Efficient Generation and Arbitrary Manipulation of Chiral Terahertz Waves Emitted from Bi₂Te₃–Fe Heterostructures

Abstract

Polarization arbitrary manipulated terahertz (THz) pulses with a prescribed amplitude temporal evolution and deposited electric‐field vectors can promote many disruptive technologies and enable enormous applications in polarization‐sensitive THz spectroscopy and imaging, ultrafast THz optospintronics, information encryption, and space exploration. However, the severe shortage of dynamically tunable THz polarization devices has impeded the proliferation of THz science and technology. Herein, a method of efficient generation and arbitrary manipulation of chiral THz waves in the topological insulator (TI)–iron (Fe) heterostructures through delicately engineering the linear photogalvanic effect (LPGE) and spin‐to‐charge conversion (SCC) effect induced by femtosecond laser pulses is proposed and demonstrated. Utilizing the intrinsic merits of optical‐controlled LPGE and magnetic field direction‐adjusted SCC effect, the TI–Fe can radiate chiral THz waves with arbitrarily tailored chirality and ellipticity. To verify the capability of such a novel chiral THz source, helical substructure associates THz circular dichroism spectroscopy is implemented on several (bio)materials, exemplified by the beetle exoskeletons. Furthermore, ultrafast switching between two THz chirality states can be realized by a double‐pulse excitation scheme. Such versatile chiral THz emitters with high efficiency and easy integration may have some disruptive applications.

Temperature‐Dependent Terahertz Emission from Co/Mn2Au Spintronic Bilayers

“…To further verify the contribution of the inverse Faraday effect (IFE), [5,45] inverse spin-orbit torque effect (ISOT), [46] spindependent photogalvanic effect (SDPGE) [38,47] to the THz generation, the pump pulse helicity-dependent excitation are carried out. As shown in Figure 3a, by pumping the Co (3)/Mn 2 Au (5) with linearly polarized (LP), left circularly polarized (LCP), and right circularly polarized (RCP) pulses, the THz emission gives almost the same result.…”

“…A crucial missing is a direct experimental observation of ultrafast spin-charge conversion of AFM within the THz-frequency range, although it has been widely investigated in paramagnetic heavy metals, [31][32][33][34] 2D MoS 2 , [35] and topological insulators of Bi 2 Se 3 and Bi 2 Te 3 . [36][37][38] In this work, we use ultrafast laser pumping-induced THz emission, as an method to investigate the ultrafast spin-charge conversion in Co/Mn 2 Au bilayer on a femtosecond timescale. A series of experiments have been carried out to reveal that laser-induced spin transport plays a dominant role in the THz emission from Co/Mn 2 Au nanofilms.…”

“…A crucial missing is a direct experimental observation of ultrafast spin–charge conversion of AFM within the THz‐frequency range, although it has been widely investigated in paramagnetic heavy metals, [ 31–34 ] 2D MoS 2 , [ 35 ] and topological insulators of Bi 2 Se 3 and Bi 2 Te 3 . [ 36–38 ]…”

Ultrafast Spin‐Charge Conversion at SnBi2Te4/Co Topological Insulator Interfaces Probed by Terahertz Emission Spectroscopy

“…More interestingly, the THz E-field phase is flipped by π while comparing THz pulse from Co/Pt and SnBi 2 Te 4 /Co with the same M orientation. By noticing the IR pump hits the Pt layer then Co in the first sample and conversely hits first AlO x then Co and SnBi 2 Te 4 in the latter, it indicates a same SCC sign for SnBi 2 Te 4 and Pt owing to the opposite spin flow from Co. [21,37] Moreover, from the maximal THz amplitude and from its Fourier transform, one notices that SnBi 2 Te 4 /Co E THz is about 25% of the Co/Pt reference emitter. Figure 2b shows the signature of the dipolar THz emission from SnBi 2 Te 4 (5SL)/Co(4)/AlO x (3) sample, by varying ( ) θ M .…”

Nanoplasmonic‐Enhanced Spintronic Terahertz Emission

“…[18] High-efficiency conversion from spin currents to charge currents can be realized by using heterostructures such as topological materials or heavy metals. [19][20][21] THz emission spectroscopy can be used for contactless detect femtosecond Recently fashionable spintronic terahertz (THz) emission provides fresh pathways for contactless diagnosing femtosecond spin currents, opens the door for developing next-generation high-performance THz emitters, and accelerates the interdisciplinary of ultrafast THz optospintronics. However, one of the research highlights of ultrafast magnetism and the difficulty for further improving the spintronic THz emission productivity is how to efficiently reduce the energy consumption of all-optical magnetitic manipulation and improve the optical spin injection efficiency.…”