Nonlinear thermotics: nonlinearity enhancement and harmonic generation in thermal metasurfaces Gaole Dai, Jin Shang, Ruizhe Wang and Jiping Huang Eur. Phys. J. B, 91 3 (2018) 59 Published online: 29 March 2017 DOI: 10.1140/epjb/e2018-80596-8