UC San Diego

Sm̳2̳-x̳C̳ex̳CuO̳4̳-̳y belongs to a class of materials known as electron-doped superconductors (Ln̳2̳-x̳Mx̳CuO̳4̳-̳y;Ln = Pr, Nd, Sm, Eu; M = Ce, Th) and has a moderately high superconducting critical temperature, T̳c, of ̃ 20 K at optimal doping (x = 0.15). The trivalent rare earth site is doped with tetravalent Ce or Th; hence the name "electron-doped". Sm̳2̳-x̳C̳ex̳CuO̳4̳-̳y also exhibits a unique magnetic structure at low temperatures (T < 6 K) due to the antiferromagnetic ordering of the Sm³⁺ ions. In this study, thin films of the electron-doped superconductor Sm̳2̳-x̳C̳ex̳CuO̳4̳-̳y (SCCO) have been grown by pulsed laser deposition (PLD) for a cerium concentration range of x = 0.13 to x = 0.19. The films have been characterized through x-ray diffraction, electrical transport, and thermal transport measurements. A temperature versus cerium content (T-x) phase diagram has been constructed from the electrical transport measurements and yields a superconducting region similar to that of two of the other electron-doped superconductors Nd̳2̳-x̳C̳ex̳CuO̳4̳-̳y and Pr̳2̳- x̳C̳ex̳CuO̳4̳-̳y. Thermopower measurements were also performed on the samples and show a dramatic change from the underdoped region (x < 0.15) to the overdoped region (x < 0.15). Additionally, the standard Fisher-Fisher-Huse (FFH) vortex glass scaling model has been applied to the magnetoresistance data, as well as a modified scaling model (RRA), and the analysis yields values of the vortex glass melting temperature, T̳g, and critical exponent, v(z- 1). A magnetic field versus temperature (H-T) phase diagram has been constructed for the films with cerium content x >̲ 0.14, displaying the vortex glass melting lines. Magnetoresistance data taken as a function of angle, [theta], is also discussed in the context of the vortex glass scaling model