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Nonequilibrium thermal rectification at the junction of harmonic chains
A thermal diode or rectifier is a system that transmits heat or energy in one direction better than in the opposite
direction. We investigate the influence of the distribution of energy among wave numbers on the diode effect for
the junction of two dissimilar harmonic chains. An analytical expression for the diode coefficient, characterizing
the difference between heat fluxes through the junction in two directions, is derived. It is shown that the diode
coefficient depends on the distribution of energy among wave numbers. For an equilibrium energy distribution,
the diode effect is absent, while for non-equilibrium energy distributions the diode effect is observed even though
the system is harmonic. We show that the diode effect can be maximized by varying the energy distribution and
relative position of spectra of the two harmonic chains. Conditions are formulated under which the system acts
as an ideal thermal rectifier, i.e., transmits heat only in one direction. The results obtained are important for
understanding the heat transfer in heterogeneous low-dimensional nanomaterials.