Tunable Electronic Transport in Pd$_3$O$_2$Cl$_2$ Kagome Bilayers: Interplay of Stacking Configuration and Strain

TL;DR

This study uses first-principles density functional theory to examine Pd$_3$O$_2$Cl$_2$ kagome bilayers across four stackings (AA, AA', AB, AB'), assessing stability, mechanics, and electronic structure. It finds stacking-dependent band gaps spanning $\sim$0.08–0.76 eV, with AB' as the most stable configuration; AB' also exhibits significant strain-tunable gaps and pronounced hole-mass modulation under deformation. The work demonstrates that stacking order and uniaxial strain jointly enable controlled modulation of electronic transport in these 2D kagome systems, while maintaining robust mechanical properties (Young's moduli $Y^{2D} \approx$ 55–62 N/m and ductility). Overall, Pd$_3$O$_2$Cl$_2$ bilayers emerge as a mechanically resilient, strain-tunable kagome platform for next-generation quantum and flexible electronic devices.

Abstract

Kagome lattice bilayers offer unique opportunities for engineering electronic properties through interlayer stacking and strain. We report a comprehensive first-principles study of Pd$_3$O$_2$Cl$_2$ kagome bilayers, examining four stacking configurations (AA, AA$'$, AB, AB$'$). Our calculations reveal dramatic stacking-dependent band gap modulation from 0.08 to 0.76~eV, with the AB$'$ configuration being the most thermodynamically stable. All stackings exhibit robust mechanical stability with Young's moduli of 54.82-61.97~N/m and ductile behavior suitable for flexible electronics. Carrier effective masses show significant stacking dependence, ranging from 2.39-6.35~$m_0$ for electrons and 0.67-1.55~$m_0$ for holes. Strain engineering of the AB$'$ bilayer demonstrates non-monotonic band gap tuning and asymmetric modulation of carrier masses, with hole effective masses showing stronger strain sensitivity. These results establish Pd$_3$O$_2$Cl$_2$ bilayers as a promising platform for strain-engineered kagome-based quantum devices, where stacking order and mechanical deformation provide complementary control over electronic transport.

Figures (4)

• Figure 1: Crystal structures of Pd$_3$O$_2$Cl$_2$ (a) Monolayer (top and side view) and Bilayers with different stacking configurations (b) AA (c) AA$'$ (d) AB (e) AB$'$
• Figure 2: Angular dependence of in–plane acoustic velocities and elastic moduli for the AB$'$ Pd$_3$O$_2$Cl$_2$ bilayer. (a) Polar plot of the transverse acoustic sound velocity $V_\mathrm{T}(\theta)$, showing a weak four–lobed modulation associated with slight shear–wave anisotropy. (b) Polar plot of the longitudinal acoustic sound velocity $V_\mathrm{L}(\theta)$, which is nearly isotropic and varies only weakly with direction. (c) Directional Young’s modulus $E(\theta)$, exhibiting an almost perfectly circular contour and indicating quasi–isotropic in–plane stiffness. (d) Directional Poisson’s ratio $\nu(\theta)$, which remains positive and nearly constant for all in–plane directions, confirming the absence of auxetic behavior and the overall elastic isotropy of the AB$'$ bilayer.
• Figure 3: Band structures and density of states of BL Pd$_3$O$_2$Cl$_2$ (a) $AA$ (b) $AA'$ (c) $AB$ (d) $AB'$. High-registry stackings (AA and AB) show narrow semiconducting gaps of 0.08 eV and 0.17 eV, respectively, due to enhanced Pd–4$d$ interlayer orbital overlap, while the flipped and shifted configurations (AA$'$ and AB$'$) yield substantially larger gaps of 0.76 eV and 0.71 eV. The DOS highlights the dominant contributions of Pd 4$d$ and O 2$p$ orbitals near the valence band, and Pd 4$d$/Cl $p$ hybridization at the conduction edge, illustrating how stacking order governs the redistribution of spectral weight and gap opening in the BL system.
• Figure 4: Strain induced effect on the AB' BL (a) Band gap as a function of strain. (b) Electron and hole effective masses under uniaxial strain.