| 1. |
- Kramer, K. P., et al.
(author)
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Revealing the Orbital Composition of Heavy Fermion Quasiparticles in CeRu 2 Si 2
- 2023
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In: Journal of the Physical Society of Japan. - 1347-4073 .- 0031-9015. ; 92:10
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Journal article (peer-reviewed)abstract
- We present a resonant angle-resolved photoemission spectroscopy (ARPES) study of the electronic band structure and heavy fermion quasiparticles in CeRu2Si2. Using light polarization analysis, considerations of the crystal field environment and hybridization between conduction and f electronic states, we identify the d-electronic orbital character of conduction bands crossing the Fermi level. Resonant ARPES spectra suggest that the localized Ce f states hybridize with eg and t2g states around the zone center. In this fashion, we reveal the orbital structure of the heavy fermion quasiparticles in CeRu2Si2 and discuss its implications for metamagnetism and superconductivity in the related compound CeCu2Si2
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| 2. |
- Küspert, Julia, et al.
(author)
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Pseudogap suppression by competition with superconductivity in La-based cuprates
- 2022
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In: Physical Review Research. - 2643-1564. ; 4:4
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Journal article (peer-reviewed)abstract
- We carried out a comprehensive high-resolution angle-resolved photoemission spectroscopy (ARPES) study of the pseudogap interplay with superconductivity in La-based cuprates. The three systems La2-xSrxCuO4, La1.6-xNd0.4SrxCuO4, and La1.8-xEu0.2SrxCuO4 display slightly different pseudogap critical points in the temperature versus doping phase diagram. We studied the pseudogap evolution into the superconducting state for doping concentrations just below the critical point. In this setting, near optimal doping for superconductivity and in the presence of the weakest possible pseudogap, we uncover how the pseudogap is partially suppressed inside the superconducting state. This conclusion is based on the direct observation of a reduced pseudogap energy scale and re-emergence of spectral weight suppressed by the pseudogap. Altogether these observations suggest that the pseudogap phenomenon in La-based cuprates is in competition with superconductivity for antinodal spectral weight.
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| 3. |
- Simutis, Gediminas, et al.
(author)
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In situ uniaxial pressure cell for x-ray and neutron scattering experiments
- 2023
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 94:1
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Journal article (peer-reviewed)abstract
- We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes.
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| 4. |
- Simutis, Gediminas, et al.
(author)
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Single-domain stripe order in a high-temperature superconductor
- 2022
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In: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 5:1
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Journal article (peer-reviewed)abstract
- The coupling of spin, charge and lattice degrees of freedom results in the emergence of novel states of matter across many classes of strongly correlated electron materials. A model example is unconventional superconductivity, which is widely believed to arise from the coupling of electrons via spin excitations. In cuprate high-temperature superconductors, the interplay of charge and spin degrees of freedom is also reflected in a zoo of charge and spin-density wave orders that are intertwined with superconductivity. A key question is whether the different types of density waves merely coexist or are indeed directly coupled. Here we profit from a neutron scattering technique with superior beam-focusing that allows us to probe the subtle spin-density wave order in the prototypical high-temperature superconductor La1.88Sr0.12CuO4 under applied uniaxial pressure to demonstrate that the two density waves respond to the external tuning parameter in the same manner. Our result shows that suitable models for high-temperature superconductivity must equally account for charge and spin degrees of freedom via uniaxial charge-spin stripe fluctuations.
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| 5. |
- Wang, Q., et al.
(author)
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Charge order lock-in by electron-phonon coupling in La 1.675 Eu 0.2 Sr 0.125 CuO 4
- 2021
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In: Science advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:27
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Journal article (peer-reviewed)abstract
- Charge order is universal to all hole-doped cuprates. Yet, the driving interactions remain an unsolved problem. Electron-electron interaction is widely believed to be essential, whereas the role of electron-phonon interaction is unclear. We report an ultrahigh-resolution resonant inelastic x-ray scattering (RIXS) study of the in-plane bond-stretching phonon mode in stripe-ordered cuprate La1.675Eu0.2Sr0.125CuO4. Phonon softening and lifetime shortening are found around the charge ordering wave vector. In addition to these self-energy effects, the electron-phonon coupling is probed by its proportionality to the RIXS cross section. We find an enhancement of the electron-phonon coupling around the charge-stripe ordering wave vector upon cooling into the low-temperature tetragonal structure phase. These results suggest that, in addition to electronic correlations, electron-phonon coupling contributes substantially to the emergence of long-range charge-stripe order in cuprates.
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| 6. |
- Wang, Qisi, et al.
(author)
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Charge order lock-in by electron-phonon coupling in La1.675Eu0.25Sr0.125CuO4
- 2021
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:27
-
Journal article (peer-reviewed)abstract
- Charge order is universal to all hole-doped cuprates. Yet, the driving interactions remain an unsolved problem. Electron-electron interaction is widely believed to be essential, whereas the role of electron-phonon interaction is unclear. We report an ultrahigh-resolution resonant inelastic x-ray scattering (RIXS) study of the in-plane bondstretching phonon mode in stripe-ordered cuprate La1.675Eu0.25Sr0.125CuO4. Phonon softening and lifetime shortening are found around the charge ordering wave vector. In addition to these self-energy effects, the electron-phonon coupling is probed by its proportionality to the RIXS cross section. We find an enhancement of the electron-phonon coupling around the charge-stripe ordering wave vector upon cooling into the low-temperature tetragonal structure phase. These results suggest that, in addition to electronic correlations, electron-phonon coupling contributes substantially to the emergence of long-range charge-stripe order in cuprates.
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| 7. |
- Wang, Q., et al.
(author)
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Uniaxial pressure induced stripe order rotation in La 1.88 Sr 0.12 CuO 4
- 2022
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 13:1
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Journal article (peer-reviewed)abstract
- Static stripe order is detrimental to superconductivity. Yet, it has been proposed that transverse stripe fluctuations may enhance the inter-stripe Josephson coupling and thus promote superconductivity. Direct experimental studies of stripe dynamics, however, remain difficult. From a strong-coupling perspective, transverse stripe fluctuations are realized in the form of dynamic “kinks”—sideways shifting stripe sections. Here, we show how modest uniaxial pressure tuning reorganizes directional kink alignment. Our starting point is La1.88Sr0.12CuO4 where transverse kink ordering results in a rotation of stripe order away from the crystal axis. Application of mild uniaxial pressure changes the ordering pattern and pins the stripe order to the crystal axis. This reordering occurs at a much weaker pressure than that to detwin the stripe domains and suggests a rather weak transverse stripe stiffness. Weak spatial stiffness and transverse quantum fluctuations are likely key prerequisites for stripes to coexist with superconductivity.
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