  Symmetry plays a critical role in determining various properties of a
material. Semiconducting p-n junction diode exemplifies the engineered skew
electronic response and is at the heart of contemporary electronic circuits.
The non-reciprocal charge transport in a diode arises from doping-induced
breaking of inversion symmetry. Breaking of time-reversal, in addition to
inversion symmetry in some superconducting systems, leads to an analogous
device - the superconducting diode. Following the pioneering first
demonstration of the superconducting diode effect (SDE), a plethora of new
systems showing similar effects have been reported. SDE lays the foundation for
realizing ultra-low dissipative circuits, while Josephson phenomena-based diode
effect (JDE) can enable realization of protected qubits. However, SDE and JDE
reported thus far are at low temperatures ($\sim$ 4 K or lower) and impede
their adaptation to technological applications. Here we demonstrate a Josephson
diode working up to 77 K using an artificial Josephson junction (AJJ) of
twisted layers of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (BSCCO). The
non-reciprocal response manifests as an asymmetry in the magnitude of switching
currents and their distributions and appears for all twist angles. The
asymmetry is induced by and tunable with a very small magnetic field applied
perpendicular to the junction. We report a record asymmetry of 60 % at 20 K. We
explain our results within a vortex-based scenario. Our results provide a path
toward realizing superconducting quantum circuits at liquid nitrogen
temperature.
