We present comprehensive measurements of the structural, magnetic and electronic properties of layered van-der-Waals ferromagnet VI3 down to low temperatures. Despite belonging to a wellstudied family of transition metal trihalides, this material has received very little attention. We outline, from high-resolution powder x-ray diffraction measurements, a corrected room-temperature crystal structure to that previously proposed and uncover a structural transition at 79 K, also seen in the heat capacity. Magnetization measurements confirm VI3 to be a hard ferromagnet (9.1 kOe coercive field at 2 K) with a high degree of anisotropy, and the pressure dependence of the magnetic properties provide evidence for the two-dimensional nature of the magnetic order. Optical and electrical transport measurements show this material to be an insulator with an optical band gap of 0.67 eV -the previous theoretical predictions of d-band metallicity then lead us to believe VI3 to be a correlated Mott insulator. Our latest band structure calculations support this picture and show good agreement with the experimental data. We suggest VI3 to host great potential in the thriving field of low-dimensional magnetism and functional materials, together with opportunities to study and make use of low-dimensional Mott physics.Two-dimensional van-der-Waals (vdW) magnetic materials have in recent years become the subject of a wide range of intense research 1 . While a large portion of research into two-dimensional materials has centered on graphene, the addition of magnetism into such a system leads to many interesting fundamental questions and opportunities for device applications 2-6 . Particularly for future spintronics applications, semiconducting or metallic materials which exhibit ferromagnetism down to monolayer thickness are an essential ingredient. This has led to a large volume of recent publications on two-dimensional honeycomb ferromagnet CrI 3 7-12 . CrI 3 and VI 3 belong to a wider family of MX 3 transition metal trihalides, with X = Cl, Br, I, which were synthesized in the 60s 13,14 but have since seen little interest until recently 15 . VI 3 is an insulating two-dimensional ferromagnet with a Curie Temperature, T c , given as 55 K and reported to have the layered crystal structure of BiI 3 with space group R-3 [16][17][18] . As shown in a recent review 15 , there is very little available information on VI 3 other than the structure and the expected S = 1 from the 3d 2 configuration of the vanadium sites. Calculations using density functional theory, which additionally yield the exchange constants, have suggested VI 3 to not only remain ferromagnetic down to a single crystalline layer, but to also exhibit Dirac half-metallicity, of interest for spintronic applications 19 .In these vdW materials, hydrostatic pressure forms an extremely powerful tuning parameter. Given the weak mechanical forces between the crystal planes, the application of pressure will dominantly have the effect of pressing the ab planes together, and gradually an...

The quasiperiodic structure of high-pressure bismuth gives rise to unusually strong electron-phonon coupling.

The iron-based intermetallic YFe2Ge2 stands out among transition metal compounds for its high Sommerfeld coefficient of the order of 100 mJ/(molK 2 ), which signals strong electronic correlations. A new generation of high quality samples of YFe2Ge2 show superconducting transition anomalies below 1.8 K in thermodynamic as well as transport measurements, establishing that superconductivity is intrinsic in this layered iron compound outside the known superconducting iron pnictide or chalcogenide families. The Fermi surface geometry of YFe2Ge2 resembles that of KFe2As2 in the high pressure collapsed tetragonal phase, in which superconductivity at temperatures as high as 10 K has recently been reported, suggesting an underlying connection between the two systems.

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