Signatures of a high-temperature collective electronic phase with superconductivity-like characteristics and a giant pressure effect in networks of boron-doped ultrathin carbon nanotubes

Abstract

We present data consistent with a high-temperature collective electronic phase with superconductivity-like characteristics in three dimensional networks of boron doped, ultrathin carbon nanotubes (CNTs) grown inside the 5 Angstrom channels of ZSM-5 zeolite. Confinement stabilizes (2,1) CNTs that are otherwise dynamically unstable, while boron doping shifts the Fermi level towards a van Hove singularity, as supported by ab-initio calculations. The resulting CNT network exhibits multiple, mutually consistent signatures of an electronic condensate with the typical characteristics of a high temperature superconductor at ambient pressure. DC magnetization and AC susceptibility measurements reveal the onset of a Meissner response between 220 and 250K, with compacted samples achieving up to 93 percent of full diamagnetic screening. Electrical transport shows a sharp resistive transition with extrapolated Tc = 239K and vanishing resistance in optimized samples. Specific heat measurements display a reproducible anomaly at 233 to 236 K that broadens under magnetic field, consistent with strong fluctuations. Point contact spectroscopy identifies three energy gaps, including a leading gap of 30 meV whose temperature dependence follows BCS expectations for Tc = 224K, and exhibits particle-hole symmetry and Andreev reflection. Remarkably, applying pressures below 0.1 kbar enhances Tc by nearly 100K and modulates the room temperature resistance by more than three orders of magnitude, suggesting a pressure driven 1D to 3D crossover in the CNT network. These results identify boron doped ultrathin CNT networks as a promising carbon-based platform for near ambient temperature superconductivity and reveal an unusually large pressure sensitivity with potential technological relevance.