Search

The covalently bonded in-plane heterostructure (HS) of monolayer transition-metal dichalcogenides (TMDCs) possesses huge potential for high-speed electronic devices in terms of valleytronics. In this study, high-quality monolayer MoSe2-WSe2lateral HSs are grown by pulsed-laser-deposition-assisted selenization method. The sharp interface of the lateral HS is verified by morphological and optical characterizations. Intriguingly, photoluminescence spectra acquired from the interface show rather clear signatures of pristine MoSe2and WSe2with no intermediate energy peak related to intralayer excitonic matter or formation of MoxW(1–x)Se2alloys, thereby confirming the sharp interface. Furthermore, the discrete nature of laterally attached TMDC monolayers, each with doubly degenerated but nonequivalent energy valleys marked by (KM, K′M) for MoSe2and (KW, K′W) for WSe2in kspace, allows simultaneous control of the four valleys within the excitation area without any crosstalk effect over the interface. As an example, KMand KWvalleys or K′Mand K′Wvalleys are simultaneously polarized by controlling the helicity of circularly polarized optical pumping, where the maximum degree of polarization is achieved at their respective band edges. The current work provides the growth mechanism of laterally sharp HSs and highlights their potential use in valleytronics.

We report the observation of coherent lattice vibrations in mono- and few-layer WSe2in the time domain, which were obtained by performing time-resolved transmission measurements. Upon the excitation of ultrashort pulses with the energy resonant to that of Aexcitons, coherent oscillations of the A1goptical phonon and longitudinal acoustic phonon at the M point of the Brillouin zone (LA(M)) were impulsively generated in monolayer WSe2. In multilayer WSe2flakes, the interlayer breathing mode (B1) is found to be sensitive to the number of layers, demonstrating its usefulness in characterizing layered transition metal dichalcogenide materials. On the basis of temperature-dependent measurements, we find that the A1goptical phonon mode decays into two acoustic phonons through the anharmonic decay process.

Employing first-principles electronic structure calculations, we investigate the thermodynamic stability, magnetization, and magnetic anisotropy energy (MAE) at the interface between the ultrathin Fe(001) and PbTiO3(001) (PTO) layers. Herein we demonstrate the ferroelectric polarization driven magnetization reorientation at the Fe/PTO interface. Changes in energy levels of the strong spin–orbit coupled Fe 3d and Pb 6p orbital states under the reversible ferroelectric polarization of Ti displacement are responsible for the magnetization reorientation at the Fe/PTO interface. Furthermore, we reveal that magnetization reversal persists for Fe-film thicknesses of >1 nm and even under a practically achievable strain of 1%. The present study provides a viable route for achieving the electric-field-only manipulation of magnetization switching in magnetoelectric spintronics.

The spin–orbit torque (SOT) resulting from a spin current generated in a nonmagnetic transition metal layer offers a promising magnetization switching mechanism for spintronic devices. To fully exploit this mechanism, in practice, materials with high SOT efficiencies are indispensable. Moreover, new materials need to be compatible with semiconductor processing. This study introduces W–Ta and W–V alloy layers between nonmagnetic β-W and ferromagnetic CoFeB layers in β-W/CoFeB/MgO/Ta heterostructures. We carry out first-principles band structure calculations for W–Ta and W–V alloy structures to estimate the spin Hall conductivity. While the predicted spin Hall conductivity values of W–Ta alloys decrease monotonically from −0.82 × 103S/cm for W100at% as the Ta concentration increases, those of W–V alloys increase to −1.98 × 103S/cm for W75V25at% and then gradually decrease. Subsequently, we measure the spin Hall conductivities of both alloys. Experimentally, when β-W is alloyed with 20 at% V, the absolute value of the spin Hall conductivity considerably increases by 36% compared to that of the pristine β-W. We confirm that the W–V alloy also improves the SOT switching efficiency by approximately 40% compared to that of pristine β-W. This study demonstrates a new material that can act as a spin current-generating layer, leading to energy-efficient spintronic devices.