Development of Nb-GaAs based superconductor semiconductor hybrid platform by combining in-situ dc magnetron sputtering and molecular beam epitaxy

We present Nb thin films deposited in-situ on GaAs by combining molecular beam epitaxy and magnetron sputtering within an ultra-high vacuum cluster. Nb films deposited at varying power, and a reference film from a commercial system, are compared. The results show clear variation between the in-situ and ex-situ deposition which we relate to differences in magnetron sputtering conditions and chamber geometry. The Nb films have critical temperatures of around $9 \textrm{K}$. and critical perpendicular magnetic fields of up to $B_{c2} = 1.4 \textrm{T}$ at $4.2 \textrm{K}$. From STEM images of the GaAs-Nb interface we find the formation of an amorphous interlayer between the GaAs and the Nb for both the ex-situ and in-situ deposited material.Comment: 12 pages paper, 9 pages supplementary, 6 figures paper, 7 figures supplementar

DC magnetron sputtering system for in-situ deposition of superconductors on III-V semiconductors

The possibility of realizing anyons in solid state physics [243, 365] fuels the development of superconductor semiconductor hybrid structures. A host of physical phenomena, which are rooted in the interaction between superconductors and semiconductors, have produced spectacular experimental results [5, 102, 127, 235]. Theoretical treatise [101, 243, 293] raise expectations, conditioned on continued material improvement. The state of the art of epitaxial superconductor - semiconductor materials, are Aluminum thin films deposited in the molecular beam epitaxy machine after growth of the semiconductor [180], whose superconducting properties limit the experimental work. A DC magnetron sputtering system was built and connected to two molecular beam epitaxy machines, to deposit superconductors with improved properties on the semiconductors without breaking vacuum. This enables oxide free interfaces, which are necessary to achieve epitaxy of the superconductor on the semiconductor. DC magnetron sputtering can deposit low vapor pressure metals at low temperatures. Furthermore, it provides a wide variety of possible compound materials and versatility in tuning the deposition parameters. The system had to be custom built, due to the stringent ultra high vacuum conditions set by the molecular beam epitaxy machines. The deposition of niobium on gallium arsenide with the new DC magnetron system was investigated as a function of deposition power and the effect of the interface oxide. The thereby calibrated films are studied in their charge transport behavior across the superconductor semiconductor interface and showed signatures of Andreev reflection. First results from experiments using the semiconductor-superconductor hybrid materials are presented. The magnetic field mediated interaction between the type II superconductor niobium and a two dimensional electron system in gallium arsenide have been investigated. The semiconductor structure grown by molecular beam epitaxy is based on shallow inverted two dimensional electron systems in gallium arsenide, previously optimized in the group [183, 184]. After the deposition of the superconductor, the material was processed into a Hall structure with self-aligned contacts and a global backgate. The samples show the typical Hall and Shubiknov deHaas traces associated with a two dimensional electron gas and the niobium is still superconducting. However, there are no signatures of an interaction between the type II superconductor and the two dimensional electron gas. This is likely due to the dirty limit niobium and the high electron density in the two dimensional electron gas

The ATLAS experiment at the CERN Large Hadron Collider: a description of the detector configuration for Run 3

Abstract The ATLAS detector is installed in its experimental cavern at Point 1 of the CERN Large Hadron Collider. During Run 2 of the LHC, a luminosity of  ℒ = 2 × 1034 cm-2 s-1 was routinely achieved at the start of fills, twice the design luminosity. For Run 3, accelerator improvements, notably luminosity levelling, allow sustained running at an instantaneous luminosity of  ℒ = 2 × 1034 cm-2 s-1, with an average of up to 60 interactions per bunch crossing. The ATLAS detector has been upgraded to recover Run 1 single-lepton trigger thresholds while operating comfortably under Run 3 sustained pileup conditions. A fourth pixel layer 3.3 cm from the beam axis was added before Run 2 to improve vertex reconstruction and b-tagging performance. New Liquid Argon Calorimeter digital trigger electronics, with corresponding upgrades to the Trigger and Data Acquisition system, take advantage of a factor of 10 finer granularity to improve triggering on electrons, photons, taus, and hadronic signatures through increased pileup rejection. The inner muon endcap wheels were replaced by New Small Wheels with Micromegas and small-strip Thin Gap Chamber detectors, providing both precision tracking and Level-1 Muon trigger functionality. Trigger coverage of the inner barrel muon layer near one endcap region was augmented with modules integrating new thin-gap resistive plate chambers and smaller-diameter drift-tube chambers. Tile Calorimeter scintillation counters were added to improve electron energy resolution and background rejection. Upgrades to Minimum Bias Trigger Scintillators and Forward Detectors improve luminosity monitoring and enable total proton-proton cross section, diffractive physics, and heavy ion measurements. These upgrades are all compatible with operation in the much harsher environment anticipated after the High-Luminosity upgrade of the LHC and are the first steps towards preparing ATLAS for the High-Luminosity upgrade of the LHC. This paper describes the Run 3 configuration of the ATLAS detector.</jats:p