Extended scattering continua characteristic of spin fractionalization in the two-dimensional frustrated quantum magnet Cs 2 CuCl 4 observed by neutron scattering

摘要: The magnetic excitations of the quasi-2D spin-1/2 frustrated Heisenberg antiferromagnet ${\mathrm{Cs}}_{2}{\mathrm{CuCl}}_{4}$ are explored throughout 2D Brillouin zone using high-resolution time-of-flight inelastic neutron scattering. Measurements made both in magnetically ordered phase, stabilized at low temperatures by weak interlayer couplings, as well spin liquid phase above ordering temperature ${T}_{N},$ when layers decoupled. In dynamical correlations dominated highly dispersive excitation continua, a characteristic signature fractionalization $S=1$ waves into pairs deconfined $S=1/2$ spinons and hallmark resonating-valence-bond (RVB) state. boundaries continua have strong 2D-modulated incommensurate dispersion relations. Upon cooling below ${T}_{N}$ order an spiral forms due to couplings. this sharp magnons carrying small part total scattering weight observed energies, but dominant continuum which occurs medium high energies is essentially unchanged compared phase. Linear spin-wave theory including one- two-magnon processes can describe magnon excitation, not scattering, instead described parametrized two-spinon cross section. Those results suggest crossover nature from could be understood if was close proximity transition between fractional RVB A large renormalization factor $[R=1.63(5)],$ indicating quantum fluctuations ground state, obtained exchange couplings determined saturation-field measurements. We provide independent consistency check measurements second moment paramagnetic