Hidden Pseudogap and Superconductivity in Electron Doped High-Temperature Superconductors
The ground state of superconductors is characterized by the long range order of condensed Cooper-pairs. While this is the only order in conventional superconductors, in high-temperature (high-Tc) superconductors the presence of other competing groundstates might be responsible for their complicated phase diagram. A suppression of the accessible electronic states at the Fermi-level in the normal state of high-Tc superconductors which is called pseudogap [1,2] is interpreted as precursor superconductivity [3,4] or as indication of another near-by groundstate which can be separated from the superconducting state by a quantum critical point governing the interplay between the two states [5,6]. Here we report the existence of a second hidden order parameter  within the superconducting phase of the underdoped electron doped high-Tc superconductor Pr2-xCexCuO4-y and the newly synthesized electron doped material La2-xCexCuO4-y . Our observation is consistent with the presence of a (quantum) phase transition at T = 0 which is discussed to be a key concept to understand high-temperature superconductivity. The existence of a pseudogap when superconductivity is suppressed excludes clearly precursor superconductivity as its origin . This supports the picture that the physics of high-Tc superconductors is determined by the interplay between competing and coexisting groundstates.
KeywordsSuperconducting Phase Quantum Critical Point Superconducting Order Parameter Doping Dependence Schematic Phase Diagram
Unable to display preview. Download preview PDF.