We consider a microscopic model for a doped quantum ferromagnet as a test case for the systematic low-energy effective field theory for magnons and holes, which is constructed in complete analogy to the case of quantum antiferromagnets. In contrast to antiferromagnets, for which the effective field theory approach can be tested only numerically, in the ferromagnetic case both the microscopic and the effective theory can be solved analytically. In this way the low-energy parameters of the effective theory are determined exactly by matching to the underlying microscopic model. The low-energy behavior at half-filling as well as in the single- and two-hole sectors is described exactly by the systematic low-energy effective field theory. In particular, for weakly bound two-hole states the effective field theory even works beyond perturbation theory. This lends strong support to the quantitative success of the systematic low-energy effective field theory method not only in the ferromagnetic but also in the physically most interesting antiferromagnetic case.
Orbital Ordering Induced Antiferromagnetic Spin Fluctuations in the Ferromagnetic State of 50 % Hole-doped Manganites: Pr{1/2}Sr{1/2}MnO3 and Nd{1/2}Sr{1/2}MnO3
Efficiency of Continuous-Time Quantum Monte Carlo Updates in the Ferromagnetic State of the Doped SU(3) Fermi-Hubbard Model
Institute of Science Tokyo（东京科学大学）；Osaka Metropolitan University（大阪公立大学）；Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP)（南部阳一郎理论与实验物理研究所）；Chuo University（中央大学）
Superconductivity and Ferromagnetism in Hole-Doped RbEuFe$_4$As$_4$
我们发现砷化铁RbEuFe $_4$ As $_4$具有强的超导性和铁磁性共存。新材料在RbFe $_2$ As $_2$和EuFe $_2$ As $_2$的共生结构中结晶，使得Eu子晶格变成原始的，而不是EuFe $_2$ As $_2$中的体心。FeAs层的特征在于不对称的As配位，由于电荷均匀化而被空穴掺杂。我们的电输运，磁化强度和热容量的综合测量明确和一致地表明在36.5 K的FeAs层和铁磁性在15 K的Eu亚晶格的体超导性。有趣的是，Eu自旋铁磁有序属于一个罕见的三级转变，根据相变的Escherfest分类。我们还确定了一个额外的异常在$\sim$ 5 K，这可能是与超导性和铁磁性之间的相互作用。
Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridate Y2Ir2O7
烧绿石铱酸盐在凝聚态物理中具有实现新拓扑态的潜力，近年来引起了人们越来越多的兴趣。为了获得这样的量子态，理解这些化合物的磁性是非常必要的，因为它们的电子结构与它们的磁性基态是强耦合的。在这项工作中，我们报告了一个系统的研究烧绿石Y2 Ir 2 O 7及其空穴掺杂化合物的磁性进行磁，电子自旋共振，电输运，和X射线光电子能谱学（XPS）测量。我们证明了在未掺杂的化合物中，在大的反铁磁背景之上存在弱铁磁性。空穴掺杂钙被发现，以提高铁磁性和导电性。XPS分析表明，在未掺杂的化合物中，Ir 4+和Ir 5+共存，并且随着Ca的掺杂，Ir 5+的含量增加，这说明了Ir 5+形成的弱铁磁性的可能来源.我们还观察到场冷后M-H曲线的垂直移动，这可能是由于铁磁相和反铁磁背景之间的强耦合.
Exotic superconductivity in the doped Kitaev quantum spin liquid
Institute for Solid State Physics, University of Tokyo（东京大学固体物理研究所）；Department of Applied Science, Graduate School of Sciences and Technology for Innovation, Yamaguchi University（山口大学理工学综合研究科应用科学系）
