| Popis: |
Interesting emergent behavior in quantum materials arises when the interaction of electrons with the lattice leads to localization and ordering. The triangular lattice of some transition metal dichalcogenides results in additional interplay of interactions involving spin, localized charge and lattice degrees of freedom. In the light of such complexity, the dominant mechanism that drives the formation of different orders is quite difficult to ascertain. Here we present a study of local symmetry breaking of the lattice structure in the prototype layered dichalcogenide material 1T-TaS2 to investigate the origin of the multiple charge and spin ordered phases. Remarkably, x-ray pair-distribution function measurements show symmetry-breaking polaronic distortions of the lattice structure around individual localized electrons at temperatures well above any of the known long-range ordered phases. The characteristic polaronic broken symmetry signatures remain present on cooling from 800 K to 15 K, through the purported quantum spin liquid (QSL) and charge ordered states, additionally revealing a new transition near 50 K to a state displaying partially restored symmetry and significant inter-layer dimerization. The appearance of locally broken symmetry and the associated order parameter at temperatures well above the appearance of long range order implies that charge ordering is driven by the Wigner crystallization of polarons, rather than Fermi surface nesting or conventional electron-phonon coupling. The local lattice distortions are consistent with a QSL state at intermediate temperatures where interlayer dimerization is incomplete. The breakup of the QSL state below 50 K is concurrent with the disappearance of domains in the charge order. |
