Spin-liquid signatures in geometrically frustrated layered kagome compounds YBa Co 4 − x Fe x O 7 + δ

Experimental detection of spin dynamics of the quantum spin liquid phase, which occurs when the quantum fluctuations lead to fractionalized spin states, remains a challenge. In this paper, we illustrate spin-liquid signatures in the geometrically frustrated layered kagome system $\mathrm{YBa}{\mathrm{Co}}_{4\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{7+\ensuremath{\delta}}$ ($x=0$ and $x=0.6$) over a wide temperature range using micro-Raman spectroscopy. The thermal response of the gapped broad band over a high temperature range possibly marks a spin liquid phase in this system. We report the appearance of sharp spectral features in the high temperature regime with unusual thermal behavior for $\mathrm{YBa}{\mathrm{Co}}_{4\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{7+\ensuremath{\delta}}$ ($x=0.6$). Besides, atypical oscillation of a phonon mode frequency with temperature suggests an unconventional electron-lattice coupling in the doped compound via a strong correlation between their lattice vibration and magnetic spin dynamics.