Spin density wave instabilities in the NbS2 monolayer

VERONICA LAURA VILDOSOLA

San Pablo

Workshop; Next quantum generation; 2016

UNESP

n the present work, we study the magnetic properties of the NbS2 monolayerby first-principles calculations. The transition metal dichalcogenides (TMDC)are a family of laminar materials presenting exciting properties such as chargedensity waves (CDW), superconductivity and metal-insulating transitions amongothers. 2H-NbS2 is a particular case within the family, because it is the onlyone that is superconductor without exhibiting a CDW order. Although no longrange magnetic order was experimentally observed in the TMDC, we show here thatthe single monolayer of NbS2 is on the verge of a spin density wave (SDW)phase. Our calculations indicate that a wave-like magnetic order is stabilizedin the NbS2 monolayer in the presence of magnetic defects or within zig-zagnanoribbons, due to the presence of unpaired electrons. We calculate the realpart of the bare electronic susceptibilty and the corresponding nestingfunction of the clean NbS2 monolayer, showing that there are strong electronicinstabilities at the same wavevector asociated with the calculated SDWs, alsocorresponding with one of the main nesting vectors of the Fermi surface. Weconclude that the physical mechanism behind the spin-wave instabilities are thenesting properties, accentuated by the quasi 2D character of this system, andthe rather strong Coulomb interactions of the 4d band of the Nb atom. We alsoestimate the amplitude of the spin-fluctuations and find that they are ratherlarge, as expected for a system on the verge of a quantum critical transition.