Current amplification and rectification in a chain of four spins individually coupled to different heat baths

In this work, we considered a linear chain consisting of four spins individually coupled to different heat baths. We calculated numerically the heat currents by solving the transition rate equations as previously discussed in Ref. [1]. The temperature of the heat bath of the first spin is held constant. The temperatures of the second and third heat baths are set to be the average of the heat baths at the edges while the temperature of the fourth heat bath at the edge is allowed to vary from zero to twice the temperature of the first heat bath.