CDWs

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.

Example papers

1. 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) [Abs] [PDF] [HTML] [Supp]

   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.

2. 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) [Abs] [PDF] [HTML] [Supp]

   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.

3. 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) [Abs] [PDF] [HTML] [Supp] [BNL Press Release]

   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.

4. 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) [Abs] [PDF] [HTML] [arXiv] [Supp]

   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.

5. Formation of Incommensurate Charge Density Waves in Cuprates H. Miao, R. Fumagalli, M. Rossi, J. Lorenzana, G. Seibold, F. Yakhou-Harris, K. Kummer, N. B. Brookes, G. D. Gu, L. Braicovich, G. Ghiringhelli, and M. P. M. Dean Phys. Rev. X 9, 031042 (2019) [Abs] [PDF] [HTML] [Supp]

   Although charge density waves (CDWs) are omnipresent in cuprate high-temperature superconductors, they occur at significantly different wave vectors, confounding efforts to understand their formation mechanism. Here, we use resonant inelastic x-ray scattering to investigate the doping- and temperature-dependent CDW evolution in La_2-xBa_xCuO₄ (x=0.115–0.155). We discover that the CDW develops in two stages with decreasing temperature. A precursor CDW with a quasicommensurate wave vector emerges first at high temperature. This doping-independent precursor CDW correlation originates from the CDW phase mode coupled with a phonon and “seeds” the low-temperature CDW with a strongly doping-dependent wave vector. Our observation reveals the precursor CDW and its phase mode as the building blocks of the highly intertwined electronic ground state in the cuprates.

6. 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) [Abs] [PDF] [HTML] [Supp] [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.

7. 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) [Abs] [PDF] [HTML] [Supp]

   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.

8. 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) [Abs] [PDF] [HTML] [BNL Press Release]

   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

9. 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) [Abs] [PDF] [HTML] [Supp] [BNL Press Release]

   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.