Cryogen-free dilution refrigerator system with selected options

• Subject Area: Condensed Matter Physics
• Term: Funded in 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448942660

We propose to purchase a cryogen-free dilution refrigerator appropriate for the incorporation of a SQUID magnetometer, for the purpose of studying magnetization properties at millikelvin temperatures. While Squid operating down to about 1.5K are omnipresent, systems working at lower temperatures are absent in the field. There are however significant questions, with regards to magnetic and superconducting properties of Topological insulators which require precisely such an instrument to address. For example, consider the electrical quantum effects that form the basis of the new SI unit system. A promising new material class for applications in this field are the magnetic topological insulators, which allows the quantum Hall resistors to be realized without a magnetic field, in the form of the quantum anomalous Hall effect (QAHE). However, the nature of the ferromagnetic state in these topological insulators is still unclear. To understand this state, it must be measured under the same conditions where the samples exhibit the QAHE, which at present is well below 1K. A major objective is thus to develop techniques to accurately characterize the magnetic and structural properties of the QAHE devices, especially V-doped (Bi,Sb)Te system with high resolution using the SQUID sensor that can work in variable temperatures from 30K down to 10mK, which will allow us to answer some fundamental physics questions on the nature of the ferromagnetic state in this material. In addition to this primary aim, the availability of mK-SQUID will be beneficial to projects on topological superconductivity and to our other investigation on magnetic TIs in general. This instrument will provide a unique functionality in this field, and will allow us to significantly move forward the understanding of these important novel materials.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Kryogenfreier Mischkryostat mit ausgewählten Optionen
• Instrumentation Group: 8580 Behälter für flüssige Gase
• Applicant Institution: Julius-Maximilians-Universität Würzburg
• Leader: Professor Dr. Laurens W. Molenkamp