Two-dimensional multiferroics in monolayer group IV monochalcogenides

Abstract

Low-dimensional multiferroic materials hold great promises in miniaturized device applications such as nanoscale transducers, actuators, sensors, photovoltaics, and nonvolatile memories. Here, using first-principles theory we predict that two-dimensional (2D) monolayer group IV monochalcogenides including GeS, GeSe, SnS, and SnSe are a class of 2D semiconducting multiferroics with giant strongly-coupled in-plane spontaneous ferroelectric polarization and spontaneous ferroelastic lattice strain that are thermodynamically stable at room temperature and beyond, and can be effectively modulated by elastic strain engineering. Their optical absorption spectra exhibit strong in-plane anisotropy with visible-spectrum excitonic gaps and sizable exciton binding energies, rendering the unique characteristics of low-dimensional semiconductors. More importantly, the predicted low domain wall energy and small migration barrier together with the coupled multiferroic order and anisotropic electronic structures suggest their great potentials for tunable multiferroic functional devices by manipulating external electrical, mechanical, and optical field to control the internal responses, and enable the development of four device concepts including 2D ferroelectric memory, 2D ferroelastic memory, and 2D ferroelastoelectric nonvolatile photonic memory as well as 2D ferroelectric excitonic photovoltaics.

Electrically tunable polarizer based on 2D orthorhombic ferrovalley materials

“…The spontaneous in-plane polarization (P s ) estimated in monolayer GeSe can reach to 3.5×10 -10 C/m, which is well consistent with previous works [39][40][41]. [12], the spontaneous valley polarization is induced by ferromagnetism.…”

“…In analogy to black phosphorus [33], group-IV monochalcogenides [34][35][36][37][38][39][40][41] exhibit waved structures. For paravalley materials with hexagonal lattice, the circularly polarized optical selectivity for valleys has been proposed which is essentially rooted in conservation of overall azimuthal quantum number [42].…”

Two-dimensional square buckled Rashba lead chalcogenides

“…The lattice constant a and buckling angle θ for buckled (planar) structure are 3.74Å (4.07Å) and 21.6 • (0 • ), respectively. It is known that potential barriers in bistable materials, such as ferroelectrics, are strain dependent [26]. We follow procedure by Ref.…”

“…To compare the electric polarization of monolayer PbS to the typical bulk ferroelectrics, we approximate the thickness as twice the distance between S and Pb atom which is roughly half of the lattice constant of bulk PbS. Similar approximations have also been used in other several works [24][25][26].…”

Allotropes of Phosphorus with Remarkable Stability and Intrinsic Piezoelectricity

“…Large numbers of 2D material have been reported as potential piezoelectric materials with remarkable piezoelectric coefficients comparable to traditional three-dimensional (3D) piezoelectric materials. For example, the metal dichalcogenides (MX 2 , M=Cr, Mo, W, Nb, Ta; X=S, Se, Te) [3,7,[9][10][11][12][13], the hexagonal group III-V (MX, M=B, Al, Ga, In, X=N, P, As, Sb) [7,12,14,15], the group II oxides [7,16], and the group-IV monochalcogenides (GeS, GeSe, SnS and SnSe) [5,6,[17][18][19][20]. These new discoveries significantly expanded the application fields of these 2D materials to nano-sized sensors, piezotronics and energy harvesting in portable electronic nano-devices [21,22].…”