Effect of Mechanical Strain on the Optical Properties of Quantum Dots: Controlling Exciton Shape, Orientation, and Phase with a Mechanical Strain

We show how a nanomechanical strain can be used to dynamically reengineer the optics of quantum dots, giving a tool to manipulate mechanoexciton shape, orientation, fine structure splitting, and optical transitions, transfer carriers between dots, and interact qubits for quantum processing. Most importantly, a nanomechanical strain reengineers both the magnitude and phase of the exciton exchange coupling to tune exchange splittings, change the phase of spin mixing, and rotate the polarization of mechanoexcitons, providing phase and energy control of excitons.

Figure 1

Schematic of a bend applied to a QD in a nanobridge: (left) symmetric (biaxial deformation) bend with a QD at an antinode, and (right) vertical shearing bend with a QD at a node. $S$ is the bend amplitude for clamped ends.

Figure 2

Electron $1S$ and $1P$ energies for (a) a biaxial deformation and (b) a shearing bend. Blue or red band gap shift $\Delta E_g$ and redistribution $\Delta {\rho }_{e,v}$ of the lowest conduction ($e$) and highest valence state ($v$) for different bends.

Figure 3

Schematics for (a) relaxation due to lattice mismatch in a flat bridge and (b) additional relaxation [grey (red) arrow] in a bent bridge. (c) Lattice shift along the vertical axis through the QD center for biaxial deformation, $\Delta z_n$ is the extra relaxation of atom $n$ from its position in a flat bridge for atoms ordered along the axis, and (d) conduction band profile along the vertical axis for a flat bridge and biaxially deformed bridges. The dotted curve is the unrelaxed band profile.

Figure 4

Exciton fine structure for (a) biaxial deformation and (b) shearing bend. (c) Energy splittings for biaxial deformation. (d) Absorption strength of the lowest BE for biaxial deformation and polarization along QD diagonals ($x+y$, $x-y$) and QD sides parallel ($x$) and perpendicular ($y$) to the bend.

Figure 5

(a) Change of $V_{\mathrm{Coul}}$, $V_{\mathrm{exch},\mathrm{sc}}$, and $|V_{\mathrm{exch},\mathrm{mix}}|$ for a biaxial deformation. (b) Phase of $V_{\mathrm{exch},\mathrm{mix}}$.