We explore the potential of highly mismatched alloys (HMAs) for realizing lossless plasmonics. Systems with a plasmon frequency at which there are no interband or intraband processes possible are called lossless, as there is no two-particle loss channel for the plasmon. We find that the band splitting in HMAs with a conduction band anticrossing guarantees a lossless frequency window. When such a material is doped, producing plasmonic behavior, we study the conditions required for the plasmon frequency to fall in the lossless window, realizing lossless plasmons. Considering a generic class of HMAs with a conduction band anticrossing, we find universal contours in their parameter space within which lossless plasmons are possible for some doping range. Our analysis shows that HMAs with heavy effective masses and small high-frequency permittivity are most promising for realizing a lossless plasmonic material.
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