Despite nearly a century of research since the discovery of superconductivity, there is still no general model able to predict which materials will become superconducting, even in the comparatively simple case of the pure elements.  Thus, systematic studies, through chemical substitution or high-pressure, continue to be the primary means of discovering new superconductors.

 

In my graduate work I used a diamond anvil cell to study pressure-induced superconductivity, predominantly in pure elemental materials.  I performed high pressure experiments on yttrium metal to over 1 Mbar, where T_c reached 20 K. This value, at the time, held the record for the highest T_c of a pure element.  Our analysis of the results of this experiment uncovered an interesting correlation between T_c and the ratio of the Wigner-Seitz radius to the ion core radius leading us to search for high T_c values in scandium and lutetium under pressure.  In scandium, T_c reached 8.2 K at 0.74 Mbar. In lutetium T_c reached 12 K at 1.74 Mbar, among the highest pressures at which a superconducting transition has ever been measured.

 

As a postdoctoral researcher, I have learned several of the sample synthesis methods practiced in this laboratory.  I have focused largely on the growth and characterization of new Fe-based superconductors.  Recently we grew the first single crystals of LaFePO and discovered that, under pressure, T_c is nearly doubled from 7 to 14 K.

 

J. J. Hamlin, R. E. Baumbach, D. A. Zocco, T. A. Sayles and M. B. Maple, "Superconductivity in single crystals of LaFePO", submitted to Journal of Physics: Condensed Matter

 

M. Debessai, J. J. Hamlin and J. S. Schilling, "Comparison of the pressure dependences of Tc in the trivalent d-electron superconductors Sc, Y, La and Lu to Mbar pressures", submitted to Phys. Rev. B

 

T. Matsuoka, M. Debessai, J. J. Hamlin, A. K. Gangopadhyay, J. S. Schilling and K. Shimizu, "Pressure-Induced Superconductivity in CaLi₂", Phys. Rev. Lett. 100, 197003 (2008)

 

J. J. Hamlin and J. S. Schilling, "Pressure-induced superconductivity in Sc to 74 GPa", Phys. Rev. B 76, 012505 (2007)

 

J. J. Hamlin, V. G. Tissen and J. S. Schilling, "Superconductivity at 20 K in yttrium metal at pressures exceeding 1 Mbar", Physica C 451, 82-85 (2007)

 

T. Tomita, J. J. Hamlin, J. S. Schilling, D. G. Hinks and J. D. Jorgensen, "Dependence of Tc on hydrostatic pressure in superconducting MgB₂", Phys. Rev. B 64, 092505 (2001)