We construct the systems of bi-orthogonal polynomials on the unit circle where the Toeplitz structure of the moment determinants is replaced by $ \det(w_{ 2j-k})_{ 0\leq j,k \leq N-1} $ and the corresponding Vandermonde modulus squared is replaced by $ \prod_{ 1 \le j < k \le N}(\zeta^{ 2}_k - \zeta^{ 2}_j)(\zeta^{ -1}_k - \zeta^{ -1}_j) $. This is the simplest case of a general system of $pj-qk$ with $p,q$ co-prime integers. We derive analogues of the structures well known in the Toeplitz case: third order recurrence relations, determinantal and multiple-integral representations, their reproducing kernel and Christoffel-Darboux sum, and associated (Carath{ \'e}odory) functions. We close by giving full explicit details for the system defined by the simple weight $ w(\zeta)=e^{ \zeta}$, which is a specialisation of a weight arising from averages of moments of derivatives of characteristic polynomials over $USp(2N)$, $SO(2N)$ and $O^-(2N)$.
Categories: math.CA math-ph math.MP