Mottness in two-dimensional van der Waals <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Nb</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>X</mml:mi><mml:mn>8</mml:mn></mml:msub></mml:mrow></mml:math> monolayers <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:mi>X</mml:mi><mml:mo>=</mml:mo><mml:mi>Cl</mml:mi><mml:mo>,</mml:mo><mml:mi>Br</mml:mi><mml:mo>,</mml:mo><mml:mspace width="0.28em"/><mml:mtext>and</mml:mtext><mml:mspace width="0.28em"/><mml:mi mathvariant="normal">I</mml:mi><mml:mo>)</mml:mo></mml:math>
Yi Zhang, Yuhao Gu, Hongming Weng, Kun Jiang, Jiangping Hu
Abstract
We investigate strong electron-electron correlation effects on two-dimensional van der Waals materials ${\mathrm{Nb}}_{3}{X}_{8} (X=\mathrm{Cl},\mathrm{Br},\phantom{\rule{0.28em}{0ex}}\text{and}\phantom{\rule{0.28em}{0ex}}\mathrm{I})$. We find that the monolayers ${\mathrm{Nb}}_{3}{X}_{8}$ are ideal systems close to the strong correlation limit. They can be described by a half-filled single band Hubbard model in which the ratio between the Hubbard, $U$, and the bandwidth, $W, U/W\ensuremath{\approx}5--10$. Both Mott and magnetic transitions of the material are calculated by the slave boson mean-field theory. Doping the Mott state, a ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}+i{d}_{xy}$ superconducting pairing instability is found. We also construct a tunable bilayer Hubbard system for two sliding ${\mathrm{Nb}}_{3}{X}_{8}$ layers. The bilayer system displays a crossover between the band insulator and Mott insulator.