Twist angle of the hBL described in the main text, measured by second-harmonic generation (SHG) spectroscopy. a, Polarization-dependent (SHG) signal measured on the ML WS2 (green open circles) and MoSe2 (blue filled squares) regions of the hBL, and the corresponding fits with sinusoidal functions (green and blue solid lines). b, The SHG signal from the ML WS2, ML MoSe2 and hBL regions, measured with the same experimental configurations. The suppressed SHG signal from the hBL, resulting from destructive interference, indicates that the stacking order is H-stacking. The twist angle is determined to be 56.5° ± 0.8°.