Superconductivity in undoped T’-RE2CuO4 with Tc over 30K

Abstract

In this article, we report the superconductivity in T'-RE 2 CuO 4 (RE = Pr, Nd, Sm, Eu, and Gd), which have been for a long time believed as a Mott insulator. Our discovery was achieved by using metal-organic decomposition (MOD), an inexpensive and easy-to-implement thin-film process. The keys to prepare the superconducting films are firing with low partial-pressure of oxygen and reduction at low temperatures. The highest T c of undoped T'-RE 2 CuO 4 is over 30 K, substantially higher than "electron-doped" analogs.Remarkably, Gd 2 CuO 4 , even the derivatives of which have not shown superconductivity so far, gets superconducting with T c onset as high as 20 K. The implication of our discovery is briefly discussed.

Direct theoretical evidence for weaker correlations in electron-doped and Hg-based hole-doped cuprates

“…Our results can provide natural explanations for recent experiments78910111213141516 in which the phase diagram of the electron-doped cuprates exhibits monotonically increasing T c toward zero doping (see Fig. 1(b)).…”

“…1(b)). This behavior has been observed in the carefully-annealed samples of both thin film and single crystal forms78910111213141516. If it is indeed the case, the implication can be profound and the electron-doped side of the phase diagram should be re-drawn (Fig.…”

“…According to a systematic re-investigation of electron-doped samples, RE 2 CuO 4 (RE = rare-earth: Nd, Pr, Sm, etc. ), the superconducting region does not cease to exist as the carrier concentration decreases, but this region extends to very low doping, quite close to zero56789101112131415161718. Further, as the doping approaches zero, the superconducting transition temperature ( T c ) seems to keep increasing with no indication of the dome (see Fig.…”

Material characterization of superconducting T′-Nd2CuO4 films synthesized by metal organic decomposition

“…Recently, however, we have reported superconductivity with T c over 30 K in the parent compounds, T 0 -RE 2 CuO 4 (RE = Pr, Nd, Sm, Eu, and Gd) [1][2][3]. The origin of the sharp contradiction between the past and our results can be traced to impurity oxygen (O ap ) at the apical site.…”

Tunable superconductivity in parent cuprate Pr2CuO4±δ thin films*

“…In 1995, T c of the underdoped Pr 2−x Ce x CuO 4 (PCCO) by the protected annealing was enhanced comparable to that of the optimally doped one 3 . In 2008, the superconductivity in parent thin films T -R 2 CuO 4 (R= Nd, Pr, Sm, Eu, Gd) was achieved by low-temperature annealing under the highvacuum environment 4 . This momentous discovery seemingly challenges the commonly accepted model that high-T c superconductivity results from doping extra carriers into Mott insulators.…”