Fractional matter coupled to the emergent gauge field in a quantum spin ice
Fractional matter coupled to the emergent gauge field in a quantum spin ice
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2023-04
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通讯作者：
Victor Por'ee;Han Yan;Félix Desrochers;S. Petit;E. Lhotel;M. Appel;J. Ollivier;Yong Baek Kim;A. Nevidomskyy;R. Sibille
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作者：
Victor Por'ee;Han Yan;Félix Desrochers;S. Petit;E. Lhotel;M. Appel;J. Ollivier;Yong Baek Kim;A. Nevidomskyy;R. Sibille
电子自旋可以形成凝聚态物质的长程纠缠相，称为量子自旋液体。它们的存在是在二维或三维受挫磁体模型中概念化的，这些磁体可以避开低至零温度的对称破缺秩序。量子自旋冰（QSI）是由新兴量子电动力学描述的理论上成熟的例子，其激发行为类似于光子和物质准粒子。后者是分数带电的，相当于一维单线态相干相中出现的“自旋子”，存在明确的分数化实验证明。然而，在受挫磁体中，仍然很难为量子自旋液体基态及其分数激发建立一致的证据。在这里，我们使用背散射中子光谱来实现候选 QSI 材料 Ce$_2$Sn$_2$O$_7$ 的时间相关磁响应的极高分辨率。我们发现了一个带隙光谱，其特征是阈值和峰值与与背景规范场强耦合的分数物质激发（自旋子）的配对产生和传播理论相匹配。多个峰是 QSI 的 $\pi$-通量相的特定特征，为三维量子自旋液体中的分级提供了光谱证据。
Electronic spins can form long-range entangled phases of condensed matter named quantum spin liquids. Their existence is conceptualized in models of two- or three-dimensional frustrated magnets that evade symmetry-breaking order down to zero temperature. Quantum spin ice (QSI) is a theoretically well-established example described by an emergent quantum electrodynamics, with excitations behaving like photon and matter quasiparticles. The latter are fractionally charged and equivalent to the `spinons' emerging from coherent phases of singlets in one dimension, where clear experimental proofs of fractionalization exist. However, in frustrated magnets it remains difficult to establish consensual evidence for quantum spin liquid ground states and their fractional excitations. Here, we use backscattering neutron spectroscopy to achieve extremely high resolution of the time-dependent magnetic response of the candidate QSI material Ce$_2$Sn$_2$O$_7$. We find a gapped spectrum featuring a threshold and peaks that match theories for pair production and propagation of fractional matter excitations (spinons) strongly coupled to a background gauge field. The multiple peaks are a specific signature of the $\pi$-flux phase of QSI, providing spectroscopic evidence for fractionalization in a three-dimensional quantum spin liquid.