Second-harmonic generation in submicrometerGaAs−AlxGa1−xAswires and rings

Second-harmonic generation has been observed in submicrometer wires fabricated in $\mathrm{GaAs}-{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures. The length and width of the wires are less than the elastic and inelastic mean free paths, while the width is comparable to the Fermi wavelength. In contrast with measurements on diffusive metal wires, the voltage response at the nth harmonic $V\left(\mathrm{nf}\right)\mathrm{}$ to a small current excitation $I\left(f\right)\mathrm{}$ obeys $V\left(\mathrm{nf}\right)\mathrm{}\propto I^n\mathrm{}\left(f\right)\mathrm{}$. In concurrence with the Larkin-Khmelnitskii model, we propose that the source of the nonlinearity is quantum interference.