Unconventional excitonic states with phonon sidebands in layered silicon diphosphide.

Complex correlated states emerging from many-body interactions between quasiparticles (electrons, excitons and phonons) are at the core of condensed matter physics and material science. In low-dimensional materials, quantum confinement affects the electronic, and subsequently, optical properties for these correlated states. Here, by combining photoluminescence, optical reflection measurements and ab initio theoretical calculations, we demonstrate an unconventional excitonic state and its bound phonon sideband in layered silicon diphosphide (SiP2), where the bound electron-hole pair is composed of electrons confined within one-dimensional phosphorus-phosphorus chains and holes extended in two-dimensional SiP2 layers. The excitonic state and emergent phonon sideband show linear dichroism and large energy redshifts with increasing temperature. Our ab initio many-body calculations confirm that the observed phonon sideband results from the correlated interaction between excitons and optical phonons. With these results, we propose layered SiP2 as a platform for the study of excitonic physics and many-particle effects.

Room Temperature Ferromagnetism of Monolayer Chromium Telluride with Perpendicular Magnetic Anisotropy.

The realization of long-range magnetic ordering in 2D systems can potentially revolutionize next-generation information technology. Here, the successful fabrication of crystalline Cr3 Te4 monolayers with room temperature (RT) ferromagnetism is reported. Using molecular beam epitaxy, the growth of 2D Cr3 Te4 films with monolayer thickness is demonstrated at low substrate temperatures (≈100 °C), compatible with Si complementary metal oxide semiconductor technology. X-ray magnetic circular dichroism measurements reveal a Curie temperature (Tc ) of v344 K for the Cr3 Te4 monolayer with an out-of-plane magnetic easy axis, which decreases to v240 K for the thicker film (≈7 nm) with an in-plane easy axis. The enhancement of ferromagnetic coupling and the magnetic anisotropy transition is ascribed to interfacial effects, in particular the orbital overlap at the monolayer Cr3 Te4 /graphite interface, supported by density-functional theory calculations. This work sheds light on the low-temperature scalable growth of 2D nonlayered materials with RT ferromagnetism for new magnetic and spintronic devices.

Continuously Tuning Electronic Properties of Few-Layer Molybdenum Ditelluride with in Situ Aluminum Modification toward Ultrahigh Gain Complementary Inverters.

Semiconducting molybdenum ditelluride (2H-MoTe2), a two-dimensional (2D) transition metal dichalcogenide, has attracted extensive research attention due to its favorable physical properties for future electronic devices, such as appropriate bandgap, ambipolar transport characteristic, and good chemical stability. The rational tuning of its electronic properties is a key point to achieve MoTe2-based complementary electronic and optoelectronic devices. Herein, we demonstrate the dynamic and effective control of the electronic properties of few-layer MoTe2, through the in situ surface modification with aluminum (Al) adatoms, with a view toward high-performance complementary inverter devices. MoTe2 is found to be significantly electron doped by Al, exhibiting a continuous transport transition from p-dominated ambipolar to n-type unipolar with enhanced electron mobility. Using a spatially controlled Al doping technique, both p- and n-channels are established on a single MoTe2 nanosheet, which gives complementary inverters with a record-high gain of ∼195, which stands out in the 2D family of materials due to the balanced p- and n-transport in Al-modified MoTe2. Our studies coupled with the tunable nature of in situ modification enable MoTe2 to be a promising candidate for high-performance complementary electronics.