Events

Abstract: Since its invention over 40 years ago, Scanning Tunneling Microscopy (STM) has provided an unprecedented window into matter at the atomic scale. By measuring tunneling conductance as a function of voltage with atomic precision, modern millikelvin STM offers a direct method to characterize the ground state of quantum materials with high energy resolution. I will discuss recent millikelvin STM experiments in the heavy fermion unconventional superconductor UTe2. UTe2 has a unique phase diagram, which is associated to equal spin pairing superconductivity and may potentially host topological modes at the surface. In this system we have identified a novel electron driven surface charge density wave (CDW)[1]. CDWs are often observed in dichalcogenides, cuprates, and pnictides, and arise from features in the lattice that facilitate electronic charge ordering. CDWs are considered to compete with Kondo screening and are relatively rare in heavy fermion metals. I will discuss the exceptional case of UTe2 and show how we identified the primitive wavevectors of the CDW and established the relationship between the surface CDW and the heavy fermion bulk properties. I will also briefly present recent advances and future prospects for STM, including novel routes to map the Josephson current at atomic scale [2], observation of surface superconductivity [3], STM in high vectorial magnetic fields [4] and Replica-STM [5].

 

[1] Surface charge density wave in UTe2, P. García et al, arXiv:2504.12505
[2] The feedback driven atomic scale Josephson microscope, S.D. Escribano et al, Nat Com 16, 5842 (2025).
[3] Robust surface superconductivity and vortex lattice in the Weyl semimetal g-PtBi2, J. Moreno et al, Arxiv 2508.04867.
[4] Scanning Tunneling Microscopy in high vectorial magnetic fields, J. Rumeu et al, Rev. Sci. Instrum. 97, 033705 (2026).
[5] Bridging atomic and mesoscopic length scales with Replica Scanning Tunneling Microscopy: Visualizing the intra-unit cell pair density modulation of superconducting FeSe at micron length scale, M. Agueda, Arxiv 2602.19678.