论文标题
石墨烯中的Skyrmion动物园在强磁场中的电荷中立性
Skyrmion zoo in graphene at charge neutrality in a strong magnetic field
论文作者
论文摘要
由于石墨烯中的近似自旋谷对称性，在电荷中立的石墨烯中电子的基态是特定的su（4）量子 - 量子孔铁磁铁，以最大程度地减少其交换能量。如果仅考虑了库仑的相互作用，则该铁磁铁可以提高自由度的自由度或等效于山谷伪自由度的自由度。然后，选择的自由会受到明确打破SU（4）对称性的转向型能量尺度的限制，最简单的是由Zeeman效应给出的，该效应使旋转在磁场方向上表现为旋转。另外，还可能由短程相互作用或电子 - 音波耦合引起山谷对称性术语。在这里，我们建立在相图上，该相图已由Kharitonov [Phys。 Rev. B \ TextBf {85}，155439（2012）]，以识别与这些类型的量子座Ferromagnets兼容的不同天空。与Ferromagnet类似，电荷中立性的天际含量由中心的$ \ text {gr}（2,4）$ Grassmannian描述，这使我们能够构建Skyrmion Spinors。然后，就其余的自由参数而在不固定的剩余自由参数中，从其中心远距离固定的剩余自由参数就可以在变异方法中最小化其能量，从而获得了不同的天空类型。我们表明，不同的天空类型在局部，sublattice分辨的自旋磁化强度中具有明显的特征，在扫描键盘显微镜和光谱中原则上可以访问。
As a consequence of the approximate spin-valley symmetry in graphene, the ground state of electrons in graphene at charge neutrality is a particular SU(4) quantum-Hall ferromagnet to minimize their exchange energy. If only the Coulomb interaction is taken into account, this ferromagnet can appeal either to the spin degree of freedom or equivalently to the valley pseudo-spin degree of freedom. This freedom in choice is then limited by subleading energy scales that explicitly break the SU(4) symmetry, the simplest of which is given by the Zeeman effect that orients the spin in the direction of the magnetic field. In addition, there are also valley symmetry breaking terms that can arise from short-range interactions or electron-phonon couplings. Here, we build upon the phase diagram, which has been obtained by Kharitonov [Phys. Rev. B \textbf{85}, 155439 (2012)], in order to identify the different skyrmions that are compatible with these types of quantum-Hall ferromagnets. Similarly to the ferromagnets, the skyrmions at charge neutrality are described by the $\text{Gr}(2,4)$ Grassmannian at the center, which allows us to construct the skyrmion spinors. The different skyrmion types are then obtained by minimizing their energy within a variational approach, with respect to the remaining free parameters that are not fixed by the requirement that the skyrmion at large distances from their center must be compatible with the ferromagnetic background. We show that the different skyrmion types have a clear signature in the local, sublattice-resolved, spin magnetization, which is in principle accessible in scanning-tunneling microscopy and spectroscopy.
