研究目的
To explore the evolution of the electronic structure of PbTe heavily doped with Na up to the solubility limit, identifying deviations from a Kane-type dispersion and their implications for thermoelectric properties.
研究成果
The electronic structure of heavily doped PbTe deviates from a Kane-type dispersion around 180 meV, leading to a sharp increase in the density of states and changes in the Hall effect. Nonellipsoidicity of the L pocket near a saddle point is the most likely cause, contributing to high thermopower. This calls for reassessment of carrier densities in heavily doped PbTe.
研究不足
The study is limited to heavily doped PbTe with Na, and the quantum oscillation measurements did not resolve the entire Fermi surface, particularly higher frequency orbits. The Hall effect may not accurately represent carrier density at high dopings, and the specific heat measurements require low temperatures due to small Sommerfeld coefficients.
1：Experimental Design and Method Selection:
The study uses complementary techniques including Hall effect measurements, quantum oscillations, specific heat measurements, and electron microprobe analysis (EMPA) to characterize the electronic structure. Quantum oscillations were measured using a mutual inductance technique, and specific heat was measured to determine the Sommerfeld coefficient.
2：Sample Selection and Data Sources:
Single crystals of Pb1-xNaxTe were grown via a self-flux technique with varying Na concentrations up to the solubility limit. Samples were characterized for homogeneity and phase purity using EMPA.
3：List of Experimental Equipment and Materials:
Equipment includes mutual inductance setups for quantum oscillations (up to 65 T at NHMFL), Hall effect measurement systems (up to 30 T at NHMFL, 14 T PPMS from Quantum Design, 16 T system from Cryogenic Ltd.), specific heat measurement systems (dilution refrigerator option for PPMS from Quantum Design), and a JEOL JXA-8230 SuperProbe Electron Probe Microanalyzer for EMPA. Materials include Pb, Na, Te, and alumina crucibles.
4：Experimental Procedures and Operational Workflow:
Crystals were grown in Te-rich melts, slow-cooled, and separated by centrifugation. Hall effect measurements used a transverse contact geometry with field symmetrization. Quantum oscillation data were processed with background subtraction and FFT analysis. Specific heat data were fitted to extract the Sommerfeld coefficient. EMPA was performed to measure Na content and check for impurities.
5：Data Analysis Methods:
Data analysis involved fitting quantum oscillation amplitudes to the Lifshitz-Kosevitch formula to determine effective masses and Dingle temperatures, using the Kane model to relate Fermi energy to carrier density, and polynomial fitting for specific heat data.
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