We describe a scanning tunneling microscope (STM) that operates at magnetic fields up to 22 T and temperatures down to 80 mK. We discuss the design of the STM head, with an improved coarse approach, the vibration isolation system, and efforts to improve the energy resolution using compact filters for multiple lines. We measure the superconducting gap and Josephson effect in aluminum and show that we can resolve features in the density of states as small as 8 μeV. We measure the quantization of conductance in atomic size contacts and make atomic resolution and density of states images in the layered material 2H–NbSe2. The latter experiments are performed by continuously operating the STM at magnetic fields of 20 T in periods of several days without interruption.
A Scanning Tunneling Microscope (STM) is one of the most important scanning probe tools available to study and manipulate matter at the nanoscale. In a STM, a tip is scanned on top of a surface with a separation of a few Å. Often, the tunneling current between tip and sample is maintained constant by modifying the distance between the tip apex and the surface through a feedback mechanism acting on a piezoelectric transducer. This produces very detailed images of the electronic properties of the surface. The feedback mechanism is nearly always made using a digital processing circuit separate from the user computer. Here we discuss another approach, using a computer and data acquisition through the USB port. We find that it allows succesful ultra low noise studies of surfaces at cryogenic temperatures. We show results on different compounds, a type II Weyl semimetal (WTe 2 ), a quasi two-dimensional dichalcogenide superconductor (2H-NbSe 2 ), a magnetic Weyl semimetal (Co 3 Sn 2 S 2 ) and an iron pnictide superconductor (FeSe).
The magnetoresistance (MR) of iron pnictide superconductors is often dominated by electron–electron correlations and deviates from the H
2 or saturating behaviors expected for uncorrelated metals. Contrary to similar Fe-based pnictide systems, the superconductor LaRu2P2 (T
c = 4 K) shows no enhancement of electron–electron correlations. Here we report a non-saturating MR deviating from the H
2 or saturating behaviors in LaRu2P2. We present results in single crystals of LaRu2P2, where we observe a MR following H
1.3 up to 22 T. We discuss our result by comparing the bandstructure of LaRu2P2 with that of Fe based pnictide superconductors. The different orbital structures of Fe and Ru leads to a 3D Fermi surface with negligible bandwidth renormalization in LaRu2P2, that contains a large open sheet over the whole Brillouin zone. We show that the large MR in LaRu2P2 is unrelated to the one obtained in materials with strong electron–electron correlations and that it is compatible instead with conduction due to open orbits on the rather complex Fermi surface structure of LaRu2P2.
The magnetoresistance of iron pnictide superconductors is often dominated by electron-electron correlations and deviates from the H 2 or saturating behaviors expected for uncorrelated metals.Contrary to similar Fe-based pnictide systems, the superconductor LaRu 2 P 2 (T c = 4 K) shows no enhancement of electron-electron correlations. Here we report a non-saturating magnetoresistance deviating from the H 2 or saturating behaviors in LaRu 2 P 2 . We have grown and characterized high quality single crystals of LaRu 2 P 2 and measured a magnetoresistance following H 1.3 up to 22 T. We discuss our result by comparing the bandstructure of LaRu 2 P 2 with Fe based pnictide superconductors. The different orbital structures of Fe and Ru leads to a 3D Fermi surface with negligible bandwidth renormalization in LaRu 2 P 2 , that contains a large open sheet over the whole Brillouin zone. We show that the large magnetoresistance in LaRu 2 P 2 is unrelated to the one obtained in materials with strong electron-electron correlations and that it is compatible instead with conduction due to open orbits on the rather complex Fermi surface structure of LaRu 2 P 2 .
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