Imaging Thermally Fluctuating Néel Vectors in van der Waals Antiferromagnet NiPS.

Studying antiferromagnetic domains is essential for fundamental physics and potential spintronics applications. Despite their importance, few systematic studies have been performed on antiferromagnet (AFM) domains with high spatial resolution in van der Waals (vdW) materials, and direct probing of the Néel vectors remains challenging. In this work, we found multidomain states in the vdW AFM NiPS, a material extensively investigated for its unique magnetic exciton.

Terahertz Spectroscopy and DFT Analysis of Phonon Dynamics of the Layered Van der Waals Semiconductor Nb ( = Cl, I).

We have conducted a terahertz spectroscopic study and a density functional theory analysis of the phonon dynamics of the layered van der Waals semiconductors NbCl and NbI. Several infrared-active phonon modes were observed in the terahertz region, and their frequencies were found to be in excellent agreement with our first-principles lattice dynamics calculations. For NbCl, the observed phonon spectra are consistent with a structural transition at 90 K from the high-temperature 3̅1 phase to the low-temperature 3̅ phase.

Multiferroic-Enabled Magnetic-Excitons in 2D Quantum-Entangled Van der Waals Antiferromagnet NiI.

Matter-light interaction is at the center of diverse research fields from quantum optics to condensed matter physics, opening new fields like laser physics. A magnetic exciton is one such rare example found in magnetic insulators. However, it is relatively rare to observe that external variables control matter-light interaction.

Air-Stable and Layer-Dependent Ferromagnetism in Atomically Thin van der Waals CrPS.

Ferromagnetism in two-dimensional materials presents a promising platform for the development of ultrathin spintronic devices with advanced functionalities. Recently discovered ferromagnetic van der Waals crystals such as CrI, readily isolated two-dimensional crystals, are highly tunable through external fields or structural modifications. However, there remains a challenge because of material instability under air exposure.

Exciton-driven antiferromagnetic metal in a correlated van der Waals insulator.

Collective excitations of bound electron-hole pairs-known as excitons-are ubiquitous in condensed matter, emerging in systems as diverse as band semiconductors, molecular crystals, and proteins. Recently, their existence in strongly correlated electron materials has attracted increasing interest due to the excitons' unique coupling to spin and orbital degrees of freedom. The non-equilibrium driving of such dressed quasiparticles offers a promising platform for realizing unconventional many-body phenomena and phases beyond thermodynamic equilibrium.

Possible Persistence of Multiferroic Order down to Bilayer Limit of van der Waals Material NiI.

Realizing a state of matter in two dimensions has repeatedly proven a novel route of discovering new physical phenomena. Van der Waals (vdW) materials have been at the center of these now extensive research activities. They offer a natural way of producing a monolayer of matter simply by mechanical exfoliation.

Gigantic Current Control of Coercive Field and Magnetic Memory Based on Nanometer-Thin Ferromagnetic van der Waals Fe GeTe.

Controlling magnetic states by a small current is essential for the next-generation of energy-efficient spintronic devices. However, it invariably requires considerable energy to change a magnetic ground state of intrinsically quantum nature governed by fundamental Hamiltonian, once stabilized below a phase-transition temperature. Here, it is reported that, surprisingly, an in-plane current can tune the magnetic state of the nanometer-thin van der Waals ferromagnet Fe GeTe from a hard magnetic state to a soft magnetic state.

Tuning dimensionality in van-der-Waals antiferromagnetic Mott insulators TMPS.

We present an overview of our recent work in tuning and controlling the structural, magnetic and electronic dimensionality of 2D van-der-Waals antiferromagnetic compounds (Transition-Metal)PS. Low-dimensional magnetic systems such as these provide rich opportunities for studying new physics and the evolution of established behaviours with changing dimensionality. These materials can be exfoliated to monolayer thickness and easily stacked and combined into functional heterostructures.

Hard ferromagnetic van-der-Waals metal (Fe,Co)GeTe: a new platform for the study of low-dimensional magnetic quantum criticality.

The widely-studied ferromagnetic van-der-Waals (vdW) metal FeGeTe has great promise for studies of quantum criticality in the 2D limit, but is limited by a relatively high Curie temperature in excess of 200 K. To help render the quantum critical point achievable in such a system within the reach of practically possible tuning methods, we have grown single crystals of a variant of (Fe,Co)GeTe with useful physical properties for both this purpose and the wider study of low-dimensional magnetism and spin transport. (Fe,Co)GeTe is found through x-ray diffraction and electron microscopy to have an equivalent crystal structure to FeGeTe, with a random distribution of the cobalt dopant sites.