Vortex state studies in a weakly pinned low Tc superconductor - Ca3Rh4Sn13

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Synopsis:-In type–II superconductors, the mixed phase of the (H-T) phase diagram has been constantly under purview both from experimental and theoretical view points, since its inception. After the discovery of high Tc superconductors [1], vortex phase diagram of conventional low Tc type–II superconductors like Nb [2, 3], 2H-NbSe2 [4–6], YNi2B2C [7, 8], Ca3Rh4Sn13 [9– 12], etc. have been revisited several times to search for similarities/differences with that of the high Tc superconductors [9, 13–17]. This (H-T) phase diagrams are affected by a lot of parameters like coherence length (ξ ), penetration depth (λ ), static disorder, anisotropy, quantum fluctuations, temperature fluctuations, order parameter, etc. Hence, it is the natural interest of a physicist to study the various vortex phases and its transformations in the (H-T) phase space of a low Tc type–II superconductor to prove its genericness with that of the high Tc superconductors. The critical current density (Jc), which arises due to the presence of inhomogeneities in the atomic lattice, has the potential to provide the information about the correlation volume (Vc) within the vortex matter, via the collective pinning description (Jc ∝ V−1/2 c ) [18, 19]. Apart from the direct measurement, the information of this material attribute Jc, can be derived from the width of the magnetization hysteresis loop [20]. The two well documented anomalous features of the magnetization hysteresis loops observed in the mixed phase of the type–II superconductors are the second magnetization peak (SMP) and the peak effect (PE) phenomena. The PE phenomenon is interpreted as a rapid collapse of the elastic moduli of the vortex solid compared with that of the pinning force at the incipient flux line lattice melting transition [2, 21–25]. The SMP on the other hand is now widely accepted as a fingerprint of transition from a Bragg glass (BG) phase (i.e., a vortex state without topological dislocations) to a multi-domain vortex glass (VG) phase, a state with dislocations [11, 26–28].
Supervisor: Dilip Pal