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Establishing the appropriate theoretical framework for unconventional superconductivity in the iron-based materials requires correct understanding of both the electron correlation strength and the role of Fermi surfaces. This fundamental issue becomes especially relevant with the discovery of the iron chalcogenide superconductors. Here, we use angle-resolved photoemission spectroscopy to measure three representative iron chalcogenides, FeTe 0.56 Se 0.44 , monolayer FeSe grown on SrTiO 3 and K 0.76 Fe 1.72 Se 2 . We show that these superconductors are all strongly correlated, with an orbital-selective strong renormalization in the d xy bands despite having drastically different Fermi surface topologies. Furthermore, raising temperature brings all three compounds from a metallic state to a phase where the d xy orbital loses all spectral weight while other orbitals remain itinerant. These observations establish that iron chalcogenides display universal orbital-selective strong correlations that are insensitive to the Fermi surface topology, and are close to an orbital-selective Mott phase, hence placing strong constraints for theoretical understanding of iron-based superconductors. A proper theoretical description for unconventional superconductivity in iron-based compounds remains elusive. Here, the authors, to capture the electron correlation strength and the role of Fermi surfaces, report ARPES measurements of three iron chalcogenide superconductors to establish universal features.

The interactions that lead to the emergence of superconductivity in iron-based materials remain a subject of debate. It has been suggested that electron-electron correlations enhance electron-phonon coupling in iron selenide (FeSe) and related pnictides, but direct experimental verification has been lacking. Here we show that the electron-phonon coupling strength in FeSe can be quantified by combining two time-domain experiments into a “coherent lock-in” measurement in the terahertz regime. X-ray diffraction tracks the light-induced femtosecond coherent lattice motion at a single phonon frequency, and photoemission monitors the subsequent coherent changes in the electronic band structure.Comparison with theory reveals a strong enhancement of the coupling strength in FeSe owing to correlation effects. Given that the electron-phonon coupling affects superconductivity exponentially, this enhancement highlights the importance of the cooperative interplay between electron-electron and electron-phonon interactions.

A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials, such as the cuprate high-temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates, where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping- and temperature-dependence ARPES study of spectral gaps in Bi ₂Sr ₂CaCu ₂O ₈₊δ, covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p = 0.19 for the pseudogap phase and p = 0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T c and exists p > 0.19 at higher temperatures. Our data imply a revised phase diagram that reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.

In addition to a bulk energy gap, topological insulators accommodate a conducting, linearly dispersed Dirac surface state. This state is predicted to become massive if time reversal symmetry is broken, and to become insulating if the Fermi energy is positioned inside both the surface and bulk gaps. We introduced magnetic dopants into the three-dimensional topological insulator dibismuth triselenide (Bi₂Se₃) to break the time reversal symmetry and further position the Fermi energy inside the gaps by simultaneous magnetic and charge doping. The resulting insulating massive Dirac fermion state, which we observed by angle-resolved photoemission, paves the way for studying a range of topological phenomena relevant to both condensed matter and particle physics.

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T c ), entangled in an energy-momentum—dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.

The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerging in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of measuring material properties at atomic and electronic time scales out of equilibrium, can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here we combine time-resolved femotosecond optical and resonant X-ray diffraction measurements on charge ordered La 1.75 Sr 0.25 NiO 4 to reveal unforeseen photoinduced phase fluctuations of the charge order parameter. Such fluctuations preserve long-range order without creating topological defects, distinct from thermal phase fluctuations near the critical temperature in equilibrium. Importantly, relaxation of the phase fluctuations is found to be an order of magnitude slower than that of the order parameter's amplitude fluctuations, and thus limits charge order recovery. This new aspect of phase fluctuations provides a more holistic view of the phase's importance in ordering phenomena of quantum matter. Time- and momentum-resolved spectroscopy gives dynamical information on complex materials, enabling disentanglement of their coupled degrees of freedom. Using time-resolved X-ray diffraction at a free electron laser, Lee et al . investigate the charge order parameter in a striped nickelate.

Surface stability of nearly defect-free epitaxial SrRuO3 thin films grown by pulsed laser deposition was studied using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and electron spectroscopies. Even after exposure to atmosphere, surfaces exhibited distinct LEED patterns providing evidence of unusual chemical stability. Surface order disappeared after heating to 200 °C in vacuum. To investigate, SrRuO3 thin films were annealed up to 800 °C in high vacuum and examined for chemical state and topography. Formation of unit-cell deep pits and the Ru-rich particles begins at low temperatures. Hydrocarbon contamination on the surface contributes to this process.

Mott transitions, which are metal-insulator transitions (MITs) driven by electron-electron interactions, are usually accompanied in bulk by structural phase transitions. In the layered perovskite Ca₁.₉Sr₀.₁RuO₄, such a first-order Mott MIT occurs in the bulk at a temperature of 154 kelvin on cooling. In contrast, at the surface, an unusual inherent Mott MIT is observed at 130 kelvin, also on cooling but without a simultaneous lattice distortion. The broken translational symmetry at the surface causes a compressional stress that results in a 150% increase in the buckling of the Ca/Sr-O surface plane as compared to the bulk. The Ca/Sr ions are pulled toward the bulk, which stabilizes a phase more amenable to a Mott insulator ground state than does the bulk structure and also energetically prohibits the structural transition that accompanies the bulk MIT.

Introduction/BackgroundNiraparib improves progression-free survival (PFS) in patients (pts) with newly diagnosed advanced ovarian cancer after 1st-line (1L) platinum-based chemotherapy (CT). We report the efficacy of niraparib in pts by biomarker status.MethodologyThis double-blind, placebo (PBO)-controlled, phase 3 study randomized 733 pts with newly diagnosed advanced ovarian, primary peritoneal, or fallopian tube cancer with a complete or partial response (CR or PR) to 1L platinum-based CT. Stratification factors were best response to the 1L CT (CR/PR), receipt of neoadjuvant CT (yes/no), and homologous recombination status (deficient/proficient/not determined). Pts received niraparib or PBO once daily. The primary endpoint of PFS assessed by blinded independent central review was analyzed using a stratified Cox proportional hazards model and hierarchically tested in homologous recombination deficient pts, then the overall population.ResultsOf 733 randomized pts (niraparib, 487; PBO, 246), 373 (51%) were homologous recombination deficient (niraparib, 247; PBO, 126) and 249 (34%) were homologous recombination proficient (niraparib, 169; PBO, 80). Overall, 35% had stage IV disease, 67% received NACT, and 31% had a PR to 1L CT. Niraparib-treated pts in all the biomarkers groups had a statistically significant and clinically meaningful benefit in PFS (table 1). The most common grade ≥3 adverse events were anemia (31%), thrombocytopenia (29%), and neutropenia (13%).Abstract – Table 1Disease characteristicsHazard ratio (95% CI)P ValueOverall0.62 (0.502–0.755)<0.0001Homologous recombination deficient0.43 (0.310–0.588)<0.0001BRCAmut0.40 (0.265–0.618)<0.0001BRCAwt0.50 (0.305–0.831)0.0064Homologous recombination proficient0.68 (0.492–0.944)0.0203ConclusionNiraparib improved PFS as evidenced by reduction in the risk of recurrence or death due to any cause in the overall population of advanced ovarian cancer. No new safety signals were identified.CI=confidence interval; mut=mutated; wt=wild typeDisclosureAMG: Consulting: AstraZeneca, TESARO, Roche, Pharmamar, Clovis, Merck, Genmab, ImmunoGen, Oncoinvent AS BP, RDC: Advisory: TESARO IV: Personal: Advaxis, Eisai, MSD Belgium, Roche NV, Genmab, Roche, Pharmamar, Millennium Pharmaceuticals, Clovis, Astrazeneca NV, Tesaro, Immunogen, Sotio. Grants: Amgen, Stichting tegen Kanker, Roche. Contracted Research: Oncoinvent AS, Genmab WG: Consulting: TESARO MM: Leadership/Other ownership: Karyopharm Therapeutics, Sera Prognostics. Personal Fees: Roche, AstraZeneca, Clovis, Pfizer, TESARO, Genmab, BioCad, Sotio, Geneos Therapeutics, Merck, Oncology Venture, Seattle Genetics, Sera Prognostics, Takeda, Zailab. Grants: AstraZeneca, Clovis, Pfizer, TESARO, Boehringer Ingelheim CCM, PH, KHB, KJ, CGAV, BL, AFH, MJR-P, WHB, IB: none DL: Personal: AstraZeneca, Clovis, Genmab, Immunogen, Pharma Mar SA, Amgen, Merck. Grants: Pharma Mar SA, Merck GF: Personal: TESARO, AstraZeneca, Clovis, Roche, Bristol-Meyers Squibb, MSD, Pfizer, Novartis. Grants: AstraZeneca, Roche AR: Research funding/Advisory role: Pharmamar, Roche, Eisai,AstraZeneca, TESARO RGM: Research: Angle PLC. Consulting: Fujirebio Diagnostics REO: Advisory: Clovis, TESARO, GlaxoSmithKline FB: Advisory: TESARO, Clovis, Agenus, Merck, Eisai. Grant: Clovis, Merck, Eisai, Immunogen. Lecture: CEC Oncology MPBG: Lecture/Advisory board: TESARO, AstraZeneca, Roche, Clovis, Pharmamar, MSD. MSS: Personal: TESARO, Merck, Astra Zeneca, Clovis, Pacira Pharamceuticals. Grant: TESARO GM: Personal: AstraZeneca, TESARO. Non-Financial Support: TESARO, Roche. BJM: Speaker bureau, Grant: TESARO KS, IM, YL, DG: TESARO employee.

Obtaining insight into microscopic cooperative effects is a fascinating topic in condensed matter research because, through self-coordination and collectivity, they can lead to instabilities with macroscopic impacts like phase transitions. We used femtosecond time- and angle-resolved photoelectron spectroscopy (trARPES) to optically pump and probe TbTe{sub 3}, an excellent model system with which to study these effects. We drove a transient charge density wave melting, excited collective vibrations in TbTe{sub 3}, and observed them through their time-, frequency-, and momentum-dependent influence on the electronic structure. We were able to identify the role of the observed collective vibration in the transition and to document the transition in real time. The information that we demonstrate as being accessible with trARPES will greatly enhance the understanding of all materials exhibiting collective phenomena.