Using finite temperature strong coupling expansions for the SU(N) Hubbard Model, we calculate the thermodynamic properties of the model in the infinite-$U$ limit for arbitrary density $0\leq ρ\leq 1$ and all $N$. We express the ferromagnetic susceptibility of the model as a Curie term plus a $Δχ$, an excess susceptibility above the Curie-behavior. We show that, on a bipartite lattice, graph by graph the contributions to $Δχ$ are non-negative in the limit that the hole density $δ=1-ρ$ goes to zero. By summing the contributions from all graphs consisting of closed loops we find that the low hole-density ferromagnetic susceptibility diverges exponentially as $\exp{Δ/T}$ as $T \to 0$ in two and higher dimensions. This demonstrates that Nagaoka-Thouless ferromagnetic state exists as a thermodynamic state of matter at low enough density of holes and sufficiently low temperatures. The constant $Δ$ scales with the SU(N) parameter $N$ as $1/N$ implying that ferromagnetism is gradually weakened with increasing $N$ as the characteristic temperature scale for ferromagnetic order goes down.
Finite-temperature properties of extended Nagaoka ferromagnetism
Advanced Science Research Center, Japan Atomic Energy Agency（日本原子力机构先进科学研究中心）；Department of Physics, Graduate School of Science, The University of Tokyo（东京大学理学研究科物理学系）
Instability of Nagaoka State and Quantum Phase Transition via Kinetic Frustration Control
Emory University（埃默里大学）；California State University, Northridge（北岭加州州立大学）；Institute of Quantum Information and Matter（量子信息与物质研究所）；California Institute of Technology（加州理工学院）；Department of Physics, Florida State University（佛罗里达州立大学物理系）；National High Magnetic Field Laboratory（国家高磁场实验室）
Exact Nagaoka-to-spiral transition in the doped infinite-U triangular lattice
Department of Physics and Astronomy, University of Tennessee（田纳西大学物理与天文系）；Min H. Kao Department of Electrical Engineering and Computer Science, University of Tennessee（田纳西大学明浩高电气与计算机工程系）；Shull Wollan Center, Oak Ridge National Laboratory（橡树岭国家实验室肖尔-沃伦中心）
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。
Theory and simulations of critical temperatures in CrI3 and other 2D materials: Easy-axis magnetic order and easy-plane Kosterlitz-Thouless transitions
Carrier Density and Thickness Dependent Proximity Effect in Doped Topological Insulator -- Metallic Ferromagnet Bilayers
利用磁导率研究了磁邻近效应对掺杂拓扑绝缘体表面态的影响。我们的双层由一层Fe $_7$ Se $_8$，这是一种金属亚铁磁体和一层Bi $_{0.8}$ Sb $_{1.2}$ Te $_{3}$，这是一种高度空穴掺杂的拓扑绝缘体。利用输运测量和修改后的Hikami-Larkin-Nagaoka模型，我们表明，铁磁体显着缩短表面态的有效相干长度，这表明在狄拉克点处打开了一个间隙。我们表明，磁感应间隙持续的表面状态，从磁铁分开的拓扑绝缘体层厚为170 [nm]。此外，发现间隙的大小与我们从反常霍尔效应中提取的磁化强度成正比。我们的结果给出了拓扑绝缘体/铁磁体双层膜中载流子密度、感生磁化强度和磁感应能隙之间的关系。这些信息对于拓扑绝缘体中磁相互作用的理论理解和这种双层的实际制造都是重要的，这是各种建议技术的基础，如自旋电子器件，远红外探测器等。
