2001/08/27 by Ch. Niedermayer, C. Bernhard, Todd Holden +4 · 5 citations
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Superconductivity in MgB2 and Alloys #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.65.094512
published as Phys. Rev. B 65, 094512 (2002) · 15 pages, 4 figures
arxiv created 2001/08/27 · openalex publication_date 2002/02/13 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/30
The magnetic vortex lattice (VL) of polycrystalline MgB2 has been investigated by transverse-field muon spin relaxation (TF-\ensuremathμSR). The evolution of the TF-\ensuremathμSR depolarization rate \ensuremathσ, which is proportional to the second moment of the field distribution of the VL, has been studied as a function of temperature and applied magnetic field. The low-temperature value \ensuremathσ exhibits a pronounced peak near Hext=75mT. This behavior is characteristic of strong-pinning-induced distortions of the VL which put into question the interpretation of the low-field TF-\ensuremathμSR data in terms of the magnetic penetration depth \ensuremathλ(T). An approximately constant value of \ensuremathσ, such as expected for an ideal VL in the London limit, is observed at higher fields of Hext>0.4T. The TF-\ensuremathμSR data at Hext=0.6T are analyzed in terms of a two-gap model. We obtain values for the gap size of \ensuremathΔ1=6.0(3)meV [2\ensuremathΔ1/kBTc=3.6(2)], \ensuremathΔ2=2.6(2)meV [2\ensuremathΔ2/kBTc=1.6(1)], a comparable spectral weight of the two bands, and a zero-temperature value for the magnetic penetration depth of \ensuremathλab\ensuremath≈100nm. In addition, we performed \ensuremathμSR measurements in zero external field. We obtain evidence that the muon site (at low temperature) is located on a ring surrounding the center of the boron hexagon. Muon diffusion sets in already at rather low temperature of T>10K. The nuclear magnetic moments can account for the observed relaxation rate and no evidence for electronic magnetic moments has been obtained.