Taken together, time-reversal and spatial inversion symmetries impose a two-fold spin degeneracy of the electronic states in crystals. In centrosymmetric materials, this degeneracy can be lifted by introducing magnetism, either via an externally applied field or through internal magnetization. However, a correlated alignment of spins, even in the paramagnetic phase, can lift the spin degeneracy of electronic states. Here, we report an in-depth study of the electronic band structure of the Eu-ternary pnictide EuZn2Sb2 through a combination of high-resolution angle-resolved photoemission spectroscopy measurements and first principles calculations. An analysis of the photoemission lineshapes over a range of incident photon energies and sample temperatures is shown to reveal the presence of band spin degeneracy-lifting in the paramagnetic phase. Our ARPES results are in good agreement with theoretical ferromagnetic-phase calculations, which indicates the importance of ferromagnetic fluctuations in the system. Through our calculations, we predict that spin-polarized bands in EuZn2Sb2 generate a single pair of Weyl nodes. Our observation of band-splitting in EuZn2Sb2 provides a key step toward realizing time-reversal symmetry breaking physics in the absence of long-range magnetic order.
Competing orders and cascade of degeneracy lifting in doped Bernal bilayer graphene
最近的实验[H。Zhou，\emph{et al.}，Science { \bf 375}，774（2022）和S. C. de la Barrera，\emph{et al.}，arXiv：2110.13907]，在这里，我们提出了在掺杂的Bernal双层石墨烯中电子带的谷和/或自旋简并提升的一般机制，其受到电位移（$D$）场的影响。$D$ -场诱导层极化（LP），当伴随有哈伯德排斥驱动层反铁磁体（LAF）和次近邻排斥驱动量子反常霍尔（QAH）阶时，提升了电子带的四倍简并性，对于小掺杂产生四分之一金属，如在ABC三层石墨烯中也观察到的。随着QAH阶的消失，电子能带恢复两倍谷简并，从而在中等掺杂下形成常规或补偿（具有多数载流子和少数载流子）半金属，这取决于LP和LAF的相对强度。在更高的掺杂和弱$D$场只有LAF生存和费米面恢复四倍简并。我们还表明，一个纯粹的排斥电子相互作用介导的三重$f$波配对出现从一个父相关的半导体液体或补偿半金属时，在平面磁场施加到系统。
Voltage Dependent Symmetry Breaking Effects in the Spin Excitation Spectrum of Spin-$\frac{1}{2}$ Paramagnetic Molecular Junctions Driven Out of Equilibrium
在目前的工作中，我们考虑的自旋1/2顺磁性二聚体嵌入在磁性隧道结驱动的平衡，通过施加的电压和施加的温度梯度，在存在的外部磁偏置，这可以打开/关闭。在这里，我们推导出的自旋激发光谱的两个自旋1/2系统的分析和显示，需要一个外部的磁场，以解除三重态的简并，无论是两个自旋单位经历的磁场在相同的方向或在相反的交错方向。我们表明，在没有一个磁场的情况下，施加的偏置电压，从磁引线的磁化转移到嵌入在分子中的自旋单元，从而打破了对称性和解除三重态简并在没有外部磁化。在此基础上，我们提出了两种磁驱动方案，分别命名为PMD（Parallel Magnetic Driving）和AMD（Anti-Parallel Magnetic Driving）。我们认为，对称性破缺，然后需要项目的自旋二聚体的配置到量子输运测量，因此提出了不同的计划来检测自旋三重态和自旋单重态的非简并非对称配置的自旋二聚体使用微分电导测量，并比较我们的结果与文献中报道的。
