AC-Susceptibility study on vortex-molecule lattice in supermultilayer cuprate HgBa2Can-1CunO2n+2+δ (n=14)

We investigated that in HgBa2Can-1CunO2n+2+delta, [Hg-1 2(n-1)n], for n >= 6, T-c of about 105 K, vortex melting lines remains constant and independent of number of inner plane CuO2 layers. However the vortex dynamics of the supermultilayer system could be crucially different from that of single or double layer cuprates. Therefore we measured the fundamental and third harmonic AC susceptibility responses to see the vortex dynamics and vortex matter phase diagram of Hg-12(n-1)n (n= 14), the higher member of super-multilayered cuprate superconductors. The Lindemann type vortex melting line was estimated using onset of third harmonic susceptibility (chi 3), at very low h(AC) (50 mOe), and represented by 3D Ginzburg Landau rescaling. Frequency dependence of out of phase susceptibility chi"(T) measured at lower fields of 500 and 1000 Oe. for 10 Hz to 10 kHz, showed resonance behaviour in the temperature region 55-68 K, suggesting rotational and translational creep dynamics of vortex molecule, even below usual melting line. We present schematic vortex phase diagram, considering the response of vortex dynamics to applied AC frequencies, taking into account the crossover temperatures obtained from critical slowing down of spin glass model and extended thermal activated model. (C) 2008 Elsevier B.V. All rights reserved.