Publications by authors named "Noah Yuan"
Article Synopsis
- Superconductors can exhibit a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state due to the Zeeman effect from an external magnetic field, which affects Cooper pairings when symmetries like time-reversal are broken.
- In materials lacking local inversion symmetry, the interplay of the Zeeman effect with spin-orbit coupling (SOC), especially Rashba SOC, allows for the emergence of more accessible Rashba FFLO states across a larger area of the phase diagram.
- The discovery of an unconventional orbital FFLO state in the multilayer Ising superconductor 2H-NbSe offers a new understanding of finite-momentum superconductivity, featuring a defined phase diagram that identifies multiple
Cooper pairs in non-centrosymmetric superconductors can acquire finite centre-of-mass momentum in the presence of an external magnetic field. Recent theory predicts that such finite-momentum pairing can lead to an asymmetric critical current, where a dissipationless supercurrent can flow along one direction but not in the opposite one. Here we report the discovery of a giant Josephson diode effect in Josephson junctions formed from a type-II Dirac semimetal, NiTe.
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- The research highlights the discovery of finite-momentum superconductivity, particularly through the "supercurrent diode effect," which is gaining attention in experimental physics.
- It explains how Cooper pairs, which are essential for superconductivity, can gain finite momentum when subjected to an external magnetic field.
- This results in differing critical currents when flowing in directions parallel and antiparallel to the Cooper pair momentum, suggesting potential applications in superconducting technologies.
Article Synopsis
- Strongly interacting electrons in solid-state systems can show multiple broken symmetries, leading to complex phase diagrams, particularly evident in magic-angle twisted bilayer graphene (TBG).
- Research reveals an anisotropic phase in TBG that appears above the underdoped region of the superconducting dome, where its intersection with the dome correlates with a drop in critical temperature.
- The superconducting state in TBG demonstrates direction-dependent responses to magnetic fields, suggesting that nematic ordering and fluctuations are significant in the behavior of its low-temperature phases.
Crystalline two-dimensional (2D) superconductors (SCs) with low carrier density are an exciting new class of materials in which electrostatic gating can tune superconductivity, electronic interactions play a prominent role, and electrical transport properties may directly reflect the topology of the Fermi surface. Here, we report the dramatic enhancement of superconductivity with decreasing thickness in semimetallic -MoTe, with critical temperature () increasing up to 7.6 K for monolayers, a 60-fold increase with respect to the bulk .
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- The study explores how a Zeeman field (a magnetic field) can trigger a change in the topological properties of two-dimensional metals that have spin-orbit coupling.
- It also reveals that this field can cause a first-order phase transition in superconductors, which involves a sudden shift in the momentum of Cooper pairs.
- Different strengths of spin-orbit coupling result in various phase diagrams for these two-dimensional superconductors when subjected to an in-plane magnetic field.
Room-temperature skyrmion phase in bulk CuOSeO under high pressures.
Proc Natl Acad Sci U S A
April 2020
Article Synopsis
- Skyrmion states in noncentrosymmetric helimagnets have potential applications in areas like high-density data storage and spintronics due to their unique spin textures.
- Researchers expanded the temperature range for skyrmion stability in single-crystalline CuOSeO from a narrow band (55-58.5 K) to a broad range (5-300 K) by applying pressures up to 42.1 GPa and utilizing advanced magnetization techniques.
- The findings suggest that skyrmion states can be more widely present across different crystal symmetries and are stable even at higher temperatures, indicating a greater versatility in their occurrence.
The van Hove singularity in density of states generally exists in periodic systems due to the presence of saddle points of energy dispersion in momentum space. We introduce a new type of van Hove singularity in two dimensions, resulting from high-order saddle points and exhibiting power-law divergent density of states. We show that high-order van Hove singularity can be generally achieved by tuning the band structure with a single parameter in moiré superlattices, such as twisted bilayer graphene by tuning twist angle or applying pressure, and trilayer graphene by applying vertical electric field.
View Article and Find Full Text PDFWe investigate the magnetic phase diagram near the upper critical field of KFe_{2}As_{2} by magnetic torque and specific heat experiments using a high-resolution piezorotary positioner to precisely control the parallel alignment of the magnetic field with respect to the FeAs layers. We observe a clear double transition when the field is strictly aligned in the plane and a characteristic upturn of the upper critical field line, which goes far beyond the Pauli limit at 4.8 T.
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- * A study using group theory reveals different possible pairing symmetries for heavily gated MoS2, including exotic and conventional phases based on electron interactions and spin-orbit coupling.
- * The exotic spin-singlet p+ip-wave phase is notable because it's a topological superconducting phase that breaks time-reversal symmetry and supports unique edge states, which could have implications for quantum computing.