Pub Date : 2026-02-20DOI: 10.1038/s41535-026-00865-9
Takumi Sato, Satoru Hayami
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 d -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.
{"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}
Pub Date : 2026-02-17DOI: 10.1038/s41535-026-00857-9
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
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 2 Mo 3 O 8 . 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.
{"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}
Pub Date : 2026-02-13DOI: 10.1038/s41535-026-00864-w
Zachary M. Raines, Andrey V. Chubukov
We analyze superconductivity in a ferromagnetically ordered state of multi-layer graphene system in proximity to WSe2. We model this material by a two-valley system of interacting fermions with small pockets and Ising spin-orbit coupling. The magnetically-ordered state is a half-metal with a canted ferromagnetic order. We obtain the magnon spectrum and derive two types of magnon-mediated 4-fermion interactions: spin-flip interactions mediated by a single magnon and spin-preserving interactions mediated by two magnons. We argue that both have to be included into the pairing interaction between fermions from the filled bands. The full magnon-mediated interaction satisfies Adler criterion and is attractive in a spin-triplet, valley-odd and spatially-even pairing channel. The attraction is induced by spin-orbit coupling and is confined to energies which are parametrically smaller than the Fermi energy. We argue that near the onset of a canted ferromagnetic order this attraction wins over a repulsive intra-valley density-density interaction.
{"title":"Superconductivity induced by spin-orbit coupling in a two-valley ferromagnet","authors":"Zachary M. Raines, Andrey V. Chubukov","doi":"10.1038/s41535-026-00864-w","DOIUrl":"https://doi.org/10.1038/s41535-026-00864-w","url":null,"abstract":"We analyze superconductivity in a ferromagnetically ordered state of multi-layer graphene system in proximity to WSe2. We model this material by a two-valley system of interacting fermions with small pockets and Ising spin-orbit coupling. The magnetically-ordered state is a half-metal with a canted ferromagnetic order. We obtain the magnon spectrum and derive two types of magnon-mediated 4-fermion interactions: spin-flip interactions mediated by a single magnon and spin-preserving interactions mediated by two magnons. We argue that both have to be included into the pairing interaction between fermions from the filled bands. The full magnon-mediated interaction satisfies Adler criterion and is attractive in a spin-triplet, valley-odd and spatially-even pairing channel. The attraction is induced by spin-orbit coupling and is confined to energies which are parametrically smaller than the Fermi energy. We argue that near the onset of a canted ferromagnetic order this attraction wins over a repulsive intra-valley density-density interaction.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"334 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146196762","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}
Pub Date : 2026-02-13DOI: 10.1038/s41535-026-00863-x
Maryia Zinouyeva, Rolf Heid, Giacomo Merzoni, Riccardo Arpaia, Nikolai Andreev, Marco Biagi, Nicholas B. Brookes, Daniele Di Castro, Alexei Kalaboukhov, Kurt Kummer, Floriana Lombardi, Leonardo Martinelli, Francesco Rosa, Matteo Rossi, Flora Yakhou-Harris, Lucio Braicovich, Marco Moretti, Paolo G. Radaelli, Giacomo Ghiringhelli
The experimental determination of the magnitude and momentum dependence of electron-phonon coupling (EPC) is an outstanding problem in condensed matter physics. The intensity of phonon peaks in Resonant Inelastic X-ray Scattering (RIXS) spectra can be related to the underlying EPC strength under significant approximations whose validity deserves careful verification. We measured the Cu L3 RIXS phonon intensity as a function of incident photon energy and momentum transfer in several layered cuprates. For CaCuO2, La2−xSrxCuO4+δ, and YBa2Cu3O6, using a generally accepted theoretical model, we quantitatively estimate the EPC for the bond-stretching mode along the high-symmetry directions (ζ,0) and (ζ,ζ), and as a function of the azimuthal angle φ at fixed q∥. We compare our results with theoretical predictions and find that the q∥-dependence of the phonon RIXS intensity can be largely ascribed to the phonon symmetry. However, a more satisfactory prediction of the experimental results requires an accurate description of the electronic structure close to the Fermi level. Our extensive investigation indicates that Cu L3 RIXS can reliably determine the momentum dependence of EPC for the bond-stretching modes of cuprates. Moreover, the large experimental basis provided here constitutes a stringent test for advanced theoretical predictions on the EPC.
{"title":"The influence of phonon symmetry and electronic structure on the electron-phonon coupling momentum dependence in cuprates","authors":"Maryia Zinouyeva, Rolf Heid, Giacomo Merzoni, Riccardo Arpaia, Nikolai Andreev, Marco Biagi, Nicholas B. Brookes, Daniele Di Castro, Alexei Kalaboukhov, Kurt Kummer, Floriana Lombardi, Leonardo Martinelli, Francesco Rosa, Matteo Rossi, Flora Yakhou-Harris, Lucio Braicovich, Marco Moretti, Paolo G. Radaelli, Giacomo Ghiringhelli","doi":"10.1038/s41535-026-00863-x","DOIUrl":"https://doi.org/10.1038/s41535-026-00863-x","url":null,"abstract":"The experimental determination of the magnitude and momentum dependence of electron-phonon coupling (EPC) is an outstanding problem in condensed matter physics. The intensity of phonon peaks in Resonant Inelastic X-ray Scattering (RIXS) spectra can be related to the underlying EPC strength under significant approximations whose validity deserves careful verification. We measured the Cu L3 RIXS phonon intensity as a function of incident photon energy and momentum transfer in several layered cuprates. For CaCuO2, La2−xSrxCuO4+δ, and YBa2Cu3O6, using a generally accepted theoretical model, we quantitatively estimate the EPC for the bond-stretching mode along the high-symmetry directions (ζ,0) and (ζ,ζ), and as a function of the azimuthal angle φ at fixed q∥. We compare our results with theoretical predictions and find that the q∥-dependence of the phonon RIXS intensity can be largely ascribed to the phonon symmetry. However, a more satisfactory prediction of the experimental results requires an accurate description of the electronic structure close to the Fermi level. Our extensive investigation indicates that Cu L3 RIXS can reliably determine the momentum dependence of EPC for the bond-stretching modes of cuprates. Moreover, the large experimental basis provided here constitutes a stringent test for advanced theoretical predictions on the EPC.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"40 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146196761","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}
Pub Date : 2026-02-11DOI: 10.1038/s41535-026-00854-y
Jonathan Gaudet, Dalmau Reig-i-Plessis, Bogeng Wen, Thomas J. Hicken, Jonas A. Krieger, Jan Peter Embs, Hubertus Luetkens, Adam A. Aczel, Stuart A. Calder, Matthew B. Stone, Hae-Young Kee, Alannah M. Hallas
We investigate the magnetic ground state of CuNdO2, which is a delafossite with a triangular lattice of magnetic Nd3+ ions that are well separated by non-magnetic Cu spacer layers. From inelastic neutron scattering measurements of the crystal electric field, we determine the strong Ising character of the pseudo-spin 1/2 Nd3+ moments. Magnetic susceptibility and heat capacity measurements reveal the onset of long-range antiferromagnetic order at TN = 0.78 K. While the magnetic transition is definitively observed with muon spin relaxation, accompanied by the formation of a weakly dispersing spin wave excitation, no dipole-ordered moment is detected with neutron diffraction. We show that the apparent absence of a dipolar ordered moment is a consequence of the dominant Ising character of the antiferromagnetically coupled Nd3+ moments, which experience extreme frustration on the triangular lattice. Consequently, the frustration in CuNdO2 is relieved through in-plane ordering of the substantially smaller perpendicular component of the Nd3+ moments into a 120° structure, with a nearly vanishing ordered moment.
{"title":"Vanishing ordered moment in the frustrated triangular lattice antiferromagnet CuNdO2","authors":"Jonathan Gaudet, Dalmau Reig-i-Plessis, Bogeng Wen, Thomas J. Hicken, Jonas A. Krieger, Jan Peter Embs, Hubertus Luetkens, Adam A. Aczel, Stuart A. Calder, Matthew B. Stone, Hae-Young Kee, Alannah M. Hallas","doi":"10.1038/s41535-026-00854-y","DOIUrl":"https://doi.org/10.1038/s41535-026-00854-y","url":null,"abstract":"We investigate the magnetic ground state of CuNdO2, which is a delafossite with a triangular lattice of magnetic Nd3+ ions that are well separated by non-magnetic Cu spacer layers. From inelastic neutron scattering measurements of the crystal electric field, we determine the strong Ising character of the pseudo-spin 1/2 Nd3+ moments. Magnetic susceptibility and heat capacity measurements reveal the onset of long-range antiferromagnetic order at TN = 0.78 K. While the magnetic transition is definitively observed with muon spin relaxation, accompanied by the formation of a weakly dispersing spin wave excitation, no dipole-ordered moment is detected with neutron diffraction. We show that the apparent absence of a dipolar ordered moment is a consequence of the dominant Ising character of the antiferromagnetically coupled Nd3+ moments, which experience extreme frustration on the triangular lattice. Consequently, the frustration in CuNdO2 is relieved through in-plane ordering of the substantially smaller perpendicular component of the Nd3+ moments into a 120° structure, with a nearly vanishing ordered moment.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"95 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146152278","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}
Pub Date : 2026-02-10DOI: 10.1038/s41535-026-00862-y
Jinhao Zhang, Zhanshan Sun, Jiawei Yao, Fengting Zhao, Yi Lin, Di Sang, Kai Yang, Qiang An, Yunqi Fu
Rydberg atomic receiver holds distinctive advantages of ultra-wide operating bandwidth and inherently high sensitivity in electric field measurement1, in particular, it promises unique superiority of miniaturization for low-frequency especially kHz-band signals, which hold pivotal value in applications such as long-range navigation, ground-penetrating radar, and underwater communication. However, the capability of kHz atomic receivers remains severely constrained by the shielding effects of adsorbed alkali metal atoms. Here, we propose a conceptually new self-dressing kHz signal measurement paradigm by converting the undesired coupling-laser-induced DC field to an atomic dressing, and deftly building atomic superheterodyne inside the sapphire vapor cell, which is prepared to adequately suppress the low-frequency shielding through resistivity manipulation engineering. Further, we realize strengthened interaction between the atoms and kHz field by localized enhancement of the incident signals, and finally achieve an ultrahigh sensitivity of 13.5 nV/cm/Hz1/2 at 100 kHz. This architecture represents a significant advance, with the potential to greatly accelerate the practical applications of Rydberg atomic receivers in kHz-band detection, communication, and related fields.
{"title":"Self-dressing Rydberg atomic receiver based on laser-induced DC field","authors":"Jinhao Zhang, Zhanshan Sun, Jiawei Yao, Fengting Zhao, Yi Lin, Di Sang, Kai Yang, Qiang An, Yunqi Fu","doi":"10.1038/s41535-026-00862-y","DOIUrl":"https://doi.org/10.1038/s41535-026-00862-y","url":null,"abstract":"Rydberg atomic receiver holds distinctive advantages of ultra-wide operating bandwidth and inherently high sensitivity in electric field measurement1, in particular, it promises unique superiority of miniaturization for low-frequency especially kHz-band signals, which hold pivotal value in applications such as long-range navigation, ground-penetrating radar, and underwater communication. However, the capability of kHz atomic receivers remains severely constrained by the shielding effects of adsorbed alkali metal atoms. Here, we propose a conceptually new self-dressing kHz signal measurement paradigm by converting the undesired coupling-laser-induced DC field to an atomic dressing, and deftly building atomic superheterodyne inside the sapphire vapor cell, which is prepared to adequately suppress the low-frequency shielding through resistivity manipulation engineering. Further, we realize strengthened interaction between the atoms and kHz field by localized enhancement of the incident signals, and finally achieve an ultrahigh sensitivity of 13.5 nV/cm/Hz1/2 at 100 kHz. This architecture represents a significant advance, with the potential to greatly accelerate the practical applications of Rydberg atomic receivers in kHz-band detection, communication, and related fields.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"32 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146152298","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}
Pub Date : 2026-02-06DOI: 10.1038/s41535-026-00853-z
Markus Weißenhofer, M. S. Mrudul, Sergiy Mankovsky, Peter M. Oppeneer
Rotating magnon wave packets carrying orbital moments offer a pathway to unconventional transport phenomena. Here, we investigate magnon orbital moments and the magnon orbital Nernst effect in the prototypical altermagnets RuO 2 and CrSb using first-principles calculations, linear response theory, and symmetry analysis. While symmetry constraints enforce vanishing equilibrium magnon orbital moments, we find that in thermal non-equilibrium a finite and robust magnon orbital Nernst effect emerges from the anisotropic Heisenberg exchange, regardless of spin-orbit coupling. This effect is intrinsically tied to the unique exchange splitting of magnon dispersions in altermagnets and is absent in conventional antiferromagnets. Magnon orbital moment transport displays markedly reduced sensitivity to the orientation of the Néel vector, temperature gradient, and magnetic domain structure compared to the magnon spin Seebeck and spin Nernst effects, enabling its persistence even in polycrystalline samples with arbitrary domain configurations. Our results position magnon orbital transport as a promising and robust functional mechanism for orbitronic and spintronic devices, and as a potential indirect probe of altermagnetism in disordered insulating systems.
{"title":"Magnon orbital Nernst effect in altermagnets","authors":"Markus Weißenhofer, M. S. Mrudul, Sergiy Mankovsky, Peter M. Oppeneer","doi":"10.1038/s41535-026-00853-z","DOIUrl":"https://doi.org/10.1038/s41535-026-00853-z","url":null,"abstract":"Rotating magnon wave packets carrying orbital moments offer a pathway to unconventional transport phenomena. Here, we investigate magnon orbital moments and the magnon orbital Nernst effect in the prototypical altermagnets RuO <jats:sub>2</jats:sub> and CrSb using first-principles calculations, linear response theory, and symmetry analysis. While symmetry constraints enforce vanishing equilibrium magnon orbital moments, we find that in thermal non-equilibrium a finite and robust magnon orbital Nernst effect emerges from the anisotropic Heisenberg exchange, regardless of spin-orbit coupling. This effect is intrinsically tied to the unique exchange splitting of magnon dispersions in altermagnets and is absent in conventional antiferromagnets. Magnon orbital moment transport displays markedly reduced sensitivity to the orientation of the Néel vector, temperature gradient, and magnetic domain structure compared to the magnon spin Seebeck and spin Nernst effects, enabling its persistence even in polycrystalline samples with arbitrary domain configurations. Our results position magnon orbital transport as a promising and robust functional mechanism for orbitronic and spintronic devices, and as a potential indirect probe of altermagnetism in disordered insulating systems.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"16 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146135495","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}
Pub Date : 2026-02-06DOI: 10.1038/s41535-026-00860-0
N. Drichko, V. S. Thoi, N. P. Armitage
{"title":"Much ado about MOFs: metal-organic-frameworks as quantum materials","authors":"N. Drichko, V. S. Thoi, N. P. Armitage","doi":"10.1038/s41535-026-00860-0","DOIUrl":"https://doi.org/10.1038/s41535-026-00860-0","url":null,"abstract":"","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"30 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146135497","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}
We report the electronic structure of the thermoelectric semimetal Ta 2 PdSe 6 with a large thermoelectric power factor and giant Peltier conductivity by means of angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra reveal the coexistence of a sharp hole band with a light electron mass and a broad electron band with a relatively heavy electron mass, which originate from different quasi-one-dimensional (Q1D) chains in Ta 2 PdSe 6 . Moreover, the electron band around the Brillouin-zone (BZ) boundary shows a replica structure with respect to the energy originating from plasmonic polarons due to electron-plasmon interactions. The different scattering effects and interactions in each atomic chain lead to asymmetric transport lifetimes of carriers: a large Seebeck coefficient can be realized even in a semimetal. Our findings pave the way for exploring the thermoelectric materials in previously overlooked semimetals and provide a new platform for low-temperature thermoelectric physics, which has been challenging with semiconductors.
{"title":"Band-selective plasmonic polaron in thermoelectric semimetal Ta2PdSe6 with ultra-high power factor","authors":"Daiki Ootsuki, Akitoshi Nakano, Urara Maruoka, Takumi Hasegawa, Masashi Arita, Miho Kitamura, Koji Horiba, Teppei Yoshida, Ichiro Terasaki","doi":"10.1038/s41535-026-00858-8","DOIUrl":"https://doi.org/10.1038/s41535-026-00858-8","url":null,"abstract":"We report the electronic structure of the thermoelectric semimetal Ta <jats:sub>2</jats:sub> PdSe <jats:sub>6</jats:sub> with a large thermoelectric power factor and giant Peltier conductivity by means of angle-resolved photoemission spectroscopy (ARPES). The ARPES spectra reveal the coexistence of a sharp hole band with a light electron mass and a broad electron band with a relatively heavy electron mass, which originate from different quasi-one-dimensional (Q1D) chains in Ta <jats:sub>2</jats:sub> PdSe <jats:sub>6</jats:sub> . Moreover, the electron band around the Brillouin-zone (BZ) boundary shows a replica structure with respect to the energy originating from plasmonic polarons due to electron-plasmon interactions. The different scattering effects and interactions in each atomic chain lead to asymmetric transport lifetimes of carriers: a large Seebeck coefficient can be realized even in a semimetal. Our findings pave the way for exploring the thermoelectric materials in previously overlooked semimetals and provide a new platform for low-temperature thermoelectric physics, which has been challenging with semiconductors.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"7 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146135496","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}
Pub Date : 2026-02-04DOI: 10.1038/s41535-026-00859-7
Marvin Kopp, Charu Garg, Sarah Krebber, Kristin Kliemt, Cornelius Krellner, Sudhaman R. Balguri, Mira Mahendru, Fazel Tafti, Theodore L. Breeze, Nathan P. Bentley, Francis L. Pratt, Thomas J. Hicken, Hubertus Luetkens, Jonas A. Krieger, Stephen J. Blundell, Tom Lancaster, M. Victoria Ale Crivillero, Steffen Wirth, Jens Müller
The interplay between magnetism and charge transport is central to understanding colossal magnetoresistance (CMR), a phenomenon well studied in ferromagnets. Recently, antiferromagnetic (AFM) EuCd 2 P 2 has attracted considerable interest due to its remarkable CMR, for which magnetic fluctuations and the formation of ferromagnetic clusters have been proposed as key mechanisms. Here we provide direct evidence that these effects originate from the formation and percolation of magnetic polarons. We employ a complementary set of sensitive probes that allows for a direct comparison of electronic and magnetic properties on multiple time scales revealing pronounced electronic and magnetic phase separation below T* ≈ 2 TN . These measurements indicate an inhomogeneous, percolating electronic system below T* and well above the magnetic ordering temperature TN = 11 K. In applied magnetic fields, the onset of the pronounced negative MR in the paramagnetic regime emerges at a universal critical magnetization. The characteristic size of the magnetic polarons near the percolation threshold is estimated to be ~6−10 nm. Our results establish dynamic polaron percolation within an AFM matrix as the microscopic origin of CMR in EuCd 2 P 2 , providing a unified framework for magnetotransport in Eu-based correlated semiconductors.
{"title":"Robust magnetic polaron percolation in the antiferromagnetic CMR system EuCd2P2","authors":"Marvin Kopp, Charu Garg, Sarah Krebber, Kristin Kliemt, Cornelius Krellner, Sudhaman R. Balguri, Mira Mahendru, Fazel Tafti, Theodore L. Breeze, Nathan P. Bentley, Francis L. Pratt, Thomas J. Hicken, Hubertus Luetkens, Jonas A. Krieger, Stephen J. Blundell, Tom Lancaster, M. Victoria Ale Crivillero, Steffen Wirth, Jens Müller","doi":"10.1038/s41535-026-00859-7","DOIUrl":"https://doi.org/10.1038/s41535-026-00859-7","url":null,"abstract":"The interplay between magnetism and charge transport is central to understanding colossal magnetoresistance (CMR), a phenomenon well studied in ferromagnets. Recently, antiferromagnetic (AFM) EuCd <jats:sub>2</jats:sub> P <jats:sub>2</jats:sub> has attracted considerable interest due to its remarkable CMR, for which magnetic fluctuations and the formation of ferromagnetic clusters have been proposed as key mechanisms. Here we provide direct evidence that these effects originate from the formation and percolation of magnetic polarons. We employ a complementary set of sensitive probes that allows for a direct comparison of electronic and magnetic properties on multiple time scales revealing pronounced electronic and magnetic phase separation below <jats:italic>T</jats:italic> <jats:sup>*</jats:sup> ≈ 2 <jats:italic>T</jats:italic> <jats:sub> <jats:italic>N</jats:italic> </jats:sub> . These measurements indicate an inhomogeneous, percolating electronic system below <jats:italic>T</jats:italic> <jats:sup>*</jats:sup> and well above the magnetic ordering temperature <jats:italic>T</jats:italic> <jats:sub> <jats:italic>N</jats:italic> </jats:sub> = 11 K. In applied magnetic fields, the onset of the pronounced negative MR in the paramagnetic regime emerges at a universal critical magnetization. The characteristic size of the magnetic polarons near the percolation threshold is estimated to be ~6−10 nm. Our results establish dynamic polaron percolation within an AFM matrix as the microscopic origin of CMR in EuCd <jats:sub>2</jats:sub> P <jats:sub>2</jats:sub> , providing a unified framework for magnetotransport in Eu-based correlated semiconductors.","PeriodicalId":19283,"journal":{"name":"npj Quantum Materials","volume":"22 1","pages":""},"PeriodicalIF":5.7,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146115719","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}
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