Investigation of the formation of high T c 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 (T c ), 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 T c superconducting powders Formation was dependent upon the application of a critical electric field Powder did not exhibit this property at temperatures above the T c Superconducting ball 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 V High T c 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 T c powders: YBa 2 Cu 3 O x (87K) and Bi 2 Sr 2 CaCu 2 O 8+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 T c 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 T c 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).