A Scanning Tunneling Microscope for a Dilution Refrigerator M. Marz ∗ and G. Goll † Physikalisches Institut, Karlsruher Institut f¨ ur Technologie, 76131 Karlsruhe H. v. L¨ohneysen Physikalisches Institut and Institut f¨ ur Festk¨ orperphysik, Karlsruher Institut f¨ ur Technologie, 76131 Karlsruhe (Dated: October 12, 2018) We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T ≈ 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly-ordered pyrolytic graphite (HOPG) and the dichalcogenide superconductor NbSe 2 have been imaged with atomic resolution down to T ≈ 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe 2 in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence ∝ 1 $_{/}$√$_{B}$ and measurements in the STS mode clearly show the superconductive density of states with Andreev bound states in the vortex core. Abstract arXiv:1002.0812v1 [cond-mat.supr-con] 3 Feb 2010 $^{∗}$Electronic address: Michael.Marz@kit.edu $^{†}$Electronic address: Gernot.Goll@kit.edu 1