Twist-enhanced thermoelectric effect in Cr(pyz)₄-based heterojunction via tuning spin quantum interference

Quantum interference, which usually occurs in some symmetric molecular rings, has great potential for the realization of high-performance thermoelectric conversion. Twisting molecular rings in molecular junctions provides a unique approach to tuning quantum interference, thus enabling the development of high-performance molecular thermoelectric devices. In this work, using density functional theory combined with the non-equilibrium Green’s function method, we investigate the spin-dependent thermoelectric properties of a Cr(pyz)₄(pyz=pyrazine) magnetic molecule sandwiched between two ferromagnetic zigzag graphene nanoribbon (ZGNR) electrodes. The results show that twisting between the pyrazine rings and graphene electrodes can significantly enhance the electronic conductance and the Seebeck coefficient. The main reason is that twisting can modulate quantum interference: it enhances the transmission of spin-up electrons via constructive spin interference, thus increasing the conductance; meanwhile, it induces sharp antiresonances for spin-down electrons via destructive spin interference, thus enhancing the Seebeck coefficient. In addition, twisting can also strengthen phonon scattering, leading to a lower phonon thermal conductance. Combining these factors, we find that our results demonstrate that the thermoelectric performance can be effectively regulated and greatly improved in twisted Cr(pyz)₄-based heterojunctions: the Z_spT exceeds 4 at 300 K and reaches 6 at 340 K.