Evidence of surface superconductivity and multi-quanta vortex states in a weakly-pinned single crystal of Ca3Ir4Sn13

• Field-cooled magnetization in superconducting Ca3Ir4Sn13 reveals multi-valuedness.
• The field-cooled magnetization can display paramagnetic peaks.
• M-H curves just below TcTc have features resembling those articulated for multi-quanta vortices.
• Multi-quanta states are considered as characteristics of mesoscopic-sized samples.
• Crossover from multi-quanta to single-quantum vortices follows numerous paths.

We report here the observation of anomalous paramagnetic signal(s) in the isofield field-cooled cool-down magnetization scans (MFCC(T)MFCC(T)) recorded for a single crystal of a low TcTc superconductor Ca3Ir4Sn13. Novel features emanating from the MFCC(T)MFCC(T) response include an oscillatory magnetization behavior below TcTc and a rich multiplicity (non-uniqueness) in magnetization ranging from diamagnetism to paramagnetism at a given H,T value. The metastability in MFCC(T)MFCC(T) has been ascribed to non-unique coexistence of multi-quanta vortex states (LΦ0,Φ0=hc/2e, L>1L>1) and single quantum (L=1L=1, Abrikosov) vortices. Additionally, the isothermal M(H)M(H) scans recorded across a short window of temperature just below TcTc show evidence for only the multi-quanta vortex states in the domain of surface superconductivity, with no fingerprint(s) of pinned Abrikosov lattice.