Microwave

In the Armitage lab, we employ two types of microwave techniques. The first is a Corbino geometry, which works in reflection mode. The Corbino geometry is a measurement configuration that is capable of broadband microwave spectroscopy. It is compatible with low T and high field cryogenic environments and capable of broadband microwave spectroscopy measurements from 10 MHz to 40 GHz. In a Corbino geometry spectrometer a microwave signal from a network analyzer is fed into a coaxial transmission line. The signal propagates down the coaxial line and is reflected from a sample that terminates an open ended coaxial connector. The network analyzer determines the complex reflection coefficient of the sample, which can be related to the complex sample impedance. Because the sample geometry is well defined, knowledge of the sample impedance yields intrinsic quantities like the complex conductivity.

In the summer of 2011, we added a magnet to the microwave system.

The second technique we use in the microwave regime is a microwave cavity perturbation technique (MCPT). MCPT is a widely used method for measuring the complex conductivity in the microwave spectral range. In this method, the shift in the resonant frequency and bandwidth of a small cavity resonator upon inclusion of a sample is measured. These quantities are directly related to both the real and imaginary parts of the conductivity of the sample through knowledge of the sample geometry. Our system, which was built 2012 – 2013, employs an NbTi (Tc 10 K) superconducting cavity operating in the TE011 mode which has been shown to have the lowest loss and highest Q factor at cryogenic temperatures. Our system is capable of reaching temperatures as low as 350 mK with current Q factors as high as 10⁵.

Interactive view of the microwave spectroscopy lab: Click on any image for a view as if you were in our microwave lab!

A view of the microwave system:

A full view of the microwave system and the surrounding lab area, including the FTIR spectrometer: