Measuring thermal conductivity in extreme conditions: Sub-Kelvin temperatures and high (27 T) magnetic fields

Thermal conductivity and electric resistivity of a bulk sample were measured using a one-heater-two-thermometer setup. The measurements were performed at low temperatures down to 0.1 K and in magnetic fields up to 27 T. A vacuum chamber containing the sample and thermometers was introduced into the mixing chamber of a top-loading dilution refrigerator to overcome the problem of mechanical vibrations. Coulomb blockade thermometry was used to measure the temperature in the field range where the magnetoresistance of thermometers was far from negligible.