Magnetism

Magnetic excitations and interactions

We are interested in the nature of magnetism in strongly correlated materials—including complex transition-metal oxides and magnetic van der Waals materials—and how it relates to emergent phenomena such as high-temperature superconductivity and quantum spin liquids. Our primary tool is resonant inelastic x-ray scattering (RIXS), as illustrated in Fig. 1, in which an x-ray core-hole resonance couples x-rays to the spin and orbital degrees of freedom of a material, enabling measurements of collective magnetic excitations across the full Brillouin zone. Beyond conventional magnons, RIXS can access higher-order spin correlations such as spinon continua, multi-magnon excitations.

Nickelates have recently emerged as a compelling new frontier. We have characterized magnetic excitations across multiple nickelate families: the spin-1 layered antiferromagnet La₂₋ₓSrₓNiO₄, low-valence d⁹⁻ᵟ nickelates where we established strong cuprate-like superexchange interactions, and Ruddlesden–Popper nickelates Nd_n+1Ni_nO_3n+1 whose magnetic excitations we have tracked as a function of layer number. These measurements directly inform our understanding of the magnetic energy scales relevant to the recently discovered superconductivity in layered nickelates.

Figure 1: The resonant inelastic x-ray scattering (RIXS) process. The initial, intermediate, and final states are shown from left to right. Photons are represented as wavy red lines and electronic transitions are shown as green arrows. In this process spin excitations are created and their dispersion can be measured by determining the energy and momentum change of the photon.

References

2025

Beyond-Hubbard Pairing in a Cuprate Ladder

Hari Padma, Jinu Thomas, Sophia F. R. TenHuisen, Wei He, Ziqiang Guan, Jiemin Li, Byungjune Lee, Yu Wang, Seng Huat Lee, Zhiqiang Mao, Hoyoung Jang, Valentina Bisogni, Jonathan Pelliciari, Mark P. M. Dean, Steven Johnston, and Matteo Mitrano

Phys. Rev. X 15, 021049 (2025)

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The Hubbard model is believed to capture the essential physics of cuprate superconductors. However, recent theoretical studies suggest that it fails to reproduce a robust and homogeneous superconducting ground state. Here, using resonant inelastic x-ray scattering and density matrix renormalization group calculations, we show that magnetic excitations in the prototypical cuprate ladder Sr_14⁢Cu_24⁢O₄₁ are inconsistent with those of a simple Hubbard model. The magnetic response of hole carriers, contributing to an emergent branch of spin-flip excitations, is strongly suppressed. This effect is the consequence of strong d-wavelike pairing, enhanced by nearly an order of magnitude through a large nearest-neighbor attractive interaction and persisting up to at least 260 K. The close connection between the physics of cuprate ladders and that of the two-dimensional compounds suggests that such an enhanced hole pairing may be a universal feature of superconducting cuprates.
@article{padma2025beyond, dimensions = {true}, title = {Beyond-Hubbard Pairing in a Cuprate Ladder}, author = {Padma, Hari and Thomas, Jinu and TenHuisen, Sophia F. R. and He, Wei and Guan, Ziqiang and Li, Jiemin and Lee, Byungjune and Wang, Yu and Lee, Seng Huat and Mao, Zhiqiang and Jang, Hoyoung and Bisogni, Valentina and Pelliciari, Jonathan and Dean, Mark P. M. and Johnston, Steven and Mitrano, Matteo}, journal = {Phys. Rev. X}, volume = {15}, issue = {2}, pages = {021049}, numpages = {10}, year = {2025}, month = may, publisher = {American Physical Society}, doi = {10.1103/PhysRevX.15.021049}, url = {https://link.aps.org/doi/10.1103/PhysRevX.15.021049} }

2024

Evolution of the Magnetic Excitations in Electron-Doped La_2-xCe_xCuO₄

X. T. Li, S. J. Tu, L. Chaix, C. Fawaz, M. d’Astuto, X. Li, F. Yakhou-Harris, K. Kummer, N. B. Brookes, M. Garcia-Fernandez, Ke-Jin Zhou, Z. F. Lin, J. Yuan, K. Jin, M. P. M. Dean, and X. Liu

Phys. Rev. Lett. 132, 056002 (2024)

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We investigated the high energy spin excitations in electron-doped La2−xCexCuO4, a cuprate superconductor, by resonant inelastic x-ray scattering (RIXS) measurements. Efforts were paid to disentangle the paramagnon signal from non-spin-flip spectral weight mixing in the RIXS spectrum at Q∥=(0.6π,0) and (0.9π,0) along the (1 0) direction. Our results show that, for doping level x from 0.07 to 0.185, the variation of the paramagnon excitation energy is marginal. We discuss the implication of our results in connection with the evolution of the electron correlation strength in this system.
@article{li2024evolution, dimensions = {true}, title = {Evolution of the Magnetic Excitations in Electron-Doped La2-xCexCuO4}, author = {Li, X. T. and Tu, S. J. and Chaix, L. and Fawaz, C. and d'Astuto, M. and Li, X. and Yakhou-Harris, F. and Kummer, K. and Brookes, N. B. and Garcia-Fernandez, M. and Zhou, Ke-Jin and Lin, Z. F. and Yuan, J. and Jin, K. and Dean, M. P. M. and Liu, X.}, journal = {Phys. Rev. Lett.}, volume = {132}, issue = {5}, pages = {056002}, numpages = {7}, year = {2024}, month = feb, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.132.056002}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.132.056002} }

2022

Emergence of Spinons in Layered Trimer Iridate Ba₄Ir₃O₁₀

Y. Shen, J. Sears, G. Fabbris, A. Weichselbaum, W. Yin, H. Zhao, D. G. Mazzone, H. Miao, M. H. Upton, D. Casa, R. Acevedo-Esteves, C. Nelson, A. M. Barbour, C. Mazzoli, G. Cao, and M. P. M. Dean

Phys. Rev. Lett. 129, 207201 (2022)

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Spinons are well known as the elementary excitations of one-dimensional antiferromagnetic chains, but means to realize spinons in higher dimensions is the subject of intense research. Here, we use resonant x-ray scattering to study the layered trimer iridate Ba₄Ir₃O₁₀, which shows no magnetic order down to 0.2 K. An emergent one-dimensional spinon continuum is observed that can be well described by XXZ spin-1/2 chains with a magnetic exchange of 55 meV and a small Ising-like anisotropy. With 2% isovalent Sr doping, magnetic order appears below TN=130 K along with sharper excitations in (Ba_1-xSr_x)₄Ir₃O₁₀ . Combining our data with exact diagonalization calculations, we find that the frustrated intratrimer interactions effectively reduce the system into decoupled spin chains, the subtle balance of which can be easily tipped by perturbations such as chemical doping. Our results put Ba₄Ir₃O₁₀ between the one-dimensional chain and two-dimensional quantum spin liquid scenarios, illustrating a new way to suppress magnetic order and realize fractional spinons.
@article{shen2022emergence, dimensions = {true}, title = {Emergence of Spinons in Layered Trimer Iridate Ba4Ir3O10}, author = {Shen, Y. and Sears, J. and Fabbris, G. and Weichselbaum, A. and Yin, W. and Zhao, H. and Mazzone, D. G. and Miao, H. and Upton, M. H. and Casa, D. and Acevedo-Esteves, R. and Nelson, C. and Barbour, A. M. and Mazzoli, C. and Cao, G. and Dean, M. P. M.}, journal = {Phys. Rev. Lett.}, volume = {129}, issue = {20}, pages = {207201}, numpages = {7}, year = {2022}, month = nov, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.129.207201}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.129.207201} }
Role of Oxygen States in the Low Valence Nickelate La₄Ni₃O₈

Y. Shen, J. Sears, G. Fabbris, J. Li, J. Pelliciari, I. Jarrige, Xi He, I. Bozovic, M. Mitrano, Junjie Zhang, J. F. Mitchell, A. S. Botana, V. Bisogni, M. R. Norman, S. Johnston, and M. P. M. Dean

Phys. Rev. X 12, 011055 (2022)

[BNL Press Release]

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The discovery of superconductivity in square-planar low valence nickelates has ignited a vigorous debate regarding their essential electronic properties: Do these materials have appreciable oxygen charge-transfer character akin to the cuprates, or are they in a distinct Mott-Hubbard regime where oxygen plays a minimal role? Here, we resolve this question using O K-edge resonant inelastic x-ray scattering (RIXS) measurements of the low valence nickelate La4Ni3O8 and a prototypical cuprate La2−xSrxCuO4 (x=0.35). As expected, the cuprate lies deep in the charge-transfer regime of the Zaanen-Sawatzky-Allen (ZSA) scheme. The nickelate, however, is not well described by either limit of the ZSA scheme and is found to be of mixed charge-transfer–Mott-Hubbard character with the Coulomb repulsion U of similar size to the charge-transfer energy Δ. Nevertheless, the transition-metal-oxygen hopping is larger in La4Ni3O8 than in La2−xSrxCuO4, leading to a significant superexchange interaction and an appreciable hole occupation of the ligand O orbitals in La4Ni3O8 despite its larger Δ. Our results clarify the essential characteristics of low valence nickelates and put strong constraints on theoretical interpretations of superconductivity in these materials.
@article{shen2022role, dimensions = {true}, title = {Role of Oxygen States in the Low Valence Nickelate La4Ni3O8}, author = {Shen, Y. and Sears, J. and Fabbris, G. and Li, J. and Pelliciari, J. and Jarrige, I. and He, Xi and Bozovic, I. and Mitrano, M. and Zhang, Junjie and Mitchell, J. F. and Botana, A. S. and Bisogni, V. and Norman, M. R. and Johnston, S. and Dean, M. P. M.}, journal = {Phys. Rev. X}, volume = {12}, issue = {1}, pages = {011055}, numpages = {13}, year = {2022}, month = mar, publisher = {American Physical Society}, doi = {10.1103/PhysRevX.12.011055}, url = {https://link.aps.org/doi/10.1103/PhysRevX.12.011055}, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=221189" target="_blank">BNL Press Release</a>]} }

2021

Strong Superexchange in a d^9-δ Nickelate Revealed by Resonant Inelastic X-Ray Scattering

J. Q. Lin, P. Villar Arribi, G. Fabbris, A. S. Botana, D. Meyers, H. Miao, Y. Shen, D. G. Mazzone, J. Feng, S. G. Chiuzbăian, A. Nag, A. C. Walters, M. Garcı́a-Fernández, Ke-Jin Zhou, J. Pelliciari, I. Jarrige, J. W. Freeland, Junjie Zhang, J. F. Mitchell, V. Bisogni, X. Liu, M. R. Norman, and M. P. M. Dean

Phys. Rev. Lett. 126, 087001 (2021)

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The discovery of superconductivity in a d^9-δ nickelate has inspired disparate theoretical perspectives regarding the essential physics of this class of materials. A key issue is the magnitude of the magnetic superexchange, which relates to whether cuprate-like high-temperature nickelate superconductivity could be realized. We address this question using Ni L-edge and O K-edge spectroscopy of the reduced d^9-1/3 trilayer nickelates R4Ni3O8 (where R=La, Pr) and associated theoretical modeling. A magnon energy scale of ∼80 meV resulting from a nearest-neighbor magnetic exchange of J=69(4) meV is observed, proving that d^9-δ nickelates can host a large superexchange. This value, along with that of the Ni-O hybridization estimated from our O K-edge data, implies that trilayer nickelates represent an intermediate case between the infinite-layer nickelates and the cuprates. Layered nickelates thus provide a route to testing the relevance of superexchange to nickelate superconductivity.
@article{lin2021strong, dimensions = {true}, title = {Strong Superexchange in a d9-\delta Nickelate Revealed by Resonant Inelastic X-Ray Scattering}, author = {Lin, J. Q. and Villar Arribi, P. and Fabbris, G. and Botana, A. S. and Meyers, D. and Miao, H. and Shen, Y. and Mazzone, D. G. and Feng, J. and Chiuzbăian, S. G. and Nag, A. and Walters, A. C. and Garc\'{\i}a-Fern\'andez, M. and Zhou, Ke-Jin and Pelliciari, J. and Jarrige, I. and Freeland, J. W. and Zhang, Junjie and Mitchell, J. F. and Bisogni, V. and Liu, X. and Norman, M. R. and Dean, M. P. M.}, journal = {Phys. Rev. Lett.}, volume = {126}, issue = {8}, pages = {087001}, numpages = {8}, year = {2021}, month = feb, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.126.087001}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.126.087001} }

2019

Anomalous magnetoresistance due to longitudinal spin fluctuations in a Jeff = 1/2 Mott semiconductor

Lin Hao, Zhentao Wang, Junyi Yang, D. Meyers, Joshua Sanchez, Gilberto Fabbris, Yongseong Choi, Jong-Woo Kim, Daniel Haskel, Philip J. Ryan, Kipton Barros, Jiun-Haw Chu, M. P. M. Dean, Cristian D. Batista, and Jian Liu

Nature Communications 10, 5301 (2019)

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As a hallmark of electronic correlation, spin-charge interplay underlies many emergent phenomena in doped Mott insulators, such as high-temperature superconductivity, whereas the half-filled parent state is usually electronically frozen with an antiferromagnetic order that resists external control. We report on the observation of a positive magnetoresistance that probes the staggered susceptibility of a pseudospin-half square-lattice Mott insulator built as an artificial SrIrO3/SrTiO3 superlattice. Its size is particularly large in the high-temperature insulating paramagnetic phase near the Néel transition. This magnetoresistance originates from a collective charge response to the large longitudinal spin fluctuations under a linear coupling between the external magnetic field and the staggered magnetization enabled by strong spin-orbit interaction. Our results demonstrate a magnetic control of the binding energy of the fluctuating particle-hole pairs in the Slater-Mott crossover regime analogous to the Bardeen-Cooper-Schrieffer-to-Bose-Einstein condensation crossover of ultracold-superfluids.
@article{hao2019anomalous, dimensions = {true}, author = {Hao, Lin and Wang, Zhentao and Yang, Junyi and Meyers, D. and Sanchez, Joshua and Fabbris, Gilberto and Choi, Yongseong and Kim, Jong-Woo and Haskel, Daniel and Ryan, Philip J. and Barros, Kipton and Chu, Jiun-Haw and Dean, M. P. M. and Batista, Cristian D. and Liu, Jian}, title = {Anomalous magnetoresistance due to longitudinal spin fluctuations in a Jeff = 1/2 Mott semiconductor}, journal = {Nature Communications}, month = nov, year = {2019}, volume = {10}, number = {1}, pages = {5301}, issn = {2041-1723}, doi = {10.1038/s41467-019-13271-6}, url = {https://doi.org/10.1038/s41467-019-13271-6} }

2018

Giant magnetic response of a two-dimensional antiferromagnet

Lin Hao, D Meyers, Hidemaro Suwa, Junyi Yang, Clayton Frederick, Tamene R Dasa, Gilberto Fabbris, Lukas Horak, Dominik Kriegner, Yongseong Choi, Jong-Woo Kim, Daniel Haskel, Philip J. Ryan, Haixuan Xu, Cristian D. Batista, M. P. M. Dean, and Jian Liu

Nature Physics 14, 806 (2018)

[BNL Press Release]

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A fundamental difference between antiferromagnets and ferromagnets is the lack of linear coupling to a uniform magnetic field due to the staggered order parameter1. Such coupling is possible via the Dzyaloshinskii–Moriya (DM) interaction2,3, but at the expense of reduced antiferromagnetic (AFM) susceptibility due to the canting-induced spin anisotropy4. We solve this long-standing problem with a top-down approach that utilizes spin–orbit coupling in the presence of a hidden SU(2) symmetry. We demonstrate giant AFM responses to sub-tesla external fields by exploiting the extremely strong two-dimensional critical fluctuations preserved under a symmetry-invariant exchange anisotropy, which is built into a square lattice artificially synthesized as a superlattice of SrIrO₃ and SrTiO₃. The observed field-induced logarithmic increase of the ordering temperature enables highly efficient control of the AFM order. Our results demonstrate that symmetry can be exploited in spin–orbit-coupled magnets to develop functional AFM materials for fast and secured spintronic devices5,6,7,8,9.
@article{hao2018giant, dimensions = {true}, title = {Giant magnetic response of a two-dimensional antiferromagnet}, author = {Hao, Lin and Meyers, D and Suwa, Hidemaro and Yang, Junyi and Frederick, Clayton and Dasa, Tamene R and Fabbris, Gilberto and Horak, Lukas and Kriegner, Dominik and Choi, Yongseong and Kim, Jong-Woo and Haskel, Daniel and Ryan, Philip J. and Xu, Haixuan and Batista, Cristian D. and Dean, M. P. M. and Liu, Jian}, journal = {Nature Physics}, volume = {14}, number = {8}, pages = {806}, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=213028" target="_blank">BNL Press Release</a>]}, note1 = {[<a href="http://www.phys.utk.edu/news/2018/hidden-symmetry.html" target="_blank">UTK Press Release</a>]}, year = {2018}, note2 = {[<a href="https://www.aps.anl.gov/APS-Science-Highlight/2018-06-11/hidden-magnetism-appears-under-hidden-symmetry" target="_blank">ANL Highlight</a>]}, month = jun, doi = {10.1038/s41567-018-0152-6}, publisher = {Nature Publishing Group} }
Imaging antiferromagnetic antiphase domain boundaries using magnetic Bragg diffraction phase contrast

Min Gyu Kim, Hu Miao, Bin Gao, S-W Cheong, C Mazzoli, A Barbour, Wen Hu, SB Wilkins, Ian K Robinson, MPM Dean, and V. Kiryukhin

Nature communications 9, 5013 (2018)

[BNL Press Release]

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Manipulating magnetic domains is essential for many technological applications. Recent breakthroughs in Antiferromagnetic Spintronics brought up novel concepts for electronic device development. Imaging antiferromagnetic domains is of key importance to this field. Unfortunately, some of the basic domain types, such as antiphase domains, cannot be imaged by conventional techniques. Herein, we present a new domain projection imaging technique based on the localization of domain boundaries by resonant magnetic diffraction of coherent X rays. Contrast arises from reduction of the scattered intensity at the domain boundaries due to destructive interference effects. We demonstrate this approach by imaging antiphase domains in a collinear antiferromagnet Fe₂Mo₃O₈, and observe evidence of domain wall interaction with a structural defect. This technique does not involve any numerical algorithms. It is fast, sensitive, produces large-scale images in a single-exposure measurement, and is applicable to a variety of magnetic domain types.
@article{kim2018imaging, dimensions = {true}, title = {Imaging antiferromagnetic antiphase domain boundaries using magnetic Bragg diffraction phase contrast}, author = {Kim, Min Gyu and Miao, Hu and Gao, Bin and Cheong, S-W and Mazzoli, C and Barbour, A and Hu, Wen and Wilkins, SB and Robinson, Ian K and Dean, MPM and Kiryukhin, V.}, journal = {Nature communications}, volume = {9}, number = {1}, pages = {5013}, year = {2018}, month = nov, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=113211" target="_blank">BNL Press Release</a>]}, doi = {10.1038/s41467-018-07350-3}, publisher = {Nature Publishing Group} }

2017

High-temperature charge density wave correlations in La_1.875Ba_0.125CuO₄ without spin–charge locking

H Miao, José Lorenzana, Götz Seibold, YY Peng, A Amorese, F Yakhou-Harris, K Kummer, NB Brookes, RM Konik, V Thampy, G. D. Gu, G. Ghiringhelli, L. Braicovich, and M. P. M. Dean

Proceedings of the National Academy of Sciences 114, 12430–12435 (2017)

[BNL Press Release]

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Although all superconducting cuprates display charge-ordering tendencies, their low-temperature properties are distinct, imped- ing efforts to understand the phenomena within a single con- ceptual framework. While some systems exhibit stripes of charge and spin, with a locked periodicity, others host charge den- sity waves (CDWs) without any obviously related spin order. Here we use resonant inelastic X-ray scattering to follow the evolution of charge correlations in the canonical stripe-ordered cuprate La_1.875Ba_0.125CuO₄ across its ordering transition. We find that high-temperature charge correlations are unlocked from the wavevector of the spin correlations, signaling analogies to CDW phases in various other cuprates. This indicates that stripe order at low temperatures is stabilized by the coupling of otherwise inde- pendent charge and spin density waves, with important implica- tions for the relation between charge and spin correlations in the cuprates. charge
@article{miao2017high, dimensions = {true}, title = {High-temperature charge density wave correlations in La1.875Ba0.125CuO4 without spin--charge locking}, author = {Miao, H and Lorenzana, Jos{\'e} and Seibold, G{\"o}tz and Peng, YY and Amorese, A and Yakhou-Harris, F and Kummer, K and Brookes, NB and Konik, RM and Thampy, V and Gu, G. D. and Ghiringhelli, G. and Braicovich, L. and Dean, M. P. M.}, journal = {Proceedings of the National Academy of Sciences}, volume = {114}, number = {47}, pages = {12430--12435}, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=212619" target="_blank">BNL Press Release</a>]}, doi = {10.1073/pnas.1708549114}, year = {2017}, month = may, publisher = {National Academy of Sciences} }
Doping dependence of collective spin and orbital excitations in the Spin-1 quantum antiferromagnet La_2-xSr_xNiO₄ Observed by X rays

G Fabbris, D Meyers, L Xu, VM Katukuri, L Hozoi, X Liu, ZY Chen, J Okamoto, T Schmitt, AC Uldry, B. Delley, G. D. Gu, D. Prabhakaran, A. T. Boothroyd, J. Brink, D. J. Huang, and M. P. M. Dean

Phys. Rev. Lett. 118, 12430–12435 (2017)

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We report the first empirical demonstration that resonant inelastic x-ray scattering (RIXS) is sensitive to collective magnetic excitations in S=1 systems by probing the Ni L₃ edge of La_2−xSr_xNiO₄ (x=0, 0.33, 0.45). The magnetic excitation peak is asymmetric, indicating the presence of single and multi-spin-flip excitations. As the hole doping level is increased, the zone boundary magnon energy is suppressed at a much larger rate than that in hole doped cuprates. Based on the analysis of the orbital and charge excitations observed by RIXS, we argue that this difference is related to the orbital character of the doped holes in these two families. This work establishes RIXS as a probe of fundamental magnetic interactions in nickelates opening the way towards studies of heterostructures and ultrafast pump-probe experiments.
@article{fabbris2017doping, dimensions = {true}, title = {Doping dependence of collective spin and orbital excitations in the Spin-1 quantum antiferromagnet La2-xSrxNiO4 Observed by X rays}, author = {Fabbris, G and Meyers, D and Xu, L and Katukuri, VM and Hozoi, L and Liu, X and Chen, ZY and Okamoto, J and Schmitt, T and Uldry, AC and Delley, B. and Gu, G. D. and Prabhakaran, D. and Boothroyd, A. T. and van den Brink, J. and Huang, D. J. and Dean, M. P. M.}, journal = {Phys. Rev. Lett.}, volume = {118}, number = {15}, year = {2017}, month = apr, doi = {10.1103/PhysRevLett.118.156402}, publisher = {American Physical Society} }

2013

Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed 3 d- 5 d Transition-Metal Compound Sr₃CuIrO₆

Wei-Guo Yin, X Liu, AM Tsvelik, MPM Dean, MH Upton, Jungho Kim, D Casa, A Said, T Gog, TF Qi, G. Cao, and J. P. Hill

Phys. Rev. Lett. 111, 057202 (2013)

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We report a combined experimental and theoretical study of the unusual ferromagnetism in the one- dimensional copper-iridium oxide Sr₃CuIrO₆. Utilizing Ir L3 edge resonant inelastic x-ray scattering, we reveal a large gap magnetic excitation spectrum. We find that it is caused by an unusual exchange anisotropy generating mechanism, namely, strong ferromagnetic anisotropy arising from antiferromag- netic superexchange, driven by the alternating strong and weak spin-orbit coupling on the 5d Ir and 3d Cu magnetic ions, respectively. From symmetry consideration, this novel mechanism is generally present in systems with edge-sharing Cu²⁺O₄ plaquettes and Ir⁴⁺O₆ octahedra. Our results point to unusual magnetic behavior to be expected in mixed 3d-5d transition-metal compounds via exchange pathways that are absent in pure 3d or 5d compounds.
@article{yin2013ferromagnetic, dimensions = {true}, nosupp = {}, title = {Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed 3 d- 5 d Transition-Metal Compound Sr3CuIrO6}, author = {Yin, Wei-Guo and Liu, X and Tsvelik, AM and Dean, MPM and Upton, MH and Kim, Jungho and Casa, D and Said, A and Gog, T and Qi, TF and Cao, G. and Hill, J. P.}, journal = {Phys. Rev. Lett.}, volume = {111}, number = {5}, pages = {057202}, year = {2013}, month = aug, doi = {10.1103/PhysRevLett.111.057202}, publisher = {American Physical Society} }
High-energy magnetic excitations in the cuprate superconductor Bi₂Sr₂CaCu₂O_8+δ: towards a unified description of its electronic and magnetic degrees of freedom

MPM Dean, AJA James, RS Springell, X Liu, C Monney, KJ Zhou, RM Konik, JS Wen, ZJ Xu, GD Gu, V. N. Strocov, T. Schmitt, and J. P. Hill

Phys. Rev. Lett. 110, 147001 (2013)

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We investigate the high-energy magnetic excitation spectrum of the high-T(c) cuprate superconductor Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) using Cu L(3) edge resonant inelastic x-ray scattering. Broad, dispersive magnetic excitations are observed, with a zone boundary energy of ∼ 300 meV and a weak dependence on doping. These excitations are strikingly similar to the bosons proposed to explain the high-energy "kink" observed in photoemission. A phenomenological calculation of the spin response, based on a parametrization of the the angle-resolved photoemission spectroscopy derived electronic structure and Yang-Rice-Zhang quasiparticles, provides a reasonable prediction of the energy dispersion of the observed magnetic excitations. These results indicate a possible unified framework to reconcile the magnetic and electronic properties of the cuprates and we discuss the advantages and disadvantages of such an approach.
@article{dean2013high, dimensions = {true}, title = {High-energy magnetic excitations in the cuprate superconductor Bi2Sr2CaCu2O8+δ: towards a unified description of its electronic and magnetic degrees of freedom}, author = {Dean, MPM and James, AJA and Springell, RS and Liu, X and Monney, C and Zhou, KJ and Konik, RM and Wen, JS and Xu, ZJ and Gu, GD and Strocov, V. N. and Schmitt, T. and Hill, J. P.}, journal = {Phys. Rev. Lett.}, volume = {110}, number = {14}, pages = {147001}, year = {2013}, month = apr, doi = {10.1103/PhysRevLett.110.147001}, publisher = {American Physical Society} }
Persistence of magnetic excitations in La_2-xSr_xCuO₄ from the undoped insulator to the heavily overdoped non-superconducting metal

M. P. M. Dean, G. Dellea, R. S. Springell, F. Yakhou-Harris, K. Kummer, N. B. Brookes, X. Liu, Y.-J. Sun, J. Strle, T. Schmitt, and J. P. Hill

Nature Materials 12, 1019–1023 (2013)

[BNL Press Release]

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One of the most intensely studied scenarios of high- temperature superconductivity (HTS) postulates pairing by exchange of magnetic excitations1. Indeed, such excitations have been observed up to optimal doping in the cuprates2–7. In the heavily overdoped regime, neutron scattering mea- surements indicate that magnetic excitations have effectively disappeared8–10, and this has been argued to cause the demise of HTS with overdoping1,8,10. Here we use resonant inelastic X-ray scattering, which is sensitive to complementary parts of reciprocal space, to measure the evolution of the magnetic excitations in La_2−xSr_xCuO₄ across the entire phase diagram, from a strongly correlated insulator (x = 0) to a non-superconducting metal (x=0.40). For x=0, well-defined magnon excitations are observed11. These magnons broaden with doping, but they persist with a similar dispersion and comparable intensity all the way to the non-superconducting, heavily overdoped metallic phase. The destruction of HTS with overdoping is therefore caused neither by the general disappearance nor by the overall softening of magnetic excitations. Other factors, such as the redistribution of spectral weight, must be considered.
@article{dean2013persistence, dimensions = {true}, title = {Persistence of magnetic excitations in La2-xSrxCuO4 from the undoped insulator to the heavily overdoped non-superconducting metal}, author = {Dean, M. P. M. and Dellea, G. and Springell, R. S. and Yakhou-Harris, F. and Kummer, K. and Brookes, N. B. and Liu, X. and Sun, Y.-J. and Strle, J. and Schmitt, T. and Hill, J. P.}, journal = {Nature Materials}, doi = {10.1038/nmat3723}, note = {[<a href="https://www.bnl.gov/newsroom/news.php?a=111564" target="_blank">BNL Press Release</a>]}, volume = {12}, month = aug, pages = {1019--1023}, year = {2013} }