Effects of the Spin Heat Accumulation on the Heat Generation in a Quantum Dot Coupled to Leads

Heat generation by a spin-polarized current in a single-level quantum dot (QD) subjected to spin heat accumulation (SHA), which denotes the spin-dependent electron temperature, is studied by using the nonequilibrium Green's function technique. The heat generation originates from the energy exchange between the conduction electrons and the phonon reservoir coupled to the QD. Due to the SHA, the spin-up and spin-down heat generations are opposite in sign, and each has a maximum when the QD level is aligned to the chemical potentials of the leads, where the electric current is zero. Under a magnetic field, the maxima of the spin-up and spin-down heat generations are shifted to different dot level regimes. Now total negative heat generation emerges, indicating that the electron absorbs heat from the phonon reservoir to the dot. By tuning the dot levels and the system temperature, the magnitude of the negative heat generation can be enhanced accompanied by weakened electric current, an ideal condition for the realization of nanorefrigerator.