Adiabatic transverse thermoelectric conversion enhanced by heat current manipulation in artificially tilted multilayers

Abstract

We phenomenologically formulate and experimentally observe an adiabatic transverse thermoelectric conversion enhanced by a heat current re-orientation in artificially tilted multilayers (ATMLs). By alternately stacking two materials with different thermal conductivities and rotating its multilayered structure with respect to a longitudinal temperature gradient, off-diagonal components in the thermal conductivity tensor are induced. This off-diagonal thermal conduction (ODTC) generates a finite transverse temperature gradient and Seebeck-effect-induced thermopower in the adiabatic condition, which is superposed on the isothermal transverse thermopower driven by the off-diagonal Seebeck effect (ODSE). In this study, we calculate and observe the two-dimensional temperature distribution and the resultant transverse thermopower in ATMLs comprising thermoelectric Co${}_2$MnGa Heusler alloys and Bi${}_{2-a}$Sb${}_a$Te${}_3$ compounds. By changing the tilt angle from 0° to 90°, the transverse temperature gradient obviously appeared in the middle angles and the transverse thermopower increases up to -116.1 $\hat{I}¼$V/K in Co${}_2$MnGa/Bi${}_{0.2}$Sb${}_{1.8}$Te${}_3$-based ATML at the tilt angle of 45° whereas the isothermal contribution is estimated to be -82.6 $\hat{I}¼$V/K from the analytical calculation. This hybrid action derived from ODTC results in the significant variation of the maximum reduced efficiency for transverse thermoelectric conversion from 3.1% in the isothermal limit to 8.1% in the adiabatic limit.

12 pages, 6 figures