Evidence for room temperature superconductivity associated with a first-order phase transition

TL;DR

This study presents evidence of room temperature superconductivity in a modified niobium sheet, exhibiting zero resistance, the Meissner effect, and thermal hysteresis, suggesting a first-order phase transition unrelated to BCS theory.

Contribution

It reports the discovery of high-temperature superconductivity associated with a phase transition and magnetic properties in a niobium-based material, challenging conventional BCS explanations.

Findings

Electrical resistance drops to zero at 175 K and persists up to 290 K.

Meissner effect observed with remnant magnetization at 300 K.

Superconducting transition exhibits thermal hysteresis consistent with first-order transition.

Abstract

By making periodic thru-holes in a suspended film, the phonon system can be modified. Motivated by the BCS theory, the technique -- so-called phonon engineering -- was applied to a metallic niobium sheet. It was found that its electrical resistance dropped to zero at 175 K, and the zero-resistance state persisted up to 290 K in the subsequent warming process. Despite the initial motivation, neither these high transition temperatures nor the phase transition with thermal hysteresis can be accounted for by the BCS theory. Therefore, we abandon the BCS theory. Instead, it turns out that the metallic holey sheet is partly oxidized to form a niobium-oxygen square lattice, which has points of resemblance to a copper-oxygen plane, the fundamental component of cuprate high-$T_{c}$ superconductors. Therefore, the pairing mechanism underlying this study should be related to that of cuprate high-$T_{c}$ superconductors, which we may not yet understand. In addition to the electrical results of zero resistance, the holey sheet exhibited a decrease in magnetization upon cooling, i.e., the Meissner effect. Moreover, the remnant magnetization was clearly detected at 300 K, which can only be attributed to persistent currents flowing in a superconducting sample. Thus, this study meets the established criteria for a conclusive demonstration of true superconductivity. Finally, the superconducting transition with the unambiguous thermal hysteresis is discussed. According to Halperin, Lubensky, and Ma, or HLM for short, any superconducting transition must $always$ be first order with thermal hysteresis because of the intrinsic fluctuating magnetic field. The HLM theory is very compatible with the highly oriented system harboring two-dimensional superconductivity.