Real Space Observation of Structural Phase Segregation in Fe₅GeTe₂ using STM/STS

Fe_5-xGeTe₃ is a material that exhibits highly sought-after properties, having a Van der Waals coupled 2d structure and exhibiting itinerant ferromagnetism down to the monolayer limit with a near room temperature T_c.¹ These make it a useful tool to add to the device physicists toolbox of materials to make heterostructure devices with. A remaining problem that hinders our total understanding of the material however is its complex crystal structure, with inherently split sites combined with a strong tendency to be Fe deficient leading to differing phases with locally broken inversion symmetry.² A fuller picture of the microstructure of these phases and their electronic structures is therefore desired to clarify these issues.

We present a low-temperature scanning tunnelling microscopy/scanning tunnelling spectroscopy study of Fe_5-xGeTe₂, showing a clear phase segregation of different surface structures which exhibit a long-range lattice superstructure. We discuss the detailed crystal structure of the three observed phases, in addition to discussing the differing near-Ef electronic surface structure of using dI/dV mapping of the local density of states.

1. Fujita, R. et al. ACS Nano 16, 10545–10553 (2022).

2. May, A. F. et al. ACS Nano 13, 4436–4442 (2019).