Investigation of the formation of high Tc superconducting balls in the presence of

an electric field

Wesley T. Ryle,Kenny Purcell and Angela Adams

Supervised by: Dr. Doug Harper, Dr. George Levin

Solid State Physics Laboratory Western Kentucky University

Overview

• Background information on superconductors• Recent observation of superconducting “balls”• Experimental setup• Results and observations• Possible explanations• Future refinements and studies• Acknowledgements

Superconductivity

• Certain materials that exhibit unique properties when brought to extremely low temperatures

• At a certain critical temperature (Tc), the resistance of a material will sharply fall off to zero

• In addition, the substance is able to repel external magnetic fields

• The critical temperature is an inherent property of a given material

• For some substances, this temperature is relatively high (70-90K)

* This project seeks to examining a recently discovered property of superconductors - the formation of macroscopic spheres in the presence of an electric field

Ball-formation phenomenon

• Recently observed in 1999 by Tao et al.

• Ball formed with various high Tc superconducting powders

• Formation was dependent upon the application of a critical electric field

• Powder did not exhibit this property at temperatures above the Tc

Superconductingball

R. Tao et al., Phys. Rev Lett. 83, 5575 (1999).

Reasons for investigation

• No significant investigation since research by Tao, et al. In 1999

• The mechanisms behind the phenomenon are not understood very well

• Explanation of the phenomenon could lead to further applications

• The experiment is relatively easy to setup (“a table top experiment”)

Experimental Setup

VHigh Tc powder

Aluminum electrodes

Liquid Nitrogen Bath

High speed camera

Experimental Setup II

• Camera with zoom lens mounted directed over the cell

• Styrofoam insulator container for liquid nitrogen bath

• Power supplied from a high voltage source (3000V)

Detailed view of cell

• Cell is surrounded by liquid nitrogen bath

• This brings cell and powder down to a temperature of approx. 77K

• Potential supplied through wires attach be clothes pin (high-tech!)

Parameters for preliminary trials

• Used two high Tc powders: YBa2Cu3Ox (87K) and Bi2Sr2CaCu2O8+x (84K)

• Deposited powder into cooled cell after liquid nitrogen boiling became minimal

• Starting from zero potential, gradually increased the voltage applied to the plates in the cell

• Recorded using a high speed camera capable of a shutter speed of 1/1000 second and frame rate of 1/30 second

Results: Formation of chains at low electric fields

• As the applied voltage is increased, the particles align into chains, allowing a small current to flow across the capacitor

• This is expected of dielectric particles that have become polarized

• As the field strength increases (0-1500V), the chains become tighter and more defined

Breakdown of chains at reported critical field

• Literature reported the formation of superconducting balls is dependent on electric field

• For YBaCuO, this field was reported at 0.45 kV/mm, or for our device, about 1.8 kV.

• At approximately 1700V, the chains of powder broke apart and separated into multiple balls oscillating between the two electrodes

Characteristics of the superconducting balls

• Unlike the results of Tao, et al., we were able to see multiple spheres bouncing between electrodes

• The largest diameter of the balls was on the order of 0.4 mm, consistent with the size reported by Tao, et al.

• Have not yet witnessed to the coagulation of particles into one large ball

0.39 mm

Particle Behavior

• Superconducting balls travel very quickly between the electrodes

• Area of most activity seem centered at edges of electrodes

• Fringing of the electric field apparently traps the particles

Possible reasons for discrepancy with other observations

• Previous paper reported 10% by volume mixture of powder and liquid nitrogen

• When using a large amount of powder, discharging the capacitor became a problem

• Fringing effect of the plates could act as a deterrent for formation

• Difference in the properties of the powders used?

Proposed explanations of the ball formation

• Proposed by original researchers Tao, et al.

• One type of surface tension causes water drops to form spheres

• Another type of surface tension could cause the superconducting particles to form balls

• This theory has an inherent dependence on the electric field

• Superconducting balls will form only at or above a critical electrical field

1. Surface tension effect

2. A close-range attractive force inherent to superconductors

• In this case, two superconducting surfaces, brought in very close proximity to one another (1-3 angstroms) will experience a very strong attractive force

• Due to the Josephson junction effect, two superconducting surfaces will decrease in energy when brought close together

• In this theory, the presence of the electric field is simply a catalyst for collisions between particles

• Once bonded, the force is very strong and hard to overcome

Proposed explanations of the ball formation

Future Refinements and Research

• Additional trials and observations can be executed easily

• A small amount of powder (50g) goes a long way

• Experiment is very low cost yet can still produce important results

• Further trials would attempt to narrow down the explanations for the phenomenon

• Trials must be carried out at room temperature in order to verify the property is superconductive in nature

• Ordinary metals or ceramics can be used to examine and compare behavior

• New and better cells (electrodes) can be fabricated to improve results

Conclusions

• Research conducted thus far at the Solid State Physics Laboratory is a first step toward verifying this property

• Observations made clearly show the formation of multiple balls in the presence of an electric field at temperatures less than Tc

• Results achieved in this experiment do not directly reproduce those results from Tao et al.

• Further study is required to validate data and gain a better understanding of the mechanisms involved in the formation of high Tc superconducting balls

Acknowlegements

• Research funded by a grant from the Kentucky Space Grant Consortium

• Special thanks to Dr. John Andersland, Dept. of Biology for generous use of equipment

• Thanks to Dr. George Levin for proposal of the research project and continued consultation on superconductors

• Research based off work completed at Southern Illinois Univeristy (R. Tao et al., Phys. Rev Lett. 83, 5575 (1999).