Anisotropic Picosecond Spin-Photocurrent from Weyl Semimetal WTe₂

Abstract

The generation and detection of ultrafast spin current, preferably reaching a frequency up to terahertz, is the core of spintronics. Studies have shown that the Weyl semimetal WTe 2 is of great potential in generating spin currents. However, the prior studies have been limited to the static measurements with the inplane spin orientation. In this work, we demonstrate a picosecond spin-photocurrent in a Td-WTe 2 thin film via a terahertz time domain spectroscopy with a circularly polarized laser excitation. The anisotropic dependence of the circular photogalvanic effect (CPGE) in the terahertz emission reveals that the picosecond spinphotocurrent is generated along the rotational asymmetry a-axis. Notably, the generated spins are aligned along the out-of-plane direction under the light normally incident to the film surface, which provides an efficient means to manipulate magnetic devices with perpendicular magnetic anisotropy. A spin-splitting band induced by intrinsic inversion symmetry breaking enables the manipulation of a spin current by modulating the helicity of the laser excitation. Moreover, CPGE nearly vanishes at a transition temperature of ∼175 K due to the carrier compensation. Our work provides an insight into the dynamic behavior of the anisotropic spin-photocurrent of Td-WTe 2 in terahertz frequencies and shows a great potential for the future development of terahertz-spintronic devices with Weyl semimetals.

Strain-enhanced giant Rashba spin splitting in ultrathin KTaO3 films for spin-polarized photocurrents

“…We also show that such giant Rashba effect can be used to generate spin-polarized photocurrents in terms of the circular photogalvanic effect. [18][19][20][21][22][23] Therefore, these giant Rashba phenomena may open a new door to promising spintronic and optoelectronic applications.…”

“…Because of the giant Rashba spin splitting, the KTO ultrathin lms can be used for achieving circular photogalvanic effect (CPGE) to generate spin-polarized photocurrents. [18][19][20][21][22][23] For the right-handed (le-handed) circularly polarized light, its photon has the angular momentum of +1 (À1), labeled by s + (s À ), and the selection rule for necessary transitions is that the allowed zcomponent change of the total angular momentum is DJ m ¼ +1 (À1). The valence band edge, originating from the J ¼ 3/2 states, has J m ¼ AE3/2, and the conduction band edge, from the Fig.…”

“…15 Large Rashba interaction can be used to realize spin polarization and spin injection by applying electric eld 16,17 and produce spinpolarized photocurrents through polarized light. [18][19][20][21][22][23] Recently, a 2DEG was observed at KTaO 3 (KTO) (100) surface 24,25 in terms of the angle-resolved photoemission (ARPES) spectrum. 24 For another 2DEG at an amorphous-LAO/ KTO interface, an experimental analysis of the weak antilocalization effect resulted in a Rashba coupling constant 0.1 eVÅ and a 50-fold enhanced Hall mobility of charge carriers.…”

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

“…4(e) and 4(f)], they both presented the same spectral shapes, strongly indicating that both C x and L 1x shared the same physical origin and are consistent with previous observation. 25,26,[35][36][37][38] However, the D x , L 2yz , and D yz terms also presented similar shapes in the frequency domain, and very few works pay attention to the underlying mechanism about these three terms. Ours is the first observation that all five terms resemble each other in nature, and we elucidate this phenomenon in a macroscopic phenomenological PGE-induced photocurrent framework.…”

Highly Tunable Near‐Room Temperature Ferromagnetism in Cr‐Doped Layered Td‐WTe2

“…[ 11,12 ] Additionally, WTe 2 also shows controllable ferroelectric behavior [ 13,14 ] and spin relaxation within nanoseconds up to room temperature. [ 15 ] Thus, these rich features have endowed WTe 2 with tremendous potential applications such as all‐solid‐state flexible supercapacitors, [ 16 ] hydrogen evolution, [ 17 ] sodium ion batteries, [ 18 ] photodetectors, [ 19–21 ] and photothermoelectric transport. [ 22 ] Most notably, its Weyl semimetal and topological insulator behaviors have attracted tremendous research attention recently.…”