Field-Induced Instability of a Gapless Spin Liquid with a Spinon Fermi Surface

Abstract

The ground state of the quantum kagome antiferromagnet Zn-brochantite, ZnCu${}_3$(OH)${}_6$SO${}_4$, which is one of only a few known spin-liquid (SL) realizations in two or three dimensions, has been described as a gapless SL with a spinon Fermi surface. Employing nuclear magnetic resonance in a broad magnetic-field range down to millikelvin temperatures, we show that in applied magnetic fields this enigmatic state is intrinsically unstable against a SL with a full or a partial gap. A similar instability of the gapless Fermi-surface SL was previously encountered in an organic triangular-lattice antiferromagnet, suggesting a common destabilization mechanism that most likely arises from spinon pairing. A salient property of this instability is that an infinitesimal field suffices to induce it, as predicted theoretically for some other types of gapless SL's.

minor corrections

References in corpus (12)

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• Pressure-tuned spin chains in brochantite, Cu${}_4$SO${}_4$(OH)${}_6$
• Dynamical spin correlations in kagome antiferromagnets: comparison of Abrikosov fermion and Schwinger boson approaches beyond mean field
• Collapse of susceptibility and non-trivial spin dynamics in the hyper-honeycomb magnet $\beta$-Li${}_2$IrO${}_3$ under high pressure
• Multistage spin correlations in the $s$ = 1/2 stuffed hyper-star lattice Li${}_2$Cu${}_2$(MoO${}_4$)${}_3$
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