  Recent advancements in nonreciprocal thermal emitters challenge the
conventional Kirchhoff's law, which states that emissivity and absorptivity
should be equal for a given direction, frequency, and polarization. These
emitters can break Kirchhoff's law and enable unprecedented thermal photon
control capabilities. However, current studies mainly focus on increasing the
magnitude of the contrast between emissivity and absorptivity, with little
attention paid to how the sign or bandwidth of the contrast may be controlled.
In this work, we show such control ability can be achieved by coupling
resonances that can provide opposite contrasts between emissivity and
absorptivity.
