Junli Li, Jun-Qing Cheng, Trinanjan Datta, Dao-Xin Yao
{"title":"Spin order and spin excitation spectra of spin-1/2 tetramer chains","authors":"Junli Li, Jun-Qing Cheng, Trinanjan Datta, Dao-Xin Yao","doi":"10.1038/s41535-026-00855-x","DOIUrl":"https://doi.org/10.1038/s41535-026-00855-x","url":null,"abstract":"We investigate the spin dynamics of a 1D spin-1/2 Heisenberg tetramer chain. Employing a combination of density matrix renormalization group, quantum renormalization group, and perturbation theory techniques, we compute the energy levels and the quantum phase diagram, analyze the phase transitions, and evaluate the dynamical structure factor (DSF), which is related to the inelastic neutron scattering (INS) spectrum and the resonant inelastic x-ray scattering (RIXS) spectrum of fractionalized and collective excitations. Our calculations suggest that the chain can transition between a hidden Z2 × Z2 discrete symmetry preserving tetramer phase and a Haldane phase with non-vanishing string order that breaks the hidden symmetry. These two gapped phases are intervened by an intermediate deconfined quantum critical state comprising of free spins and three-site doublets, which is a gapless critical phase with deconfined spinons that can be detected either by INS or L-edge RIXS. We find that the tetramer chain can support fractionalized (spinon) and collective (triplon and quinton) excitations. In the ferromagnetic intra-tetramer limit, the chain can support a quinton excitation which has a five-fold degenerate excited state. String order parameter calculations suggest CuInVO5 should be in a Haldane-like phase whose INS or L-edge RIXS spectrum can support observable single-spin excitations including triplon and quinton excitations. We also identify possible two-particle excitations (two-singlon, two-triplon, triplon-quinton, and two-quinton excitations) resulting from the double spin-flip effect in the K-edge RIXS spectrum.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"38 6 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147496807","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":"Strain-tuned ferroelectric transitions in HfO2: role of X2−{X}_{2}^{-} mode in ferroelectric instabilities","authors":"Ilyoung Lee, Wontae Lee, Jaejun Yu","doi":"10.1038/s41535-026-00870-y","DOIUrl":"https://doi.org/10.1038/s41535-026-00870-y","url":null,"abstract":"Recent studies have identified HfO2 as a promising ferroelectric material for thin films, highlighting its potential as a state-of-the-art option for future ferroelectric applications. However, due to the complexity of the fabrication process, the underlying mechanism of the phase transition to Pca21 is still not fully understood. In this study, we aim to clarify the phase transition pathway by investigating the formation of the ferroelectric Pca21 phase via X2−{X}_{2}^{-} displacement and symmetry-allowed phonon mode instability. Our results reveal that applying tensile strain regardless of direction enhances the X2−{X}_{2}^{-} displacement and induces instabilities in the polar and antipolar modes, causing the P42/nmc phase to collapse into Pbcn or Aba2, depending on the strain direction. Emergent polar and antipolar mode displacements at the primary transition couple to X2−{X}_{2}^{-}, lowering the trilinear-coupling barrier and stabilizing Pca21. Although the X2−{X}_{2}^{-} mode alone makes only a minor contribution, its coupling with other distortion modes governs the entire energy landscape by driving the Landau coefficients to negative values, initiating the kinetic transition pathway toward the Pca21 phase. This fundamental paradigm shift toward a mechanism governed by the X2−{X}_{2}^{-} displacement provides a way to control the ferroelectric phase fraction in polycrystalline films under various substrate conditions via X2−{X}_{2}^{-} engineering, paving the way for a foundation for the practical realization of ferroelectricity in device applications.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"53 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147496816","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":"Imaging of altermagnetic domains in orthoferrite DyFeO3 using electric field-induced nonreciprocal directional dichroism","authors":"Koh Kobayashi, Takeshi Hayashida, Tsuyoshi Kimura","doi":"10.1038/s41535-026-00861-z","DOIUrl":"https://doi.org/10.1038/s41535-026-00861-z","url":null,"abstract":"Rare-earth orthoferrites (RFeO3, R: rare-earth ions) have long been studied for their unique antiferromagnetic properties arising from the interplay between two magnetic sublattices, formed by Fe³⁺ and R³⁺ ions. From a modern perspective, the antiferromagnetic order in RFeO₃ can be classified as altermagnetic, characterized by macroscopic time-reversal symmetry breaking without net magnetization. In this study, we focus on the altermagnetic Γ₁ phase of DyFeO₃, which exhibits time-reversal symmetry breaking while spontaneous magnetization is forbidden. We successfully visualize altermagnetic domains in this phase using electric field-induced nonreciprocal directional dichroism (NDD), in which the optical absorption changes with the applied electric field. We further demonstrate that the domain structure is influenced by an external magnetic field, mediated by piezomagnetic coupling through internal strain. Our results establish electric field-induced NDD as a powerful tool for probing altermagnetic domain structures, where conventional magneto-optical techniques such as the Faraday or Kerr effect are ineffective.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"54 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147454745","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}
Jixing Zhang, Cheuk Kit Cheung, Michael Kübler, Magnus Benke, Mathis Brossaud, Yihua Wang, Andrej Denisenko, Ruoming Peng, Jens Anders, Emilio Corcione, Cristina Tarín Sauer, Andrew M. Edmonds, Matthew Markham, Kazuo Nakamura, Hitoshi Sumiya, Shinobu Onoda, Junichi Isoya, Chen Zhang, Jörg Wrachtrup
{"title":"Unraveling quantum dephasing of nitrogen-vacancy center ensembles in diamond","authors":"Jixing Zhang, Cheuk Kit Cheung, Michael Kübler, Magnus Benke, Mathis Brossaud, Yihua Wang, Andrej Denisenko, Ruoming Peng, Jens Anders, Emilio Corcione, Cristina Tarín Sauer, Andrew M. Edmonds, Matthew Markham, Kazuo Nakamura, Hitoshi Sumiya, Shinobu Onoda, Junichi Isoya, Chen Zhang, Jörg Wrachtrup","doi":"10.1038/s41535-026-00869-5","DOIUrl":"https://doi.org/10.1038/s41535-026-00869-5","url":null,"abstract":"Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times (({T}_{2}^{* })) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"43 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147394035","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}
Kazuhiro Nawa, Yoshinori Imai, Maiko Kofu, Richard Mole, Hideyuki Fujihara, Takumi Hiraoka, Ryo Murasaki, Pharit Piyawongwatthana, Daisuke Okuyama, Hirotada Gotou, Kenya Ohgushi, Taku J. Sato
{"title":"Magnetic excitations of the Kitaev model candidate RuBr3","authors":"Kazuhiro Nawa, Yoshinori Imai, Maiko Kofu, Richard Mole, Hideyuki Fujihara, Takumi Hiraoka, Ryo Murasaki, Pharit Piyawongwatthana, Daisuke Okuyama, Hirotada Gotou, Kenya Ohgushi, Taku J. Sato","doi":"10.1038/s41535-026-00868-6","DOIUrl":"https://doi.org/10.1038/s41535-026-00868-6","url":null,"abstract":"The Kitaev model, which consists of bond-dependent Ising interactions on the honeycomb plane, is known as a promising model for realising a spin liquid in the exact ground state. Since bond-dependent Ising interactions are induced by orbital exchange processes via ligand ions, it is important to reveal the effect of ligand ions on the formation of bond-dependent Ising interactions experimentally. In this study, we performed powder inelastic neutron scattering on RuBr3 with a layered honeycomb structure, which is isostructural to the low-temperature structure of α-RuCl3. Strongly dispersive magnetic modes were observed near the centre of the antiferromagnetic zone below TN. With increasing temperature, the spectral weight remains near the centre of the antiferromagnetic zone just above TN, whereas it shifts to the Γ point at 3TN. Strong dispersion indicates that antiferromagnetic interactions that stabilise the zigzag antiferromagnetic order, namely, nearest-neighbour symmetric off-diagonal or third-neighbour isotropic magnetic interactions, are comparable to or even stronger than ferromagnetic Kitaev interactions, and drive the ground state of RuBr3 away from the ideal ferromagnetic Kitaev spin liquid state.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"411 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147394040","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":"Anomalous Landau levels and quantum oscillation in rotation-invariant insulators","authors":"Jianlong Fu, Chun Yu Weng, Hoi Chun Po","doi":"10.1038/s41535-026-00867-7","DOIUrl":"https://doi.org/10.1038/s41535-026-00867-7","url":null,"abstract":"Landau levels in certain models are known to protrude into the zero-field energy gap. These are known as anomalous Landau levels (ALLs). We study whether ALLs can lead to Fermi-surface like quantum oscillation in the absence of a zero-field Fermi surface. Focusing on two-dimensional multi-band low-energy models of electrons with continuous rotation symmetry, we show that an effective-band description, akin to the semiclassical treatment of Landau level problems in metals, can be used to predict the Landau level spectrum, including possible ALLs. This description describes ALL induced quantum oscillation for certain insulating models, which we demonstrate through numerical calculations. We demonstrate that these results could guide the search for ALL in 2D topological materials with effective Hamiltonian similar to that of magnetically doped (Bi, Sb)2Te3 ultrathin films.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"61 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147350627","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":"Strain-tuned ferroelectric transitions in HfO2: role of ({X}_{2}^{-}) mode in ferroelectric instabilities","authors":"Ilyoung Lee, Wontae Lee, Jaejun Yu","doi":"10.1038/s41535-025-00841-9","DOIUrl":"https://doi.org/10.1038/s41535-025-00841-9","url":null,"abstract":"Recent studies have identified HfO2 as a promising ferroelectric material for thin films, highlighting its potential as a state-of-the-art option for future ferroelectric applications. However, due to the complexity of the fabrication process, the underlying mechanism of the phase transition to Pca21 is still not fully understood. In this study, we aim to clarify the phase transition pathway by investigating the formation of the ferroelectric Pca21 phase via ({X}_{2}^{-}) displacement and symmetry-allowed phonon mode instability. Our results reveal that applying tensile strain regardless of direction enhances the ({X}_{2}^{-}) displacement and induces instabilities in the polar and antipolar modes, causing the P42/nmc phase to collapse into Pbcn or Aba2, depending on the strain direction. Emergent polar and antipolar mode displacements at the primary transition couple to ({X}_{2}^{-}), lowering the trilinear-coupling barrier and stabilizing Pca21. Although the ({X}_{2}^{-}) mode alone makes only a minor contribution, its coupling with other distortion modes governs the entire energy landscape by driving the Landau coefficients to negative values, initiating the kinetic transition pathway toward the Pca21 phase. This fundamental paradigm shift toward a mechanism governed by the ({X}_{2}^{-}) displacement provides a way to control the ferroelectric phase fraction in polycrystalline films under various substrate conditions via ({X}_{2}^{-}) engineering, paving the way for a foundation for the practical realization of ferroelectricity in device applications.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"61 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147346812","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":"A wide-range topological thermometer with Ta2Pd3Te5: from power-law response to application prospects","authors":"Yupeng Li, Anqi Wang, Senyang Pan, Dayu Yan, Guang Yang, Xingchen Guo, Yu Hong, Zhiyuan Zhang, Ziwei Dou, Guangtong Liu, Fanming Qu, Zhijun Wang, Tian Qian, Jinglei Zhang, Youguo Shi, Li Lu, Jie Shen","doi":"10.1038/s41535-026-00866-8","DOIUrl":"https://doi.org/10.1038/s41535-026-00866-8","url":null,"abstract":"In recent decades, there has been a persistent pursuit of applications for surface/edge states in topological systems, driven by their dissipationless transport effects. This work demonstrates the remarkable properties of the topological material Ta <jats:sub>2</jats:sub> Pd <jats:sub>3</jats:sub> Te <jats:sub>5</jats:sub> , as a thermometer. At low temperatures, it shows a power-law correlation in temperature-dependent resistance, while behaving like a semiconductor at high temperatures. This dual behavior effectively mitigates the issue of infinite resistance in semiconductor thermometers at ultra-low temperatures, making it ideal for millikelvin-range refrigerators. Through chemical doping, thickness adjustment, and gate voltage control, its performance can be finely tuned, and can also enable micron-scale local temperature measurement from millikelvin to room temperature. Furthermore, this thermometer exhibits excellent temperature sensitivity and resolution, and can be fine-tuned to show small magnetoresistance. In summary, the Ta <jats:sub>2</jats:sub> Pd <jats:sub>3</jats:sub> Te <jats:sub>5</jats:sub> -based thermometer, also referred to as a topological thermometer, demonstrates considerable potential for broad-temperature-range detection and merits further investigation and optimization.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"8 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146223204","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 theory of magnetic octupole in periodic crystals and application to d-wave altermagnets","authors":"Takumi Sato, Satoru Hayami","doi":"10.1038/s41535-026-00865-9","DOIUrl":"https://doi.org/10.1038/s41535-026-00865-9","url":null,"abstract":"Magnetic multipoles have been recognized as order parameters characterizing magnetic structure in solids. Recently, magnetic octupoles have been proposed as the order parameters of time-reversal-symmetry-breaking centrosymmetric antiferromagnets exhibiting nonrelativistic spin splitting, which is referred to as “altermagnet”. However, a gauge-invariant formulation of magnetic octupoles in crystalline solids remains elusive. Here, we present a gauge-invariant expression of spin magnetic octupoles in periodic crystals based on quantum mechanics and thermodynamics, which can be used to quantitatively characterize time-reversal-symmetry-breaking antiferromagnets, including <jats:italic>d</jats:italic> -wave altermagnets. The allowed physical response tensors are classified beyond symmetry considerations, and direct relationships are established for some of them in insulators at zero temperature. Furthermore, our expression reveals a contribution from an anisotropic magnetic dipole, which has the same symmetry as conventional spin and orbital magnetic dipoles but carries no net magnetization. We discuss the relation between the anisotropic magnetic dipole and the anomalous Hall effect.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"1 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146223202","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}
F. Schilberth, M. Kondákor, D. Ukolov, A. Pawbake, K. Vasin, O. Ercem, L. Prodan, V. Tsurkan, A. A. Tsirlin, C. Faugeras, P. Lemmens, K. Penc, I. Kézsmárki, S. Bordács, J. Deisenhofer
{"title":"Optical phonons as a testing ground for spin group symmetries","authors":"F. Schilberth, M. Kondákor, D. Ukolov, A. Pawbake, K. Vasin, O. Ercem, L. Prodan, V. Tsurkan, A. A. Tsirlin, C. Faugeras, P. Lemmens, K. Penc, I. Kézsmárki, S. Bordács, J. Deisenhofer","doi":"10.1038/s41535-026-00857-9","DOIUrl":"https://doi.org/10.1038/s41535-026-00857-9","url":null,"abstract":"Lattice vibrations are highly sensitive to crystal symmetries and their changes across phase transitions. The latter can modify irreducible (co)representations and corresponding infrared and Raman selection rules of phonons. This concept is established for relativistic magnetic point groups, simultaneously transforming spatial and spin coordinates. However, in altermagnets described by non-relativistic spin groups with disjunct symmetry operations for both vector spaces, the phonon selection rules have remained unexplored. Here, we present a detailed study of the infrared- and Raman-active modes in the collinear antiferromagnet and altermagnet candidate Co <jats:sub>2</jats:sub> Mo <jats:sub>3</jats:sub> O <jats:sub>8</jats:sub> . Comparing to ab initio calculations accurately capturing the eigenfrequencies, we identify all expected phonon modes at room temperature and deduce their selection rules using both symmetry approaches. Importantly, we observe the change of selection rules upon antiferromagnetic ordering, agreeing with the relativistic symmetry approach, while the spin group formalism predicts no changes. Therefore, optical phonons sensing the symmetry of the magnetic order can reveal if relevant magnon-phonon coupling is compatible with the spin-group approach or not.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"6 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146210081","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}