Theory of the Pseudospin Resonance in Semiconductor Bilayers

The pseudospin degree of freedom in a semiconductor bilayer gives rise to a collective mode analogous to the ferromagnetic-resonance mode of a ferromagnet. We present a many-body theory of the dependence of the energy and the damping of this mode on layer separation $d$. Based on these results, we discuss the possibilities of realizing transport-current driven pseudospin-transfer oscillators in semiconductors, and of using the pseudospin-transfer effect as an experimental probe of intersubband plasmons.

Figure 1

Imaginary part of the dynamical response function ${\ell }_0(\omega )$ (in units of ${\mathrm{eV}}^{-1}{\mathrm{nm}}^{-6}$) as a function of $\omega$ for a bilayer electron gas with $n=8.3\times {10}^{10}{\mathrm{cm}}^{-2}$ and ${\Delta }_{\mathrm{SAS}}=1.48\mathrm{meV}$. The solid (red) line is the asymptotic result $\mathrm{Im}{\ell }_0(\omega \to \infty )=-m{n}^2/32$. Inset: a zoom of the low-energy region. The solid (red) curve is the expression $\mathrm{Im}{\ell }_0(\omega )=-\gamma {\omega }^3$ with $\gamma \simeq 3.41\times {10}^{-4}$ [16].

Figure 2

Intrinsic linewidth ${\Gamma }_{\perp }$ of the pseudospin resonance as a function of ${\Delta }_{\mathrm{SAS}}$ for a bilayer with density $n=8.3\times {10}^{10}{\mathrm{cm}}^{-2}$ and $d=60\AA$. The S2D curve was evaluated using the bare 2D interactions $V_s(q)$ and $V_d(q)$ defined above, whereas the Q2D result was evaluated with more realistic interactions weakened by form factors [17] which account for typical quantum well widths.

Figure 3

Intrinsic linewidth ${\Gamma }_{\perp }$ of the pseudospin resonance as a function of $n$ for a bilayer with tunneling gap ${\Delta }_{\mathrm{SAS}}=1.48\mathrm{meV}$ and $d=60\AA$. The labels S2D and Q2D have the same meaning as in Fig. 2.