direct connection between chiral fermions in momentum space and chiral lattices in real space.

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Section: Discussionmentioning

confidence: 86%

Chiral fermion reversal in chiral crystals

Li¹,

Xu²,

Rao³

et al. 2019

Nat Commun

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“…We observed THz emission in the midinfrared regime (0.2-0.5 eV). We expect that the development of broadband THz emission spectroscopy provides the opportunity to reveal bulk photovoltanic 23,24,61 and spintronic responses 71 in a low-energy regime and also the possibility of probing Berry curvature in surface-state photogalvanic effect in topological insulators 72 .…”

Section: Cpge Calculationmentioning

confidence: 99%

“…The Weyl semimetal phases discovered in materials of the transition monopnictide family such as TaAs [10][11][12][13][14][15][16][17] lack inversion symmetry, which allows for nonzero second-order nonlinear optical responses and has motivated the search for topological responses using techniques of nonlinear optics. This search has resulted in the observation of giant second-harmonic generation (SHG) 18,19 , as well as interesting photogalvanic effects [20][21][22][23][24] . However, neither response can be directly attributed to the topological charge of a single band crossing, since mirror symmetry-present in most known Weyl semimetals-imposes that charges with opposite sign lie at the same energy and thus contribute equally 19,25 .…”

Section: Introductionmentioning

confidence: 99%

Linear and nonlinear optical responses in the chiral multifold semimetal RhSi

Sánchez-Martínez

et al. 2020

npj Quantum Mater.

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Chiral topological semimetals are materials that break both inversion and mirror symmetries. They host interesting phenomena such as the quantized circular photogalvanic effect (CPGE) and the chiral magnetic effect. In this work, we report a comprehensive theoretical and experimental analysis of the linear and nonlinear optical responses of the chiral topological semimetal RhSi, which is known to host multifold fermions. We show that the characteristic features of the optical conductivity, which display two distinct quasi-linear regimes above and below 0.4 eV, can be linked to excitations of different kinds of multifold fermions. The characteristic features of the CPGE, which displays a sign change at 0.4 eV and a large non-quantized response peak of around 160 μA/V2 at 0.7 eV, are explained by assuming that the chemical potential crosses a flat hole band at the Brillouin zone center. Our theory predicts that, in order to observe a quantized CPGE in RhSi, it is necessary to increase the chemical potential as well as the quasiparticle lifetime. More broadly, our methodology, especially the development of the broadband terahertz emission spectroscopy, could be widely applied to study photogalvanic effects in noncentrosymmetric materials and in topological insulators in a contact-less way and accelerate the technological development of efficient infrared detectors based on topological semimetals.

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“…In addition, highly efficient chiral terahertz emission with elliptical polarization states has been obtained from the fascinating topological phase matter, bulk Weyl semimetal TaAs with reflection terahertz emission geometry. 22 Inspired by these pioneering breakthroughs, the question of whether we can utilize the spin freedom of electrons to generate and manipulate spin-polarized terahertz waves has become very interesting.…”

Section: Introductionmentioning

confidence: 99%

Generation and manipulation of chiral terahertz waves in the three-dimensional topological insulator Bi2Te3

et al. 2020

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Arbitrary manipulation of broadband terahertz waves with flexible polarization shaping at the source has great potential in expanding numerous applications, such as imaging, information encryption, and all-optical coherent control of terahertz nonlinear phenomena. Topological insulators featuring unique spinmomentum-locked surface state have already exhibited very promising prospects in terahertz emission, detection, and modulation, which may lay a foundation for future on-chip topological insulator-based terahertz systems. However, polarization-shaped terahertz emitters based on topological insulators with an arbitrarily manipulated temporal evolution of the amplitude and the electric-field vector direction have not yet been explored. We systematically investigated the terahertz radiation from topological insulator Bi 2 Te 3 nanofilms driven by femtosecond laser pulses and successfully realized the generation of efficient chiral terahertz waves with controllable chirality, ellipticity, and principal axis. The convenient engineering of the chiral terahertz waves was interpreted by a photogalvanic effect (PGE)-induced photocurrent, while the linearly polarized terahertz waves originated from linear PGE-induced shift currents. Our work not only provides further understanding of femtosecond coherent control of ultrafast spin currents but also describes an effective way to generate spin-polarized terahertz waves at the source.

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Chiral terahertz wave emission from the Weyl semimetal TaAs

Cited by 138 publications

References 53 publications

Chiral fermion reversal in chiral crystals

Chiral fermion reversal in chiral crystals

Linear and nonlinear optical responses in the chiral multifold semimetal RhSi

Generation and manipulation of chiral terahertz waves in the three-dimensional topological insulator Bi2Te3

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