Fig. 1: Overview of charge order, inter-layer stacking and cleaved surfaces in 1T-TaS2.
From: Mottness versus unit-cell doubling as the driver of the insulating state in 1T-TaS2
a The quasi-2D undistorted structure of 1T-TaS2. b The supercell describing the periodic SD distortion within a single 1T-TaS2 layer. The solid purple and dashed black rhombuses mark the 2D projections of the undistorted atomic unit-cell, and the supercell after onset of the C-CDW, respectively. The labels A, B, and C denote the possible sites atop which successive SD clusters can stack. c The SD stacking pattern currently discussed (S not shown), with two SDs per cell and two distinct cleavage planes, 1 & 2. d Typical STM topography taken at a vacuum-cleaved 1T-TaS2 surface (V = 250 mV, Iset = 500 pA, scale bar 20 nm). The inset shows the correspondence between the topographic modulation and the SD cluster lattice (scale bar 1 nm). e Examples of conductance spectra of the two types observed at multiple cleaved surfaces. Typically, one type of spectrum or the other appears uniformly (except in the vicinity of defects) over ~1 μm areas, unless a step-terrace morphology is observed. The prominent conductance peaks at around 200 meV and −200 meV in the previously reported Type 1 spectrum have usually been identified with the upper and lower Hubbard bands. It will be shown below that the Type 1 & 2 spectra correspond to surfaces formed by cleavage at planes 1 & 2, respectively.
