Ultrafast time-resolved x-ray scattering reveals diffusive charge order dynamics in La
 
 2–
 x
 
 Ba
 
 x
 
 CuO
 4

Mitrano, Matteo; Lee, Sangjun; Husain, Ali; Delacrétaz, Luca V.; Zhu, Minhui; Munoz, Gilberto de la Peña; Sun, Stella; Joe, Young Il; Reid, Alexander H.; Wandel, Scott F.; Coslovich, Giacomo; Schlotter, W. F.; Driel, Tim van; Schneeloch, John; Gu, Genda; Hartnoll, Sean A.; Goldenfeld, Nigel; Abbamonte, Peter

doi:10.1126/sciadv.aax3346

Cited by 66 publications

(39 citation statements)

References 57 publications

(127 reference statements)

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“…Time-resolved resonant soft x-ray scattering has also been performed on La 2−x Ba x CuO 4 just above the superconducting transition temperature and found overdamped excitations at very low energies, below 2 meV [81]. Such a low excitation energy corresponds to the mass of the collective mode derived in the previous sections.…”

Section: Resonant X-ray Scatteringsupporting

confidence: 55%

Collective mode in the SU(2) theory of cuprates

2018

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Recent advances in momentum-resolved electron energy-loss spectroscopy (MEELS) and resonant inelastic X-ray scattering (RIXS) now allow one to access the charge response function with unprecedented versatility and accuracy. This allows for the study of excitations which were inaccessible recently, such as low-energy and finite momentum collective modes. The SU(2) theory of the cuprates is based on a composite order parameter with SU(2) symmetry fluctuating between superconductivity and charge order. The phase where it fluctuates is a candidate for the pseudogap phase of the cuprates. This theory has a signature, enabling its strict experimental test, which is the fluctuation between these two orders, corresponding to a charge 2 spin 0 mode at the charge ordering wave-vector. Here we derive the influence of this SU(2) collective mode on the charge susceptibility in both strong and weak coupling limits, and discuss its relation to MEELS, RIXS and Raman experiments. We find two peaks in the charge susceptibility at finite energy, whose middle is the charge ordering wave-vector, and discuss their evolution in the phase diagram.

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Section: Resonant X-ray Scatteringsupporting

confidence: 55%

Collective mode in the SU(2) theory of cuprates

2018

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“…This lack of quantum melting of CO implies that proximity to the CO QCP may be material dependent; for some materials, the QCP even may lie beyond the superconducting dome 31 . In stripe-ordered La 2−x Ba x CuO 4 , signatures of charge density wave (CDW) excitations were also reported in underdoped compounds 32,33 , and attributed to phase modes 32 . We argue that La 2−x Ba x CuO 4 near x = 1/8 probably sits in the RC regime of Fig.…”

Section: Nature Physicsmentioning

confidence: 97%

Spectroscopic fingerprint of charge order melting driven by quantum fluctuations in a cuprate

et al. 2020

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Copper oxide high-T C superconductors possess a number of exotic orders that coexist with or are proximal to superconductivity. Quantum fluctuations associated with these orders may account for the unusual characteristics of the normal state, and possibly affect the superconductivity 1-4 . Yet, spectroscopic evidence for such quantum fluctuations remains elusive. Here, we use resonant inelastic X-ray scattering to reveal spectroscopic evidence of fluctuations associated with a charge order 5-14 in nearly optimally doped Bi 2 Sr 2 CaCu 2 O 8+δ . In the superconducting state, while the quasielastic charge order signal decreases with temperature, the interplay between charge order fluctuations and bond-stretching phonons in the form of a Fano-like interference increases, an observation that is incompatible with expectations for competing orders. Invoking general principles, we argue that this behaviour reflects the properties of a dissipative system near an orderdisorder quantum critical point, where the dissipation varies with the opening of the pseudogap and superconducting gap at low temperatures, leading to the proliferation of quantum critical fluctuations, which melt charge order.Charge order (CO), which is ubiquitous in hole-doped cuprates [5][6][7][8][9][10][11][12][13][14] , is accompanied by a negligible lattice deformation (approximately 0.1 pm, ref. 15 ); however, signatures of valence electron density modulations due to CO can be detected by resonant inelastic X-ray scattering (RIXS) at the Cu L edge. RIXS resolves both the quasistatic and dynamical inelastic signals 8,16 , as highlighted in Fig. 1a, particularly the intensity of the inelastic branch of excitations below 0.1 eV. These excitations possess an energy scale similar to that of bond-stretching phonons, which exhibit anomalous softening and broadening in certain portions of reciprocal space, observed using inelastic neutron scattering and non-resonant inelastic X-ray scattering 17,18 . These behaviours have suggested a coupling with CO 17,18 and possibly some form of charge collective mode 19 . However, while neutron and non-resonant X-ray scattering measure the phonon self-energy (meaning the dynamical structure factor), RIXS largely reflects the electron-phonon coupling itself and its interplay with charge excitations 16,20 . With superb momentum resolution, RIXS at the Cu L edge has already revealed two distinct anomalies associated with CO excitations due to a Fano-like interference effect 16 , as shown in Fig. 1b: (1) an apparent softening of the RIXS phonon at the CO wave-vector (Q CO ), and (2) creation of a 'funnel'-like spectral weight emanating from Q CO with a

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“…The stripe fluctuations have been extensively searched for in experiment. Taking the canonical cuprate La 2−x Ba x CuO 4 ( x = 1∕8 ) for instance, a recent femtosecond time-resolved resonant soft X-ray scattering (pump-probe) investigation at the LCLS reported the absence of a photoinduced coherent mode [62]. This observation rules out the static charge stripe scenario in this system and indicates that the fluctuations must be gapless, i.e., relaxational in the time domain.…”

Section: Fluctuating Order In Unconventional Superconductorsmentioning

confidence: 94%

“…A myriad of papers have now been devoted to revealing the stripe fluctuations in cuprate superconductors, using inelastic neutron scattering (INS) [53,54], resonant inelastic X-ray scattering (RIXS) [55][56][57][58], and pump-probe spectroscopy [59][60][61][62][63]. Among these techniques, INS and RIXS are most powerful in measuring the coherent excitations in solids, while pump-probe methods normally evaluate the non-equilibrium states transiently created by a femtosecond optical pulse.…”

Section: Fluctuating Order In Unconventional Superconductorsmentioning

confidence: 99%

A snapshot review—Fluctuations in quantum materials: from skyrmions to superconductivity

et al. 2021

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By measuring a linear response function directly, such as the dynamic susceptibility, one can understand fundamental material properties. However, a fresh perspective can be offered by studying fluctuations. This can be related back to the dynamic susceptibility through the fluctuation–dissipation theorem, which relates the fluctuations in a system to its response, an alternate route to access the physics of a material. Here, we describe a new X-ray tool for material characterization that will offer an opportunity to uncover new physics in quantum materials using this theorem. We provide details of the method and discuss the requisite analysis techniques in order to capitalize on the potential to explore an uncharted region of phase space. This is followed by recent results on a topological chiral magnet, together with a discussion of current work in progress. We provide a perspective on future measurements planned for work in unconventional superconductivity. Graphical abstract We describe a new X-ray tool for material characterization that will offer an opportunity to uncover new physics in quantum materials using coherent, short-pulsed X-rays. We provide details of the method and discuss the requisite analysis techniques in order to capitalize on the potential to explore an uncharted region of phase space. This is followed by recent results on a topological chiral magnet, together with a discussion of current work in progress. We provide a perspective on future measurements planned for work in unconventional superconductivity.

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Ultrafast time-resolved x-ray scattering reveals diffusive charge order dynamics in La _{2–
x} Ba _x CuO ₄

Cited by 66 publications

References 57 publications

Collective mode in the SU(2) theory of cuprates

Collective mode in the SU(2) theory of cuprates

Spectroscopic fingerprint of charge order melting driven by quantum fluctuations in a cuprate

A snapshot review—Fluctuations in quantum materials: from skyrmions to superconductivity

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Ultrafast time-resolved x-ray scattering reveals diffusive charge order dynamics in La 2– x Ba x CuO 4

Cited by 66 publications

References 57 publications

Collective mode in the SU(2) theory of cuprates

Collective mode in the SU(2) theory of cuprates

Spectroscopic fingerprint of charge order melting driven by quantum fluctuations in a cuprate

A snapshot review—Fluctuations in quantum materials: from skyrmions to superconductivity

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Ultrafast time-resolved x-ray scattering reveals diffusive charge order dynamics in La _{2–
x} Ba _x CuO ₄