Scanning SQUID microscopy study of electron-doped high-T c superconductors

Abstract: Local magnetic images of electron-doped Nd2−x Ce x CuO4 (NCCO) superconducting single crystals above and below the critical temperature T c were obtained using scanning superconducting quantum interference device (SQUID) microscopy. Surface scanning of the ab-plane of an NCCO (x =0.15) crystal cooled to 3K under a low magnetic field (∼1μT) revealed vortex patterns clearly. These vortex patterns totally disappeared at temperatures higher than T c. In contrast, when the crystal is cooled below T c under an external magnetic field (i.e., additional magnetic field controlled by a coil or plating sample stage), an unusual ‘stripe-shaped’ magnetic image is observed due to alignment of the vortices in a quasi-1D manner. [Copyright &y& Elsevier]