Striking similarities between the pseudogap phenomena in cuprates and in layered organic and dichalcogenide superconductors

Abstract

Underdoped high temperature superconductors (HTS) exhibit a ‘normal’ state for energies E > E g and/or temperatures T > T 0, and a pseudogap in their electronic spectrum for E < E g and/or T 0 > T > T c . Strikingly similar behavior occurs in the transition metal dichalcogenides (TMD) 2 H-MX 2, where M = Ta, Nb, and X = S, Se, both in the ‘normal’ ( T > T 0) and in the incommensurate charge-density wave ( T ICDW > T > T c ) states. Such strikingly similar behavior has also been seen in the organic layered superconductors (OLS) κ-(ET) 2X, where ET is bis(ethylenedithio)tetrathiafulvalene, and X = Cu[N(CN) 2]Cl, Cu[N(CN) 2]Br, and Cu(SCN) 2, both in the ‘normal’ region T > T SDW > T c and in the spin-density wave region T SDW > T > T c . In all three materials classes, the anomalous transport and thermodynamic properties associated with the pseudogap or density-wave regime are completely independent of the applied magnetic field strength, whereas the same properties below T c are all strongly field-dependent. Hence, we propose that the pseudogap in the HTS arises from charge- and/or spin-density waves, and not from either superconducting fluctuations or “preformed” charged quasiparticle pairs.