The fundamental absorption lines of substitutional boron acceptor impurity in germanium, which lie between 1 and $3\mathrm{THz}$, now have been measured in magnetic fields to $18\mathrm{T}$, greatly extending the reach of both previous experiments (to $7\mathrm{T}$) and theory (to $10\mathrm{T}$). The Faraday configuration was employed with the magnetic field $\mathbf{B}\Vert ⟨110⟩$. Unexpected behavior has been observed relating to the magnetic-field-induced splitting of the ground and first two excited states (all of which are fourfold degenerate): (a) One pair of Zeeman ground states splits at only half the rate predicted with field; this behavior continues to high field. The other pair shows a rapid increase with field. (b) The two pairs of Zeeman states emerging from the first excited state initially separate with field, then, above $10\mathrm{T}$, converge, almost meeting by $18\mathrm{T}$. (c) One pair of the Zeeman states from the second excited state begins to plateau at high field; the other shows a dramatic decrease above $9\mathrm{T}$, extrapolated to become zero at around $24\mathrm{T}$. Taken together, these results suggest modification to the existing theory is required, and may have implications for quantum computation involving substitutional impurities.

• Received 1 March 2007

DOI:https://doi.org/10.1103/PhysRevB.77.115212