Hc6 Stabilizes in Robust Ferrimagnetic Ground State, Suppressing Superconductivity Despite 37.4 K Tc and 0.175 eV Energy Difference

Two-dimensional hydrogenated carbon, known as HC6, presents a compelling opportunity to discover novel electronic behaviours, and scientists predicted it might exhibit superconductivity due to its unique electronic properties. However, Jakkapat Seeyangnok and Udomsilp Pinsook, both from Chulalongkorn University, alongside their colleagues, now demonstrate that HC6 surprisingly favours a robust ferrimagnetic state, energetically more stable than the superconducting phase. This discovery challenges initial expectations and reveals that magnetism, rather than superconductivity, dominates the material’s ground state, with an energy difference substantial enough to persist even at room temperature. The findings illuminate how high electron densities in these materials can lead to competing electronic states, offering valuable insights for the design of future carbon-based magnetic systems.

Researchers discovered that HC6, despite possessing characteristics often linked to superconductivity, unexpectedly stabilizes in a ferrimagnetic ground state. This magnetic state is energetically favoured by 0. 175 electron volts per unit cell over the non-magnetic metallic phase, demonstrating a robust magnetic order that persists even at room temperature. Although the superconducting condensation energy lowers the total energy by approximately 7 meV, this is insufficient to overcome the energetic preference for the ferrimagnetic state, rendering the superconducting phase metastable.

Density Functional Theory of Hydrogenated Carbon

Scientists employed sophisticated computational methods, harnessing density functional theory, to investigate the electronic properties of two-dimensional hydrogenated carbon, designated HC6. Calculations were performed with high precision, employing detailed representations of the electronic structure and refined k-point meshes to ensure reliable results. To facilitate convergence, a smearing technique was applied. To explore magnetic ordering, spin-polarized calculations were conducted for various configurations, consistently converging to a ferrimagnetic phase established as the robust ground state of HC6 with an energy 0. 175 eV per unit cell lower than the non-magnetic state. The team investigated the potential for superconductivity by calculating electron-phonon coupling, revealing a condensation energy of approximately 7 meV, though insufficient to overcome the stability of the ferrimagnetic phase.

Ferrimagnetism Suppresses Superconductivity in Hydrogenated Carbon

This work presents a detailed investigation into the electronic, magnetic, and superconducting properties of two-dimensional hydrogenated carbon, designated HC6, using first-principles calculations. Researchers discovered that despite a high density of states near the Fermi level, a characteristic often associated with superconductivity, HC6 unexpectedly stabilizes in a ferrimagnetic ground state. This magnetic state is energetically favoured by 0. 175 electron volts per unit cell over the non-magnetic metallic phase, demonstrating a robust magnetic order that persists even at room temperature. Calculations reveal that the superconducting condensation energy lowers the total energy by approximately 7 meV, however, this is insufficient to overcome the energetic preference for the ferrimagnetic state, rendering the superconducting phase metastable.

Further analysis revealed extended periodic magnetic ordering with alternating spin orientations. These calculations utilized dense meshes of k-points and q-points, with a Gaussian broadening applied to both electrons and phonons. This research highlights HC6 as a platform for studying the interplay between magnetism and superconductivity in hydrogenated carbon-based materials, providing insight into phase competition and potential routes for functional tuning.

HC6 Favours Magnetism Over Superconductivity

This research demonstrates that two-dimensional hydrogenated carbon, known as HC6, exhibits a robust ferrimagnetic ground state, despite possessing electronic characteristics conducive to superconductivity. Calculations reveal that the ferrimagnetic phase is energetically favoured by a substantial margin, exceeding the energy gained from a potential superconducting state. While the material displays strong electron-phonon coupling, suggesting a critical temperature of 37. 4 Kelvin for superconductivity, this effect is insufficient to overcome the energetic stability of the ferrimagnetic order, leaving superconductivity in a metastable condition.

These findings establish HC6 as a model system for understanding competing electronic instabilities in two-dimensional materials, where a high density of electronic states at the Fermi level can simultaneously promote both magnetism and superconductivity. The team acknowledges that the observed superconductivity remains metastable under equilibrium conditions, but suggests that external factors, such as altering the material’s composition, applying strain, or pressure, may offer routes to stabilize superconductivity or achieve a coexistence of magnetic and superconducting phases. Such control could potentially unlock novel quantum phenomena and enable the development of innovative devices for spintronics and magnetic superconductivity applications.