While many physical properties of graphene can be understood qualitatively on the basis of bare Dirac bands, there is specific evidence that electron-electron (EE) and electron-phonon (EP) interactions can also play an important role. We discuss strategies for extracting separate images of the EE and EP interactions as they present themselves in the electron spectral density and related self-energies. While for momentum, $k$, equal to its Fermi value, $k_F$, a composite structure is obtained which can be difficult to separate into its two constituent parts, at smaller values of $k$ the spectral function shows distinct incoherent sidebands on the left and right of the main quasiparticle line. These image respectively the EE and EP interactions, each being most prominent in its own energy window. We employ a maximum entropy inversion technique on the self energy to reveal the electron-phonon spectral density separate from the excitation spectrum due to coulomb correlations. Our calculations show that this technique can provide important new insights into inelastic scattering processes in graphene.
The ground state of clean and defected graphene: Coulomb interactions of massless Dirac fermions, pair-distribution functions and spin-polarized phases
Nonreciprocal perfect Coulomb drag in electron-hole bilayers: coherent exciton superflow as a diode
Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University（上海交大李政道研究所与物理与天文学院）；Shanghai Branch, Hefei National Laboratory（合肥国家实验室上海分部）
Tilted-Cone-induced easy-plane pseudo-spin ferromagnet and Kosterlitz-Thouless transition in massless Dirac fermions
本文研究了在压力作用下二维无质量Dirac费米子在填充因子为$ν=0$的情况下的量子Hall铁磁体，其中二维Dirac费米子在压力作用下具有斜锥和时间反演对称性导致的双重谷简并，在$α$ -（BEDT-TTF）$_2$ I $_3$中的零能（N=0）朗道能级.在没有倾斜的狄拉克锥的情况下，N=0朗道能级中的长程库仑相互作用表现出SU（2）谷赝自旋对称性，甚至达到$O(a/l_{\rm H})$级，这与$N \ne 0$朗道能级相反，其中$a$和$l_{\rm H}$分别代表晶格常数和磁长度。这种特性来自于这样一个事实，即在特定谷中的零能态仅限于其中一个旋量分量，而另一个旋量分量必然为零。在$α$ -（BEDT-TTF）$_2$ I $_3$中发现的倾斜狄拉克锥的情况下，人们得到第二分量的非零值，然后谷之间的ack散射过程变得非零。结果表明，这一事实可以导致易平面赝自旋铁磁性（XY型）。在这种情况下，序参量的相位起伏可以用XY模型来描述，导致在较低温度下的Kosterlitz-无相变。根据这些理论结果，讨论了$α$ -（BEDT-TTF）$_2$ I $_3$的电阻率实验结果。
Excitonic instability of two-dimensional tilted Dirac cones
Dirac-Weyl半金属中的电子-电子库仑相互作用包含了一种新的关联效应范式，它将固态物理的不同领域与相对论对应物杂交。强相互作用的无质量狄拉克费米子的激子凝聚驱动自发质量获取就是这样一个例子，其确切性质仍有争议。在这里，通过聚焦于二维倾斜狄拉克锥的有机盐$α$ -（BEDT-TTF）$_2$ I $_3$，我们表明，激子的不稳定性是由一个小的化学势移动和面内磁场控制。在基于重整化群方法和梯形近似的联合分析中，我们证明了核弛豫速率是扩展参数区域中激子自旋涨落的一个很好的探针。比较核磁共振（NMR）的实验表明，这一结果很好的协议，共同揭示了场诱导，自旋分裂费米口袋相反的电荷极性之间的谷间嵌套的重要性。我们的工作为寻找强相互作用无质量费米子的激子不稳定性提供了一个精确的框架。
