  Nonlinear transport enabled by symmetry breaking in quantum materials has
aroused considerable interest in condensed matter physics and interdisciplinary
electronics. However, the nonlinear optical response in centrosymmetric Dirac
semimetals via the defect engineering has remained highly challenging. Here, we
observe the helicity-dependent terahertz (THz) emission in Dirac semimetal
PtTe2 thin films via circular photogalvanic effect (CPGE) under normal
incidence. This is activated by artificially controllable out-of-plane
Te-vacancy defect gradient, which is unambiguously evidenced by the electron
ptychography. The defect gradient lowers the symmetry, which not only induces
the band spin splitting, but also generates the giant Berry curvature dipole
(BCD) responsible for the CPGE. Such BCD-induced helicity-dependent THz
emission can be manipulated by the Te-vacancy defect concentration.
Furthermore, temperature evolution of the THz emission features the minimum of
the THz amplitude due to the carrier compensation. Our work provides a
universal strategy for symmetry breaking in centrosymmetric Dirac materials for
efficient nonlinear transport and facilitates the promising device applications
in integrated optoelectronics and spintronics.
