  Hyperbolic (or indefinite) materials have attracted significant attention due
to their unique capabilities for engineering electromagnetic space and
controlling light propagation. A current challenge is to find a hyperbolic
material with wide working frequency window, low energy loss, and easy
controllability. Here, we propose that naturally existing electride materials
could serve as high-performance hyperbolic medium. Taking the electride Ca$_2$N
as a concrete example and using first-principles calculations, we show that the
material is hyperbolic over a wide frequency window from short-wavelength to
near infrared. More importantly, it is almost lossless in the window. We
clarify the physical origin of these remarkable properties, and show its
all-angle negative refraction effect. Moreover, we find that the optical
properties can be effectively tuned by strain. With moderate strain, the
material can even be switched between elliptic and hyperbolic for a particular
frequency. Our result points out a new route toward high-performance natural
hyperbolic materials, and it offers realistic materials and novel methods to
achieve controllable hyperbolic dispersion with great potential for
applications.
