Contactless technique for thermal conductivity measurement at very low temperature

We present a low-temperature thermal conductivity measurement, which requires no electrical wire in contact with the sample. The temperature gradient in the sample is generated via optical heating and detected by two magnetization thermometers with inductively coupled dc-SQUID readouts. The parasitic heat leak and power dissipation of the setup can be arranged to be below 10−15 W. Therefore this contact-free method is well-suited for measuring samples with very small thermal conductiviy at low temperature. We present results for BK7 glass and a-SiO2 down to 5.3 mK.