Efficient Terahertz Harmonic Generation with Coherent Acceleration of Electrons in the Dirac Semimetal Cd3As2

Abstract

Correspondence to: matsunaga@issp.u-tokyo.ac.jp †The authors contributed equally.High harmonic generation (HHG), the frequency conversion of an ac electric field, plays a key role in high-speed electronics at terahertz (THz) frequencies as well as in ultrafast photonics. Recent discoveries of material-based HHG have facilitated the search of the best system for high conversion efficiency. Here we report the appearance of strong THz range third harmonics in thin films of Cd3As2, a three-dimensional Dirac semimetal with linearly dispersing electronic states. THz pump-THz probe spectroscopy gives evidence for the microscopic mechanism originating in the coherent acceleration of Dirac electrons in momentum space as theoretically anticipated. The extreme conversion efficiency, which is detectable using only a tabletop THz source and exceeds that of graphene by over a factor of 100 times, paves the way toward novel devices for ultrafast THz electronics and photonics based on topological semimetals.

High-order nonlinear optical response of a twisted bilayer graphene

“…The largest amplitude exists in the vicinity of the K and K points and this tendency is commonly seen for the other harmonic orders n. This observation means that large nonlinear currents are carried by the Dirac electrons [see Fig. 1(d)] consistently with the experimental results showing that the Dirac electrons generate harmonics very efficiently [44,45].…”

“…This phenomenon has attracted interest not only for compact frequency converter applications [12,13] but also as a probe of electron dynamics in intense optical fields [14]. Among various systems such as semiconductors [15][16][17][18][19][20][21][22][23][24][25], superconductors [26][27][28], strongly correlated systems [29][30][31][32][33][34], quantum magnets [35][36][37], and topological insulators [38,39], Dirac materials have turned out to have extremely large nonlinear susceptibility from the mid-infrared [40][41][42] down to the teraherz [43][44][45] frequency regimes. In particular, nonlinear response of graphene has been studied extensively [46][47][48][49][50].…”

High Mobility 3D Dirac Semimetal (Cd3As2) for Ultrafast Photoactive Terahertz Photonics

“…[ 21–23 ] Furthermore, the terahertz nonlinearity through higher‐harmonic generation induced by the coherent intraband acceleration of Dirac electrons was recently observed via the terahertz‐pump and terahertz‐probe study. [ 24 ] In another report, a periodic array of Cd 3 As 2 grating structure is shown to support the excitation of plasmonic resonances at terahertz frequencies possessing finite kinetic inductance. [ 25 ] Besides, with ultrahigh mobility, large‐area fabrication capabilities and low‐Fermi energy that falls in the infrared and terahertz frequencies, [ 26–28 ] Cd 3 As 2 is highly desirable for the development of terahertz functional devices that could offer exciting prospects for terahertz science and technology.…”

Emerging Dirac materials for THz plasmonics

“…The generation efficiency is comparable to that of Bi2Se3 TI films. Another, very recent example of THz non linearity has been observed in Cd3As2 3D Dirac material where a THz harmonic up to the 7 th and 3 rd order has been detected and associated with a coherent acceleration of Dirac electrons in momentum space [30,31]. More in general, the THz non-linearity is expected to occur in all materials showing linearly dispersive electronic bands as listed in the Section 3 and 4.…”

“…While bulk α-Sn, with the diamond lattice structure, stable only below 13°C, thin films of α-Sn grown on In can be stable up to ∼170°C [30]. The lattices of α-Sn a InSb are nearly matched, but a slight mismatch results an in-plane compressive strain of 0.14% for the αoverlayer [19,31]. The crystal structure of (111)-orien α-Sn films is shown in Fig.…”