量子自旋冰中涌现激发的热力学光谱学
Thermodynamic Spectroscopy of Emergent Excitations in Quantum Spin Ice
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中文总结 AI 辅助
本研究针对量子自旋冰的环交换尺度，提出利用热膨胀系数差或磁化温度导数的热力学探测方案，可区分其零通量与π通量态，解决了涌现激发探测的难题。
中文摘要 AI 辅助
量子自旋冰（QSI）是一种三维量子自旋液体，其中分数化的自旋子与涌现光子相互作用。烧绿石晶格上的XXZ模型实现了这类U(1)量子自旋液体，众多烧绿石磁体已被作为候选材料开展研究，但涌现激发的探测一直是一项重大挑战。预期比热会呈现高能自旋子激发，以及在环交换尺度处的低能反常，该尺度同时决定了光子带宽和涌现磁单极子（或 vison）的能量。实际中，低能峰在基于非克拉默斯Pr的体系中被核肖特基反常掩盖，而在基于Ce的偶极-八极体系中则无法与自旋子贡献清晰区分。本研究提出一种针对难以捉摸的环交换尺度的新型热力学探测方法：当存在与赝自旋自由度横向分量耦合的弱微扰时，与该弱微扰力共轭的可观测量的温度导数对环交换尺度高度敏感。采用该方案，对于非克拉默斯QSI，沿[100]和[010]方向的热膨胀系数之差应在环交换尺度处出现峰值；类似地，在弱磁场下，偶极-八极烧绿石的磁化强度温度导数dM/dT也可探测到相同信号，且这些特征的符号可区分零通量和π通量QSI态。
英文摘要
Quantum spin ice (QSI) is a three-dimensional quantum spin liquid where fractionalized spinons interact with emergent photons. The XXZ model on the pyrochlore lattice realizes such a $U(1)$ quantum spin liquid and a number of pyrochlore magnets have been investigated as candidate materials, but the detection of emergent excitations has been a major challenge. The specific heat is expected to show the higher-energy spinon excitations and a lower-energy anomaly at the ring-exchange scale, which sets both the photon bandwidth and the energy of the emergent magnetic monopoles (or visons). In reality, the lower-energy peak is obscured by the nuclear Schottky anomaly in non-Kramers Pr-based systems, while it is not clearly resolved from the spinon contributions in Ce-based dipolar-octupolar systems. In this work, we propose a novel thermodynamic probe of the elusive ring-exchange energy scale. We show that in the presence of a weak perturbation coupled to the transverse component of the pseudospin degrees of freedom, the temperature derivative of an observable conjugate to such a weak perturbing force is highly sensitive to the ring-exchange energy scale. Using this scheme, it is shown that the difference between thermal expansion coefficients along the [100] and [010] directions should show a peak at the ring-exchange energy scale for non-Kramers QSI. Similarly, the temperature derivative of the magnetization, $dM/dT$, of dipolar-octupolar pyrochlores under a weak magnetic field can also detect the same signal. Moreover, the sign of these signatures distinguishes the zero-flux and $π$-flux QSI states.
