三维双分网络中的量子自旋液体：通过增强的有效各向异性稳定
Quantum spin liquid on a 3D bipartite lattice of spin trimers stabilized by enhanced effective anisotropy
AI总结：
研究通过增强的有效各向异性稳定了三维双分网络中的量子自旋液体，发现KBa$_3$Ca$_4$Cu$_3$V$_7$O$_{28}$具有强耦合的Cu$^{2+}$三元组，形成有效伪自旋-1/2自由度，表现出无序的动态基态。
摘要：
量子自旋液体（QSLs）代表高度纠缠的物质状态，在其中因摩擦导致的量子涨落抑制了任何对称破缺相变，直到绝对零度，产生分数化激发和涌现的规范场。理论上，键各向异性可以在双分晶格上稳定QSLs，如Kitaev蜂窝模型所示；然而，至今尚未有材料能实现这种状态作为真实基态。本文识别了三维自旋三元磁体KBa$_3$Ca$_4$Cu$_3$V$_7$O$_{28}$作为双分量子自旋液体的候选材料。强耦合的Cu$^{2+}$三元组在冷却时形成有效的伪自旋-1/2自由度，进而构成三维双分网络。体热力学测量、中子散射、μSR和NMR检测到20 mK下无自旋冻结或对称破缺相变，但揭示了无能隙的动态基态，具有代数自旋自相关性。互补的蒙特卡罗和精确对角化计算显示，这种状态通过强增强的有效各向异性稳定：弱的微观Cu-Cu交换各向异性约为15%，在三元组水平上普遍放大，产生有效的伪自旋-伪自旋相互作用各向异性为60到100%。我们的结果表明，基于三元组的网络是实现各向异性稳定量子纠缠态的有前景平台，即使在只有弱微观各向异性的三维双分系统中。
英文摘要：
Quantum spin liquids (QSLs) represent highly entangled states of matter in which frustration-induced quantum fluctuations suppress any symmetry-breaking phase transition down to absolute zero, giving rise to fractionalized excitations and emergent gauge fields. Theoretically, bond anisotropy can stabilize QSLs even on bipartite lattices, as exemplified by the Kitaev honeycomb model; however, no material has so far been established to realize such a state as its true ground state. Here we identify the three-dimensional spin-trimer magnet KBa$_3$Ca$_4$Cu$_3$V$_7$O$_{28}$ as a promising candidate for a bipartite quantum spin liquid persisting to the lowest temperatures. Strongly coupled Cu$^{2+}$ trimers form effective pseudospin-1/2 degrees of freedom upon cooling, which in turn constitute a three-dimensional bipartite network. Bulk thermodynamic measurements, neutron scattering, $μ$SR, and NMR detect no spin freezing or symmetry-breaking phase transition down to 20 mK, but instead reveal a gapless dynamical ground state with algebraic spin autocorrelations. Complementary Monte Carlo and exact-diagonalization calculations show that this state is stabilized by a strong enhancement of effective anisotropy: a weak microscopic Cu-Cu exchange anisotropy of approximately 15 percent is generically amplified at the trimer level, producing effective pseudospin-pseudospin interaction anisotropies of 60 to 100 percent. Our results establish trimer-based networks as a promising platform for realizing anisotropy-stabilized quantum entangled states, even in three-dimensional bipartite systems with only weak microscopic anisotropy.
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