17 research outputs found
Direct visualization of coexisting channels of interaction in CeSb
Our understanding of correlated electron systems is vexed by the complexity of their interactions. Heavy fermion compounds are archetypal examples of this physics, leading to exotic properties that weave magnetism, superconductivity and strange metal behavior together. The Kondo semimetal CeSb is an unusual example where different channels of interaction not only coexist, but have coincident physical signatures, leading to decades of debate about the microscopic picture describing the interactions between the f moments and the itinerant electron sea. Using angle-resolved photoemission spectroscopy, we resonantly enhance the response of the Ce f electrons across the magnetic transitions of CeSb and find there are two distinct modes of interaction that are simultaneously active, but on different kinds of carriers. This study reveals how correlated systems can reconcile the coexistence of different modes on interaction-by separating their action in momentum space, they allow their coexistence in real space.11Ysciescopu
Electronic Structure of the BaFeAs Family of Iron Pnictides
We use high resolution angle-resolved photoemission spectroscopy to study the
band structure and Fermi surface topology of the BaFeAs iron pnictides.
We observe two electron bands and two hole bands near the X-point,
of the Brillouin zone, in the paramagnetic state for different doping levels,
including electron-doped Ba(CoFe)As, undoped
BaFeAs, and hole-doped BaKFeAs. Among these
four bands, only the electron bands cross the Fermi level, forming two electron
pockets around X, while the hole bands approach but never reach the Fermi
level. We show that the band structure of the BaFeAs family matches
reasonably well with the prediction of LDA calculations after a
momentum-dependent shift and renormalization. Our finding resolves a number of
inconsistencies regarding the electronic structure of pnictides.Comment: 5 pages, 4 figure
Principles of crystal growth of intermetallic and oxide compounds from molten solutions
We present a tutorial on the principles of crystal growth of intermetallic
and oxide compounds from molten solutions, with an emphasis on the fundamental
principles governing the underlying phase equilibria and phase diagrams of
multicomponent systems.Comment: 43 pages, 24 figures; Philosophical Magazine, 201
STM imaging of electronic waves on the surface of BiTe: topologically protected surface states and hexagonal warping effects
Scanning tunneling spectroscopy studies on high-quality BiTe crystals
exhibit perfect correspondence to ARPES data, hence enabling identification of
different regimes measured in the local density of states (LDOS). Oscillations
of LDOS near a step are analyzed. Within the main part of the surface band
oscillations are strongly damped, supporting the hypothesis of topological
protection. At higher energies, as the surface band becomes concave,
oscillations appear which disperse with a particular wave-vector that may
result from an unconventional hexagonal warping term.Comment: 4 pages, 4 figures. Revised manuscript with improved analysis and
figure
Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator BiSe
We characterize the occupied and unoccupied electronic structure of the
topological insulator BiSe by one-photon and two-photon angle-resolved
photoemission spectroscopy and slab band structure calculations. We reveal a
second, unoccupied Dirac surface state with similar electronic structure and
physical origin to the well-known topological surface state. This state is
energetically located 1.5 eV above the conduction band, which permits it to be
directly excited by the output of a Ti:Sapphire laser. This discovery
demonstrates the feasibility of direct ultrafast optical coupling to a
topologically protected, spin-textured surface state.Comment: Accepted to Physical Review Letter
Quantum Oscillation Studies of the Fermi Surface of LaFePO
We review recent experimental measurements of the Fermi surface of the
iron-pnictide superconductor LaFePO using quantum oscillation techniques. These
studies show that the Fermi surface topology is close to that predicted by
first principles density functional theory calculations, consisting of
quasi-two-dimensional electron-like and hole-like sheets. The total volume of
the two hole sheets is almost equal to that of the two electron sheets, and the
hole and electron Fermi surface sheets are close to a nesting condition. No
evidence for the predicted three dimensional pocket arising from the Fe
band is found. Measurements of the effective mass suggest a
renormalisation of around two, close to the value for the overall band
renormalisation found in recent angle resolved photoemission measurements.Comment: Submitted to Physica C special issue on iron-pnictide superconductor
EPIdemiology of Surgery-Associated Acute Kidney Injury (EPIS-AKI) : Study protocol for a multicentre, observational trial
More than 300 million surgical procedures are performed each year. Acute kidney injury (AKI) is a common complication after major surgery and is associated with adverse short-term and long-term outcomes. However, there is a large variation in the incidence of reported AKI rates. The establishment of an accurate epidemiology of surgery-associated AKI is important for healthcare policy, quality initiatives, clinical trials, as well as for improving guidelines. The objective of the Epidemiology of Surgery-associated Acute Kidney Injury (EPIS-AKI) trial is to prospectively evaluate the epidemiology of AKI after major surgery using the latest Kidney Disease: Improving Global Outcomes (KDIGO) consensus definition of AKI. EPIS-AKI is an international prospective, observational, multicentre cohort study including 10 000 patients undergoing major surgery who are subsequently admitted to the ICU or a similar high dependency unit. The primary endpoint is the incidence of AKI within 72 hours after surgery according to the KDIGO criteria. Secondary endpoints include use of renal replacement therapy (RRT), mortality during ICU and hospital stay, length of ICU and hospital stay and major adverse kidney events (combined endpoint consisting of persistent renal dysfunction, RRT and mortality) at day 90. Further, we will evaluate preoperative and intraoperative risk factors affecting the incidence of postoperative AKI. In an add-on analysis, we will assess urinary biomarkers for early detection of AKI. EPIS-AKI has been approved by the leading Ethics Committee of the Medical Council North Rhine-Westphalia, of the Westphalian Wilhelms-University MĂŒnster and the corresponding Ethics Committee at each participating site. Results will be disseminated widely and published in peer-reviewed journals, presented at conferences and used to design further AKI-related trials. Trial registration number NCT04165369
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ARPES studies of the electronic structure of LaOFe(P,As)
We report a comparison study of LaOFeP and LaOFeAs, two parent compounds of recently discovered iron-pnictide superconductors, using angle-resolved photoemission spectroscopy. Both systems exhibit some common features that are very different from well-studied cuprates. In addition, important differences have also been observed between these two ferrooxypnictides. For LaOFeP, quantitative agreement can be found between our photoemission data and the LDA band structure calculations, suggesting that a weak coupling approach based on an itinerant ground state may be more appropriate for understanding this new superconducting compound. In contrast, the agreement between LDA calculations and experiments in LaOFeAs is relatively poor, as highlighted by the unexpected Fermi surface topology around ({pi},{pi}). Further investigations are required for a comprehensive understanding of the electronic structure of LaOFeAs and related compounds
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Quantum Oscillations in the Parent pnictide BaFe2As2 : Itinerant Electrons in the Reconstructed State
We report quantum oscillation measurements that enable the direct observation of the Fermi surface of the low temperature ground state of BaFe{sub 2}As{sub 2}. From these measurements we characterize the low energy excitations, revealing that the Fermi surface is reconstructed in the antiferromagnetic state, but leaving itinerant electrons in its wake. The present measurements are consistent with a conventional band folding picture of the antiferromagnetic ground state, placing important limits on the topology and size of the Fermi surface
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Fermi surface of SrFe2P2 determined by de Haas-van Alphen effect
We report measurements of the Fermi surface (FS) of the ternary iron-phosphide SrFe{sub 2}P{sub 2} using the de Haas-van Alphen effect. The calculated FS of this compound is very similar to SrFe{sub 2}As{sub 2}, the parent compound of the high temperature superconductors. Our data show that the Fermi surface is composed of two electron and two hole sheets in agreement with bandstructure calculations. Several of the sheets show strong c-axis warping emphasizing the importance of three-dimensionality in the non-magnetic state of the ternary pnictides. We find that the electron and hole pockets have a different topology, implying that this material does not satisfy a ({pi},{pi}) nesting condition