Combinatorial tuning of electronic structure and thermoelectric properties in Co$_2$MnAl$_{1-x}$Si$_x$ Weyl semimetals

Abstract

A tuning of Fermi level (E$_F$) near Weyl points is one of the promising approaches to realize large anomalous Nernst effect (ANE). In this work, we introduce an efficient approach to tune E$_F$ for the Co$_2$MnAl Weyl semimetal through a layer-by-layer combinatorial deposition of Co$_2$MnAl$_{1-x}$Si$_x$ (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 single-phase CMAS alloy throughout the composition range with a gradual improvement of L2$_1$ 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 E$_F$ shift of approximately 0.40 eV towards the composition gradient direction from x = 0 to 1. The anomalous Ettingshausen effect (AEE), the reciprocal of ANE, has been measured for 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 the AEE measurement on the composition spread film is an effective approach to investigate the composition dependence of ANE of Weyl semimetal thin films and realize the highest performance without fabricating several films, which will accelerate the research for ANE-based energy harvesting