Lab exchange grant: liquid helium-cooled material measurements

Sivaloganathan Kumaran, PhD student at the University of Cambridge, was awarded an M4QN laboratory exchange grant to visit the Ultra-fast Photonics Group at University College London.

The purpose of the visit

Kumaran writes:

“During my M4QN exchange at UCL, I engaged in a multifaceted research project aimed at advancing my understanding and practical skills in various aspects of material measurement and analysis. The visit primarily focused on learning to operate and implement cryogenic equipment into the existing spectroscopy setup, in order to take low temperature (liquid helium-cooled) measurements of different material classes to assess their interactions with terahertz (THz) radiation.

A significant part of my work involved mastering the use of a continuous flow cryostat and its control system. This experience was complemented by designing CAD parts for holding samples, which was crucial for improving experimental setups. Additionally, I delved into the components of a fibre-based system and continuous wave (CW) laser operation, exploring measurements with high amplitude sensitivity and understanding the limitations posed by phase-based sensitivity.

We tackled issues related to mode hopping and phase noise, implementing strategies to counter these problems and considering system-level implications. This comprehensive approach allowed me to build a robust understanding of the metrics used in system setups, going beyond just the key material metrics needed for extraction.

Data analysis formed a core part of my research, particularly smoothing in frequency domain methods. I tested three types of novel semiconductor materials to determine if useful material metrics could be extracted, though further comparisons with Terahertz Time-Domain Spectroscopy (TDS) are required.

Looking ahead, my future work will focus on the order of measurements and employing statistical methods to enhance repeatability and resolution of metrics. This exchange has been instrumental in honing my experimental techniques and analytical skills, laying a strong foundation for continued research in this field.”

Benefits to the UK materials and quantum community

“This exchange significantly benefits the UK materials and quantum community by advancing experimental techniques and analytical methodologies for material measurements at low temperatures, crucial for quantum applications. The skills and knowledge gained in liquid helium temperature measurements, continuous flow cryostat systems, and fibre-based THz interactions directly contribute to the development of more precise and reliable quantum technologies. This aligns with the M4QN initiative’s aim to foster innovation and collaboration in quantum materials research, enhancing the UK’s leadership in this field. The findings and methodologies developed will aid my PhD research and have fostered future collaborations between my host and home research groups.”

Visit outcomes

Kumaran says, “These include characterisation of quantum materials, sharing of knowledge regarding THz detection, exchange of ideas between material science, engineering and physics, and further collaboration and visits to advance material characterisation and compare time domain and frequency domain systems. The findings and methodologies developed will aid my PhD research and have fostered future collaborations between my host (Ultrafast Photonics) and home (Semiconductor Physics, Cambridge Centre for Gallium Nitride) research groups. Many thanks to Dr. Harvey Beere, Prof. Rachel Oliver, Dr. Menno Kappers, Prof. Cyril Renaud, and most of all, Dr. James Seddon, for all their support and leadership in the pursuit of cross-disciplinary research.”