A new old triangular lattice quantum magnet
e-mail: masuda@issp.u-tokyo.ac.jpLanguage in Speech : English
Abstract：
The distorted triangular lattice has long served as a vehicle for importing exotic one-dimensional physics into two dimensions. Using neutron diffraction and high-resolution neutron and THz spectroscopies we study the realization of this model in Cs2CoBr4, which additional features bond-dependent XY-anisotropy. At wave vectors where interchain interactions cancel out at the mean field level, the excitations are reminiscent of Zeeman ladders of bound kinks in individual chains. Elsewhere in the Brillouin zone the true two-dimensional structure and propagation of these modes are revealed. In applied magnetic fields the system goes through a zoo of peculiar phases. One is an incommensurate spin density wave phase similar to that in spin-chains, where it is caused by spinon Fermi surface nesting and has a field-dependent propagation vector. Another is a fan-type structure, or what remains of a transverse-polarized helix in XY geometry, with the propagation vector set by the frustration ratio alone. Additional commensurate phases and extremely strong magneto-elastic effects are observed.
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