New Films Bring Quantum Computing a Step Closer to Reality

Growing palladium ditelluride (PdTe) thin films with properties matching bulk crystals has now been achieved. Hee Taek Yi of Rutgers University, the University of Science and Technology of China, Carnegie Mellon University, and the Chinese Academy of Sciences, and colleagues have successfully grown high-quality, superconducting PdTe films using molecular beam epitaxy (MBE). The resulting films exhibit superconductivity, a state where electrical current flows without resistance. Achieving this required a specific growth technique, MBE, utilising a structural transformation during the deposition process.

These films demonstrate superconducting properties comparable to bulk materials and show excellent stability in air. Hee Taek Yi and colleagues have fabricated high-quality, superconducting films of palladium ditelluride (PdTe), a promising candidate for topological superconductivity which could underpin the development of strong quantum computers. Creating these thin films with properties matching bulk crystals has historically been a key challenge, but MBE proved successful.

MBE is a highly precise method of building materials layer by layer, with atomic precision. The resulting PdTe films exhibit superconductivity at approximately 4.43 Kelvin, with excellent stability when exposed to air, and demonstrate two-dimensional superconducting behaviour. These findings open new avenues for exploring Majorana physics and topological superconductivity, with further details regarding the growth process and characterisation of these films presented below.

Superconductivity emerges in palladium ditelluride films via topotactic structural control

A superconducting transition onset temperature of 4.43 K has been achieved in molecular beam epitaxy-grown palladium ditelluride (PdTe) films, comparable to bulk crystals but previously unattainable in thin film form. Earlier attempts to create PdTe thin films with similar superconducting properties consistently failed due to the material’s delicate structure and the difficulty of replicating it without imperfections. The breakthrough hinged on a topotactic transformation, a structural rearrangement, from a PdTe₂ buffer layer into the desired PdTe phase under carefully controlled tellurium-deficient conditions.

Exceptionally high carrier mobilities were revealed within the films, reaching 434 and 2,885 cm²/Vs for holes, and 343 and 2,573 cm²/Vs for electrons, measured at 7 Kelvin. These values indicate minimal scattering and suggest the high quality of the grown material. Detailed Hall effect measurements confirmed these findings, alongside carrier densities of 7.3x 10²⁰/cm³ and 2.6x 10¹⁹/cm³ for electrons, with corresponding values for holes. A strong residual resistance ratio, or RRR, was demonstrated across varying film compositions, indicating strong superconductivity, and atomic force microscopy showed a smooth film surface for optimised samples, free from excess palladium clusters observed in less successful growths.

Researchers of Singapore are edging closer to realising fault-tolerant quantum computers, with new superconducting materials offering potential building blocks. A viable method for growing palladium ditelluride films has been found, a promising candidate for hosting Majorana zero modes, quasiparticles theorised to be essential for stable quantum information. However, achieving superconductivity and air stability, as demonstrated here, is insufficient; definitively proving the existence of these elusive Majorana modes within the material’s structure remains the key next step.

These 4.43 K results are promising, but do not yet demonstrate the emergence of Majorana zero modes, and scaling up production remains a significant hurdle. Despite the ongoing need to confirm the presence of Majorana zero modes, demonstrating air-stable superconductivity in palladium ditelluride films represents an important advance. Successfully growing these high-quality films via molecular beam epitaxy provides a reliable platform for further investigation into topological superconductivity and potentially, fault-tolerant quantum computing architectures.

Establishing a pathway to stable, two-dimensional superconductivity in palladium ditelluride opens new research directions in topological quantum computation. Crucially, these films exhibit air stability alongside superconductivity at approximately 4.43 Kelvin, a combination vital for practical device development. Investigation is now prompted into whether these films host Majorana zero modes, quasiparticles theorised to be essential for building strong quantum computers; confirming their presence is the next critical step.

Researchers have successfully grown high-quality, superconducting palladium ditelluride films using molecular beam epitaxy. This achievement addresses a key challenge in materials science, as previous attempts struggled to create films with robust superconducting properties comparable to bulk crystals, reaching 4.43 K. The resulting films also demonstrate excellent air stability and two-dimensional superconducting behaviour, making them a promising material for exploring topological superconductivity. The authors suggest that further investigation will focus on confirming the presence of Majorana zero modes within these films.