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

• Published in: arXiv.org
• Main Authors: Li, Yuesheng, Bachus, Sebastian, Liu, Benqiong, Radelytskyi, Igor, Bertin, Alexandre, Schneidewind, Astrid, Tokiwa, Yoshifumi, Tsirlin, Alexander A, Gegenwart, Philipp
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 22.03.2019
• Subjects: Bonding; Excitation; Freezing; Inelastic scattering; Kagome lattice; Magnetic permeability; Magnetism; Neutron scattering; Neutrons; Physics - Materials Science; Physics - Strongly Correlated Electrons; Physics - Superconductivity
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1903.09574

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 (\(E\) \(\leq\) \(J_0\) \(\sim\) 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.