A tunable and unidirectional one-dimensional electronic system Nb_2n+1Si_nTe_4n+2

One dimensional (1D) electronic system is a versatile platform hosting novel physics, such as charge density wave, Su-Schrieffer-Heeger (SSH) topological state and solitons, Tomonaga-Luttinger Liquid etc. However, since real 1D materials do not exist in nature, quasi-1D structures in 3D crystals become a practical substitute. Here, we systemically study the surface electronic properties on layered composition-tunable compounds Nb_2n+1SinTe_4n+2 (n=1~5), which is predicted to be a nodal-line semimetal when n=1 (Nb₃SiTe₆). Via scanning tunneling microscopy/spectroscopy, we observe 1D chains spontaneous formed on the surface of the compounds. We uncover that with the increasing of n, the distance between the chains becomes larger, and the 1D electronic state is developed in the compounds with n ≥ 3. Our first-principle calculations reveal that the nodal-line in Nb₃SiTe₆ and the 1D electronic state in the crystals with higher n in fact arise from the same bands, which are protected by the same nonsymmorphic symmetry. Furthermore, we can understand the evolution of the electronic states based on a simple SSH type picture. Our experiment demonstrates the first tunable 1D electronic system, which offers a concrete platform for the exploration of intriguing 1D electron physics.