Fig. 2: The second harmonic Hall current spectra in h-BN.
From: Second harmonic Hall responses of insulators as a probe of Berry curvature dipole
a and b are the top views of the three-fold D3h symmetric pristine and the two-fold C2v symmetric uniaxial strained h-BN monolayers, respectively. The blue dashed lines represent the mirror planes: Mx is perpendicular to the x-axis; M120° and M240° are obtained by rotating the Mx plane clockwise 120° and 240° around the z-axis, respectively. The upper plane of c is the real-time profile of the continuous light field applied to the pristine h-BN. The solid brown and dotted green oscillating lines in the lower plane are the transverse current density responses obtained by the real-time time-dependent density functional theory (TDDFT) calculations with the polarization of the applied field in the x-axis and y-axis, respectively. d The Fourier transformation of the current densities given in c for the time interval of 20 fs ≤ t ≤ 60 fs (the black horizontal arrowed line). The horizontal dashed line depicts the second harmonic generation (SHG) yield. e The SHG yields obtained from TDDFT (brown squares) and the theoretical SHG susceptibility spectra (black lines) for the pristine h-BN (with D3h symmetry) with respect to various driving frequencies. f The same plots as e for a strained h-BN (with C2v symmetry). The light frequency in the horizontal axis is normalized with the bandgap of each structure (4.75 eV for D3h and 3.61 eV for C2v).
