Scanning SQUID microscopy study of electron-doped high-Tc superconductors

Local magnetic images of electron-doped Nd2−xCexCuO4 (NCCO) superconducting single crystals above and below the critical temperature Tc 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 3 K under a low magnetic field (∼1 μT) revealed vortex patterns clearly. These vortex patterns totally disappeared at temperatures higher than Tc. In contrast, when the crystal is cooled below Tc 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.