The dance of the electrons

On the day I returned to the lab, Marcus Teague, a post-doc leader in the Yeh Group, was orienting two summer undergraduate interns. As he asked the students questions regarding superconductors and scanning tunneling microscopes (STM) I was happy with the amount of information I readily recalled from previous years. It was a good sign that I was ready to build on the content and skills I had already mastered. This may be expected of a graduate student at Caltech, but I am not a graduate student at Caltech. I am a High School physics teacher.

One of the first tasks assigned to me this summer, as I returned for my third year as an IQIM research intern, was to build and solder a connecting cord for the cryocooler in which we stored superconductors. That’s right – I have been working on cutting edge research involving high temperature superconductivity. But back to the soldering. This cord would communicate information, such as temperature and voltage, from the sensor. It had been years since my undergraduate soldering days at UCLA, but it turned out I was not so rusty. I was able to solder the tiny connecting pieces and show the undergraduate research students how to solder.

This summer I made additional tips for STM. Again, we chemically etched the tips using a Calcium Chloride solution in order to reach an ideal thickness of 1 atom across. We also employed the physical stretch and clip approach to make tips. Each person in the lab has their own philosophy on the best method to make tips. It’s amusing and interesting to compare the different techniques for attempting to make sharp, symmetric tips. Whether chemical or physical, the process to make sharp tips is tedious and time consuming, but imperative for a scan with good resolution.

I also worked with Kyle Chen again for certain projects, one of which involved making a low pass filter which would cut out signals above 2 GHz. We wrapped copper wire around a skewer in order to make a tiny solenoid. Care was taken to ensure the number of loops in one direction was matched in the other to avoid creating a net magnetic field. My first attempt was pathetic, but with each trial and error, I was able to construct decent solenoids. The completed solenoids were soldered to a SMA connector (like the one used for coaxial cable) which became one end of the RF filter. In order to connect the copper tube and SMA electrically, a silver epoxy is used. The solenoids were slid carefully into a small copper tube and then filled with the epoxy, a mixture of copper powder and Stycast A and B at a ratio of 100:28. Silver apoxy needs high temperature baking, above 100 degrees Celsius, in order to set, so the system was then baked in order to solidify our new low pass filter to be placed alongside the sample for STM testing.

This summer we also continued testing the YBCO superconducting samples I helped to make two summers ago with Professor Feng. After etching, the procedure to load the sample into the long, cylindrical, central tube required detailed planning. As with last year, the hood was flushed with Argon gas and then vacuum pumped in order to reduce contaminants. Using gloves in the hood, the sample is daintily set into place. Lifting the giant cylinder with the sample took four of us: two for lifting, one for holding it from the base within the hood and one person adjusting the gas levels.

Next we took the cylinder with the sample downstairs to the subbasement to be vacuum pumped and baked in order to expel all gaseous particles. Finally the central tube was loaded into the STM central chamber and the cooling process began, first with liquid nitrogen and then with liquid helium. Finally, it was time to scan the superconducting samples.

Last summer’s scans of the superconductor were in the 500 mV range. However, this summer’s scans are within 150 mV which will lead to much better resolution of the image and possibly valuable enough data to publish.

Each Friday Nai-Chung Yeh has a group meeting with everyone working in the lab. She thoughtfully discusses each persons’ progress, contributions, and questions from the past week. Her genuine curiosity and passion to discuss the best methods for experimentation are inspirational. She is expressive with her hands as she explains a concept, such as how she thinks the polymer doping is affecting the graphene samples. Each week she inevitably goes to the whiteboard and draws a picture of the hypothesized phenomenon observed in the data for that week. She gives insights from her vast wealth of background knowledge and suggests applicable equations, troubleshooting techniques, and information found in the current literature. It is fascinating to watch her warmly lead this group to a deeper understanding of the research topics at hand. I am moved by her work ethic and ability to balance oversight of the graphene projects, topological insulators, superconductors, and possible new solar cell technology. She supervises each sub-projects’ progress while writing papers, traveling the world over to present, as well as secure funding for research.

It is difficult to believe yet another year has passed. Again it is time to return to my classroom to meet my new 150 students, to get them fired up for learning about the exciting world of Physics. I am eager to share my learning experiences from the last three summers at Caltech.

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