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Current may flow in helical paths along the boundary between two tilted anisotropic conductors in circumstances when current flow in either conductor alone is restrained by the extreme anisotropy. We are able to explain number of features of the electrical properties of (103)/(013) oriented YBa 2 Cu 3 O 7 thin films deposited onto (110) SrTiO 3 substrates in terms of helical current paths involving the 90 • twist boundaries. These include the absence of weak link behaviour in the superconducting state for current flow along the substrate (110) direction, the temperature dependence of the normal state resistivity for current flow in that direction, and the normal state electrical anisotropy. We predict that there are circumstances where currents will preferentially circulate around the boundaries of a tilt domain. The existence of these natural conduction loops may explain the period of recently observed quantum-interference behaviour in these films.

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