Combinatorial tuning of electronic structure and thermoelectric properties in Co2MnAl1−xSix Weyl semimetals

Tuning of the Fermi level (EF) near Weyl points is one of the promising approaches to realize the large anomalous Nernst effect (ANE). In this work, we introduce an efficient approach to tune EF for the Co2MnAl Weyl semimetal through a layer-by-layer combinatorial deposition of the Co2MnAl1−xSix (CMAS) thin film. A single-crystalline composition-spread film with x varied from 0 to 1 was fabricated. The structural characterization reveals the formation of a single-phase CMAS alloy throughout the composition range with a gradual improvement of L21 order with x similar to the co-sputtered single layered film, which validates the present fabrication technique. Hard x-ray photoemission spectroscopy for the CMAS composition-spread film directly confirmed the rigid band-like EF shift of ∼0.40 eV toward the composition gradient direction from x = 0 to 1. The anomalous Ettingshausen effect (AEE), the reciprocal of the ANE, has been measured for the whole x range using a single strip along the composition gradient using the lock-in thermography technique. The similarity of the x dependence of observed AEE and ANE signals clearly demonstrates that AEE measurement on the composition-spread film is an effective approach to investigate the composition dependence of the ANE of Weyl semimetal thin films and realize the highest performance without fabricating several films, which will accelerate the research on ANE-based energy harvesting.