Two-dimensional Helical Superconductivity and Gapless Edge Modes Emerge in 1T-WS/2H-WS Heterostructures
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The pursuit of novel superconducting states is driving innovation in materials science, and recent work by Xuance Jiang, Jennifer Cano, and Yuan Ping, along with colleagues at Brookhaven National Laboratory, presents a promising new platform for achieving two-dimensional helical superconductivity. They demonstrate that combining layers of tungsten diselenide with differing structural properties creates a heterostructure exhibiting this unusual state, where superconductivity and topological properties intertwine. This carefully constructed bilayer supports finite-momentum Cooper pairing and, crucially, induces superconductivity in its edge states, leading to a controllable transition to a gapless phase with unique electronic properties. The ability to manipulate these edge states offers a potential pathway towards realising non-reciprocal superconducting transport and building advanced devices based on Majorana particles, representing a significant step forward in the field of topological superconductivity. Superconducting Diodes and Symmetry Breaking Mechanisms Recent research focuses on the superconducting diode effect, a phenomenon where a superconducting device exhibits asymmetric current flow, behaving like a diode but without resistance. This emerging field attracts significant attention as scientists explore ways to break time-reversal symmetry within superconducting materials to achieve this effect. Investigations center on various materials and mechanisms to induce and enhance this asymmetry. Researchers are exploring approaches including manipulating spin-orbit coupling, controlling vortex behavior, utilizing unusual electronic structures, and manipulating chirality within superconducting states. Creating bistable vortex states and engineering asymmetry at material interfaces are also under investigation. These efforts aim to understand and control the fundamental physics driving the superconducting diode effect. Current research involves meticulous material engineering, synthesizing and stacking materials with specific properties to induce asymmetry. Scientists are also fabricating nanoscale devices, such as Josephson junctions and nanowires, to observe and control the effect. Theoretical modeling plays a crucial role, providing frameworks to understand the underlying physics and predict new materials and device designs. Investigations extend to Josephson junctions, exploring the superconducting diode effect within these essential superconducting circuit components. Researchers are also creating devices based on asymmetric vortex behavior. Connections between the superconducting diode effect and topological superconductivity are being explored, alongside the potential for creating Majorana modes. This rapidly evolving field promises new superconducting devices with unique functionalities, combining materials science, condensed matter physics, and nanotechnology. Van der Waals Stacking Induces Helical Superconductivity Scientists have engineered a novel two-dimensional material by van der Waals stacking a monolayer of 1T-WS₂ on top of a monolayer of 2H-WS₂ to realize helical superconductivity, a state characterized by an intrinsic energy gap. This stacking configuration breaks the inversion symmetry of the 1T-WS₂ layer, enhancing Rashba spin-orbit coupling and creating a helical spin texture due to spin-momentum locking. Precise control over the stacking process ensures optimal interlayer alignment and minimized total energy, as confirmed through detailed simulations.
The team employed density functional theory with advanced methods to accurately model van der Waals interactions within the heterostructure. They constructed a tight-binding model using Wannier functions to further analyze the electronic properties. Calculations reveal a charge transfer from the 2H phase to the 1T’ phase, creating an interface dipole potential and realigning the band structures of the two materials, enhancing the superconducting properties. Analysis of the band structure demonstrates that hybridization between the 2H and 1T’ phases pushes the valence band of the 1T’ phase to higher energies, creating hole pockets and increasing the electron density of states at the Fermi level. The low-energy bands are dominated by specific atomic orbitals, consistent with previous analyses of monolayer 1T-WS₂.
Helical Superconductivity Emerges in Van der Waals Heterostructure Scientists have achieved the creation of a two-dimensional helical superconducting phase by combining transition metal dichalcogenide heterostructures. The research demonstrates that van der Waals stacking a monolayer of 1T-WS₂ onto a monolayer of 2H-WS₂ results in a bilayer material exhibiting Rashba superconductivity and finite-momentum Cooper pairing, evidenced by a divergence in particle-particle susceptibility. Experiments reveal that applying an external in-plane magnetic field to this bilayer induces a transition in the helical edge states, moving them from a gapped superconducting phase to a one-dimensional gapless phase characterized by narrow Fermi segments containing zero-energy Bogoliubov quasi-particles. This controllable phase transition serves as a clear experimental signature of 2D helical superconductivity, allowing one edge of the material to remain gapped while the opposite edge becomes gapless. Detailed analysis using density functional theory reveals a charge transfer from the 2H phase to the 1T’ phase, creating an interface dipole potential and realigning the bands of the two phases. Calculations demonstrate that hybridization between the 2H and 1T’ phases pushes the valence band of the 1T’ bands to higher energies, resulting in hole pockets.
The team’s theoretical model captures the nontrivial band topology and spin texture of the Fermi pockets, confirming the potential for tunable states based on this unique heterostructure. Helical Superconductivity in Layered Materials This research demonstrates the potential to realize two-dimensional helical superconductivity through a carefully designed heterostructure composed of transition metal dichalcogenides. By combining specific layers of tungsten diselenide, scientists have created a system exhibiting a unique superconducting state where Cooper pairs possess finite momentum. Calculations reveal that applying an external magnetic field induces divergences in the pair susceptibility, providing strong evidence for this finite-momentum pairing. Importantly, the team predicts that this helical superconducting state manifests in the edge states of the material, and can transition to a gapless phase with a moderate magnetic field, creating a readily observable experimental signature. This transition, characterized by the emergence of zero-energy Bogoliubov quasi-particles, offers a clear fingerprint for identifying this novel superconducting state. While acknowledging the complexity of these layered materials, the researchers suggest this design strategy can be extended to other transition metal dichalcogenide systems, opening avenues for exploring a wider range of two-dimensional helical superconductors. The resulting materials hold promise for applications in nonreciprocal superconducting transport, spintronics, and the development of devices based on Majorana particles. 👉 More information 🗞 Two-dimensional helical superconductivity and gapless superconducting edge modes in the 1T -WS /2H-WS heterophase bilayer 🧠 ArXiv: https://arxiv.org/abs/2512.10157 Tags: