Intrinsic dependence of Tc on hydrostatic (He-gas) pressure for superconducting LaFePO, PrFePO, and NdFePO single crystals

N. J. Hillier,1 N. Foroozani,1 D. A. Zocco,2,3 J. J. Hamlin,2,4 R. E. Baumbach,2,5 I. K. Lum,2 M. B. Maple,2 and J. S. Schilling1,* 1Department of Physics, Washington University, CB 1105, One Brookings Dr., St. Louis, Missouri 63130, USA 2Department of Physics, University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA 3Karlsruhe Institut für Technologie, Institut für Festkörperphysik (IFP), Eggenstein-Leopoldshafen, Germany 4Department of Physics, University of Florida, Gainesville, Florida 32611, USA 5Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA (Received 10 November 2012; revised manuscript received 11 December 2012; published 26 December 2012)