TlCuCl $_3$中的Higgs-Axion相互作用和反常磁phase diagram
Higgs-Axion interplay and anomalous magnetic phase diagram in TlCuCl$_3$
摘要：
TlCuCl 3中有什么独特之处，它驱动了这种化合物中如此多独特的磁性特征？为了研究这些性质，我们采用了从头算能带结构，紧束缚模型，和有效的量子场论的组合。在密度泛函理论（DFT）计算中，我们发现了一个意想不到的没有自旋轨道耦合（SOC）的体狄拉克锥。追溯到它的起源，我们确定，第一次，存在一个苏-Schrieffer-Heeger（SSH）一样的二聚铜链躺在三维晶体结构。SSH链，结合SOC，规定了一个各向异性的3D狄拉克锥的手征和螺旋状态交织在一起。作为海森堡相互作用的介绍，我们表明，二聚铜亚晶格的SSH链冷凝成自旋单重态，二聚磁体。在磁基态，我们也发现了一个拓扑相，区分的轴子角。最后，为了研究拓扑轴子项如何与磁激发耦合，我们从3D SSH Hamilton中推导出Chern-Simons-Ginzburg-Landau作用量。我们发现，轴子项为Higgs模提供了一个附加的质量项，为顺磁子提供了一个寿命项，它们与量子临界物理无关。轴子和希格斯粒子的相互作用可以通过相互平行或反平行的电场和磁场来探测。
英文摘要：
What is so unique in TlCuCl3 which drives so many unique magnetic features in this compound? To study these properties, here we employ a combination of ab-initio band structure, tight-binding model, and an effective quantum field theory. Within a density-functional theory (DFT) calculation, we find an unexpected bulk Dirac cone without spin-orbit coupling (SOC). Tracing back to its origin, we identify, for the first time, the presence of a Su-Schrieffer-Heeger (SSH) like dimerized Cu chain lying in the 3D crystal structure. The SSH chain, combined with SOC, stipulates an anisotropic 3D Dirac cone where chiral and helical states are intertwined. As a Heisenberg interaction is introduced, we show that the dimerized Cu sublattices of the SSH chain condensate into spin-singlet, dimerized magnets. In the magnetic ground state, we also find a topological phase, distinguished by the axion angle. Finally, to study how the topological axion term couples to magnetic excitations, we derive a Chern-Simons-Ginzburg-Landau action from the 3D SSH Hamiltonian. We find that axion term provides an additional mass term to the Higgs mode, and a lifetime to paramagnons, which are independent of the quantum critical physics. The axion-Higgs interplay can be probed with electric and magnetic field applied parallel or anti-parallel to each other.
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