EN
For one-dimensional Dirac operators of the form
$Ly = i\begin{pmatrix} 1 & 0 \\ 0 & -1 \end{pmatrix} dy/dx + vy$, $v = \begin{pmatrix) 0& Q\\ P & 0\end{pmatrix}$, $y = \begin{pmatrix}y₁\\y₂\end{pmatrix}$, x ∈ ℝ,
we single out and study a class X of π-periodic potentials v whose smoothness is determined only by the rate of decay of the related spectral gaps γₙ = |λ⁺ₙ - λ¯ₙ|, where $λₙ^{±}$ are the eigenvalues of L = L(v) considered on [0,π] with periodic (for even n) or antiperiodic (for odd n) boundary conditions.