Magnetic field dependence of the coherence length and penetration depth ofMgB2single crystals

We report on specific heat and Hall probe magnetization measurements in magnesium diboride single crystals. A magnetic field dependence of the coherence length has been deduced from the former assuming that the electronic excitations are localized in field dependent vortex cores in which case is related to the Sommerfeld coefficient = Cp /T T→0 throughout, H /a0 2 a0 being the vortex spacing . The reversible part of the magnetization has been analyzed with a phenomenological Ginzburg-Landau model introducing field dependent parameters i.e., penetration depth and which account for the decreasing contribution of the -band with increasing field. This approach perfectly reproduces the experimental data by combining the field dependence of deduced from Cp 1/ 2 B with an almost linear increase of from 450 A at low field to 700 A close to Hc2. These field dependences can then be used to consistently describe the field dependence of the critical current density, small angle neutron scattering form factor, and muon spin relaxation rate.