Intersection and anticrossing of far-infrared modes in elliptical quantum dots with tunable ellipticity

We have investigated elliptically shaped quantum dots in modulation-doped ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}-\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures with far-infrared spectroscopy. We observe series of modes ${\omega }_{+i}$ and ${\omega }_{-i}$ which increase in frequency with increasing mode index i. The frequencies ${\omega }_{+i}$ and ${\omega }_{-i}$ at a given i represent, at a magnetic field $B=0,$ oscillations along the short and long axes of the dot, respectively. With a gate voltage we can vary the ellipticity of the dot; in particular, we can tune the ${\omega }_{-2}$ mode through the ${\omega }_{+1\mathrm{}}$ mode. This leads to an interesting mode intersection and, at $B>\mathrm{}0,$ to an anticrossing behavior.