Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:Ox_{x}

We report an unusual persistence of superconductivity against high magnetic fields in the iron chalcogenide film FeTe:O$_{x}$ below ~ 2.5 K. Instead of saturating like a mean-field behavior with a single order parameter, the measured low-temperature upper critical field increases progressively, suggesting a large supply of superconducting states accessible via magnetic field or low-energy thermal fluctuations. We demonstrate that superconducting states of finite momenta can be realized within the conventional theory, despite its questionable applicability. Our findings reveal a fundamental characteristic of superconductivity and electronic structure in the strongly-correlated iron-based superconductors.Comment: 10 pages, 3 figure

Initialization by measurement of a two-qubit superconducting circuit

We demonstrate initialization by joint measurement of two transmon qubits in 3D circuit quantum electrodynamics. Homodyne detection of cavity transmission is enhanced by Josephson parametric amplification to discriminate the two-qubit ground state from single-qubit excitations non-destructively and with 98.1% fidelity. Measurement and postselection of a steady-state mixture with 4.7% residual excitation per qubit achieve 98.8% fidelity to the ground state, thus outperforming passive initialization.Comment: 5 pages, 4 figures, and Supplementary Information (7 figures, 1 table

Coercive Field and Magnetization Deficit in Ga(1-x)Mn(x)As Epilayers

We have studied the field dependence of the magnetization in epilayers of the diluted magnetic semiconductor Ga(1-x)Mn(x)As for 0.0135 < x < 0.083. Measurements of the low temperature magnetization in fields up to 3 T show a significant deficit in the total moment below that expected for full saturation of all the Mn spins. These results suggest that the spin state of the non-ferromagnetic Mn spins is energetically well separated from the ferromagnetism of the bulk of the spins. We have also studied the coercive field (Hc) as a function of temperature and Mn concentration, finding that Hc decreases with increasing Mn concentration as predicted theoretically.Comment: 15 total pages -- 5 text, 1 table, 4 figues. Accepted for publication in MMM 2002 conference proceedings (APL

Relevance of the Heisenberg-Kitaev model for the honeycomb lattice iridates A_2IrO_3

Combining thermodynamic measurements with theoretical density functional and thermodynamic calculations we demonstrate that the honeycomb lattice iridates A2IrO3 (A = Na, Li) are magnetically ordered Mott insulators where the magnetism of the effective spin-orbital S = 1/2 moments can be captured by a Heisenberg-Kitaev (HK) model with Heisenberg interactions beyond nearest-neighbor exchange. Experimentally, we observe an increase of the Curie-Weiss temperature from \theta = -125 K for Na2IrO3 to \theta = -33 K for Li2IrO3, while the antiferromagnetic ordering temperature remains roughly the same T_N = 15 K for both materials. Using finite-temperature functional renormalization group calculations we show that this evolution of \theta, T_N, the frustration parameter f = \theta/T_N, and the zig-zag magnetic ordering structure suggested for both materials by density functional theory can be captured within this extended HK model. Combining our experimental and theoretical results, we estimate that Na2IrO3 is deep in the magnetically ordered regime of the HK model (\alpha \approx 0.25), while Li2IrO3 appears to be close to a spin-liquid regime (0.6 < \alpha < 0.7).Comment: Version accepted for publication in PRL. Additional DFT and thermodynamic calculations have been included. 6 pages of supplementary material include

Temperature dependent d-d excitations in manganites probed by resonant inelastic x-ray scattering

We report the observation of temperature dependent electronic excitations in various manganites utilizing resonant inelastic x-ray scattering (RIXS) at the Mn K-edge. Excitations were observed between 1.5 and 16 eV with temperature dependence found as high as 10 eV. The change in spectral weight between 1.5 and 5 eV was found to be related to the magnetic order and independent of the conductivity. On the basis of LDA+U and Wannier function calculations, this dependence is associated with intersite d-d excitations. Finally, the connection between the RIXS cross-section and the loss function is addressed.Comment: 5 pages, 5 figure

Magnitude of the Difference Between Clinic and Ambulatory Blood Pressures and Risk of Adverse Outcomes in Patients With Chronic Kidney Disease.

Background Obtaining 24-hour ambulatory blood pressure ( BP ) is recommended for the detection of masked or white-coat hypertension. Our objective was to determine whether the magnitude of the difference between ambulatory and clinic BP s has prognostic implications. Methods and Results We included 610 participants of the AASK (African American Study of Kidney Disease and Hypertension) Cohort Study who had clinic and ambulatory BPs performed in close proximity in time. We used Cox models to determine the association between the absolute systolic BP ( SBP ) difference between clinic and awake ambulatory BPs (primary predictor) and death and end-stage renal disease. Of 610 AASK Cohort Study participants, 200 (32.8%) died during a median follow-up of 9.9&nbsp;years; 178 (29.2%) developed end-stage renal disease. There was a U-shaped association between the clinic and ambulatory SBP difference with risk of death, but not end-stage renal disease. A 5- to &lt;10-mm&nbsp;Hg higher clinic versus awake SBP (white-coat effect) was associated with a trend toward higher (adjusted) mortality risk (adjusted hazard ratio, 1.84; 95% CI, 0.94-3.56) compared with a 0- to &lt;5-mm&nbsp;Hg clinic-awake SBP difference (reference group). A ≥10-mm&nbsp;Hg clinic-awake SBP difference was associated with even higher mortality risk (adjusted hazard ratio, 2.31; 95% CI, 1.27-4.22). A ≥-5-mm&nbsp;Hg clinic-awake SBP difference was also associated with higher mortality (adjusted hazard ratio, 1.82; 95% CI, 1.05-3.15) compared with the reference group. Conclusions A U-shaped association exists between the magnitude of the difference between clinic and ambulatory SBP and mortality. Higher clinic versus ambulatory BPs (as in white-coat effect) may be associated with higher risk of death in black patients with chronic kidney disease

Riemann-Hilbert problems for monogenic functions in axially symmetric domains

We consider Riemann-Hilbert boundary value problems (for short RHBVPs) with variable coefficients for axially symmetric monogenic functions defined in axial symmetric domains. This is done by constructing a method to reduce the RHBVPs for axially symmetric monogenic functions defined in four-dimensional axial symmetric domains into the RHBVPs for analytic functions defined over the complex plane. Then we derive solutions to the corresponding Schwarz problem. Finally, we generalize the results obtained to null-solutions of (D−α)ϕ=0, α∈R, where R denotes the field of real numbers

Effects of annealing time on defect-controlled ferromagnetism in Ga1-xMnxAs

We have studied the evolution of the magnetic, electronic, and structural properties of annealed epilayers of Ga1-xMnxAs grown by low temperature molecular beam epitaxy. Annealing at the optimal temperature of 250 C for less than 2 hours significantly enhances the conductivity and ferromagnetism, but continuing the annealing for longer times suppresses both. These data indicate that such annealing induces the defects in Ga1-xMnxAs to evolve through at least two different processes, and they point to a complex interplay between the different defects and ferromagnetism in this material.Comment: 14 pages, pdf only, submitted to Applied Physics Letter