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Instruments / Technical Area	Publication Details	Published
I05-ARPES	Pseudogap suppression by competition with superconductivity in La-based cuprates J. Küspert , R. Cohn Wagner , C. Lin , K. Von Arx , Q. Wang , K. Kramer , W. R. Pudelko , N. C. Plumb , C. E. Matt , C. G. Fatuzzo , D. Sutter , Y. Sassa , J.-Q. Yan , J.-S. Zhou , J. B. Goodenough , S. Pyon , T. Takayama , H. Takagi , T. Kurosawa , N. Momono , M. Oda , M. Hoesch , C. Cacho , T. K. Kim , M. Horio , J. Chang Physical Review Research 4 DOI: 10.1103/PhysRevResearch.4.043015 Diamond Proposal Number(s): [27768, 10550] Open Access Show Abstract ▼ 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 La 2 − x Sr x CuO 4 , La 1.6 − x Nd 0.4 Sr x CuO 4 , and La 1.8 − x Eu 0.2 Sr x CuO 4 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.	Oct 2022
I05-ARPES	Decoupling of lattice and orbital degrees of freedom in an iron-pnictide superconductor C. E. Matt , O. Ivashko , M. Horio , J. Choi , Q. Wang , D. Sutter , N. Dennler , M. H. Fischer , S. Katrych , L. Forro , J. Ma , B. Fu , B. Q. Lv , M. V. Zimmermann , T. K. Kim , N. C. Plumb , N. Xu , M. Shi , Johan Chang Physical Review Research 3 DOI: 10.1103/PhysRevResearch.3.023220 Diamond Proposal Number(s): [16104] Open Access Show Abstract ▼ Abstract: The interplay between structural and electronic phases in iron-based superconductors is a central theme in the search for the superconducting pairing mechanism. While electronic nematicity is competing with superconductivity, the effect of purely structural orthorhombic order is unexplored. Here, using x-ray diffraction and angle-resolved photoemission spectroscopy, we reveal a structural orthorhombic phase in the electron-doped iron-pnictide superconductor Pr 4 Fe 2 As 2 Te 0.88 O 4 ( T c = 25 K), which is distinct from orthorhombicity in the nematic phase in underdoped pnictides. Despite the high electron doping we find an exceptionally high orthorhombic onset temperature ( T ort ∼ 250 K), no signatures of phase competition with superconductivity, and absence of electronic nematic order as the driving mechanism for orthorhombicity. Combined, our results establish a high-temperature phase in the phase diagram of iron-pnictide superconductors and impose strong constraints for the modeling of their superconducting pairing mechanism.	Jun 2021
I21-Resonant Inelastic X-ray Scattering (RIXS)	Charge order lock-in by electron-phonon coupling in La1.675Eu0.2Sr0.125CuO4 Qisi Wang , Karin Von Arx , Masafumi Horio , Deepak John Mukkattukavil , Julia Kuespert , Yasmine Sassa , Thorsten Schmitt , Abhishek Nag , Sunseng Pyon , Tomohiro Takayama , Hidenori Takagi , Mirian Garcia-Fernandez , Ke-Jin Zhou , Johan Chang Science Advances 7 DOI: 10.1126/sciadv.abg7394 Diamond Proposal Number(s): [24481] Open Access Show Abstract ▼ 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.	Jun 2021
I05-ARPES	Electronic reconstruction forming a C2-symmetric Dirac semimetal in Ca3Ru2O7 M. Horio , Q. Wang , V. Granata , K. P. Kramer , Y. Sassa , S. Jöhr , D. Sutter , A. Bold , L. Das , Y. Xu , R. Frison , R. Fittipaldi , T. K. Kim , C. Cacho , J. E. Rault , P. Le Fèvre , F. Bertran , N. C. Plumb , M. Shi , A. Vecchione , M. H. Fischer , J. Chang Npj Quantum Materials 6 DOI: 10.1038/s41535-021-00328-3 Diamond Proposal Number(s): [20259] Open Access Show Abstract ▼ Abstract: Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or electronic order. In the stoichiometric ruthenate Ca3Ru2O7, numerous Fermi surface-sensitive probes indicate a low-temperature electronic reconstruction. Yet, the causality and the reconstructed band structure remain unsolved. Here, we show by angle-resolved photoemission spectroscopy, how in Ca3Ru2O7 a C2-symmetric massive Dirac semimetal is realized through a Brillouin-zone preserving electronic reconstruction. This Dirac semimetal emerges in a two-stage transition upon cooling. The Dirac point and band velocities are consistent with constraints set by quantum oscillation, thermodynamic, and transport experiments, suggesting that the complete Fermi surface is resolved. The reconstructed structure—incompatible with translational-symmetry-breaking density waves—serves as an important test for band structure calculations of correlated electron systems.	Mar 2021
I21-Resonant Inelastic X-ray Scattering (RIXS)	High-temperature charge-stripe correlations in La1.675Eu0.2Sr0.125CuO4 Q. Wang , M. Horio , K. Von Arx , Y. Shen , D. John Mukkattukavil , Y. Sassa , O. Ivashko , C. E. Matt , S. Pyon , T. Takayama , H. Takagi , T. Kurosawa , N. Momono , M. Oda , T. Adachi , S. M. Haidar , Y. Koike , Y. Tseng , W. Zhang , J. Zhao , K. Kummer , M. Garcia-Fernandez , K. Zhou , N. B. Christensen , H. M. Ronnow , T. Schmitt , J. Chang Physical Review Letters 124 DOI: 10.1103/PhysRevLett.124.187002 Diamond Proposal Number(s): [20828, 24481] Show Abstract ▼ Abstract: We use resonant inelastic x-ray scattering to investigate charge-stripe correlations in La 1.675 Eu 0.2 Sr 0.125 CuO 4 . By differentiating elastic from inelastic scattering, it is demonstrated that charge-stripe correlations precede both the structural low-temperature tetragonal phase and the transport-defined pseudogap onset. The scattering peak amplitude from charge stripes decays approximately as T − 2 towards our detection limit. The in-plane integrated intensity, however, remains roughly temperature independent. Therefore, although the incommensurability shows a remarkably large increase at high temperature, our results are interpreted via a single scattering constituent. In fact, direct comparison to other stripe-ordered compounds ( La 1.875 Ba 0.125 CuO 4 , La 1.475 Nd 0.4 Sr 0.125 CuO 4 , and La 1.875 Sr 0.125 CuO 4 ) suggests a roughly constant integrated scattering intensity across all these compounds. Our results therefore provide a unifying picture for the charge-stripe ordering in La-based cuprates. As charge correlations in La 1.675 Eu 0.2 Sr 0.125 CuO 4 extend beyond the low-temperature tetragonal and pseudogap phase, their emergence heralds a spontaneous symmetry breaking in this compound.	May 2020
I05-ARPES	Orbitally selective breakdown of Fermi liquid quasiparticles in Ca1.8 Sr0.2 RuO4 D. Sutter , M. Kim , C. E. Matt , M. Horio , R. Fittipaldi , A. Vecchione , V. Granata , K. Hauser , Y. Sassa , G. Gatti , M. Grioni , M. Hoesch , T. K. Kim , E. Rienks , N. C. Plumb , M. Shi , T. Neupert , A. Georges , J. Chang Physical Review B 99 DOI: 10.1103/PhysRevB.99.121115 Diamond Proposal Number(s): [15296] Show Abstract ▼ Abstract: We present a comprehensive angle-resolved photoemission spectroscopy study of Ca 1.8 Sr 0.2 RuO 4 . Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis and comparison to dynamical mean-field theory calculations. Bands assigned to d x z , d y z orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions—associated with a predominantly d x y band character—are shown to display non-Fermi-liquid behavior. We thus demonstrate that Ca 1.8 Sr 0.2 RuO 4 is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.	Mar 2019
I05-ARPES	Direct observation of orbital hybridisation in a cuprate superconductor C. E. Matt , D. Sutter , A. M. Cook , Y. Sassa , Martin Mansson , O. Tjernberg , L. Das , M. Horio , D. Destraz , C. G. Fatuzzo , K. Hauser , M. Shi , M. Kobayashi , V. N. Strocov , T. Schmitt , P. Dudin , M. Hoesch , S. Pyon , T. Takayama , H. Takagi , O. J. Lipscombe , S. M. Hayden , T. Kurosawa , N. Momono , M. Oda , T. Neupert , J. Chang Nature Communications 9 DOI: 10.1038/s41467-018-03266-0 Diamond Proposal Number(s): [10550] Open Access Show Abstract ▼ Abstract: The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper–oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (d x 2 −y 2 dx2-y2 and d z 2 dz2 ) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.	Mar 2018

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