Fig. 1: Surface morphology and defects for single-layer FeSe/STO films.
From: Sign changing pairing in single layer FeSe/SrTiO3 revealed by nonmagnetic impurity bound states
a Scanning tunneling microscopy (STM) topographic image of single-layer FeSe/STO films. Inset: A typical differential conductance (dI/dV) spectrum measured at 4.3 K away from defects. The two-gap feature is labeled as Δ1 and Δ2. b Atomic resolution image of various intrinsic defects. Setpoint: Bias (V) = 20 mV, tunneling current (I) = 500 pA. c, d Close-up atomic resolution images of the type A and B defects labeled in (b). Setpoint: V = 30 mV, I = 200 pA. e, f Magnetic-field-dependent dI/dV spectra for type A and B defects, respectively. The peak positions of the impurity bound states do not shift or split under an out-of-plane 9 T (B⊥) or in-plane 2 T (B//) magnetic fields, indicating their non-magnetic nature. The black spectra are measured at regions away from defects, demonstrating a typical double-gap structure. The spectra labeled as 0 T, 2 T (B//) and 9 T (B⊥) are collected at the defect center in c, d, which are offset vertically for clarity.
