Magnetic field sorting of superconducting graphite particles with T$_c$$>$400K (2410.18020v1)

Abstract: It has been claimed that graphite hosts superconductivity at room temperature, although all efforts to isolate it have been vain. Here we report a separation method that uses magnetic field gradients to sort the superconducting from normal grains out of industrial graphite powders. We have obtained a concentrate of above room temperature superconducting particles. Electrical resistance measurements on agglomerates of sorted grains of three types of graphite show transition temperatures up to T${c{{onset}}} \sim$ 700K with zero resistance up to $\sim$ 500K. Magnetization measurements confirm these values through jumps at \textit{T$_c$} in the zero field cooled curves, and by the occurrence diamagnetic hysteretic cycles shrinking with temperature. Our results open the door towards the study of above room temperature superconducting ill-stacked graphite phases.

• The paper shows superconductivity in graphite particles with transition temperatures exceeding 400K using advanced magnetic sorting techniques.
• It employs a novel Magnetic Decantation Separation method along with vertical and horizontal sorting to isolate superconducting grains.
• Electrical resistance and magnetization tests confirm transitions up to 700K, indicating promising potential for room temperature applications.

Magnetic Field Sorting of Superconducting Graphite Particles with T$_c$>$400K

The paper documents an experimental approach to ascertain superconductivity in graphite particles, claiming transition temperatures surpassing 400K, significantly above the conventional limits observed in cuprate and other known superconductors. The research employs a magnetic separation process to isolate superconducting grains from industrial graphite powders. The identified superconducting transition temperatures range up to approximately 700K, with zero resistance observed up to 500K, confirming superconductivity beyond room temperature.

Methodology and Experimental Design

The central technique utilized in this paper is Magnetic Decantation Separation (MDS), a novel method intended to differentiate between superconducting and non-superconducting graphite particles based on their magnetic properties. This process hinges on a differential migration of graphite particles, exploiting the variance in magnetic susceptibility precipitated by an inhomogeneous magnetic field. Magnetic Vertically Sorting (MVS) and Magnetic Horizontally Sorting (MHS), advanced microfluidic techniques, were also employed to ensure a broader and more selective separation of superconducting particles.

For validation, the paper conducted electrical resistance measurements and magnetization studies on the sorted graphite samples, revealing several high superconducting transition temperatures. Measurement techniques included four-probe and van der Pauw method for resistivity, as well as magnetization cycles, utilizing a Quantum Design MPMS3 magnetometer for analyzing the temperature dependence of magnetization.

Key Findings and Data Presentation

The paper reports multiple superconducting transitions with significant superconducting signals observed at temperatures around 450K to 700K, as evidenced by electrical resistance drop and magnetization cycle analysis. The results are intriguing, especially when viewed alongside diamagnetic hysteresis cycles that diminish in magnitude as the temperature rises, further supporting the occurrence of superconductivity.

The observed phenomena included typical characteristics of granular superconductivity with possible two-dimensional (2D) Berezinskii-Kosterlitz-Thouless (BKT) transitions indicated by Halperin-Nelson fits, and complex transition features pointing toward a mixed dimensionality superconductivity. Such signatures were reminiscent of those found in twisted graphene bilayers, which possibly link the phenomenon to stacking faults or interface-induced superconductivity.

Implications and Future Directions

The results, while emphasizing a promising avenue for room temperature superconductivity, raise substantive questions concerning the exact microscopic mechanism enabling such high-temperature superconductivity in graphite-related materials. The potential presence of flat band physics at play, speculative to be arising from particular stacking orders or defects, suggests an interesting direction for further theoretical exploration and experimental verification.

From an applied perspective, if the ability to isolate and augment these superconducting grains can be scaled, this could lead to revolutionary advancements in the development of materials applicable in superconducting circuits operable at ambient conditions. Future research will likely investigate whether alternative separation and synthesis methods could enhance the yield and purity of superconducting graphite, as well as work to conclusively determine the structural properties and crystal phases responsible for the superconductivity observed.

In summary, this paper significantly contributes to the ongoing exploration of room temperature superconductivity in graphite, laying foundational knowledge for potential practical applications and inviting further studies to understand the complex phenomena associated with superconductivity in carbon-based materials.