Thickness-Dependent and Magnetic-Field-Driven Suppression of Antiferromagnetic Order in Thin V₅S₈ Single Crystals

With materials approaching the 2D limit yielding many exciting systems with intriguing physical properties and promising technological functionalities, understanding and engineering magnetic order in nanoscale, layered materials is generating keen interest. One such material is V₅S₈, a metal with an antiferromagnetic ground state below the Néel temperature <i>T</i>_N ∼ 32 K and a prominent spin-flop signature in the magnetoresistance (MR) when <i>H</i>∥<i>c</i> ∼ 4.2 T. Here we study nanoscale-thickness single crystals of V₅S₈, focusing on temperatures close to <i>T</i>_N and the evolution of material properties in response to systematic reduction in crystal thickness. Transport measurements just below <i>T</i>_N reveal magnetic hysteresis that we ascribe to a metamagnetic transition, the first-order magnetic-field-driven breakdown of the ordered state. The reduction of crystal thickness to ∼10 nm coincides with systematic changes in the magnetic response: <i>T</i>_N falls, implying that antiferromagnetism is suppressed; and while the spin-flop signature remains, the hysteresis disappears, implying that the metamagnetic transition becomes second order as the thickness approaches the 2D limit. This work demonstrates that single crystals of magnetic materials with nanometer thicknesses are promising systems for future studies of magnetism in reduced dimensionality and quantum phase transitions

Photoluminescence Quenching and Charge Transfer in Artificial Heterostacks of Monolayer Transition Metal Dichalcogenides and Few-Layer Black Phosphorus

Transition metal dichalcogenides monolayers and black phosphorus thin crystals are emerging two-dimensional materials that demonstrated extraordinary optoelectronic properties. Exotic properties and physics may arise when atomic layers of different materials are stacked together to form van der Waals solids. Understanding the important interlayer couplings in such heterostructures could provide avenues for control and creation of characteristics in these artificial stacks. Here we systematically investigate the optical and optoelectronic properties of artificial stacks of molybdenum disulfide, tungsten disulfide, and black phosphorus atomic layers. An anomalous photoluminescence quenching was observed in tungsten disulfide–molybdenum disulfide stacks. This was attributed to a direct to indirect band gap transition of tungsten disulfide in such stacks while molybdenum disulfide maintains its monolayer properties by first-principles calculations. On the other hand, due to the strong build-in electric fields in tungsten disulfide–black phosphorus or molybdenum disulfide–black phosphorus stacks, the excitons can be efficiently splitted despite both the component layers having a direct band gap in these stacks. We further examine optoelectronic properties of tungsten disulfide–molybdenum disulfide artificial stacks and demonstrate their great potentials in future optoelectronic applications

Temperature-Dependent Plasmon–Exciton Interactions in Hybrid Au/MoSe₂ Nanostructures

Combining localized surface plasmons and confined excitons in hybrid metallic/semiconductor nanostructures is a promising route toward the manipulation of the light–matter interaction at the nanoscale and the generation of novel technological applications. In this context, we investigate the interference between plasmonic and excitonic resonances in hybrid MoSe₂@Au nanostructures consisting of monolayer MoSe₂ supported by Au nanodisks. The optical properties of the nanostructures are probed by means of spatially resolved optical transmission and photoluminescence spectroscopies and interpreted using an analytical model complemented by numerical simulations. A plasmonic–excitonic interaction energy of 42 ± 8 meV is obtained, clearly setting the coupling in the Fano-type regime. On the basis of numerical simulations of the electromagnetic near-field and on calculations of the excitonic transition dipole momentum, we show that the interaction energy is concentrated in the gap region between the disks. The temperature dependence of the plasmonic–excitonic interaction energy is extracted from the optical transmission measurements using a Fano line shape analysis of the observed spectra. We found that the plasmonic–excitonic interaction energy is almost constant in the investigated temperature range. The plasmonic–excitonic interaction revealed in our MoSe₂@Au nanohybrids is quite stable against temperature variation, which could enable potential applications on thermally driven plasmo-electronic transport or optically induced hyperthermia