Research group Quantum materials characterization
Our research is focused on thermodynamic, transport, and structural characterization of materials with novel electronic properties at low temperatures.
Particular focus is on superconductivity, magnetism, and other systems with electronic phase transitions, where the effects of a magnetic field and field direction are central. The main experimental technique is nanocalorimetry, sometimes combined with concurrent x-ray diffraction.
Nanocalorimetry
High-resolution specific heat provides key thermodynamic information of novel condensed matter materials. We are using nanocalorimetry to study the electronic specific heat and phase transitions of small single crystals and thin films in magnet fields at low temperature. We have developed a differential, membrane-based nanocalorimeter for general specific heat studies of very small samples as well as thin films. The typical sample size is 100 um x 100 um, but samples can range from sub-μg to 0.5 mg in mass. The temperature range is from 0.5 K to 400 K, with a resolution about 1 in 10^4 (sometime 1 in 10^5) over the whole range. It consists of a pair of cells, each of which is a stack of heaters and GeAu thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The calorimeter is also used as a sample platform, allowing concurrent calorimetry, local temperature control, and synchrotron x-ray studies.
Further reading:
K. Willa et al., Rev. Sci. Instrum. 88, 125108 (2017); https://doi.org/10.1063/1.5016592
S. Tagliati et al., Rev. Sci. Instrum. 83, 055107 (2012); https://doi.org/10.1063/1.4717676
Group description
Ultra-low temperature characterization
We are currently building up a new lab around a cryogen-free Bluefors LD250 dilution refrigerator for temperatures down to 10 mK. The system will have a 12 T superconducting magnet, optical access, quick sample loading, and two-axis rotation possibilities in the magnetic field. Measurements will include ultra-low temperature transport characterization, torque magnetometry, nanocalorimetry, and quantum optics experiments.
Low-noise electronics & software
We are using custom-designed low-noise measurement electronics, including FPGA-based platforms with real-time embedded software. Through a synchronous multi-channel lock-in amplifier system, we are able to combine changing conditions (currents, frequencies, etc.) while maintaining high resolution and accuracy in the measurements. Using the nanocalorimeter as a sample platform, the local temperature can be controlled from base temperature to above room temperature without excessively heating the entire dilution refrigerator.
Group members
Group managers
Andreas Rydh
Universitetslektor, docent
Members
Neha Kondedan
PhD Student
Akash Khansili
Phd Student
