  Two-dimensional (2D) materials with high carrier mobility and tunable
magnetism are in high demand for nanoelectronics and spintronic applications.
Herein, we predict a novel two-dimensional monolayer KTlO that possesses an
indirect band gap of 2.25 eV (based on HSE06) and high carrier mobility (1860
$\mathrm{cm^2\ V^{-1}s^{-1}}$ for electron and 2540 $\mathrm{cm^2\
V^{-1}s^{-1}}$ for hole) by means of ab initio calculations. KTlO monolayer has
a calculated cleavage energy of 0.56 $\mathrm{J\ m^{-2}}$, which suggests
exfoliation of bulk material as viable means for the preparation of mono- and
few-layer materials. Remarkably, the KTlO monolayer suggests tunable magnetism
and half-metallicity with hole doping, which are attributed to the novel
Mexican-hat-like bands and van Hove singularities in its electron structure.
Furthermore, monolayer KTlO exhibits moderate optical absorption over visible
light and ultraviolet region. The band gap value and band characteristics of
monolayer KTlO can be strongly manipulated by biaxial and uniaxial strains to
meet the requirements of various applications. All these novel properties
render monolayer KTlO a promising functional material for future
nanoelectronics and spintronic applications.
