自旋梯磁体中的超低场三重子凝聚
Ultralow-Field Triplon Condensation in a Spin-Ladder Magnet
AI总结：
本研究在自旋梯磁体Henmilite中首次实现超低场三重子玻色-爱因斯坦凝聚，结合多种实验测量与量子蒙特卡洛模拟，推翻零场反铁磁序的原有结论，揭示量子无序耦合梯母态及非对称有序穹顶，拓展了超低场三重子凝聚的研究范畴。
AI中文摘要：
我们在自旋梯磁体中首次实现了三重子的超低场玻色-爱因斯坦凝聚，在蓝铜矾（$\mathrm{Ca_2Cu(OH)_4[B(OH)_4]_2}$）中发现了仅为$μ_0 H_{c1}=0.17$ T的量子临界点。与二聚体磁体不同，自旋梯在其有能隙母态中保留了延伸的一维关联，使得这一极限区域以强涨落为主导。热力学测量、磁弹性测量、$μ$SR以及中子衍射测量推翻了此前关于零场反铁磁序的结论，确立了具有持续低能动力学的量子无序耦合梯母态。而微弱的低温反常现象标志着从关联梯区域到激活型量子无序态的能隙受控渡越。这些测量进一步揭示了一个延伸至$μ_0 H_{c2}\simeq 8.2$ T的极度不对称的有序穹顶。针对相关自旋哈密顿量开展的量子蒙特卡洛模拟表明，蓝铜矾恰好处于零场梯序不稳定性的有能隙一侧，这自然解释了交换尺度与剩余能隙尺度之间的巨大差异以及极小的临界场。我们的研究将超低场三重子凝聚拓展到了二聚体范式之外，并确立蓝铜矾作为在涨落主导的自旋梯中实现跨量子临界态可控调控的研究平台。
英文摘要：
We realise the first ultralow-field Bose-Einstein condensation of triplons in a spin-ladder magnet, uncovering a quantum critical point at only $μ_0 H_{c1}=0.17$ T in Henmilite ($\mathrm{Ca_2Cu(OH)_4[B(OH)_4]_2}$). Unlike dimer magnets, a ladder retains extended one-dimensional correlations in its gapped parent state, making this limit strongly fluctuation dominated. Thermodynamic, magnetoelastic, $μ$SR, and neutron-diffraction measurements overturn the previous assignment of zero-field antiferromagnetic order, establishing a quantum-disordered coupled-ladder parent state with persistent low-energy dynamics. The weak low-temperature anomaly instead marks a gap-controlled crossover from the correlated ladder regime into the activated quantum-disordered state. These measurements further reveal an exceptionally asymmetric ordered dome extending to $μ_0 H_{c2}\simeq 8.2$ T. Quantum Monte Carlo simulations for the relevant spin Hamiltonian place Henmilite just on the gapped side of the zero-field ladder-ordering instability, naturally accounting for the strong separation between the exchange and residual-gap scales and the tiny critical field. Our findings extend ultralow-field triplon condensation beyond the dimer paradigm and establish Henmilite as a platform for controlled tuning across quantum criticality in a fluctuation-dominated spin ladder.
