Fig. 2.

Valley polarization with CW laser excitation. a, b Valley polarization at 0 T. Right and left circularly polarized light are labeled as σ₊ and σ₋. Under σ₊ laser excitation, σ₊ PL output component is more than σ₋ and vice versa for σ₋ excitation. This shows evidence of valley polarization. c, d Valley polarization at −7 T. Valley polarization is enhanced by applying magnetic field perpendicular to the sample surface. e The valley polarization degree as a function of applied magnetic field in the z direction. The solid line is the fitting result following equation $P^j=P_0^j\pm P_1^j\left(1-\frac{1}{r^2+r\sqrt{1+r^2}+1}\right)$, $r=∣B∣\mathrm{∕}\alpha$ where j indicates the excitation polarization, $P_0^j$ is the residual degree of polarization at 0 T due to the valley polarization, $P_1^j$ is the saturation level of degree of polarization, and α represents the intervalley scattering between the dark exciton. f, The valley polarization degree as a function of applied magnetic field in the y direction with B_z = 0T