Thermionic emission in nodal-ring semimetals

Abstract

We theoretically investigate the thermionic emission from nodal-ring semimetals. The thermionic emission is found to be anisotropic in the x- and y-directions. The anisotropic emission can be enhanced by increasing the radius of nodal-ring b. The main feature of nodal-ring semimetals not only results in anisotropic thermionic emission but also affects the value of thermionic emission current density (TECD). The TECD of the lower branch of the energy–momentum dispersion increases with b, while the TECD of the upper branch decreases with b. Unlike in conventional materials, the TECD in nodal-ring semimetals depends on Fermi energy that is similar to the situation in Dirac semimetals. The underlined reason is that Dirac semimetals and nodal-ring semimetals have a linear or a linear-like energy–momentum dispersion while conventional materials have a parabolic energy–momentum dispersion. The TECD of nodal-ring semimetals depends strongly on work function and temperature.