铁基超导体多轨道模型中的电子关联与轨道选择

大部分铁基超导体的正常态呈现坏金属行为, 这表明体系中存在较强的电子关联效应. 最近的实验与理论研究显示, 铁基超导体中的电子关联具有多轨道的特征. 本文介绍与评论铁基超导体多轨道哈伯德模型中电子关联方面理论研究的最新进展; 着重讨论以隶自旋技术为代表的一系列量子多体计算方法在研究多轨道系统中金属绝缘体相变的应用. 理论计算给出了铁基超导体多轨道哈伯德模型基于电子关联的基态相图. 在对应母体化合物的电子填充数时, 基态存在从金属到绝缘体的莫特转变. 临近莫特转变, 体系呈现坏金属行为; 其电子性质存在较强的轨道选择性. 轨道选择性的强弱与体系中的洪德耦合和轨道的晶体场劈裂密切相关. 对钾铁硒系统, 研究发现其基态相图存在轨道选择莫特相: 其中铁的3d xy轨道已被莫特局域化, 但其他3d轨道电子仍具有巡游性. 这一新相的发现, 对理解以钾铁硒为代表的一大类铁基超导体正常态与超导之间的联系提供了重要线索.     

Dynamical signatures of the one-dimensional deconfined quantum critical point

We study the critical scaling and dynamical signatures of fractionalized excitations at two different deconfined quantum critical points (DQCPs) in an S = 1/2 spin chain using the time evolution of infinite matrix product states. The scaling of the correlation functions and the dispersion of the conserved current correlations explicitly show the emergence of enhanced continuous symmetries at these DQCPs. The dynamical structure factors in several different channels reveal the development of deconfined fractionalized excitations at the DQCPs. Furthermore, we find an effective spin-charge separation at the DQCP between the ferromagnetic (FM) and valence bond solid (VBS) phases, and identify two continua associated with different types of fractionalized excitations at the DQCP between the X-direction and Z-direction FM phases. Our findings not only provide direct evidence for the DQCP in one dimension but also shed light on exploring the DQCP in higher dimensions.     

Effective model for rare-earth Kitaev materials and its classical Monte Carlo simulation

Recently, the family of rare-earth chalcohalides were proposed as candidate compounds to realize the Kitaev spin liquid (KSL) [Chin. Phys. Lett. 38 047502 (2021)]. In the present work, we firstly propose an effective spin Hamiltonian consistent with the symmetry group of the crystal structure. Then we apply classical Monte Carlo simulations to preliminarily study the model and establish a phase diagram. When approaching to the low temperature limit, several magnetic long range orders are observed, including the stripe, the zigzag, the antiferromagnetic (AFM), the ferromagnetic (FM), the incommensurate spiral (IS), the multi-Q, and the 120° ones. We further calculate the thermodynamic properties of the system, such as the temperature dependence of the magnetic susceptibility and the heat capacity. The ordering transition temperatures reflected in the two quantities agree with each other. For most interaction regions, the system is magnetically more susceptible in the ab-plane than in the c-direction. The stripe phase is special, where the susceptibility is fairly isotropic in the whole temperature region. These features provide useful information to understand the magnetic properties of related materials.