Optical conductivity and vibrational spectra of the narrow-gap semiconductor FeGa${}_3$

Abstract

Intermetallic narrow-gap semiconductors have been intensively explored due to their large thermoelectric power at low temperatures and a possible role of strong electronic correlations in their unusual thermodynamic and transport properties. Here we study the optical spectra and vibrational properties of $\mathrm{FeG}{\mathrm{a}}_3$ single crystal. The optical conductivity indicates that $\mathrm{FeG}{\mathrm{a}}_3$ has a direct band gap of $\sim 0.7$\,eV, consistent with density functional theory (DFT) calculations. Most importantly, we find a substantial spectral weight also below 0.4~eV, which is the energy of the indirect (charge) gap found in resistivity measurements and ab initio calculations. We find that the spectral weight below the gap decreases with increasing temperature, which indicates that it originates from the impurity states and not from the electronic correlations. Interestingly, we did not find any signatures of the impurity states in vibrational spectra. The infrared and Raman vibrational lines are narrow and weakly temperature dependent. The vibrational frequencies are in excellent agreement with our DFT calculations, implying a modest role of electronic correlations. Narrow M\" ossbauer spectral lines also indicate high crystallinity of the sample.

References in corpus (9)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Use of X-ray scattering functions in Kramers-Kronig analysis of reflectance
• Thermopower of correlated semiconductors : application to FeAs2 and FeSb2
• Huge Thermoelectric Power Factor: FeSb2 versus FeAs2 and RuSb2
• Phonon-drag effect in FeGa3
• Unified picture for the colossal thermopower compound FeSb${}_2$
• Electronic correlations in FeGa${}_3$ and the effect of hole doping on its magnetic properties
• Strong electron correlations in FeSb2: An optical investigation and comparison with RuSb2