Thermoelectric Properties of Heavy-fermion Compounds UX₂Zn₂₀ (X = Co, Rh, and Ir)

Thermoelectric materials are attractive because they allow for the conversion between heat energy and electricity. This property can be harnessed as society pursues green energy sources and more efficient energy usage. However, owing to the relatively low efficiency currently found in most thermoelectric materials, their use is limited. One strategy to overcome this is seen in strongly correlated Kondo lattices, where hybridization between the f- and conduction electron states leads to enhanced Seebeck coefficients at low temperatures: e.g., as seen for YbTM₂Zn₂₀ (TM = Co, Rh, and Ir) [1, 2]. This motivates interest in other f-element analogues that might exhibit similar behavior, and in this work, we will examine the thermoelectric properties of UX₂Zn₂₀ (X = Co, Rh, and Ir). To do this, large single crystals were grown using a Zn self-flux and were characterized using X-ray diffraction and chemical analysis measurements. Magnetic susceptibility, heat capacity, and electrical resistivity measurements are used to clarify the f-electron state and results are compared to trends seen in the thermoelectric properties.

[1] Mun, et. al. Phys. Rev. B, 115110 (2012).

[2] Wei, et. al. Sci. Adv. 5, eaaw6183 (2019).