Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
Phys Rev Lett. 2018 May 25;120(21):217205. doi: 10.1103/PhysRevLett.120.217205.
The Kitaev quantum spin liquid displays the fractionalization of quantum spins into Majorana fermions. The emergent Majorana edge current is predicted to manifest itself in the form of a finite thermal Hall effect, a feature commonly discussed in topological superconductors. Here we report on thermal Hall conductivity κ_{xy} measurements in α-RuCl_{3}, a candidate Kitaev magnet with the two-dimensional honeycomb lattice. In a spin-liquid (Kitaev paramagnetic) state below the temperature characterized by the Kitaev interaction J_{K}/k_{B}∼80 K, positive κ_{xy} develops gradually upon cooling, demonstrating the presence of highly unusual itinerant excitations. Although the zero-temperature property is masked by the magnetic ordering at T_{N}=7 K, the sign, magnitude, and T dependence of κ_{xy}/T at intermediate temperatures follows the predicted trend of the itinerant Majorana excitations.
Kitaev 量子自旋液体表现出量子自旋的分数化，形成马约拉纳费米子。预测这种新兴的马约拉纳边缘电流将以有限的热霍尔效应的形式表现出来，这是拓扑超导体中常见的特征。在这里，我们报告了在 α-RuCl_{3}中的热霍尔电导率 κ_{xy}测量结果，α-RuCl_{3}是一种具有二维蜂窝晶格的候选 Kitaev 磁体。在温度低于由 Kitaev 相互作用 J_{K}/k_{B}∼80 K 所特征的自旋液体（Kitaev 顺磁）状态下，随着冷却 κ_{xy}逐渐增大，表明存在非常不寻常的巡游激发。尽管零温特性被 T_{N}=7 K 的磁有序所掩盖，但 κ_{xy}/T 在中间温度的符号、大小和 T 依赖性遵循了巡游马约拉纳激发的预测趋势。
