Twisted Bilayer WSe2 Superconductivity Evolves Smoothly across 3.65° to 5.0° Twist Angles, Linking to Fermi Surface Reconstruction

Superconductivity in layered materials gains new understanding through research into twisted bilayer tungsten diselenide, a material exhibiting remarkable electronic properties. Yinjie Guo, John Cenker, and Ammon Fischer, alongside their colleagues, investigate how the superconducting state changes with varying twist angles within the material. Their work addresses a key question arising from initial observations, which revealed seemingly different superconducting behaviours at specific angles, and demonstrates a smooth evolution of the superconducting state across a range of twist angles. This research connects previously distinct observations and establishes twisted transition metal dichalcogenides as a powerful platform for exploring correlated electronic phases, offering new insight into the fundamental mechanisms driving superconductivity in these materials.

Twisted Bilayer WSe2 Superconductivity and Phase Evolution

Researchers investigate how superconductivity changes with twist angle in twisted bilayer WSe2, a material where electrons interact strongly due to their confinement within the twisted structure. The team systematically mapped the superconducting critical temperature, identifying both conventional and unconventional superconducting phases, and discovered the superconducting behaviour peaks at approximately 5. 8 degrees before decreasing with further twisting. This detailed mapping reveals a complex interplay between superconductivity, electron correlation, and the filling of electronic states within the material.

The method involves fabricating high-quality twisted bilayer WSe2 devices and carefully measuring their electrical resistance at different temperatures. Detailed analysis demonstrates a strong connection between the superconducting temperature and the filling of the moiré flatbands, suggesting superconductivity arises from the correlated electrons within these bands. Furthermore, the team observed enhanced electron correlations near the superconducting phase, indicating a possible link between these correlations and the emergence of superconductivity. These findings establish a detailed map of the superconducting phase diagram, demonstrating a maximum critical temperature of approximately 2. 2 Kelvin at a 5. 8-degree twist angle.

Twisted Bilayer WSe2 Exhibits Robust Superconductivity

This research details the fabrication and characterization of twisted bilayer WSe2 devices to understand the emergence of superconductivity. Scientists combine experimental techniques with theoretical calculations to explore the role of electron interactions and the nature of the superconducting state. They focus on understanding how different electron orbitals and their momentum contribute to the superconducting pairing mechanism. Device fabrication begins with carefully stacking layers of twisted bilayer WSe2, graphite, and hexagonal boron nitride on a substrate. Individual flakes of these materials are exfoliated and patterned into a specific geometry using etching techniques.

Metal contacts are deposited to provide electrical connections, and the choice of contact material influences the material’s doping. Electrical measurements are performed at very low temperatures using a cryostat and a lock-in amplifier to detect subtle changes in resistance. Researchers use both four- and two-terminal measurements, and measure the differential conductance to probe the electronic density of states. The critical temperature, where superconductivity emerges, is carefully identified by sweeping across the superconducting region and finding the point of lowest resistance. Theoretical modeling employs a multi-orbital Wannier model to capture the essential physics of the moiré flat bands, using localized orbitals to describe the electronic states and including a long-ranged Coulomb interaction between electrons. Functional Renormalization Group calculations are used to study the emergence of electronic order from first principles, tracking the evolution of interactions as energy scales are lowered. Hartree-Fock calculations provide a mean-field description of the electronic structure and interactions, using a supercell to capture the relevant momentum-space structures.

Twist Angle Links Superconductivity and Antiferromagnetism

This research demonstrates a smooth evolution of superconducting and antiferromagnetic states in twisted bilayer WSe₂ across a range of twist angles. By systematically mapping the phase diagram, scientists connected previously distinct observations, revealing a consistent underlying mechanism. The findings indicate superconductivity consistently emerges adjacent to antiferromagnetic phases, regardless of the specific twist angle or the position of Van Hove singularities within the material’s electronic structure. This close association strongly suggests that spin fluctuations mediate the superconducting pairing across the entire range of angles studied. The team’s work establishes twisted transition metal dichalcogenides as a unique platform for investigating correlated electron phases, allowing systematic variation of the interaction strength relative to the electronic bandwidth. While the research indicates a trend towards stronger correlation with decreasing twist angle, even at the smallest angle examined, the material remains in an intermediate coupling regime, suggesting a gradual evolution rather than an abrupt transition to strongly correlated Mott physics.