Motional Enhancement of Exciton Magnetic Moments in Zinc-Blende Semiconductors

We report a remarkable enhancement of the magnetic moments of excitons as a result of their motion. This surprising result, which we have observed in magneto-optical studies of three distinct zinc-blende semiconductors, GaAs, CdTe, and ZnSe, becomes significant as the kinetic energy of the exciton becomes comparable with its Rydberg energy and is attributed to motionally induced changes in the internal structure of the exciton. The enhancement of the magnetic moment as a function of the exciton translational wave vector can be represented by a universal equation.

Figure 1

Left: the reflectivity spectrum from a 240 nm GaAs quantum well at 10 K and zero magnetic field. Right: the positions of the reflectivity signals on the excitonic polariton dispersion diagram. The translational quantization index $N$ appears at the top of the diagram. Open and closed circles denote light-hole and heavy-hole excitons, respectively.

Figure 2

Magnetic field dependences of the ${\sigma }_{+}$ and ${\sigma }_{-}$ energies for the 240 nm GaAs quantum well reflectivity signals for various values of $N$. Data for $N=3,17\dots$ are offset from those for $N=5,13\dots$ for clarity.

Figure 3

(a) The ${\sigma }_{+}$ (solid lines) and ${\sigma }_{-}$ (broken lines) PLE spectra at 3 K from a 144.2 nm CdTe (001) QW on ${\mathrm{Cd}}_{0.96}{\mathrm{Zn}}_{0.04}\mathrm{Te}$ in a magnetic field of 4.0 T. The increase of Zeeman splitting with quantization index $N$ is apparent. The arrow indicates the detection energy. For energies below 1.5959 eV, an attenuator was inserted. (b) Corresponding data at 6.5 T for the 66 nm (110) CdTe QW.

Figure 4

The exciton $g$ values for (001) QWs (relative to their values at $K_z=0$) and normalized to the quantity $G$ as a function of $K_Z{a}_{\mathrm{exc}}{\alpha }^{1/2}$. Open squares denote the GaAs well, closed symbols denote the CdTe wells on ${\mathrm{Cd}}_{0.96}{\mathrm{Zn}}_{0.04}\mathrm{Te}$ (the circles, triangles, and diamonds represent quantum wells of widths 66.0, 144.2, and 167.1 nm, respectively); crosses represent the CdTe wells on ${\mathrm{Cd}}_{0.89}{\mathrm{Zn}}_{0.11}\mathrm{Te}$ and stars represent the ZnSe well. The curve is from Eq. (1).