Fig. 1: CDW configurations and SC gap modulations in 2H-NbSe2.
From: Directly visualizing nematic superconductivity driven by the pair density wave in NbSe2
a The side view (upper panel) and top view (lower panel) of lattice structure of 2H-NbSe2. b The atomic resolution in topography T(r), showing the Se-terminated surface after cleavage. The typical CDW order with period ~3a0 is clearly observed, where a0 = 0.344 nm is the Se lattice constant. Scale bar: 5 nm. c The zoomed-in STM topography T(r) of AC-CDW as marked by the red square in (b). Only one brightest Se atom (red dots) appears in each AC-CDW unit cell. The AC-CDW crest is located at the brightest Se atom. Scale bar: 1 nm. d The zoomed-in STM topography T(r) of HC-CDW as marked by the yellow square in (b). Three Se atoms (yellow dots) with the same brightness appear in each HC-CDW unit cell. The HC-CDW crest is located at the center of these three Se atoms. Scale bar: 1 nm. e,f Fourier transform images T(q) of (c) and (d), showing the lattice Bragg peaks (turquoise dashed circles) and the CDW wave vectors |QiCDW | ~2π/3a0 (i = 1, 2, 3. Red/yellow dashed circles). Scale bar: 0.5 Å−1. g The dI/dV(V) spectra taken on (yellow curve) and off (purple curve) the AC-CDW crest as marked by the dots in the inset. Here, the SC gap size Δ is defined by the half energy spacing between two coherence peaks and the H is defined as the coherence peak height. h,i The zoomed-in spectra around the coherence peaks, showing the larger Δ and lower H on AC-CDW crest (yellow curves) compared to that off AC-CDW crest (purple curves). Experimental setpoints in (b-d) and (g-i): Vs = −4 mV, It = 400 pA.
