Fig. 2. Nonreciprocal charge transport in atomically thin NbSe₂.

a, Sketch of the four-terminal device based on atomically thin NbSe₂. The magnetic field is perpendicularly to the substrate plane. b, The temperature dependence of the normalized resistance of the NbSe₂ device. Inset, an optical image of the four-terminal NbSe₂ device with a thickness of five layers. Scale bar, 5 μm. c, d, Temperature-dependent R^ω and R^2ω of the device under positive and negative magnetic fields applied perpendicularly to the substrate, where R^ω(B)-T and R^ω(-B)-T curves overlap each other while R^2ω(B)-T and R^2ω(-B)-T curves are symmetric with respect to the x-axis (I₀ = 25 μA and f = 17.1 Hz). e, Magnetoresistance isotherm of the device with the temperature changing from 2 to 7 K, which are symmetric with respect to the y-axis. f, R^2ω-B curves of the device at temperatures of 2 to 7 K, showing antisymmetric behavior at T < 7 K, which is consistent with the first harmonic signal in (e). g, The extracted maximum value of R^2ω-B curves $∣R_{MAX}^{2\omega }∣$ as a function of temperature. The pink squares $∣R_{MAX1}^{2\omega }∣$ stands for the peak values in the larger magnetic field regime, the purple triangles $∣R_{MAX2}^{2\omega }∣$ stands for the peak values in the small magnetic field regime at B ≥ 5.25 K. h, Calculated temperature-dependent γ and │γ′│, where $\gamma =\frac{\sqrt{2}∣R_{MAX1}^{2\omega }∣}{B{R}^{\omega }{I}_0}$ and ${\gamma }^{\prime }=\frac{\sqrt{2}∣R_{MAX2}^{2\omega }∣}{B{R}^{\omega }{I}_0}$, respectively. γ and γ′ have an opposite sign due to the opposite nonreciprocity. i, Temperature-magnetic field phase diagram of the NbSe₂ device. The dark pink dots stand for crossover between the vortex solid (glass) state and vortex liquid state at which R^2ω goes to zero. The dark blue dots show the crossing point of the vortex liquid state and normal state. R^2ω goes to zero when further increasing the magnetic field. The yellow dots are the crossing point where R^2ω changes sign, defining the boundary between the activated pinned vortex states (light blue area) and vortex liquid state at T_M ≥ 5.25 K. Here T_M is the melting temperature above which the vortex solid melts.