CDWs

Charge density waves

Charge density waves are periodic modulations in the electronic density of states in materials. We are studying the formation mechanisms of these states by measuring CDW excitations with inelastic scattering and studying domain formation and dynamics with coherent x-rays.

Figure 1: An illustration of measuring collective CDW excitations with RIXS taken from our recent paper H. Miao et al., PRX 9, 031042 (2019).

References

2023

Electronic Character of Charge Order in Square-Planar Low-Valence Nickelates

Y. Shen, J. Sears, G. Fabbris, J. Li, J. Pelliciari, M. Mitrano, W. He, Junjie Zhang, J. F. Mitchell, V. Bisogni, M. R. Norman, S. Johnston, and M. P. M. Dean

Phys. Rev. X 13, 011021 (2023)

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[BNL Press Release]

Charge order is a central feature of the physics of cuprate superconductors and is known to arise from a modulation of holes with primarily oxygen character. Low-valence nickelate superconductors also host charge order, but the electronic character of this symmetry breaking is unsettled. Here, using resonant inelastic x-ray scattering at the Ni L₂-edge, we identify intertwined involvements of Ni 3d_x^2-y^2, 3d_3z^2-r^2, and O 2p_σ orbitals in the formation of diagonal charge order in an overdoped low-valence nickelate \La438. The Ni 3d_x^2-y^2 orbitals, strongly hybridized with planar O 2p_σ, largely shape the spatial charge distribution and lead to Ni site-centered charge order. The 3d_3z^2-r^2 orbitals play a small, but non-negligible role in the charge order as they hybridize with the rare-earth 5d orbitals. Our results reveal that the low-energy physics and ground-state character of these nickelates are more complex than those in cuprates.

2021

Charge Condensation and Lattice Coupling Drives Stripe Formation in Nickelates

Y. Shen, G. Fabbris, H. Miao, Y. Cao, D. Meyers, D. G. Mazzone, T. Assefa, X. M. Chen, K. Kisslinger, D. Prabhakaran, A. T. Boothroyd, J. M. Tranquada, W. Hu, A. M. Barbour, S. B. Wilkins, C. Mazzoli, I. K. Robinson, and M. P. M. Dean

Phys. Rev. Lett. 126, 177601 (2021)

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Revealing the predominant driving force behind symmetry breaking in correlated materials is sometimes a formidable task due to the intertwined nature of different degrees of freedom. This is the case for La_2-xSr_xNiO_4+δ, in which coupled incommensurate charge and spin stripes form at low temperatures. Here, we use resonant x-ray photon correlation spectroscopy to study the temporal stability and domain memory of the charge and spin stripes in La_2-xSr_xNiO_4+δ. Although spin stripes are more spatially correlated, charge stripes maintain a better temporal stability against temperature change. More intriguingly, charge order shows robust domain memory with thermal cycling up to 250 K, far above the ordering temperature. These results demonstrate the pinning of charge stripes to the lattice and that charge condensation is the predominant factor in the formation of stripe orders in nickelates.
Charge density waves in cuprate superconductors beyond the critical doping

H. Miao, G. Fabbris, R. J. Koch, D. G. Mazzone, C. S. Nelson, R. Acevedo-Esteves, G. D. Gu, Y. Li, T. Yilimaz, K. Kaznatcheev, E. Vescovo, M. Oda, T. Kurosawa, N. Momono, T. Assefa, I. K. Robinson, E. S. Bozin, J. M. Tranquada, P. D. Johnson, and M. P. M. Dean

npj Quantum Materials 6, 31 (2021)

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The unconventional normal-state properties of the cuprates are often discussed in terms of emergent electronic order that onsets below a putative critical doping of x_c=0.19. Charge density wave (CDW) correlations represent one such order; however, experimental evidence for such order generally spans a limited range of doping that falls short of the critical value x_c, leading to questions regarding its essential relevance. Here, we use X-ray diffraction to demonstrate that CDW correlations in La_2−xSr_xCuO₄ persist up to a doping of at least x=0.21. The correlations show strong changes through the superconducting transition, but no obvious discontinuity through x_c=0.19, despite changes in Fermi surface topology and electronic transport at this doping. These results demonstrate the interaction between CDWs and superconductivity even in overdoped cuprates and prompt a reconsideration of the role of CDW correlations in the high-temperature cuprate phase diagram.

2020

Strongly Correlated Charge Density Wave in La_2-xSr_xCuO₄ Evidenced by Doping-Dependent Phonon Anomaly

J. Q. Lin, H. Miao, D. G. Mazzone, G. D. Gu, A. Nag, A. C. Walters, M. Garcı́a-Fernández, A. Barbour, J. Pelliciari, I. Jarrige, M. Oda, K. Kurosawa, N. Momono, Ke-Jin Zhou, V. Bisogni, X. Liu, and M. P. M. Dean

Phys. Rev. Lett. 124, 207005 (2020)

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The discovery of charge-density-wave-related effects in the resonant inelastic x-ray scattering spectra of cuprates holds the tantalizing promise of clarifying the interactions that stabilize the electronic order. Here, we report a comprehensive resonant inelastic x-ray scattering study of La2−xSrxCuO4 finding that chargedensity wave effects persist up to a remarkably high doping level of x=0.21 before disappearing at x = 0.25. The inelastic excitation spectra remain essentially unchanged with doping despite crossing a topological transition in the Fermi surface. This indicates that the spectra contain little or no direct coupling to electronic excitations near the Fermi surface, rather they are dominated by the resonant cross section for phonons and charge-density-wave-induced phonon softening. We interpret our results in terms of a chargedensity wave that is generated by strong correlations and a phonon response that is driven by the chargedensity-wave-induced modification of the lattice.

2019

Charge density wave memory in a cuprate superconductor

XM Chen, C Mazzoli, Y Cao, V Thampy, AM Barbour, W Hu, M Lu, TA Assefa, H Miao, G Fabbris, G. D. Gu, J. M. Tranquada, M. P. M. Dean, S. B. Wilkins, and I. K. Robinson

Nature communications 10, 1435 (2019)

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Although CDW correlations are a ubiquitous feature of the superconducting cuprates, their disparate properties suggest a crucial role for pinning the CDW to the lattice. Here, we report coherent resonant X-ray speckle correlation analysis, which directly determines the reproducibility of CDW domain patterns in La_1.875Ba_0.125CuO₄ (LBCO 1/8) with thermal cycling. While CDW order is only observed below 54 K, where a structural phase transition creates inequivalent Cu-O bonds, we discover remarkably reproducible CDW domain memory upon repeated cycling to far higher temperatures. That memory is only lost on cycling to 240(3) K, which recovers the four-fold symmetry of the CuO₂ planes. We infer that the structural features that develop below 240 K determine the CDW pinning landscape below 54 K. This opens a view into the complex coupling between charge and lattice degrees of freedom in superconducting cuprates.

2018

Incommensurate phonon anomaly and the nature of charge density waves in cuprates

Hu Miao, D Ishikawa, Rolf Heid, Matthieu Le Tacon, Gilberto Fabbris, Derek Meyers, GD Gu, AQR Baron, and MPM Dean

Phys. Rev. X 8, 011008 (2018)

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[Spring8 Research Highlight]

While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wave vectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here, we investigate the temperature dependence of the low-energy phonons in the canonical CDW-ordered cuprate La_1.875Ba_0.125CuO₄. We discover that the phonon softening wave vector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wave vector of 0.238 reciprocal lattice units (r.l.u.) below the ordering transition temperature to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that “214”-type cuprates can host CDW correlations at a similar wave vector to previously reported CDW correlations in non-214-type cuprates such as YBa₂Cu₃O_6+δ. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low-temperature ordering wave vectors.

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)

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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
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, (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.

2016

Remarkable stability of charge density wave order in La_2-xBa_xCuO₄

XM Chen, V Thampy, C Mazzoli, AM Barbour, H Miao, GD Gu, Y Cao, JM Tranquada, MPM Dean, and SB Wilkins

Phys. Rev. Lett. 117, 167001 (2016)

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The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La_2-xBa_xCuO₄ by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2/3/4 h. We discuss the implications of these results for some of the competing theories.