Visualization of Local Magnetic Moments Emerging from Impurities in Hund's Metal States of FeSe.

Understanding the origin of the magnetism of high temperature superconductors is crucial for establishing their unconventional pairing mechanism. Recently, theory predicts that FeSe is close to a magnetic quantum critical point, and thus weak perturbations such as impurities could induce local magnetic moments. To elucidate such quantum instability, we have employed scanning tunneling microscopy and spectroscopy. In particular, we have grown FeSe film on superconducting Pb(111) using molecular beam epitaxy and investigated magnetic excitation caused by impurities in the proximity-induced superconducting gap of FeSe. Our study provides deep insight into the origin of the magnetic ordering of FeSe by showing the way local magnetic moments develop in response to impurities near the magnetic quantum critical point.

Knight Shift and Leading Superconducting Instability from Spin Fluctuations in Sr_{2}RuO_{4}.

Recent nuclear magnetic resonance studies [A. Pustogow et al., Nature 574, 72 (2019)] have challenged the prevalent chiral triplet pairing scenario proposed for Sr_{2}RuO_{4}. To provide guidance from microscopic theory as to which other pair states might be compatible with the new data, we perform a detailed theoretical study of spin fluctuation mediated pairing for this compound. We map out the phase diagram as a function of spin-orbit coupling, interaction parameters, and band structure properties over physically reasonable ranges, comparing when possible with photoemission and inelastic neutron scattering data information. We find that even-parity pseudospin singlet solutions dominate large regions of the phase diagram, but in certain regimes spin-orbit coupling favors a near-nodal odd-parity triplet superconducting state, which is either helical or chiral depending on the proximity of the γ band to the van Hove points. A surprising near degeneracy of the nodal s^{'} and d_{x^{2}-y^{2}} wave solutions leads to the possibility of a near-nodal time-reversal symmetry broken s^{'}+id_{x^{2}-y^{2}} pair state. Predictions for the temperature dependence of the Knight shift for fields in and out of plane are presented for all states.

Imaging orbital-selective quasiparticles in the Hund's metal state of FeSe.

Strong electronic correlations, emerging from the parent Mott insulator phase, are key to copper-based high-temperature superconductivity. By contrast, the parent phase of an iron-based high-temperature superconductor is never a correlated insulator. However, this distinction may be deceptive because Fe has five actived d orbitals while Cu has only one. In theory, such orbital multiplicity can generate a Hund's metal state, in which alignment of the Fe spins suppresses inter-orbital fluctuations, producing orbitally selective strong correlations. The spectral weights Zm of quasiparticles associated with different Fe orbitals m should then be radically different. Here we use quasiparticle scattering interference resolved by orbital content to explore these predictions in FeSe. Signatures of strong, orbitally selective differences of quasiparticle Zm appear on all detectable bands over a wide energy range. Further, the quasiparticle interference amplitudes reveal that [Formula: see text], consistent with earlier orbital-selective Cooper pairing studies. Thus, orbital-selective strong correlations dominate the parent state of iron-based high-temperature superconductivity in FeSe.

Discovery of orbital-selective Cooper pairing in FeSe.

The superconductor iron selenide (FeSe) is of intense interest owing to its unusual nonmagnetic nematic state and potential for high-temperature superconductivity. But its Cooper pairing mechanism has not been determined. We used Bogoliubov quasiparticle interference imaging to determine the Fermi surface geometry of the electronic bands surrounding the Γ = (0, 0) and X = (π/aFe, 0) points of FeSe and to measure the corresponding superconducting energy gaps. We show that both gaps are extremely anisotropic but nodeless and that they exhibit gap maxima oriented orthogonally in momentum space. Moreover, by implementing a novel technique, we demonstrate that these gaps have opposite sign with respect to each other. This complex gap configuration reveals the existence of orbital-selective Cooper pairing that, in FeSe, is based preferentially on electrons from the d yz orbitals of the iron atoms.

Ferroelectricity in underdoped La-based cuprates.

Doping a "parent" antiferromagnetic Mott insulator in cuprates leads to short-range electronic correlations and eventually to high-Tc superconductivity. However, the nature of charge correlations in the lightly doped cuprates remains unclear. Understanding the intermediate electronic phase in the phase diagram (between the parent insulator and the high-Tc superconductor) is expected to elucidate the complexity both inside and outside the superconducting dome, and in particular in the underdoped region. One such phase is ferroelectricity whose origin and relation to the properties of high-Tc superconductors is subject of current research. Here we demonstrate that ferroelectricity and the associated magnetoelectric coupling are in fact common in La-214 cuprates namely, La2-xSrxCuO4, La2LixCu1-xO4 and La2CuO4+x. It is proposed that ferroelectricity may result from local CuO6 octahedral distortions, associated with the dopant atoms and clustering of the doped charge carriers, which break spatial inversion symmetry at the local scale whereas magnetoelectric coupling can be tuned through Dzyaloshinskii-Moriya interaction.

Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates.

We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi_{2}Sr_{2}CaCu_{2}O_{8} can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude "filter" theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.

Robust nodal d-wave spectrum in simulations of a strongly fluctuating competing order in underdoped cuprate superconductors.

We resolve an existing discrepancy between convincing evidence for competing order in underdoped cuprates and spectroscopic data consistent with a homogeneous d-wave superconductor in the very same compounds. Specifically, we show that fluctuations of the competing order generate strongly inhomogeneous states whose spectra are almost indistinguishable from the pure d-wave superconductor. This is in contrast to the commonly studied case of homogeneously coexisting order, which typically generates a reconstructed Fermi surface with closed Fermi pockets. The signatures of the fluctuating competing order can be found mainly in a splitting of the antinodal band, and, for strong magnetic order, in small induced nodal gaps similar to those found in recent experiments on underdoped La(2-x)Sr(x)CuO4.

MRSA: A Challenge to Norwegian Nursing Home Personnel.

In Norway, methicillin-resistant Staphylococcus aureus (MRSA) is increasing in primary healthcare, associated with imported cases and outbreaks in long-term care. According to Norwegian national guidelines, MRSA-exposed healthcare workers (HCWs) and patients are tested. Carriage of MRSA leads to exclusion from work in healthcare institutions. In this study, 388 staff members in 42 nursing homes in Oslo County responded to questions about personal experience with MRSA and of own attitudes to challenges associated with the control and treatment of MRSA patients. Half (52%) of the nursing staff were concerned of becoming infected with MRSA and the consequences of this would be for own social life, family, economy, and work restriction. The concern was associated with risk factors like old buildings not suitable for modern infection control work, low staffing rate (70% without specific training in healthcare and 32% without formal healthcare education), defective cleaning and decolonization, and lack of formal routines and capacity for isolation of MRSA patients. Since the Norwegian MRSA guideline permits patients with persistent MRSA infections to move freely around in nursing homes, the anxiety of the staff to become infected and excluded from job was real.

Nonequilibrium transport through a spinful quantum dot with superconducting leads.

We study the nonlinear cotunneling current through a spinful quantum dot contacted by two superconducting leads. Applying a general nonequilibrium Green function formalism to an effective Kondo model, we study the rich variation in the IV characteristics with varying asymmetry in the tunnel coupling to source and drain electrodes. The current is found to be carried, respectively, by multiple Andreev reflections in the symmetric limit, and by spin-induced Yu-Shiba-Rusinov bound states in the strongly asymmetric limit. The interplay between these two mechanisms leads to qualitatively different IV characteristics in the crossover regime of intermediate symmetry, consistent with recent experimental observations of negative differential conductance and repositioned conductance peaks in subgap cotunneling spectroscopy.

Failure of dry mist of hydrogen peroxide 5% to kill Mycobacterium tuberculosis.

A dry mist of hydrogen peroxide (DMHP; Sterinis), was used to test for surface decontamination of air-dried samples of Mycobacterium tuberculosis, 3 x 10(5) cfu/mL in open plastic trays. No significant decontamination effect of DMHP could be observed after three ordinary cycles with hydrogen peroxide or after doubling the effect with six repeated cycles.

Rapid MRSA test in exposed persons: costs and savings in hospitals.

OBJECTIVE: To study a rapid Xpert polymerase chain reaction (PCR) method in detecting methicillin-resistant Staphylococcus aureus (MRSA) in patients and healthcare workers (HCW) exposed to MRSA, and to estimate savings associated to isolation or work restriction. METHODS: A test set of four double (one for the growth and one for the rapid test) pre-wet swabs from the nose, throat, hands/wrists and perineum was studied by a growth method and by the Xpert MRSA test. RESULTS: The total correspondence between the growth and the rapid test was 92.8%. The overall sensitivity, specificity, positive and negative predictive values were for the Xpert MRSA test: 87%, 99.6%, 68.5% and 99.9%, and for the growth test: 76%, 100%, 100%, and 99.8%, assuming a prevalence of MRSA of 0.01%. Among the MRSA positive persons, the Xpert and growth tests detected MRSA in 44.6% and 40% of nose samples, respectively, 38.2% and 45.5% throat samples, 30.8% and 11.5% hands/wrists samples, 44% and 38% perineum samples, and in 81.8% and 77.3% wound samples, respectively. By combining four anatomical sites, the detection rate increased to 87.5% by both methods. The cost for each Xpert and growth test was euro50 and euro6.25, respectively. The rapid test would save at least euro925 per exposed HCW and euro550 per patient that were MRSA negative. CONCLUSION: The MRSA Xpert test is easy to perform, has a high negative predictive value, and may be used to control healthcare workers and patients exposed to MRSA. Sampling from multiple anatomical locations is recommended. Still, more then 10% of MRSA positive cases may not be found.

Floor cleaning: effect on bacteria and organic materials in hospital rooms.

Routine surface cleaning is recommended to control the spread of pathogens in hospital environments. In Norway, ordinary cleaning of patient rooms is traditionally performed with soap and water. In this study, four floor-mopping methods--dry, spray, moist and wet mopping--were compared by two systems using adenosine triphosphate (ATP) bioluminescence (Hygiena and Biotrace). These systems assess residual organic soil on surfaces. The floor-mopping methods were also assessed by microbiological samples from the floor and air, before and after cleaning. All methods reduced organic material on the floors but wet and moist mopping seemed to be the most effective (P < 0.001, P < 0.011, respectively, ATP Hygiena). The two ATP methods were easy to use, although each had their own reading scales. Cleaning reduced organic material to 5-36% of the level present before cleaning, depending upon mopping method. All four mopping methods reduced bacteria on the floor from about 60-100 to 30-60 colony-forming units (cfu)/20cm2 floor. Wet, moist and dry mopping seemed to be more effective in reducing bacteria on the floor, than the spray mopping (P=0.007, P=0.002 and P=0.011, respectively). The burden of bacteria in air increased for all methods just after mopping. The overall best cleaning methods seemed to be moist and wet mopping.

Infection control and meticillin-resistant Staphylococcus aureus in nursing homes in Oslo.

Healthcare workers (HCWs) might be important in reducing healthcare-associated infections but infected or colonised HCWs may still spread pathogenic microbes to others. Norwegian policies for infection control in healthcare environments emphasise infection control programmes for both patients and HCWs. In this study, HCWs from 42 of 55 nursing homes in Oslo participated in an investigation concerning the implementation of infection control programmes during 2006-2007. Three separate questionnaires were used: the first aimed at nursing staff (enrolled nurses and assisting staff); the second for ward sisters; and the third for institution managers. Nearly 70% of the nursing homes had policies for controlling infection and transmission of meticillin-resistant Staphylococcus aureus (MRSA). About 60% of the institutions had policies for tracing MRSA infections. Four of five ward sisters tested patients for MRSA when wounds were not healing, when admitted from hospitals overseas, when patients shared a room with an MRSA-infected patient, or if patients had ever been MRSA positive. Two of five sisters would test patients with chronic urinary tract infection or patients admitted from another hospital. Among nursing staff, one out of five had cared for MRSA-positive patients. Only 4% of the staff had worked in healthcare institutions abroad, and only a few of them had been tested for MRSA. Almost 20% of the responding nursing staff worked at several institutions at the same time.

Imaging the impact on cuprate superconductivity of varying the interatomic distances within individual crystal unit cells.

Many theoretical models of high-temperature superconductivity focus only on the doping dependence of the CuO(2)-plane electronic structure. However, such models are manifestly insufficient to explain the strong variations in superconducting critical temperature, T(c), among cuprates that have identical hole density but are crystallographically different outside of the CuO(2) plane. A key challenge, therefore, has been to identify a predominant out-of-plane influence controlling the superconductivity, with much attention focusing on the distance d(A) between the apical oxygen and the planar copper atom. Here we report direct determination of how variations in interatomic distances within individual crystalline unit cells affect the superconducting energy-gap maximum Delta of Bi(2)Sr(2)CaCu(2)O(8+delta). In this material, quasiperiodic variations of unit cell geometry occur in the form of a bulk crystalline "supermodulation." Within each supermodulation period, we find approximately 9 +/- 1% cosinusoidal variation in local Delta that is anticorrelated with the associated d(A) variations. Furthermore, we show that phenomenological consistency would exist between these effects and the random Delta variations found near dopant atoms if the primary effect of the interstitial dopant atom is to displace the apical oxygen so as to diminish d(A) or tilt the CuO(5) pyramid. Thus, we reveal a strong, nonrandom out-of-plane effect on cuprate superconductivity at atomic scale.

Kondo-enhanced Andreev tunneling in InAs nanowire quantum dots.

We report measurements of the nonlinear conductance of InAs nanowire quantum dots coupled to superconducting leads. We observe a clear alternation between odd and even occupation of the dot, with subgap peaks at |V(sd)| = Delta/e markedly stronger (weaker) than the quasiparticle tunneling peaks at |V(sd)| = 2Delta/e for odd (even) occupation. We attribute the enhanced Delta peak to an interplay between Kondo correlations and Andreev tunneling in dots with an odd number of spins, and we substantiate this interpretation by a poor man's scaling analysis.

Comparison of UV C light and chemicals for disinfection of surfaces in hospital isolation units.

OBJECTIVE: To determine the bactericidal effect on surfaces of ceiling- and wall-mounted UV C (UVC) light (wavelength, 254 nm) in isolation units, compared with standard hospital environmental cleaning and chemical disinfection during final disinfection after patients are treated for infections. DESIGN: Microbial samples were obtained from surfaces in isolation units (patient room, anteroom, and bathroom) before and after irradiation with UVC, chloramine disinfection, and standard hospital environmental cleaning. Samples were tested using standard contact plates. SETTING: Four identical, negative air-pressure isolation units (patient room, anteroom, and bathroom) with a defined number of ceiling- and wall-mounted UVC light units. The UVC distribution was monitored in one isolation unit after irradiation for approximately 40 minutes, corresponding to doses ranging from 160 J/m2 in a shadowed area to 19,230 J/m2 at the mostly highly exposed site (which is high enough to inactivate most bacterial organisms, including spores). RESULTS: UVC disinfection significantly reduced the number of bacteria on surfaces directly or indirectly exposed to UVC to a very low number, as did 5% chloramine disinfection alone (P<.001 for both). Completely shadowed areas in the isolation unit (eg, the bed rail, lockers, and mattresses) still required disinfection by chemicals. CONCLUSION: Disinfection with UVC light may significantly reduce environmental bacterial contamination and thereby protect the next patient housed in an isolation room. UVC disinfection may not be used alone but is a good addition to chemical disinfection.

Decontamination of rooms, medical equipment and ambulances using an aerosol of hydrogen peroxide disinfectant.

A programmable device (Sterinis, Gloster Sante Europe) providing a dry fume of 5% hydrogen peroxide (H(2)O(2)) disinfectant was tested for decontamination of rooms, ambulances and different types of medical equipment. Pre-set concentrations were used according to the volumes of the rooms and garages. Three cycles were performed with increasing contact times. Repetitive experiments were performed using Bacillus atrophaeus (formerly Bacillus subtilis) Raven 1162282 spores to control the effect of decontamination; after a sampling plan, spore strips were placed in various positions in rooms, ambulances, and inside and outside the items of medical equipment. Decontamination was effective in 87% of 146 spore tests in closed test rooms and in 100% of 48 tests in a surgical department when using three cycles. One or two cycles had no effect. The sporicidal effect on internal parts of the medical equipment was only 62.3% (220 tests). When the devices were run and ventilated during decontamination, 100% (57/57) of spore strips placed inside were decontaminated. In the ambulances, the penetration of H(2)O(2) into equipment, devices, glove boxes, under mattresses, and the drivers' cabins was 100% (60/60 tests) when using three cycles, but was less effective when using one or two cycles. In conclusion, an H(2)O(2) dry fumigation system, run in three cycles, seemed to have a good sporicidal effect when used in rooms, ambulances, and external and internal parts of ventilated equipment. Further studies need to be performed concerning concentration, contact time and the number of cycles of H(2)O(2). This is especially important for inner parts of medical equipment that cannot be ventilated during the decontamination process.

Spread of methicillin-resistant Staphylococcus aureus in a neonatal intensive unit associated with understaffing, overcrowding and mixing of patients.

Over the period May-June 1999, an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) was registered in eight newborns in a neonatal intensive care unit (NICU) at the Department of Pediatrics, Ullevål University Hospital (UUH) in Oslo. Seven were infected or colonized with an indistinguishable strain, detected at the NICU, and one patient with a slightly different PFGE type (i.e. a subtype) was registered at the outpatient clinic. The MRSA strains resembled the sensitive, inbred 'Norwegian type' described four years earlier at UUH, showing a relatively low and heterogenic methicillin resistance (MIC 12-96 mg/L), and susceptibility to most other anti-staphylococcal agents. Before and during the outbreak, there was high activity, understaffing, overcrowding and a mix of patients; 42% of the staff were relatively untrained, and up to 62% (during weekends) were extra nursing staff, partly from other Scandinavian countries. All cases were isolated (air and contact isolation), and all other patients and personnel were treated as being exposed to MRSA (isolated from other departments) until the last patient had been identified, disinfection of all rooms was complete, and all screening samples from staff and other patients were negative. The NICU and the delivery suite were closed for one week for disinfection and screening. The outbreak ended after 34 days. Since then, two years later, no further cases have been detected in the NICU or the delivery suite.