Low temperature scanning tunneling microscopy/spectroscopy study of two different layers in poly-type 4Hb-TaS ₂ at 4.2 K

Using scanning tunneling microscope (STM), we have fabricated steps of 4Hb-TaS ₂ with the height ∼ 6 Å and investigated the electronic and atomic structures on the two different layers near the step region at 4.2 K. The measured STM images and tunneling spectra revealed completely different atomic and electronic structures of the 1T and 1H type layers. The 1T type layers showed the typical √13 × √13 charge-density-wave (CDW) structures showing insulating behaviors, whereas the 1H type layers showed metallic behaviors and had the triangular atomic structure with a very weak 3×3 CDW superlattice at a low bias voltage and with a superposed √13 × √13 CDW superlattice at a high positive bias voltage. The bias dependent STM image on the surface of 1H layer can be explained by the energy dependent tunneling process between STM tip and a stack of metallic 1H layer and insulating 1T layer.