| 中文题名： | NaYbSe2量子自旋液体态的中子散射研究 |
| 姓名： | |
| 保密级别： | 公开 |
| 论文语种： | 中文 |
| 学科代码： | 070205 |
| 学科专业： | |
| 学生类型： | 硕士 |
| 学位： | 理学硕士 |
| 学位类型： | |
| 学位年度： | 2021 |
| 校区： | |
| 学院： | |
| 研究方向： | 关联电子材料的中子散射研究 |
| 第一导师姓名： | |
| 第一导师单位： | |
| 提交日期： | 2021-06-07 |
| 答辩日期： | 2021-06-01 |
| 外文题名： | Neutron Scattering Investigations on Quantum Spin Liquid State of NaYbSe2 |
| 中文关键词： | |
| 外文关键词： | Quantum spin liquid ; Geometric frustration ; Spinon ; Neutron scattering ; Magnetic excitation continuum |
| 中文摘要： |
量子自旋液体是体系内未配对电子的自旋长程高度纠缠，但即使温度到达零温极限也不会有磁序形成的一种新奇基态。这一新奇基态没有任何自发的对称性破缺和相应的序参量，超越了传统朗道相变理论的描述范畴，对量子物理的理解非常重要。此外，量子自旋液体被认为与非常规超导机制密切相关，有助于对高温超导微观起源的理解，同时在量子计算方面也有重要的应用前景，因此吸引了大量研究者的兴趣。 具有-1/2有效自旋的稀土离子三角晶格体系存在强的自旋轨道耦合、晶体场以及几何阻挫作用，是探索量子自旋液体的理想平台。Yb离子化合物NaYbCh2(Ch= O, S, Se)中Yb3+构成了完美的三角晶格层，被认为是量子自旋液体的候选材料。已经有关于NaYbCh2的热输运，核磁共振和粉末中子散射测量结果表明该体系具有量子自旋液体的特征，但量子自旋液体的关键特征—由自旋量子数分数化引起的自旋激发连续谱还没有被观察到。因此本文开展了对高质量NaYbSe2单晶的磁性、热输运以及弹性和非弹性中子散射测量，进一步对NaYbCh2的基态性质进行研究，主要研究结果包括：1. 磁性和热输运测量结果都表明温度降至40mK仍没有观察到长程磁有序现象，且不存在自旋冻结；低温下磁比热的数据支持自旋子费米面的存在。2. 弹性中子散射结果进一步证实了低温下磁序的缺失；非弹性中子散射观察到的磁激发连续谱(从0.1meV持续到2.5meV)为量子自旋液体提供了关键的证据。3. 自旋激发谱具有“V”形上边界以及低能下具有高的态密度都符合具有自旋子费米面的量子自旋液体的特征，表明NaYbSe2是具有自旋子费米面的量子自旋液体。 |
| 外文摘要： |
Quantum spin liquid is an exotic state in which the spins of the unpaired electrons are highly entangled over long distances, yet they do not exhibit any long-range magnetic order in the zero temperature limit. Such a phase is not involved in any spontaneous symmetry breaking and specific order parameters, it is beyond the traditional Landau phase transition theory and is fundamentally important in understanding quantum physics. In addition, it is proposed that QSL is closely relevant to the unconventional superconducting mechanism, which is helpful to understand the origin of high-temperature superconductivity. And it also has important application prospects in quantum computing, so it has attracted the interest of many researchers. Triangular lattice of rare-earth ions with interacting effective spin-1/2 local moments is an ideal platform to explore the physics of quantum spin liquids (QSLs) in the presence of strong spin-orbit coupling, crystal electric fields, and geometrical frustration. The Yb delafossites, NaYbCh2 (Ch=O, S, Se) with Yb ions forming a perfect triangular lattice, have been suggested to be candidates for QSLs. Previous thermodynamics, nuclear magnetic resonance, and powder-sample neutron scattering measurements on NaYbCh2 have supported the suggestion of the QSL ground states. The key signature of a QSL, the spin excitation continuum, arising from the spin quantum number fractionalization, has not been observed. In this paper, we carried out the measurements of the magnetic, thermal transport and elastic and inelastic neutron scattering on high-quality NaYbSe2 single crystals, in order to further explore the ground state properties of NaYbCh2. The main research conclusions include: 1. The magnetic and thermal transport measurement results confirm the absence of long-range magnetic order down to 40mK, and there is no spin freezing; the data of magnetic specific heat at low temperature supports the existence of the spin Fermi surface. 2. The results of elastic neutron scattering further confirm the lack of magnetic order at low temperatures; The continuous magnetic excitation spectrum (from 0.1 meV to 2.5 meV) observed in inelastic neutron scattering measurements provides key evidence for quantum spin liquids. 3. The V-shaped upper bound structure of the spin excitation spectral and a high density of spinon scattering states at low energies are consistent with the characteristics of quantum spin liquid with spinon Fermi surface, which suggests that the ground state of NaYbSe2 is a QSL with a spinon Fermi surface. |
| 参考文献总数： | 70 |
| 作者简介： | 学术成果：Dai P L, Zhang G, Xie Y, et al. Spinon Fermi surface spin liquid in a triangular lattice antiferromagnet NaYbSe2[J]. 2021, Physical Review X, 11, 021044. |
| 馆藏号： | 硕070205/21024 |
| 开放日期： | 2022-06-08 |
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