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Abstract
Many high-Tc superconductors, Iron based superconductors and other recently discovered superconducting materials shows the signature of existence of a strange Pseudo Gap above the superconducting transition temperature. Various experimental techniques such as NMR, Tunneling and ARPES suggest that pseudo gap does not change with temperature. As evidenced from these experimental results, the Pseudo gap possess the d-wave pairing symmetry similar to superconducting energy gap. The physical properties shows unusual behavior in the non-superconducting state where pseudo gap exist. Based on experimental evidences we argue about the origin of pseudo gap in these superconductors. Although a complete understanding of mechanism is lacking, the existence of preformed cooper indicated by various experimental probes pairs seems to be responsible for the origin of Pseudo gap.
Keywords: Pseudo Gap, Unconventional Superconductors,