In this talk I will present new experimental possibilities of cryogenic Scanning Tunneling Microscopy, which include a very high resolution in energy and the capability to cleave in-situ at low temperatures ultra high-quality single crystals. I will discuss the discovery of two-dimensional heavy fermions (2DHF) made of 5f electrons with an effective mass 17 times the free electron mass. These 2DHF present quantized states at terraces. The energy separation between quantized levels is of a fraction of a meV and the level width is set by the interaction with correlated bulk states [1]. Interestingly, we find a new connection between bulk and surface features, which shows that the surface can be used as a powerful probe to address pressing questions about electronic correlations, such as the hidden order problem of URu2Si2. I will also describe recent work in magnetic Weyl semimetals. Finally, I will discuss future prospects of STM, including a new method to image Cooper pairs, which will be instrumental to study topological superconductors.
[1] Quantum-well states at the surface of a heavy-fermion superconductor, Edwin Herrera, Isabel Guillamón, Víctor Barrena, William J. Herrera, Jose Augusto Galvis, Alfredo Levy Yeyati, Ján Rusz, Peter M. Oppeneer, Georg Knebel, Jean Pascal Brison, Jacques Flouquet, Dai Aoki & Hermann Suderow, Nature 616, pp 465–469 (2023).
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