Intersubband electric dipole spin resonance in transition metal dichalcogenide heterobilayers

TL;DR

We address the problem of enabling spin-flip intersubband transitions in TMDCs by performing a symmetry analysis across monolayers and heterobilayers and developing a microscopic SOC-based $k\cdot p$ model. The key finding is that while monolayers forbid electric-dipole spin-flip transitions between conduction-subband states, heterobilayers with reduced $C_3$ symmetry allow such transitions, mediated by SOC-induced mixing that generates a finite inter-subband momentum matrix element $p_{\downarrow\uparrow}$ and a Rashba-like spin term. Quantitatively, the electric-dipole spin resonance rate $W_{\downarrow\uparrow}^{\mathrm{EDSR}}$ can exceed the magnetic-dipole rate by factors of $30$–$3000$, making EDSR the dominant THz mechanism. The results provide a general framework for symmetry-engineered spin control in type-II TMDC heterobilayers and can inform design principles for THz spintronic devices.

Abstract

The theory of inter-spin-subband electric dipole spin resonance in transition metal dichalcogenide heterobilayers is proposed. Our symmetry analysis demonstrates that, in contrast to monolayers, the reduced symmetry of heterobilayers enables coupling between conduction band spin subbands by an electric field. We establish the optical selection rules for all six high-symmetry stacking configurations. The microscopic mechanism of the effect is identified as the spin-orbit coupling induced mixing of Bloch states from different conduction bands, which generates a non-zero momentum matrix element between the spin-split states. It also leads to the linear-in-wavevector spin-dependent terms in the effective Hamiltonian, i.e., the Rashba effect. Our estimates show that the rate of electric-dipole spin-flip transitions exceeds by far that of the magnetic-dipole transitions in transition metal dichalcogenide heterobilayers.

Figures (3)

• Figure 1: (a) Top view of the monolayer TMDC lattice structure. Purple circles represent metal atoms, while blue circles denote the in-plane projections of chalcogen atom pairs. (b) Brillouin zone with high-symmetry points labeled. (c) Band structure close to $K^+$ and $K^-$ points, showing the highest valence band and two spin-split conduction subbands.
• Figure 2: (a) Illustration of heterobilayer in $AA/R_h^h$ stacking. Orange and magenta balls show transition metal atoms. For clarity two chalcogen atoms are represented by one blue ball. (b) Various possible high-symmetry stacking configurations of two monolayers. In H-type stackings, the layers are rotated relative to each other, while R-type stackings maintain unrotated layer alignment.
• Figure 3: Band structure in a single valley for all six high-symmetry stackings, showing the highest valence subband ($v$), two spin-split conduction subbands ($c$), and symmetry-equivalent spin-split subbands from the first ($c+1$) and second ($c+2$) excited conduction bands (additional spin subbands omitted for clarity) in the same layer. Energy splittings and curvatures of the bands are not to scale. Transition selection rules are indicated by colored arrows: red for $\sigma^+$ polarization (in-plane electric field), blue for $\sigma^-$ polarization (in-plane), and black for $z$ polarization (out-of-plane electric field).