New scenario for high-Tc cuprates:: Electronic topological transition as a motor for anomalies in the underdoped regime

We have discovered a new nontrivial aspect of electronic topological transition (ETT) in a 2D free fermion system on a square lattice. The corresponding exotic quantum critical point, delta = delta(c), T = 0 (n = 1 - delta is the electron concentration), is at the origin of anomalous behavior in the interacting system on one side of ETT, delta < delta(c). Most important is the appearance of the line of characteristic temperatures, T*(delta) proportional to delta(c) - delta. Application of the theory to high-T-c cuprates reveals a striking similarity to the behavior observed experimentally in the underdoped regime.