Current-voltage characteristics and vortex dynamics in highly underdoped La2−x Sr x CuO4

The temperature dependence of the nonlinear current-voltage (I–V) characteristics in highly underdoped La2−x Sr x CuO4 (x = 0.07 and 0.08) thick films has been studied in both zero and perpendicular magnetic fields H. Power-law behavior of V(I) is found for both H = 0 and H ≠ 0. The critical current I c was extracted, and its temperature and magnetic field dependences were studied in detail. The Berezinskii-Kosterlitz-Thouless physics dominates the nonlinear I–V near the superconducting transition at H = 0, and it continues to contribute up to a characteristic temperature T x (H). Nonlinear I–V persists up to an even higher temperature T h (H) due to the depinning of vortices