  We numerically and experimentally achieve quasi-bound states in the
continuums (BICs) with high-Q factors in the free-standing metal complementary
periodic cross-shaped resonators (CPCRs) at terahertz (THz) frequencies. Such
induced quasi-BICs arises from the breaking of the mirror symmetry of CPCRs. By
properly tuning the asymmetric factor, the measured Q factor of quasi-BIC can
reach 102, which is lower than the simulated Q factor of 166 due to the limited
system resolutions. We also simulate the electric field magnitude and vector
distributions at the quasi-BICs, where the out-phase alignment between the
electric dipoles is found. The sharp quasi-BICs realized in this thin
free-standing metal structure may immediately boost the performance of filters
and sensors in terahertz wave manipulation or biomolecular sensing.
