From charge- and spin-ordering to superconductivity in the organic charge-transfer solids

摘要: Abstract We review recent progress in understanding the different spatial broken symmetries that occur normal states of family charge-transfer solids (CTS) exhibit superconductivity (SC), and discuss how this knowledge gives insight to mechanism unconventional SC these systems. A great variety semiconducting proximate CTS, including charge ordering, antiferromagnetism spin-density wave, spin-Peierls state quantum spin liquid. show a unified theory diverse symmetry necessarily requires explicit incorporation strong electron–electron interactions lattice discreteness, most importantly, correct bandfilling one-quarter, as opposed effective half-filled band picture is often employed. Uniquely quarter-filled band, there very tendency form nearest neighbor spin–singlets, both one- two-dimension. The spin–singlet charge-disproportionated, with charge-rich pairs sites separated by charge-poor insulating state. Thus effect, drives commensurate charge-order correlated band. This charge-ordered spin–singlet, which we label paired-electron crystal (PEC), from competes antiferromagnetic (AFM) Wigner (WC) single electrons. Further, unlike classical symmetries, PEC characterized gap. two dimension enhanced frustration. concept mirrors parallel development idea density wave Cooper superconducting high T c cuprates, where also existence between phase has now been confirmed. Following characterization critically reexamine spin-fluctuation resonating valence bond theories frustration-driven within Hubbard Hubbard–Heisenberg Hamiltonians for CTS. present numerical evidence absence correlated-electron any degree then develop valence-bond reached destabilization additional pressure-induced frustration makes spin–singlets mobile. limited but accurate such order–SC duality. Our proposed same CTS instead charge-ordered, only difference former generated via fluctuating static PEC. In Appendix B point out several classes superconductors share band-filling one-quarter many materials are indications similar intertwined order SC. transferability our