npj Quantum Materials最新文献

{"title":"Intrinsic constraint on Tc for unconventional superconductivity","authors":"Qiong Qin, Yi-feng Yang","doi":"10.1038/s41535-025-00733-y","DOIUrl":"https://doi.org/10.1038/s41535-025-00733-y","url":null,"abstract":"<p>Can room temperature superconductivity be achieved in correlated materials under ambient pressure? Our answer to this billion-dollar question is probably no, at least for realistic models within the current theoretical framework. This is shown by our systematic simulations on the pairing instability of some effective models for two-dimensional superconductivity. For a square lattice model with nearest-neighbour pairing, we find a plaquette state formed of weakly-connected 2 × 2 blocks for sufficiently large pairing interaction. The superconductivity is suppressed on both sides away from its melting quantum critical point. Thus, the magnitude of <i>T</i>_<i>c</i> is constrained by the plaquette state for the <i>d</i>-wave superconductivity, in resemblance of other competing orders. We then extend our simulations to a variety of effective models covering nearest-neighbour or onsite pairings, single layer or two-layer structures, intralayer or interlayer pairings, and find an intrinsic maximum of the ratio <i>T</i>_<i>c</i>/<i>J</i> ≈ 0.04−0.07, where <i>J</i> is the pairing interaction, given by the onsite attractive interaction in the attractive Hubbard model or the exchange interaction in the repulsive Hubbard model. Our results agree well with previous quantum Monte Carlo simulations for the attractive Hubbard model. Comparison with existing experiments supports this constraint in cuprate, iron-based, nickelate, and heavy fermion superconductors, despite that these compounds are so complicated well beyond our simplified models. As a result, the known families of unconventional superconductivity, possibly except the infinite-layer nickelates, seem to almost exhaust their potentials in reaching the maximal <i>T</i>_<i>c</i> allowed by their respective <i>J</i>, while achieving room temperature superconductor would require a much larger <i>J</i> beyond 400–700 meV, which seems unrealistic in existing correlated materials and hence demands novel pairing mechanisms. The agreement also implies some deep underlying principles of the constraint that urge for a more rigorous theoretical understanding.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"9 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143054860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Z2 flux binding to higher-spin impurities in the Kitaev spin liquid","authors":"Masahiro O. Takahashi, Wen-Han Kao, Satoshi Fujimoto, Natalia B. Perkins","doi":"10.1038/s41535-025-00729-8","DOIUrl":"https://doi.org/10.1038/s41535-025-00729-8","url":null,"abstract":"<p>Stabilizing <i>Z</i>₂ fluxes in Kitaev spin liquids (KSLs) is crucial for both characterizing candidate materials and identifying Ising anyons. In this study, we investigate the effects of spin-<i>S</i> magnetic impurities embedded in the spin-1/2 KSL. Utilizing exact diagonalization and density matrix renormalization group methods, we examine the impurity magnetization and ground-state flux sector with varying impurity coupling and spin size. Our findings reveal that impurity magnetization exhibits an integer/half-integer spin dependence, which aligns with analytical predictions, and a flux-sector transition from bound-flux to zero-flux occurs at low coupling strengths, independent of the impurity spin. Notably, for spin-3/2 impurities, we observe a reentrant bound-flux sector, which remains stable under magnetic fields. By considering fermionic representations of our spin Hamiltonian, we provide phenomenological explanations for the transitions. Our results suggest a novel way of binding a flux in KSLs, beyond the proposals of vacancies or Kondo impurities.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"40 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143056225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Discovery of new topological insulators and semimetals using deep generative models","authors":"Tao Hong, Taikang Chen, Dalong Jin, Yu Zhu, Heng Gao, Kun Zhao, Tongyi Zhang, Wei Ren, Guixin Cao","doi":"10.1038/s41535-025-00731-0","DOIUrl":"https://doi.org/10.1038/s41535-025-00731-0","url":null,"abstract":"<p>Topological materials possess unique electronic properties and hold immense attraction to both fundamental physics research and practical applications. Over the past decades, the discovery of new topological materials has relied on the symmetry-based analysis of the quantum wave function. In this study, we propose an efficient inverse design method CTMT (CTMT: CDVAE, Topogivity, interatomic potentials (IAPs) as realized in M3GNet, and TQC) utilizing deep generative machine learning models to discover novel topological insulators and semimetals in a much-fast and low-cost manner. This method covers the entire process of new crystal structure generation, heuristic rule screening, fast stability estimation, and topology type diagnosis, resulting in 4 topological insulators and 16 topological semimetals. Especially, the newly discovered topological materials include several chiral Kramers-Weyl fermion semimetals and chiral materials with low symmetry, whose topology is previously considered challenging to discern. These findings demonstrate the capability of CTMT in discovering topological materials and its great potential for data-driven inverse design of advanced functional materials.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"148 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143049867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantum order by disorder is a key to understanding the magnetic phases of BaCo2(AsO4)2","authors":"Sangyun Lee, Shengzhi Zhang, S. M. Thomas, L. Pressley, C. A. Bridges, Eun Sang Choi, Vivien S. Zapf, Stephen M. Winter, Minseong Lee","doi":"10.1038/s41535-025-00728-9","DOIUrl":"https://doi.org/10.1038/s41535-025-00728-9","url":null,"abstract":"<p>BaCo₂(AsO₄)₂ (BCAO), a honeycomb cobaltate, is considered a promising candidate for materials displaying the Kitaev quantum spin liquid state. This assumption is based on the distinctive characteristics of Co²⁺ ions (3<i>d</i>⁷) within an octahedral crystal environment, resulting in spin-orbit-coupled <i>J</i>_eff = 1/2 doublet states. However, recent experimental observations and theoretical analyses have raised questions regarding this hypothesis. Despite these uncertainties, reports of continuum excitations reminiscent of spinon excitations have prompted further investigations. In this study, we explore the magnetic phases of BCAO under both in-plane and out-of-plane magnetic fields, employing dc and ac magnetic susceptibilities, capacitance, and torque magnetometry measurement. Our results affirm the existence of multiple field-induced magnetic phases, with strong anisotropy of the phase boundaries between in-plane and out-of-plane fields. To elucidate the nature of these phases, we develop a minimal anisotropic exchange model. This model, supported by combined first principles calculations and theoretical modeling, quantitatively reproduces our experimental data. In BCAO, the combination of strong bond-independent XXZ anisotropy and geometric frustration leads to significant quantum order by disorder effects that stabilize colinear phases under both zero and finite magnetic fields.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"47 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143044151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"2.5-dimensional topological superconductivity in twisted superconducting flakes","authors":"Kevin P. Lucht, J. H. Pixley, Pavel A. Volkov","doi":"10.1038/s41535-024-00719-2","DOIUrl":"https://doi.org/10.1038/s41535-024-00719-2","url":null,"abstract":"<p>Multilayer flakes of two-dimensional materials were recently shown to be tunable by twisting monolayers on their surface. This raises the question whether qualitatively new phenomena can occur in such finite-thickness moiré systems. Here we demonstrate the emergence of distinct topological phases and transitions in N-layered flakes of nodal superconductors with a single monolayer twisted on top of it. We show that a c-axis current transforms the whole system into a chiral topological superconductor. Increasing the current drives a sequence of topological transitions between states characterized by a Chern number increasing from <span>(sim {mathcal{O}}(N))</span> up to <span>(sim {mathcal{O}}({N}^{2}))</span>, well beyond the additive effect of stacking <i>N</i> layers. We predict thickness-independent signatures of these states in the thermal Hall and tunneling microscopy measurements. Twisted superconductor flakes thus provide an example of a “2.5-dimensional” material where the synergy of two-dimensional layers extended in a third dimension realize states inaccessible in either monolayer or bulk materials.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"35 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143044149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pressure-dependent magnetism of the Kitaev candidate Li2RhO3","authors":"Bin Shen, Efrain Insuasti Pazmino, Ramesh Dhakal, Friedrich Freund, Philipp Gegenwart, Stephen M. Winter, Alexander A. Tsirlin","doi":"10.1038/s41535-025-00730-1","DOIUrl":"https://doi.org/10.1038/s41535-025-00730-1","url":null,"abstract":"<p>We use magnetization measurements under pressure along with ab initio and cluster many-body calculations to investigate magnetism of the Kitaev candidate Li₂RhO₃. Hydrostatic compression leads to a decrease in the magnitude of the nearest-neighbor ferromagnetic Kitaev coupling <i>K</i>₁ and the corresponding increase in the off-diagonal anisotropy Γ₁, whereas the experimental Curie-Weiss temperature changes from negative to positive with the slope of +40 K/GPa. On the other hand, spin freezing persists up to at least 3.46 GPa with the almost constant freezing temperature of 5 K that does not follow the large changes in the exchange couplings and indicates the likely extrinsic origin of spin freezing. Magnetic frustration in Li₂RhO₃ is mainly related to the interplay between ferromagnetic <i>K</i>₁ and antiferromagnetic Γ₁, along with the weakness of the third-neighbor coupling <i>J</i>₃ that would otherwise stabilize zigzag order. The small <i>J</i>₃ distinguishes Li₂RhO₃ from other Kitaev candidates.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"45 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142992124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Understanding the microscopic origin of the magnetic interactions in CoNb2O6","authors":"Amanda A. Konieczna, David A. S. Kaib, Stephen M. Winter, Roser Valentí","doi":"10.1038/s41535-024-00715-6","DOIUrl":"https://doi.org/10.1038/s41535-024-00715-6","url":null,"abstract":"<p>Motivated by the on-going discussion on the nature of magnetism in the quantum Ising chain CoNb₂O₆, we present a first-principles-based analysis of its exchange interactions with additional modeling, addressing drawbacks of a purely density functional theory ansatz. This method allows us to extract and understand the origin of the magnetic couplings—including all symmetry-allowed terms - and resolve conflicting model descriptions in CoNb₂O₆. We find that the twisted Kitaev chain and transverse-field ferromagnetic Ising chain views are mutually compatible, although additional off-diagonal exchanges are required for a complete picture. We show that the dominant exchange interaction is a ligand-centered process—involving <i>e</i>_<i>g</i> electrons -, rendered anisotropic by low-symmetry crystal fields in CoNb₂O₆, resulting in dominant Ising exchange. Smaller bond-dependent anisotropies are found to originate from <i>d</i> − <i>d</i> kinetic exchange processes involving <i>t</i>_2<i>g</i> electrons. We demonstrate the validity of our low-energy model by comparing its predictions to measured THz and INS spectra.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"23 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142989359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Robust quantum spin liquid state in the presence of giant magnetic isotope effect in D3LiIr2O6","authors":"T. Takayama, A. S. Gibbs, K. Kitagawa, Y. Matsumoto, K. Ishii, A. Kato, R. Takano, S. Bette, R. Dinnebier, H. Takagi","doi":"10.1038/s41535-025-00727-w","DOIUrl":"https://doi.org/10.1038/s41535-025-00727-w","url":null,"abstract":"<p>The deuterium isotope effect on the honeycomb iridate H₃LiIr₂O₆, a quantum spin-orbit-entangled liquid, was examined by synthesizing D₃LiIr₂O₆. The structural refinements indicate the different character of the interlayer OH and OD bonds, which results in a giant isotope effect on the magnetic interactions; the antiferromagnetic Curie-Weiss temperature |<i>θ</i>_CW| of D₃LiIr₂O₆ increases to ~ 170 K from ~ 100 K of H₃LiIr₂O₆. Nevertheless, the quantum liquid state is robust against the deuterium isotope exchange in contrast to the theoretical prediction that the Kitaev spin liquid is stable only for a limited phase space of magnetic interactions. The bond- and site disorders associated with disordered OD(H) bonds, in combination with Kitaev physics, may play a role in realizing the quantum liquid state.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"205 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142987324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magnetoelectric effect in van der Waals magnets","authors":"Kai-Xuan Zhang, Giung Park, Youjin Lee, Beom Hyun Kim, Je-Geun Park","doi":"10.1038/s41535-025-00725-y","DOIUrl":"https://doi.org/10.1038/s41535-025-00725-y","url":null,"abstract":"<p>The magnetoelectric (ME) effect is a fundamental concept in modern condensed matter physics and represents the electrical control of magnetic polarisations or vice versa. Two-dimensional (2D) van-der-Waals (vdW) magnets have emerged as a new class of materials and exhibit novel ME effects with diverse manifestations. This review emphasizes some important recent discoveries unique to vdW magnets: multiferroicity on two dimensions, spin-charge correlation, atomic ME effect and current-induced intrinsic spin-orbit torque, and electrical gating control and magnetic control of their electronic properties. We also highlight the promising route of utilizing quantum magnetic hetero- or homo-structures to engineer the ME effect and corresponding spintronic and optoelectronic device applications. Due to the intrinsic two-dimensionality, vdW magnets with those ME effects are expected to form a new, exciting research direction.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"29 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142967785","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unconventional broadening of Rashba spin splitting in a Au2Sb surface alloy with periodic structural defects","authors":"Jinbang Hu, Xiansi Wang, Anna Cecilie Åsland, Justin W. Wells","doi":"10.1038/s41535-024-00724-5","DOIUrl":"https://doi.org/10.1038/s41535-024-00724-5","url":null,"abstract":"<p>Most Rashba spin splitting experimentally studied so far has ideal lattice with inversion symmetry broken, which limits the possibility to minimize the presence of spin-degenerate carriers near the Fermi level. Here, we report a novel 2D Au₂Sb surface alloy decorated with periodic structural defects that exhibits modulation on the Rashba spin-orbit coupling band. Spin- and angle-resolved photoemission spectroscopy reveals a Rashba spin-split band with antiparallel spin polarization, significantly broadened compared to the Au₂Sn surface alloy. From the good agreement between the experimental results and DFT calculations, we identify that the broadening of the Rashba bands comes from variations in Sb atom corrugation induced by the periodic three-pointed star-shaped defects. These periodic defects can shift the energy position of the Rashba bands without breaking the in-plane rotational and mirror symmetries. Our findings highlight the potential to tune spin-dependent properties in 2D materials for spintronic applications.</p>","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"21 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2025-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142967786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}