关键词: nodal-line semimetals, negative differential resistance (NDR) effect, horizontal mirror symmetry

Abstract: Nodal-line semimetals have become a research hot-spot due to their novel properties and great potential application in spin electronics. It is more challenging to find 2D nodal-line semimetals that can resist the spin-orbit coupling (SOC) effect. Here, we predict that 2D tetragonal ZnB is a nodal-line semimetal with great transport properties. There are two crossing bands centered on the $S$ point at the Fermi surface without SOC, which are mainly composed of the ${\rm p}_{xy}$ orbitals of Zn and B atoms and the ${\rm p}_{z}$ orbitals of the B atom. Therefore, the system presents a nodal line centered on the $S$ point in its Brillouin zone (BZ). And the nodal line is protected by the horizontal mirror symmetry $M_{z}$. We further examine the robustness of a nodal line under biaxial strain by applying up to $-4%$ in-plane compressive strain and 5% tensile strain on the ZnB monolayer, respectively. The transmission along the $a$ direction is significantly stronger than that along the $b$ direction in the conductive channel. The current in the $a$ direction is as high as 26.63 μA at 0.8 V, and that in the $b$ direction reaches 8.68 μA at 0.8 V. It is interesting that the transport characteristics of ZnB show the negative differential resistance (NDR) effect after 0.8 V along the $a (b)$ direction. The results provide an ideal platform for research of fundamental physics of 2D nodal-line fermions and nanoscale spintronics, as well as the design of new quantum devices.

Key words: nodal-line semimetals, negative differential resistance (NDR) effect, horizontal mirror symmetry