拓扑绝缘体YBiPt化合物微波趋肤深度内金属表面态的探测
Metallic Surface States Probed Within the Microwave Skin Depth of the Putative Topological Insulator YBiPt Compound
摘要：
报道了稀释Nd $^{3+}$离子在拓扑绝缘体（TI）YBiPt中的电子自旋共振（ESR）实验。研究粒度为$\approx$ 100 $μ$ μ m至$\approx$ 2，000 $μ$ μ m的粉末样品。在低温下，1.6 K $\lesssim$ \emph{T} $\lesssim$ 20 K，X波段（$9.4$ GHz）ESR谱显示\emph{g} -值为2.66（4）和Dysonian共振线形，该线形显示出显著不寻常的温度、浓度、微波功率和粒度依赖性。这些结果表明，在$δ\approx$ 15 $μ$ m的趋肤深度内，金属和绝缘行为共存。此外，在YBiPt中的Nd $^{3+}$自旋动力学与\emph{phonon-bottleneck process}的存在是一致的，其允许由Nd $^{3+}$离子在共振时吸收的能量经由YBiPt的金属表面态中的传导电子到达热浴。这些结果进行了讨论，在声称的拓扑半金属性质的YBiPt。
英文摘要：
Electron Spin Resonance (ESR) experiments of diluted Nd$^{3+}$ ions in the claimed topological insulator (TI) YBiPt are reported. Powdered samples with grain size from $\approx$ 100 $μ$m to $\approx$ 2,000 $μ$m were investigated. At low temperatures, 1.6 K $\lesssim$ \emph{T} $\lesssim$ 20 K, the X-band ($9.4$ GHz) ESR spectra show a \emph{g}-value of 2.66(4) and a Dysonian resonance lineshape which shows a remarkably unusual temperature, concentration, microwave power and particle size dependence. These results indicate that metallic and insulating behavior coexist within a skin depth of $δ\approx$ 15 $μ$m. Furthermore, the Nd$^{3+}$ spin dynamics in YBiPt are consistent with the existence of a \emph{phonon-bottleneck process} which allows the energy absorbed by the Nd$^{3+}$ ions at resonance to reach the thermal bath via the conduction electrons in the metallic surface states of YBiPt. These results are discussed in terms of the claimed topological semi-metal properties of YBiPt.
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