In the copper oxide parent compounds of the high-transition-temperature superconductors the valence electrons are localized-one per copper site-by strong intra-atomic Coulomb repulsion. A symptom of ...this localization is antiferromagnetism, where the spins of localized electrons alternate between up and down. Superconductivity appears when mobile 'holes' are doped into this insulating state, and it coexists with antiferromagnetic fluctuations. In one approach to describing the coexistence, the holes are believed to self-organize into 'stripes' that alternate with antiferromagnetic (insulating) regions within copper oxide planes, which would necessitate an unconventional mechanism of superconductivity. There is an apparent problem with this picture, however: measurements of magnetic excitations in superconducting YBa2Cu3O6+x near optimum doping are incompatible with the naive expectations for a material with stripes. Here we report neutron scattering measurements on stripe-ordered La1.875Ba0.125CuO4. We show that the measured excitations are, surprisingly, quite similar to those in YBa2Cu3O6+x (refs 9, 10) (that is, the predicted spectrum of magnetic excitations is wrong). We find instead that the observed spectrum can be understood within a stripe model by taking account of quantum excitations. Our results support the concept that stripe correlations are essential to high-transition-temperature superconductivity.
Intense debate has recently arisen regarding the photoinduced changes to the iron-chalcogenide superconductors, including the enhancement of superconductivity and a metastable state. Here, by ...employing high-energy resolution, we directly observe the melting of superconductivity on ultrafast timescales. We demonstrate a distinctly nonequilibrium response on short timescales, where the gap fills in prior to the destruction of the superconducting peak, followed by a metastable response. We propose that the former is due to pair phase decoherence and speculate that the latter is due to the increase in double-stripe correlations that are known to compete with superconductivity. Our results add to exciting new developments on the iron-based superconductors, indicating that the photoinduced metastable state possibly competes with superconductivity.
In underdoped cuprate superconductors, a rich competition occurs between superconductivity and charge density wave (CDW) order. Whether rotational symmetry-breaking (nematicity) occurs intrinsically ...and generically or as a consequence of other orders is under debate. Here, we employ resonant x-ray scattering in stripe-ordered superconductors (La,M)₂CuO₄ to probe the relationship between electronic nematicity of the Cu 3d orbitals, structure of the (La,M)₂O₂ layers, and CDW order. We find distinct temperature dependences for the structure of the (La,M)₂O₂ layers and the electronic nematicity of the CuO₂ planes, with only the latter being enhanced by the onset of CDW order. These results identify electronic nematicity as an order parameter that is distinct from a purely structural order parameter in underdoped striped cuprates.
The pairing mechanism of cuprate superconductors is still under debate. Here, Valla et al. report that mass renormalization in Bi$$_{2}$$ 2 Sr$$_{2}$$ 2 CaCu$$_{2}$$ 2 O$$_{8+\delta }$$ 8+δ weakens ...with doping and disappears precisely where superconductivity disappears, eliminating phononic mechanism for pairing.
TiCN nanocomposite films are prepared by direct current magnetron sputtering from Ti
C combined target under different nitrogen flow rates. The composition, morphology and microstructure of the ...nanocomposite films are characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. Hardness and tribological properties are tested by nanoindentation measurement and ball-on-disk tribometer, respectively. With the increase of nitrogen flow ranging from 0 to 30
sccm at a work pressure of 0.3
Pa, both crystallinity and sp
2 carbon content in the TiCN films increase. In addition, the ratio of TiN to Ti(C, N) increases as the nitrogen flow rate increases. The friction coefficient and wear rate could be greatly reduced due to the increase of sp
2 carbon and better toughness in the composite films. TiCN nanocomposite film with high hardness and good wear resistance is obtained under a nitrogen flow rate of 30
sccm.
► We prepared TiCN composite films by sputtering a Ti
C combined target. ► We studied the composition, mechanical and tribological properties in detail. ► XPS and TEM confirmed Ti(C,N) existed in the Ti
C
N composite films. ► sp
2-C content, ratio of TiN to Ti(C,N) did a great impact on the properties.
Abstract
A quantum spin Hall (QSH) insulator hosts topological states at the one-dimensional (1D) edge, along which backscattering by nonmagnetic impurities is strictly prohibited. Its 3D analogue, a ...weak topological insulator (WTI), possesses similar quasi-1D topological states confined at side surfaces. The enhanced confinement could provide a route for dissipationless current and better advantages for applications relative to strong topological insulators (STIs). However, the topological side surface is usually not cleavable and is thus hard to observe. Here, we visualize the topological states of the WTI candidate ZrTe
5
by spin and angle-resolved photoemission spectroscopy (ARPES): a quasi-1D band with spin-momentum locking was revealed on the side surface. We further demonstrate that the bulk band gap is controlled by external strain, realizing a more stable WTI state or an ideal Dirac semimetal (DS) state. The highly directional spin-current and the tunable band gap in ZrTe
5
will provide an excellent platform for applications.
Abstract
In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted ...versus the doping level
p
. In most materials,
p
cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature,
T
c
, using the assumption that the
T
c
dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi
2
Sr
2
CaCu
2
O
8+
δ
, cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to
T
c
= 91 K. We show that
p
can be determined from the underlying Fermi surfaces and that in-situ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of 2Δ
0
= (4 ± 1)
k
B
T
c
In complex materials various interactions have important roles in determining electronic properties. Angle-resolved photoelectron spectroscopy (ARPES) is used to study these processes by resolving ...the complex single-particle self-energy and quantifying how quantum interactions modify bare electronic states. However, ambiguities in the measurement of the real part of the self-energy and an intrinsic inability to disentangle various contributions to the imaginary part of the self-energy can leave the implications of such measurements open to debate. Here we employ a combined theoretical and experimental treatment of femtosecond time-resolved ARPES (tr-ARPES) show how population dynamics measured using tr-ARPES can be used to separate electron-boson interactions from electron-electron interactions. We demonstrate a quantitative analysis of a well-defined electron-boson interaction in the unoccupied spectrum of the cuprate Bi
Sr
CaCu
O
characterized by an excited population decay time that maps directly to a discrete component of the equilibrium self-energy not readily isolated by static ARPES experiments.
Topological materials and unconventional iron-based superconductors are both important areas of study but, to date, relatively little overlap has been identified between these two fields. However, ...the combination of topological bands and superconductivity promises the manifestation of exotic superconducting states, including Majorana fermions, the central component of topological quantum computation. Here, using laser-based, spin-resolved and angle-resolved photoemission spectroscopy and density functional theory calculations, we have identified both topological insulator and Dirac semimetal states near the Fermi energy in different iron-based superconducting compounds. Carrier doping can tune these topologically non-trivial bands to the Fermi energy, potentially allowing access to several different superconducting topological states in the same material. These results reveal the generic coexistence of superconductivity and multiple topological states in iron-based superconductors, indicating that this broad class of materials is a promising platform for high-temperature topological superconductivity.
Purpose
The purpose of this study was to explore the outcomes and risk factors for hepatitis B virus (HBV) reactivation after kidney transplantation in occult HBV carriers, who are hepatitis B ...surface antigen (HBsAg) seronegative and hepatitis B core antibody (HBcAb) seropositive before kidney transplantation.
Methods
We retrospectively analyzed 322 occult HBV carriers who received kidney transplantation in our hospital from January 1998 to June 2008. HBsAg and HBV DNA were routinely checked for diagnosis of HBV reactivation.
Results
Our results showed that 15 cases (4.7%) of occult HBV carriers had HBV reactivation after kidney transplantation. Kaplan–Meier analysis showed that 1‐, 3‐, 5‐, and 10‐year patient survival was 86.7%, 79.4%, 72.2%, and 65.0%, respectively, in the HBV reactivation group, and was 96.1%, 93.8%, 91.5%, and 84.5%, respectively, in the non‐HBV reactivation group (log‐rank 4.12, P = 0.042). Graft survival showed no difference between these 2 groups (P > 0.05). The incidences of impairment of liver function, liver function failure, hepatocellular carcinoma, and acute rejection were significantly higher in the HBV reactivation group compared with the non‐HBV reactivation group (P < 0.05). Logistic multivariate analysis showed that older age (>60 years) and using anti‐T‐cell antibodies were independent risk factors for HBV reactivation after kidney transplantation, while being hepatitis B surface antibody (HBsAb) seropositive and using lamivudine prophylaxis could protect occult HBV carriers from HBV reactivation after kidney transplantation (P < 0.05).
Conclusion
In conclusion, our data showed that HBV reactivation may diminish the patient survival but not graft survival. Older age and anti‐T‐cell antibodies may increase the risk of HBV reactivation, whereas lamivudine prophylaxis may prevent HBV reactivation after kidney transplantation.
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