Quantum Phase Transition in Quantum Spin Liquid Candidate Ce2Zr2O7

The interplay between symmetry and topology is a major theme of condensed matter physics. Nontrivial realization of symmetries has led to various states with different macroscopic quantum coherence. Among them, quantum spin liquid (QSL) state, which has no conventional order parameter associated with broken symmetry, can emerge in insulators containing localized spin degrees of freedom. Practically, QSL states are characterized by a fractionalized spin excitation that can be revealed by inelastic neutron scattering. A key consequence of QSL scenario is the presence of a quantum phase transition in the applied magnetic field. Such a transition is required to remove the fractionalized excitation from the spectrum. At a low field and temperature, the QSL state may support exotic excitations like magnetic monopoles, while in a higher field, the ground state is a spin-polarized ferromagnet.

对称性与拓扑的相互作用是凝聚态物理的核心研究主题之一。对称性的非平庸实现催生了多种具有不同宏观量子相干性的物态。其中，量子自旋液体（quantum spin liquid, QSL）态不存在与对称性破缺相关的传统序参量，可在带有局域自旋自由度的绝缘体中涌现。实际表征中，QSL态以分数化自旋激发为核心特征，这类激发可通过非弹性中子散射实验观测得到。QSL物理图像的一个关键推论是，在外加磁场下会发生量子相变，该相变需将分数化激发从体系的能谱中移除。在低场与低温条件下，QSL态可支持磁单极子等新奇激发；而当磁场升高至更高区间时，其基态将转变为自旋极化铁磁体。