The recently discovered superconductor, ${\mathrm{UTe}}_2$, has attracted immense scientific interest due to observations that suggest odd-parity superconductivity. It is believed that the material is a heavy-fermion metal at low temperatures although details of the normal state are unclear. Using Fourier transform infrared spectroscopy, we investigated the normal state electronic structure of ${\mathrm{UTe}}_2$ at zero applied magnetic field. Combining the measured reflectivity with the dc resistivity, the complex optical conductivity was obtained over a large frequency range. The frequency dependence of the real part of the optical conductivity exhibits a MIR peak around 4000 ${\mathrm{cm}}^{-1}$ and a narrow Drude peak that develops below 40 K. A combination of density functional and dynamic mean-field theory gives spectra in close correspondence to the experiment. Via this comparison we attribute the prominent MIR peak to interband transitions involving a narrow U $5f$ feature that develops near the Fermi level. In this regard, this comparison along with data that shows the scale of the low-temperature mass renormalization gives spectroscopic evidence for the existence of a low-energy Kondo resonance at temperatures just above the onset of superconductivity and implicates heavy electrons in the formation of the superconducting state. We find that the coherent Kondo resonance is primarily associated with a collapse of scattering and less with a transfer of spectral weight.

中文翻译：

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超导UTe2中重费米子正常态的光学研究

最近发现的超导体，${\mathrm{尿路}}_2$，由于观测表明奇宇称超导性，引起了巨大的科学兴趣。尽管正常状态的细节尚不清楚，但人们认为该材料在低温下是一种重费米子金属。使用傅里叶变换红外光谱，我们研究了正常状态的电子结构${\mathrm{尿路}}_2$在零外加磁场。将测得的反射率与直流电阻率相结合，可以在很大的频率范围内获得复光导率。光导率实部的频率依赖性在 4000 附近呈现出 MIR 峰${\mathrm{厘米}}^{-1}$和一个在 40 K 以下发展的窄 Drude 峰。密度泛函和动态平均场理论的结合给出了与实验密切对应的光谱。通过这种比较，我们将突出的 MIR 峰归因于涉及窄 U 的带间跃迁$5F$在费米能级附近发展的特征。在这方面，这种比较以及显示低温质量重整化规模的数据为在略高于超导开始的温度下存在低能 Kondo 共振提供了光谱证据，并暗示重电子的形成超导状态。我们发现相干近藤共振主要与散射的崩溃有关，而与光谱权重的转移有关。