Rearrangement of uncorrelated valence bonds evidenced by low-energy spin excitations in YbMgGaO4

Abstract

DC-magnetization data measured down to 40 mK speak against conventional freezing and reinstate YbMgGaO${}_4$ as a triangular spin-liquid candidate. Magnetic susceptibility measured parallel and perpendicular to the $c$-axis reaches constant values below 0.1 and 0.2 K, respectively, thus indicating the presence of gapless low-energy spin excitations. We elucidate their nature in the triple-axis inelastic neutron scattering experiment that pinpoints the low-energy ($E$ $\le$ $J_0$ $\sim$ 0.2 meV) part of the excitation continuum present at low temperatures ($T$ $<$ $J_0$/$k_B$), but \emph{completely} disappearing upon warming the system above $T$ $\gg$ $J_0$/$k_B$. In contrast to the high-energy part at $E$ $>$ $J_0$ that is rooted in the breaking of nearest-neighbor valence bonds and persists to temperatures well above $J_0$/$k_B$, the low-energy one originates from the rearrangement of the valence bonds and thus from the propagation of unpaired spins. We further extend this picture to herbertsmithite, the spin-liquid candidate on the kagome lattice, and argue that such a hierarchy of magnetic excitations may be a universal feature of quantum spin liquids.

accepted in Phys. Rev. Lett

References in corpus (9)

• Non-Abelian Anyons and Topological Quantum Computation
• Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO4
• Quantum critical state in a magnetic quasicrystal
• $\mu$SR evidence for the U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO${}_4$
• Crystalline Electric Field Randomness in the Triangular Lattice Spin-Liquid YbMgGaO${}_4$
• Absence of magnetic thermal conductivity in the quantum spin liquid candidate YbMgGaO4
• Dynamic Scaling in the Susceptibility of the Spin-1\2 Kagome Lattice Antiferromagnet Herbertsmithite
• Rods of Neutron Scattering Intensity in Yb2Ti2O7: Compelling Evidence for Significant Anisotropic Exchange in a Magnetic Pyrochlore Oxide
• Strong exchange anisotropy in YbMgGaO${}_4$ from polarized neutron diffraction

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• Spiral spin liquid in a frustrated honeycomb antiferromagnet: A single-crystal study of GdZnPO
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