Thursday, January 15, 2015

The Day of Inconclusive Data: Lab Book 2015_01_15

In all likelihood, we’ll go with a resistive measurement, (to detect the superconducting state or lack thereof), using a small lead wire.  The following setup is from an Alfred Leitner video.  We’ll use something even simpler, probably just a lead wire with a four point probe attached.  By the way, if you're new to the game, scroll to the bottom for background information.

We could sputter a line of lead onto a glass slide, but I don’t see the benefit yet. Working on finding out what it is.

Check this out later in the day per shaping samples:

I’m performing the check on the resistance of the primary coil as its cooled by liquid nitrogen.  The idea is that yesterday’s increase in output ignal with the superconductor ooled may have noly been do to the primary pulling more current as its resistance ramped down.  Here are a few pictures of the assembly being taken apart for the present work:






A one ohm resistor has been placed in series with the primary coil.  The readout across the resistor is proportional to the current through the circuit.  The resistor signal is the smaller signal in the following picture.

The basic lesson of the day was not to build coils that can move in any possible way.  The second attempt to check for reduced resistance, (which should happen), had contradictory results.  The first and final attempts returned the expected results, but they’re not reliable given the first two runs.  The available data follows.



First attempt:
Room temp:

Post-cooling with liquid nitrogen:


Second Experiment:
Pre-cooling:




Post-cooling:

This is also where it was observed that the oscillator has a significant phase shift.


Third experiment:
pre-cooling:


post-cooling:





Background
Hirsch's theory of hole superconductivity proposes a new BCS-compatible model of Cooper pair formation when superconducting materials phase transition from their normal to their superconducting state[1].  One of the experimentally verifiable predictions of his theory is that when a superconductor rapidly transitions, (quenches), back to its normal state, it will emit x-rays, (colloquially referred to here as H-rays because it's Hirsch's theory).

A superconductor can be rapidly transitioned back to its normal state by placing it in a strong magnetic field.  My experiment will look for H-rays emitted by both a Pb and a YBCO superconductor when it is quenched by a strong magnetic field.
This series of articles chronicles both the experimental lab work and the theory work that’s going into completing the experiment.

The lab book entries in this series detail the preparation and execution of this experiment… mostly.  I also have a few theory projects involving special relativity and quantum field theory.  Occasionally, they appear in these pages.

Call for Input
If you have any ideas, questions, or comments, they're very welcome!

References
1.  Hirsch, J. E., “Pair production and ionizing radiation from superconductors”, http://arxiv.org/abs/cond-mat/0508529

2 comments:

Blaise said...

I worked on high tc ceramic superconductors many years ago. I just wanted to point out that the reason four point resistance measurements are made on small samples (like the sputtered lead) is to increase the resistance of the sample. If the cross section of the sample is too large, it is very difficult to see a transition.

Your coil set up looks like your are attempting to measure the transition with something like a magnetic induction -- you might want to try a setup like an AC susceptometer. The trick to these is way cool. The inner coil is in two sections, with a reverse in winding in the middle. This allows the noise to cancel out, which is the principle behind the humbucker guitar pickup:

http://orbi.ulg.ac.be/bitstream/2268/20716/2/Cryogenics_38_839_authorpostprint.pdf

Hamilton Carter said...

Hi Blaise,

Thanks for the guitar pickup reference! I was trying to build a simple, quick and dirty susceptometer. Since we don't need to know the transition temperature, just the fact that the sample did transition, things should be simpler. However, it's even easier just to go with transitions on wires near the sample as a determination.