data and computer codes for "Hyperbolic phonon-polariton electroluminescence in 2D heterostructures"

Phonon-polaritons are electromagnetic waves resulting from the coherent coupling of photons with<br>optical phonons in polar dielectrics. Due to their exceptional ability to confine electric fields to deep<br>subwavelength scales with low loss, they are uniquely poised to enable a suite of applications beyond<br>the reach of conventional photonics, such as sub-diffraction imaging and near-field energy transfer.<br>The conventional approach to exciting phonon-polaritons through optical methods, however, in-<br>volves costly mid-infrared and terahertz coherent light sources along with near-field scanning probes,<br>and generally leads to low excitation efficiency due to substantial momentum mismatch between<br>phonon-polaritons and free-space photons. Here, we demonstrate that under proper conditions,<br>phonon-polaritons can be excited all-electrically by velocity-saturated charge carriers. Specifically,<br>in hexagonal boron nitride (hBN)/graphene heterostructures, by electrically driving charge carriers<br>in ultra-high-mobility graphene out of equilibrium, we observe bright electroluminescence of hBN’s<br>hyperbolic phonon-polaritons (HPhPs) at mid-IR frequencies. The HPhP electroluminescence shows<br>a temperature and carrier density dependence distinct from black-body or super-Planckian thermal<br>emission. Moreover, the carrier density dependence of HPhP electroluminescence spectra reveals<br>that HPhP electroluminescence can arise from both inter-band transition and intra-band Cherenkov<br>radiation of charge carriers in graphene. The HPhP electroluminescence offers fundamentally new<br>avenues for realizing electrically-pumped, tunable mid-IR and THz phonon-polariton light sources,<br>and efficient cooling of electronic devices.