Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 17: Invited Talk Sergey Borisenko

O 17.1: Invited Talk

Monday, February 25, 2008, 17:45–18:30, HE 101

Charge-Density Waves and Superconductivity in Two Dimensions: The ARPES View — •Sergey Borisenko — Institute for Solid State Research, IFW-Dresden

An interaction between electrons and phonons results in two fundamental quantum phenomena in solids: in three dimensions it can turn a metal into a superconductor whereas in one dimension it can turn a metal into an insulator. In two dimensions (2D) both superconductivity and charge-density waves (CDW) are anomalous. In superconducting cuprates, critical transition temperatures are unusually high and the energy gap may stay unclosed even above these temperatures (pseudogap). In CDW-bearing dichalcogenides the resistivity below the transition can decrease with temperature even faster than in the normal phase and a basic prerequisite for the CDW, the favorable nesting conditions seems to be absent. We demonstrate that the normal-state pseudogap also exists in two of the most studied 2D examples, dichalcogenides 2H−TaSe₂ and 2H−NbSe₂, and the formation of CDW is driven by a conventional nesting instability, which is masked by the pseudogap. On the other hand, we find a very unusual behavior of the pseudogap in underdoped Dy-BSCCO and Tb-BSCCO as a function of temperature overlooked in previous ARPES studies. The magnitude, character, anisotropy and temperature evolution of the 2D-CDW pseudogap are intriguingly similar to those seen in superconducting cuprates.