The transition temperature Tc of iron-based superconductors has a dome-shaped dependence on chemical doping, and the superconductivity that develops underneath may obscure a potential quantum ...critical point (QCP) residing at absolute zero. With the aim of detecting signatures of this quantum criticality, Hashimoto et al. (p 1554; see the Perspective by Sachdev ) measured the penetration depth of the pnictide series BaFe2(As1-x Px )2 as a function of x. A sharp peak right around the point where Tc has a maximum (x = 0.30) was observed, implying that the superfluid density diminishes sharply where one would expect it to be the most robust. This unusual finding is interpreted as a sign of a QCP at x = 0.30. In a superconductor, the ratio of the carrier density, n, to its effective mass, m*, is a fundamental property directly reflecting the length scale of the superfluid flow, the London penetration depth, λL. In two-dimensional systems, this ratio n/m* (~1/λL2) determines the effective Fermi temperature, TF. We report a sharp peak in the x-dependence of λL at zero temperature in clean samples of BaFe2(As1-xPx)2 at the optimum composition x = 0.30, where the superconducting transition temperature Tc reaches a maximum of 30 kelvin. This structure may arise from quantum fluctuations associated with a quantum critical point. The ratio of Tc/TF at x = 0.30 is enhanced, implying a possible crossover toward the Bose-Einstein condensate limit driven by quantum criticality. PUBLICATION ABSTRACT
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
We report measurements of the temperature dependence of both in-plane and out-of-plane penetration depths (lambda(a) and lambda(c), respectively) in 2H-NbSe2. Measurements were made with a ...radio-frequency tunnel diode oscillator circuit at temperatures down to 100 mK. Analysis of the anisotropic superfluid density shows that a reduced energy gap is located on one or more of the quasi-two-dimensional Nb Fermi surface sheets rather than on the Se sheet, in contrast with some previous reports. This result suggests that the gap structure is not simply related to the weak electron-phonon coupling on the Se sheet and is therefore important for microscopic models of anisotropic superconductivity in this compound.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
In a superconductor, the ratio of the carrier density, n, to its effective mass, m*, is a fundamental property directly reflecting the length scale of the superfluid flow, the London penetration ...depth, λ L . In two-dimensional systems, this ratio n/m* (~1/λ L ²) determines the effective Fermi temperature, T F . We report a sharp peak in the x-dependence of λ L at zero temperature in clean samples of BaFe₂(As 1-x P x )₂ at the optimum composition x = 0.30, where the superconducting transition temperature T c reaches a maximum of 30 kelvin. This structure may arise from quantum fluctuations associated with a quantum critical point. The ratio of T c /T F at x = 0.30 is enhanced, implying a possible crossover toward the Bose-Einstein condensate limit driven by quantum criticality.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Background. Health care-associated, central venous catheter-related bloodstream infections (HA-BSIs) are a major cause of morbidity and mortality. Needleless connectors (NCs) are an important ...component of the intravenous system. NCs initially were introduced to reduce health care worker needlestick injuries, yet some of these NCs may increase HA-BSI risk. Methods. We compared HA-BSI rates on wards or intensive care units (ICUs) at 5 hospitals that had converted from split septum (SS) connectors or needles to mechanical valve needleless connectors (MV-NCs). The hospitals (16 ICUs, 1 entire hospital, and 1 oncology unit; 3 hospitals were located in the United States, and 2 were located in Australia) had conducted HA-BSI surveillance using Centers for Disease Control and Prevention definitions during use of both NCs. HA-BSI rates and prevention practices were compared during the pre-MV period, MV period, and post-MV period. Results. The HA-BSI rate increased in all ICUs and wards when SS-NCs were replaced by MV-NCs. In the 16 ICUs, the HA-BSI rate increased significantly when SS-NCs or needles were replaced by MV-NCs (6.15 vs 9.49 BSIs per 1000 central venous catheter CVC-days; relative risk, 1.54; 95% confidence interval, 1.37–1.74; P<.001). The 14 ICUs that switched back to SS-NCs had significant reductions in their BSI rates (9.49 vs 5.77 BSIs per 1000 CVC-days; relative risk, 1.65; 95% confidence interval, 1.38–1.96; P<.001). BSI infection prevention strategies were similar in the pre-MV and MV periods. Conclusions. We found strong evidence that MV-NCs were associated with increased HA-BSI rates, despite similar BSI surveillance, definitions, and prevention strategies. Hospital personnel should monitor their HA-BSI rates and, if they are elevated, examine the role of newer technologies, such as MV-NCs.
Full text
Available for:
BFBNIB, NUK, PNG, UL, UM, UPUK
High-precision radio-frequency magnetic susceptibility measurements were performed on single crystals of fully deuterated κ − ( ET )2Cu N (CN)2 Br , hereafter designated as κ − (D 8 ET)2 Cu N (CN)2 ...Br . This material phase separates into superconducting and antiferromagnetic regions, the degree of which depends strongly upon the cooling rate. We show that the screening fraction η sc varies logarithmically with the cooling rate over nearly five decades. The average size of superconducting regions is estimated to vary from 5 to 40 μ m , depending upon cooling rate, consistent with previous infrared microscopy measurements. In the region T ≲ Tc/3 , the effective magnetic penetration depth exhibits power-law behavior λ (T) − λ (0) ∼ Tn with n = 1.6 , independent of the cooling rate. Changes in cooling rate and the consequent phase separation evidently do not introduce the kind of disorder that would alter the exponent n in a d -wave superconductor. The exponent remains close to n = 1.5, reported in single crystals of κ − (ET)2Cu N (CN)2 Br and κ − (ET)2 Cu (NCS)2 A. Carrington et al., Phys. Rev. Lett 83, 4172 (1999). The transition temperature fell linearly with 1 − ηsc. Measurements were also made on κ − (ET)2Cu N (CN)2 Cl of normal isotopic abundance in which a very small amount of superconducting phase ηsc ≈ 10−4 developed, presumably through the strain-induced sample mounting. This material showed a power-law exponent of n = 1.64 , independent of the cooling rate.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Women and men, female and male animals and cells are biologically different, and acknowledgement of this fact is critical to advancing medicine. However, incorporating concepts of sex-specific ...analysis in basic research is largely neglected, introducing bias into translational findings, clinical concepts and drug development. Research funding agencies recently approached these issues but implementation of policy changes in the scientific community is still limited, probably due to deficits in concepts, knowledge and proper methodology. This expert review is based on the EUGenMed project (www.eugenmed.eu) developing a roadmap for implementing sex and gender in biomedical and health research. For sake of clarity and conciseness, examples are mainly taken from the cardiovascular field that may serve as a paradigm for others, since a significant amount of knowledge how sex and oestrogen determine the manifestation of many cardiovascular diseases (CVD) has been accumulated. As main concepts for implementation of sex in basic research, the study of primary cell and animals of both sexes, the study of the influence of genetic vs. hormonal factors and the analysis of sex chromosomes and sex specific statistics in genome wide association studies (GWAS) are discussed. The review also discusses methodological issues, and analyses strength, weaknesses, opportunities and threats in implementing sex-sensitive aspects into basic research.
The magnetic penetration depth of single crystal Sm(1.85)Ce(0.15)CuO(4-y) was measured down to 0.4 K in dc fields up to 7 kOe. For insulating Sm2CuO4, Sm3+ spins order at the Ne el temperature, ...T(N)=6 K, independent of the applied field. Superconducting Sm(1.85)Ce(0.15)CuO(4-y) (T(c) approximately 23 K) shows a sharp increase in diamagnetic screening below T(*)(H) which varied from 4.0 K (H=0) to 0.5 K (H=7 kOe) for a field along the c axis. If the field was aligned parallel to the conducting planes, T(*) remained unchanged. The unusual field dependence of T(*) indicates a spin-freezing transition that dramatically increases the superfluid density.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The magnetic penetration depth {lambda}(T,H{sub J}) was measured in the presence of a slowly relaxing supercurrent j. In single crystal Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} below approximately 25 K, ...{lambda}(T,H{sub J}) is strongly hysteretic. We propose that the irreversibility arises from a shift of the vortex position within its pinning well as j changes. The Campbell length depends upon the ratio j/j{sub c} where j{sub c} is the critical current defined through the Labusch parameter. Similar effects were observed in other cuprates and in an organic superconductor.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
PDF
