Observation of supermodulation in LaO0.5F0.5BiSe2 by scanning tunneling microscopy and spectroscopy

TL;DR

This study used scanning tunneling microscopy and spectroscopy at low temperature to reveal surface structures and supermodulation in LaO0.5F0.5BiSe2, indicating structural instability rather than electronic nesting.

Contribution

First observation of supermodulation in LaO0.5F0.5BiSe2 using STM/STS, highlighting structural instability in this material.

Findings

Square Bi lattice observed at positive bias.

Stripe structures along Bi-Bi directions at negative bias.

Supermodulation with ~5 times lattice period indicating structural instability.

Abstract

We observed surface and electronic structure of LaO0.5F0.5BiSe2 single crystal by scanning tunneling microscopy/spectroscopy (STM/STS) at 4.2 K. Square lattice composed of Bi atoms was observed at a positive sample bias voltage on the surface prepared by cleavage. At a negative sample bias voltage, a stripe structure running along Bi-Bi directions was observed as in the previous report on NdO0.7F0.3BiS2. Furthermore, we observed a supermodulation running along the diagonal directions with the period of about 5 times of the lattice constant. This seems to be indicative of structural instability of this system rather than electronic instability attributed to a nesting picture.