Edge magnetism impact on electrical conductance and thermoelectric properties of graphenelike nanoribbons

Abstract

Edge states in narrow quasi two-dimensional nanostructures determine, to a large extent, their electric, thermoelectric and magnetic properties. Non-magnetic edge states may quite often lead to topological insulator type behavior. However another scenario develops when the zigzag edges are magnetic and the time reversal symmetry is broken. In this work we report on the electronic band structure modifications, electrical conductance and thermoelectric properties of narrow zigzag nanoribbons with spontaneously magnetized edges. Theoretical studies based on the Kane-Mele-Hubbard tight-binding model show that for silicene, germanene and stanene both the Seebeck coefficient and the thermoelectric power factor are strongly enhanced for energies close to the charge neutrality point. Perpendicular gate voltage lifts the spin degeneracy of energy bands in the ground state with antiparallel magnetized zigzag edges and makes the electrical conductance significantly spin-polarized. Simultaneously the gate voltage worsens the thermoelectric performance. Estimated room-temperature figures of merit for the aforementioned nanoribbons can exceed a value of 3 if phonon thermal conductances are adequately reduced.

A Perspective on Recent Advances in 2D Stanene Nanosheets

“…This behavior can be used in the fabrication of band structure‐modulated spintronic devices. Again, the types of edges (armchair, zigzag) play important roles also in the room‐temperature ferromagnetism states of graphene, silicene, germanene, and stanene . Edge manipulation through an applied electric field or functionalization creates asymmetric spin states in the stanene monolayer and provides a strong tunable magnetic field, which is suitable for inducing giant magnetoresistance and spin filters in spintronic devices.…”

Selected graphenelike zigzag nanoribbons with chemically functionalized edges: Implications for electronic and magnetic properties

“…where the expectation values are taken over the ground state of H (see [14] for details). On the one hand the out-of-plane magnetic configurations (t SO ≈ 0) will be exemplified with graphene, t 1 = −2.7 eV, and phosphorene with as many as 5 hopping parameters (in eV) t 1 = −1.22, t 2 = 3.665, t 3 = −0.205, t 4 = −0.105, t 5 = −0.055 [18,16].…”

“…On the one hand the out-of-plane magnetic configurations (t SO ≈ 0) will be exemplified with graphene, t 1 = −2.7 eV, and phosphorene with as many as 5 hopping parameters (in eV) t 1 = −1.22, t 2 = 3.665, t 3 = −0.205, t 4 = −0.105, t 5 = −0.055 [18,16]. On the other hand, in the buckled case, stanene with t 1 = −1.3eV will be considered, its parameter t SO = 0.0192eV [13] is relatively large (Sn is much heavier than C and P) implying the appearance of magnetic anisotropy favoring the in-plane configuration 8,12,14 . Incidentally, results for the out-of-plane magnetic configuration and the in-plane one do not differ from each other if there is no anisotropy.…”

“…The ground state magnetic configuration can be determined by comparing grand canonical potentials corresponding to different possible magnetic alignments (cf. [14]). Figure 2 illustrates the phase diagram of possible arrangements of mutual orientations of edge magnetic moments in graphene (panel (a)), stanene (b) and phosphorene (c).…”

“…Band structure and edge magnetism issues in those materials have been recently intensively studied (see Refs. [11][12][13][14][15][16]).…”