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).
Example papers
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Strongly Correlated Charge Density Wave in La2-xSrxCuO4 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.
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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 La1.875Ba0.125CuO4 (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.
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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 La1.875Ba0.125CuO4. 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 YBa2Cu3O6+δ. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low-temperature ordering wave vectors.
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Doping dependence of collective spin and orbital excitations in the Spin-1 quantum antiferromagnet La2-xSrxNiO4 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 La2−xSrxNiO4 (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.
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High-temperature charge density wave correlations in La1.875Ba0.125CuO4 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 La1.875Ba0.125CuO4 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
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