Development of Algorithms for Quantum Material Measurements Under Extreme Conditions

Measuring the physical properties, including electrical transport, thermal conductivity, and thermoelectricity, of quantum materials requires the use of specialized hardware and software. The Quantum Design Dynacool system can reach temperatures as low as 0.35 Kelvin with the use of a Helium-3 system and magnetic fields as high as 9 Tesla. To accurately measure the thermal conductivity and thermoelectricity, reliable thermometry readings of the material are required in addition to a carefully designed thermal puck that is free from unwanted external heat transfer. Reliable thermometry is difficult in extreme conditions because measurements are susceptible to noise and thermal drift. Also, the typical duration of a thermal conductivity or thermoelectricity measurement run can be as long as days or weeks, and therefore the data acquisition must be automated. In addition, the thermal puck design requires a thorough understanding of thermal properties at these extreme conditions to avoid external conductive heat transfer.

We report our current development of the thermal puck hardware and measurement software required to collect thermometry data. When determining the thermal conductivity and Seebeck coefficient of a material, it is essential that thermometer measurements have reached stability. The software is used to collect the temperature data from these thermometers and ensure data stability. One challenge is determining a stability condition when a large outlier in the data is present. Many different filtering algorithms were considered. The chosen algorithm to be used is an exponentially weighted moving average filter with an arbitrary filter weight. The software must be able to ensure data accuracy and precision before accepting a set value while simultaneously controlling the measurement hardware.

Another major aspect of the software is the control of the Dynacool system and the lock-in amplifiers that measure the output voltages of the thermometers. Control of the Dynacool system is required to set the sample environment such as the temperature and magnetic field. A single measurement run can range from days to weeks, so constant human monitoring is not viable. As a result, automatic control of the Dynacool and lock-in amplifiers is required. The thermal puck and control software have both been developed simultaneously to meet requirements of the existing hardware and needs of the lab. Some materials to be tested are also being synthesized in the lab. These materials include FeGa₃, CrSb₂, and FeSb₂.