Hot electron cooling in Dirac semimetal CdAs due to polar optical phonons.

A theory of hot electron cooling power due to polar optical phonons P is developed in 3D Dirac semimetal (3DDS) CdAs taking account of hot phonon effect. Hot phonon distribution N and P are investigated as a function of electron temperature T , electron density n , and phonon relaxation time [Formula: see text]. It is found that P increases rapidly (slowly) with T at lower (higher) temperature regime. Whereas, P is weakly decreasing with increasing n . The results are compared with those for three-dimensional electron gas (3DEG) in CdAs semiconductor. Hot phonon effect is found to reduce P considerably and it is stronger in 3DDS CdAs than in CdAs semiconductor. P is also compared with the hot electron cooling power due to acoustic phonons P . We find that a crossover takes place from P dominated cooling at low T to P dominated cooling at higher T . The temperature at which this crossover occurs shifts towards higher values with the increase of n . Also, hot electron energy relaxation time [Formula: see text] is discussed. It is suggested that [Formula: see text] can be tuned to achieve faster or slower energy loss for suitable applications of CdAs.