Ohmic-Polarization transition in hydrated DNA.

A quasi-two-dimensional DNA-water system was investigated under a perpendicular magnetic field of 0.5T and a constant 0.1V bias at near-room temperature. Upon cooling, the system undergoes a sharp crossover near 20 °C from a regime with finite longitudinal conduction to a regime in which the longitudinal current Ixx collapses, while the transverse voltage Vxy and a correlated photovoltage remain finite and develop slow, coherent modulations. This decoupling of longitudinal and transverse responses cannot be explained by conventional charge transport and instead indicates a transition from ohmic conduction to polarization-dominated dynamics governed by displacement currents. Complementary magnetic-field sweeps in higher-concentration samples reveal a reproducible polarization cycle, including a pronounced inversion between Vxy and Vphoto and a highly elongated Lissajous portrait, consistent with near anti-phase locking of electrical and optical degrees of freedom. These results identify a field-tunable, polarization-coherent regime in quasi-2D hydrated DNA under ambient/biological conditions, in which macroscopic voltages arise from collective polarization dynamics rather than net charge flow.