Phonon‐Related Monochromatic THz Radiation and its Magneto‐Modulation in 2D Ferromagnetic Cr₂Ge₂Te₆

Abstract

Searching multiple types of terahertz (THz) irradiation source is crucial for the THz technology. In addition to the conventional fermionic cases, bosonic quasi-/particles also promise energy-efficient THz wave emission. Here, by utilizing a 2D ferromagnetic Cr 2 Ge 2 Te 6 crystal, first a phonon-related magneto-tunable monochromatic THz irradiation source is demonstrated. With a low-photonic-energy broadband THz pump, a strong THz irradiation with frequency ≈0.9 THz and bandwidth ≈0.25 THz can be generated and its conversion efficiency could even reach 2.1% at 160 K. Moreover, it is intriguing to find that such monochromatic THz irradiation can be efficiently modulated by external magnetic field below 160 K. According to both experimental and theoretical analyses, the emergent THz irradiation is identified as the emission from the phonon-polariton and its temperature and magnetic field dependent behaviors confirm the large spin-lattice coupling in this 2D ferromagnetic crystal. These observations provide a new route for the creation of tunable monochromatic THz source which may have great practical interests in future applications in photonic and spintronic devices.

Spin–Phonon Coupling and Magnetic Transition in an Organic Molecule Intercalated Cr2Ge2Te6

“…Around and below T 1 ≈ 100 K, the phonon lifetime = c 1 2 (FWHM) is the longest, about 1.1−1.5 ps, where c is the velocity of the light. A recent THz spectroscopy study on CGT reported τ ≈ 1.15− 1.11 ps 26 along with an attenuation of FWHM due to the formation of magnetic correlations below the spin fluctuation temperature of 160 K. 26 In pristine CGT, it has been reported that lattice parameter α demonstrates the onset of a negative thermal expansion around T 1 . 1b,27 Hence, we can infer that the enhancement of τ of in-plane vibration (E g 4 mode) (see Figure 5 (b)) occurs due to the reduced phonon−phonon interactions because of lattice expansion in the ab-plane with decreasing temperature.…”

Two-dimensional chalcogenide-based ferromagnetic semiconductors

“…The preparation of high-quality 2D magnetic materials is of great significance for understanding their physical properties, magnetic regulation, and even spintronics applications. These magnetic materials are most prepared by the methods of mechanical exfoliation [36,140], chemical vapor deposition (CVD) [141,142], liquid-phase exfoliation [143], selfflux method [55,85,144,145], solution synthesis [146], and molecular beam epitaxy (MBE) [40,44,97].…”

“…In addition, the bulk CrXTe 3 single crystal also exhibit some novel physical phenomena, such as existence of a two-step magnetic order in the anisotropy of CrXTe 3 [85], an insulator-metal and structural transition at 7.5 GPa in CrSiTe 3 [160], multiple domain structure and symmetry types in CrGeTe 3 [144], coexistence of large positive magnetoresistance and negative magnetoresistance in CrSiTe 3 [161], ultra-long remagnetization behavior in the CrGeTe 3 [162], phonon-related magneto-tunable monochromatic THz irradiation [145].…”

Narrowband, Angle-Tunable, Helicity-Dependent Terahertz Emission from Nanowires of the Topological Dirac Semimetal Cd3As2

“…There has been a wealth of research into THz generation methods, namely, difference-frequency generation (DFG) with multi-color laser pulses , and optical rectification (OR) of a single broadband optical pulse in nonlinear crystals. , A range of materials, including semiconductors, , organic crystals, and ferromagnets, have been examined with demonstration of both high-energy single-cycle and multi-cycle THz pulses. For DFG, the central emission frequency and bandwidth rely on the difference between the wavelengths of the optical pulses used.…”