Origin of superconducting carriers in “non-doped” T′-(La,RE)2CuO4 (RE=Sm, Eu, Gd, Tb, Lu, and Y) prepared by molecular beam epitaxy

Abstract

and RE 3+. The absence of the Cu-O bond stretching due to electron-doping, which is commonly observed in electron-doped T' and infinite-layer superconductors, implies 1 that electron doping via oxygen deficiencies is , at least, not a main source of charge carriers.

The origin of superconductivity in nominally ‘undoped’ T′-La2−xYxCuO4 films

“…Based on our present results and the data from Tsukada et al [2,3], we present a most likely and reasonable mechanism of the superconductive in T -(La, RE) 2 CuO 4 . The electron doping originates from two different microscopic processes of oxygen deficiency, and each of them is indispensable to trigger superconductivity.…”

“…The superconducting phase diagram for Y doping is plotted in figure 3. Superconductivity exists in a narrow Y doping range, i.e., 0.10 x 0.20, which is in agreement with the previous results [3]. The best T Zero c is 13.5 K near the optimal doping x = 0.15.…”

“…For comparison, we also studied the isovalent substitution in Nd 2 CuO 4 (NCO) and Pr 2 CuO 4 (PCO) systems, and no superconductivity was found. Combining our data with the previous results [2][3][4], we present a reasonable scenario about the microscopic depletion process of oxygen upon annealing, which is necessary to induce enough carriers to trigger superconductivity in T -LYCO.…”

“…These T -phase LRCO films have been synthesized by molecular beam epitaxy (MBE), and T c as high as 20 K could be achieved at certain R dopings. There are claims that the electron doping via oxygen deficiencies was, at least, not the main source of charge carriers and that T -LRCO compounds are most plausibly conventional half-filled 'band superconductors' with weak electronic correlation [3,4]. These viewpoints gave rise to strong skepticism because they contradict the acknowledged basic picture of HTSC over the last 20 years.…”