Lap2 Demonstrates 7.8K Superconductivity at 78 GPa, Linked to Graphenelike Phosphorus Layer Structure Transition

The search for novel superconducting materials receives a significant boost as Mingxin Zhang, Cuiying Pei, and Bangshuai Zhu, from ShanghaiTech University, alongside Qi Wang, Juefei Wu, and Yanpeng Qi, report the discovery of superconductivity in lanthanum diphosphide, LaP2. The team synthesised this material and, through high-pressure experiments, observed a superconducting transition occurring around 30 gigapascals. Crucially, the critical temperature at which superconductivity emerges increases with pressure, reaching 7. 8 kelvin at 78 gigapascals, and synchrotron X-ray diffraction confirms this transition coincides with a structural change revealing graphenelike layers of phosphorus within the material. These findings not only expand our understanding of the LaP2 phase diagram under extreme conditions, but also offer valuable insights into the potential for discovering unique structures and superconducting properties within transition metal phosphides.

Materials containing layers similar to graphene attract significant attention due to their unique electronic structures and potential for superconductivity. In this study, scientists synthesized polycrystalline lanthanum diphosphide and observed a transition to a superconducting state. This research focuses on understanding the fundamental properties of layered materials and exploring their potential applications in advanced technologies, contributing to the growing field of two-dimensional materials and providing insights into the relationship between material structure and superconductivity. The team’s findings advance the development of novel superconducting materials with enhanced performance characteristics.

High-Pressure Synthesis and Electrical Resistance Measurements

Scientists investigated the behaviour of lanthanum diphosphide under high pressure, synthesizing polycrystalline LaP2 to explore its electronic and superconducting properties. The team confirmed the material’s composition using detailed microscopic analysis and spectroscopy, establishing a La to P atomic ratio of 33. 93:66. 07, closely matching the expected composition. Electrical transport measurements, performed using a specialized system and a diamond anvil cell, applied pressures up to 78 GPa, with culets of both 200 and 400μm.

Experiments utilized a beryllium copper gasket and platinum electrodes in a van der Pauw configuration, placing the polycrystalline sample directly into a cubic boron nitride hole without a pressure-transmitting medium. Pressure calibration was achieved using ruby luminescence at room temperature, ensuring accurate pressure determination during experiments. To confirm structural changes accompanying changes in electrical resistance, in situ high-pressure X-ray diffraction measurements were conducted at the Shanghai Synchrotron Radiation Facility, utilizing monochromatic X-rays with a wavelength of 0. 6199 Å and mineral oil as a pressure-transmitting medium.

Optical absorption measurements determined an initial band gap of 0. 6 eV, aligning with theoretical calculations that predicted an indirect band gap of approximately 0. 55 eV. These calculations employed advanced computational methods, including a specific functional and a projector augmented wave method with a kinetic-energy cutoff of 450 eV. The Brillouin zone was sampled using a specific scheme, and convergence criteria of 10-6 eV for total energy and 0.

003 eV/Å for atomic forces were applied. Phonon spectra were calculated using a supercell finite displacement method with 3×3×3 supercells, providing further insight into the material’s stability and electronic structure. The combination of these techniques revealed a pressure-induced superconducting transition around 30 GPa, with the critical temperature increasing monotonically with pressure, nearing saturation at 7. 8 K at 78 GPa.

Lanthanum Diphosphide Superconductivity at High Pressure

Scientists have achieved a superconducting transition in lanthanum diphosphide (LaP2) at high pressure, demonstrating a critical temperature (Tc) of 7. 8 K at 78 GPa. The research team synthesized polycrystalline LaP2 and observed the emergence of superconductivity following the suppression of semiconducting behaviour. Detailed measurements of electrical resistance reveal a clear transition to a superconducting state, with the critical temperature increasing with applied pressure. Experiments utilizing synchrotron X-ray diffraction confirm a structural phase transition to the P6/mmm phase under pressure, indicative of graphene-like phosphorus layers forming within the material.

This structural change coincides with the onset of superconductivity, suggesting a strong link between the material’s structure and its electronic properties. Theoretical calculations further support the stability of these graphene-like phosphorus layers within the high-pressure LaP2 phase. The team meticulously characterized the material, confirming its composition with spectroscopic analysis, revealing a La to P atomic ratio of 33. 93:66. 07, closely matching the stoichiometric ratio of LaP2.

Initial characterization showed LaP2 to be a semiconductor with an indirect bandgap of approximately 0. 55 eV, a value corroborated by optical absorption measurements which yielded a bandgap of 0. 6 eV. Further resistance measurements at 64. 0 GPa, conducted under varying magnetic fields, allowed the team to determine the upper critical field (μ0Hc2) as a function of the critical temperature, revealing key parameters for potential applications. These findings demonstrate a clear pathway towards understanding and potentially harnessing superconductivity in transition metal phosphides under extreme conditions.

Lanthanum Diphosphide Superconductivity and Structural Transition

This research successfully synthesized lanthanum diphosphide and investigated its behaviour under extreme pressure, up to 78 GPa. Scientists observed the emergence of superconductivity within the material following the suppression of semiconducting characteristics, with the critical temperature reaching 7. 8 K at the highest pressures tested. Crucially, in situ high-pressure X-ray diffraction measurements confirmed that this superconducting transition coincides with a structural phase transition to the P6/mmm phase, indicating the formation of graphene-like phosphorus layers within the material’s structure.

Theoretical calculations further support the stability of this P6/mmm phase, providing additional evidence for the role of these buckled phosphorus layers. To the authors’ knowledge, this represents the first experimental observation of graphene-like phosphorus layers within phosphide materials. While the research demonstrates a clear link between structural transition and superconductivity, further investigation is needed to fully understand the underlying mechanisms driving this behaviour. These findings contribute to a greater understanding of the high-pressure properties of lanthanum diphosphide and offer insights into the potential for discovering unique structures and superconductivity in other transition-metal phosphides under pressure.