Vortex phase diagram and high-field normal state of underdoped Bi₂Sr_2-xLa_xCuO_6+δ.

In underdoped cuprates, the value of the upper critical magnetic field (H_c2) and the role of charge and spin orders have been under debate. However, recent studies on the La-214 family have firmly established vortex phase diagrams that include an intermediate, viscous vortex liquid regime, regardless of the presence of charge order. We perform similar studies in underdoped Bi₂Sr_2-xLa_xCuO_6+δ (La-Bi2201), which in contrast to La-214 family exhibits only short-range charge order, and no spin order. Measurements of linear transport, voltage-current characteristics and Hall effect in H up to 45 T and temperatures (T) down to 0.017 K, reveal an insulatinglike high-field normal state and qualitatively the same vortex phase diagram as in underdoped La-214 cuprates. Therefore, our results support the universality of the vortex phase diagram with an intermediate phase, i.e. the importance of quantum phase fluctuations as T→0, in underdoped cuprates regardless of the presence of spin or charge orders.