YbMgGaO4中低能自旋激发证实的非关联价键重排
Rearrangement of uncorrelated valence bonds evidenced by low-energy spin excitations in YbMgGaO4
摘要：
测量到的直流磁化数据下降到40 mK发言对传统的冻结和恢复YbMgGaO $_4$作为三角形自旋液体的候选人。平行和垂直于$c$轴测量的磁化率分别达到0.1和0.2 K以下的恒定值，从而表明存在无间隙的低能量自旋激发。我们阐明了它们的性质在三轴非弹性中子散射实验，精确定位的低能量（$E$ $\leq$ $J_0$ $\sim$ 0.2毫电子伏）的一部分，激发连续存在于低温（$T$ $<$ $J_0$ / $k_B$），但\emph{completely}消失后，升温系统以上$T$ $\gg$ $J_0$ / $k_B$。与$E$ $>$ $J_0$的高能部分相反，低能部分源于最近邻价键的断裂，并在远高于$J_0$ / $k_B$的温度下持续存在，低能部分源于价键的重排，因此来自未配对自旋的传播。我们进一步将这一图景扩展到赫伯史密斯，在戈薇晶格上的自旋液体候选者，并认为这种磁激发的层次结构可能是量子自旋液体的普遍特征。
英文摘要：
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.
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