New Material Hosts ‘Majorana’ Particles for Robust Quantum Computing Networks

Researchers are actively pursuing higher-order topological superconductivity as a pathway to creating stable and manipulable Majorana networks, circumventing the limitations of vortex-based approaches. Yongting Shi from the Institute of Applied Physics and Computational Mathematics, Qing Wang from the Anhui Provincial Key Laboratory of Low-Energy Quantum Materials and Devices, and Zhen-Guo Fu et al. demonstrate a symmetry-protected realisation of this phenomenon within a MnXPb (X=Se, Te)-Pb heterostructure. Their work reveals that the unique boundary properties of antiferromagnetic topological insulators naturally give rise to Majorana corner modes at the interfaces between superconducting and magnetic regions. Combining first-principles calculations with theoretical modelling, the team show robust corner localisation and, crucially, the potential for purely electrical control over Majorana fusion and braiding in a two-dimensional triangular geometry, establishing MnXPb as a promising platform for future quantum computation.

This breakthrough centers on manipulating Majorana zero modes, exotic quasiparticles considered prime candidates for building stable and scalable quantum bits.

Unlike existing approaches that often rely on complex structures involving vortices or magnetic fields, this work demonstrates a route to engineer Majorana modes localized at the corners of two-dimensional materials, offering a simpler and more controllable architecture. Researchers propose utilizing heterostructures composed of antiferromagnetic topological insulators, specifically, monolayer MnXPb2 (where X represents selenium or tellurium) combined with lead, to achieve this unique state.
The core of this discovery lies in the intrinsic boundary properties of these antiferromagnetic topological insulators. These materials exhibit a dichotomy at their edges, possessing gapless Dirac states protected by time-reversal symmetry on antiferromagnetic boundaries and magnetic gaps on ferromagnetic edges.

When brought into proximity with a superconductor, this boundary contrast naturally generates Majorana corner modes, functioning as mass domain walls. First-principles calculations, combined with a calibrated effective boundary theory, confirm the robust localization of these modes and, crucially, demonstrate the possibility of electrical control over their fusion and braiding, essential operations for quantum computation.

This research establishes MnXPb2 as a promising platform for creating electrically programmable Majorana networks. The team’s calculations reveal that the interplay between superconducting and magnetic edges effectively binds Majorana zero modes at the corners, offering a pathway to manipulate these modes without the need for external magnetic fields or intricate geometries.

By leveraging the symmetry-enforced properties of the material, the study showcases a method for controlling the quantum state of these corner modes through purely electrical means, paving the way for more practical and scalable quantum devices. The findings represent a significant step towards realizing fault-tolerant quantum computation based on topologically protected qubits.

Computational and Experimental Determination of Magnetic Ground State Properties

Monolayer MnXPb2, where X represents selenium or tellurium, forms the basis of this research into higher-order topological superconductivity. First-principles calculations were performed to confirm the dynamical stability of the trigonal crystal structure, revealing no imaginary modes in the phonon dispersion.

Total-energy comparisons between nonmagnetic, ferromagnetic, Néel antiferromagnetic, and collinear antiferromagnetic configurations identified a collinear in-plane antiferromagnetic ground state as the most stable magnetic ordering. Temperature-dependent magnetic susceptibility measurements, fitted using a Curie, Weiss form, determined a Néel temperature of approximately 92 Kelvin.

The study demonstrates that antiferromagnetic topological insulators possess an intrinsic boundary dichotomy, with antiferromagnetic edges supporting gapless Dirac modes protected by effective time-reversal symmetry. Conversely, ferromagnetic edges exhibit magnetic gaps, creating a natural setting for Majorana corner modes at the intersections of these edge states.

Superconducting proximity then converts the antiferromagnetic edges into one-dimensional topological superconductors, further localizing Majorana zero modes as mass domain walls. Researchers combined these first-principles calculations with a calibrated effective boundary theory to demonstrate robust corner localization of the Majorana modes.

This allowed for the investigation of purely electrical control of Majorana fusion and braiding within a triangular geometry. The work establishes MnXPb2 as a promising platform for electrically programmable Majorana networks in two dimensions, circumventing the need for vortices or external magnetic fields typically required in other proposals.

Structural and magnetic ground state properties of monolayer MnXPb2 compounds

Monolayer MnXPb2, where X represents selenium or tellurium, crystallizes within a trigonal structure exhibiting space group P3m1. Structural optimization reveals lattice constants of 4.72 Å for both a and b parameters, with Mn, X and Pb, Pb bond lengths measuring 2.90 Å and 3.01 Å respectively, for the case of X being tellurium.

These bond lengths are notably shorter than the 3.48 Å observed between manganese and lead atoms, indicating strong intralayer coupling and weak interlayer hybridization. Phonon dispersion calculations confirm dynamical stability, demonstrating the absence of imaginary frequencies throughout the Brillouin zone.

Total-energy comparisons of various magnetic configurations, nonmagnetic, ferromagnetic, Néel antiferromagnetic, and collinear antiferromagnetic, identify the collinear antiferromagnetic configuration as the ground state. Magnetic anisotropy calculations demonstrate an energy preference of 2.62 meV per four manganese atoms for in-plane spin orientation over out-of-plane orientation.

Temperature-dependent magnetic susceptibility measurements, fitted using a Curie, Weiss form, yield a Néel temperature of approximately 92 K. This research introduces a route to higher-order topological superconductivity rooted in the symmetry and boundary structure of antiferromagnetic topological insulators.

These materials possess a boundary dichotomy, with antiferromagnetic edges supporting gapless Dirac modes protected by effective time-reversal symmetry and ferromagnetic edges exhibiting magnetic gaps. Superconducting proximity converts the antiferromagnetic edges into one-dimensional topological superconductors, and the intersections between superconducting and magnetic edges bind Majorana zero modes as mass domain walls. First-principles calculations and effective boundary theory demonstrate robust corner localization and purely electrical control of Majorana fusion and braiding within a triangular geometry, establishing MnXPb2 as a promising platform for electrically programmable Majorana networks in two dimensions.

Majorana modes and electrical control in antiferromagnetic topological superconductor heterostructures

Researchers have demonstrated a symmetry-enforced higher-order topological superconductivity utilising antiferromagnetic topological insulators, specifically within MnXPb (where X represents Selenium or Tellurium) integrated with Lead. This approach generates Majorana corner modes, particles with unique quantum properties, localised at the corners of the material, offering a potential pathway towards scalable and controllable quantum networks without the need for vortices or magnetic fields.

The formation of these modes arises from a natural boundary dichotomy within the antiferromagnetic material, creating mass domain walls when combined with induced superconductivity. First-principles calculations, alongside a calibrated theoretical model, confirm the robust localisation of these Majorana modes at the corners and reveal the possibility of purely electrical control over their fusion and braiding, essential operations for quantum computation, within a triangular arrangement.

This two-dimensional architecture supports dense packing and electrical control, presenting a scalable route for programmable Majorana networks. The authors acknowledge that the stability of the zero modes relies on moderate variations in chemical potential and phase differences, indicating operation within the higher-order topological gap.

This work establishes MnXPb as a promising materials platform for higher-order topological superconductivity, extending beyond this specific compound to encompass other antiferromagnetic topological insulators possessing effective time-reversal symmetry and sizable bulk gaps. The proposed platform is compatible with established thin-film growth and gating techniques, with predicted proximity-induced gaps and magnetic exchange fields suggesting a robust topological regime achievable at cryogenic temperatures. Future research may focus on experimentally verifying these predictions and exploring the potential for integrating magnetism, topology, and superconductivity to create advanced quantum devices.