Tuning the Phase Diagram of MgB$_2$ through Magnetic and Non-magnetic Doping
ORAL
Abstract
Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in MgB$_2$ have revealed a complex VL phase diagram as well as an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski $et$ $al.$, Phys. Rev. Lett. {\bf 111}, 107002 (2013)]. The VL phase diagram is governed by non-local vortex-vortex interactions, which depend sensitively on Fermi surface anisotropies and the mean free path of the host superconductor. We have investigated the effects of modifying the vortex-vortex interaction by non-magnetic (C) as well as magnetic (Mn) doping. SANS studies revealed substantial modifications of the VL phase diagram in single crystals of Mg(B$_x$C$_{1-x}$)$_2$ and (Mg$_x$Mn$_{1-x}$)B$_2$. In the Mn-doped case, a large increase in the longitudinal correlation length ($\xi_L$) was observed. However, VL metastability was still present despite this increase of vortex pinning.
*This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Awards DE-FG02-10ER46783 and DE-AC02-07CH11358. This research is funded in part by the Gordon and Betty Moore Foundation's EPiQS Initiative Grant GBMF4411.
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