Spin-induced and orbital quantum backflow in Pauli theory

Abstract: We show that quantum backflow in spin-$\tfrac{1}{2}$ systems within the Pauli framework can arise from spin-dependent contributions to the probability current. We construct explicit two-mode states in which the orbital current reduces to a uniform drift, so that no interference between longitudinal momentum components is present in this sector. In such configurations, backflow is generated entirely by spinor structure, which induces time-dependent modulations of the local current leading to flux reversal, while the longitudinal momentum distribution remains strictly supported on positive momenta. We derive analytical conditions for backflow in terms of spinor and momentum parameters, allowing direct control of the effect via internal degrees of freedom. We further analyze spatial coarse-graining, showing exponential suppression of interference and a qualitatively different scaling of orbital and spin contributions, with spin-induced backflow remaining robust in regimes where orbital effects are strongly suppressed.