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APS » Journals » Phys. Rev. Lett. » Volume 103 » Issue 12
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Phys. Rev. Lett. 103, 127003 (2009) [4 pages]

Evidence for a Nodal Energy Gap in the Iron-Pnictide Superconductor LaFePO from Penetration Depth Measurements by Scanning SQUID Susceptometry

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Clifford W. Hicks1, Thomas M. Lippman1, Martin E. Huber2, James G. Analytis1, Jiun-Haw Chu1, Ann S. Erickson1, Ian R. Fisher1, and Kathryn A. Moler1
1Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, 94305, USA and Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
2Departments of Physics and Electrical Engineering, University of Colorado Denver, Denver, Colorado, 80217, USA

Received 1 April 2009; published 18 September 2009

We measure changes in the penetration depth λ of the Tc≈6  K superconductor LaFePO. In the process, scanning SQUID susceptometry is demonstrated as a technique for accurately measuring local temperature-dependent changes in λ, ideal for studying early or difficult-to-grow materials. λ is found to vary linearly with temperatures from 0.36 to ∼2  K, with a slope of 143±15  Å/K, suggesting line nodes in the superconducting order parameter. The linear dependence up to ∼Tc/3, similar to the cuprate superconductors, indicates well-developed nodes.

© 2009 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.103.127003
DOI:
10.1103/PhysRevLett.103.127003
PACS:
74.25.Nf, 74.20.Rp
 
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