Critical change in the Fermi surface of iron arsenic superconductors at the onset of superconductivity

The phase diagram of a correlated material is the result of a complex interplay between several degrees of freedom, providing a map of the material's behavior. One can understand (and ultimately control) the material's ground state by associating features and regions of the phase diagram, with specific physical events or underlying quantum mechanical properties. The phase diagram of the newly discovered iron arsenic high temperature superconductors is particularly rich and interesting. In the AE(Fe1-xTx)2As2 class (AE being Ca, Sr, Ba, T being transition metals), the simultaneous structural/magnetic phase transition that occurs at elevated temperature in the undoped material, splits and is suppressed by carrier doping, the suppression being complete around optimal doping. A dome of superconductivity exists with apparent equal ease in the orthorhombic / antiferromagnetic (AFM) state as well as in the tetragonal state with no long range magnetic order. The question then is what determines the critical doping at which superconductivity emerges, if the AFM order is fully suppressed only at higher doping values. Here we report evidence from angle resolved photoemission spectroscopy (ARPES) that critical changes in the Fermi surface (FS) occur at the doping level that marks the onset of superconductivity. The presence of the AFM order leads to a reconstruction of the electronic structure, most significantly the appearance of the small hole pockets at the Fermi level. These hole pockets vanish, i. e. undergo a Lifshitz transition, at the onset of superconductivity. Superconductivity and magnetism are competing states in the iron arsenic superconductors. In the presence of the hole pockets superconductivity is fully suppressed, while in their absence the two states can coexist.Comment: Updated version accepted in Nature Physic

Phase Separation and Magnetic Order in K-doped Iron Selenide Superconductor

Alkali-doped iron selenide is the latest member of high Tc superconductor family, and its peculiar characters have immediately attracted extensive attention. We prepared high-quality potassium-doped iron selenide (KxFe2-ySe2) thin films by molecular beam epitaxy and unambiguously demonstrated the existence of phase separation, which is currently under debate, in this material using scanning tunneling microscopy and spectroscopy. The stoichiometric superconducting phase KFe2Se2 contains no iron vacancies, while the insulating phase has a \surd5\times\surd5 vacancy order. The iron vacancies are shown always destructive to superconductivity in KFe2Se2. Our study on the subgap bound states induced by the iron vacancies further reveals a magnetically-related bipartite order in the superconducting phase. These findings not only solve the existing controversies in the atomic and electronic structures in KxFe2-ySe2, but also provide valuable information on understanding the superconductivity and its interplay with magnetism in iron-based superconductors

Consistent model of magnetism in ferropnictides

The discovery of superconductivity in LaFeAsO introduced the ferropnictides as a major new class of superconducting compounds with critical temperatures second only to cuprates. The presence of magnetic iron makes ferropnictides radically different from cuprates. Antiferromagnetism of the parent compounds strongly suggests that superconductivity and magnetism are closely related. However, the character of magnetic interactions and spin fluctuations in ferropnictides, in spite of vigorous efforts, has until now resisted understanding within any conventional model of magnetism. Here we show that the most puzzling features can be naturally reconciled within a rather simple effective spin model with biquadratic interactions, which is consistent with electronic structure calculations. By going beyond the Heisenberg model, this description explains numerous experimentally observed properties, including the peculiarities of the spin wave spectrum, thin domain walls, crossover from first to second order phase transition under doping in some compounds, and offers new insight in the occurrence of the nematic phase above the antiferromagnetic phase transition.Comment: 5 pages, 3 figures, revtex

Automated Error Labeling in Radiation Oncology via Statistical Natural Language Processing

A report published in 2000 from the Institute of Medicine revealed that medical errors were a leading cause of patient deaths, and urged the development of error detection and reporting systems. The field of radiation oncology is particularly vulnerable to these errors due to its highly complex process workflow, the large number of interactions among various systems, devices, and medical personnel, as well as the extensive preparation and treatment delivery steps. Natural language processing (NLP)-aided statistical algorithms have the potential to significantly improve the discovery and reporting of these medical errors by relieving human reporters of the burden of event type categorization and creating an automated, streamlined system for error incidents. In this paper, we demonstrate text-classification models developed with clinical data from a full service radiation oncology center (test center) that can predict the broad level and first level category of an error given a free-text description of the error. All but one of the resulting models had an excellent performance as quantified by several metrics. The results also suggest that more development and more extensive training data would further improve future results

Validating differential regulation of mRNAs during MSU crystal inflammation in mouse peritoneal macrophages

Cells were harvested at the indicated time points after the addition of medium containing monosodium urate (MSU) crystals (200 μg/ml) or medium alone. RNA was analyzed by TaqMan real-time reverse transcription PCR for expression of the targets indicated in the figure. Results represent the averages of two experiments. Induction of target mRNAs in negative control (medium only) cells was negligible in nearly all cases. Therefore, the curves corresponding to the negative controls are not shown. However, numeric values for mean fold expression changes in MSU stimulated and negative controls with respect to t = 0 hours are listed below for the time points of maximal induction by MSU crystals. Tumour necrosis factor (TNF)-α (2 hours: MSU:medium = 28.1:1.2), IL-6 (1 hour: MSU:medium = 49.7:1.2), IL-1β (2 hours: MSU:medium = 13.1:0.5); and early growth response (Egr)-1 (1 hour: MSU:medium = 17.4:1). Irg1 (6 hours: MSU:medium = 60.0:6.8); prokineticin (PROK)-2 (6 hours: MSU:medium, 11.0:1.0), histidine decarboxylase (Hdc; 9 hours: MSU:medium = 11.6:0.9) and protein upregulated on macrophages activated with interferon-γ (PUMA-g; 9 hours: MSU:medium = 73.5:2.5). Comparison of fold induction by MSU crystals in dissected membranes versus macrophage culture.<p><b>Copyright information:</b></p><p>Taken from "Identification of novel monosodium urate crystal regulated mRNAs by transcript profiling of dissected murine air pouch membranes"</p><p>http://arthritis-research.com/content/10/3/R64</p><p>Arthritis Research & Therapy 2008;10(3):R64-R64.</p><p>Published online 3 Jun 2008</p><p>PMCID:PMC2483455.</p><p></p

Validating differential regulation of mRNAs during MSU crystal inflammation in dissected air pouch membranes

Results were obtained from dissected membranes from the pouches used for the time course shown in Figure 1b. Negative control pouches were injected with 1 ml phosphate-buffered saline (PBS) and dissected at 9 hours. A, C and D: RNA was analyzed with TaqMan real-time reverse transcription PCR for the targets indicated. The legend text also shows values for mean fold expression changes that were measured at 9 hours (relative to 0 hours) in monosodium urate (MSU) crystal stimulated versus PBS injected (control) membranes. mRNA quantification of tumour necrosis factor (TNF)-α (MSU:PBS at 9 h = 14.1:1.7), interleukin (IL)-6 (MSU:PBS = 12.9:0.5), IL-1β (MSU:PBS = 34.7:0.7), and early growth response (Egr)-1 (MSU:PBS = 3.7:1.4). Left: determination of IL-6 protein concentration at 9 hours in the pouch exudate from pouches injected with PBS or MSU crystals (immunoassay). Center and right: immunohistochemical detection of IL-6 in the air pouch membrane. Chromogen: DAB (brown). Center: striated muscle (m) showing specific IL-6 immunostain; hair follicles (f) with nonspecific immunostain that was also seen with control immunoglobulin (original magnification, 50×). Right: specific IL-6 immunostaining in the inflamed pouch membrane (original magnification, 400×). mRNA quantification of triggering receptor expressed on myeloid cells (TREM)-1 (MSU:PBS at 9 h = 15.3:0.6), immunoresponsive gene (Irg)1 (MSU:PBS, 65:1.0), prokineticin (PROK)-2 (MSU:PBS = 58.4:1.0), histidine decarboxylase (Hdc; MSU:PBS = 60.4:1.3), and protein upregulated on macrophages activated with interferon-γ (PUMA-g; MSU:PBS = 120:1.3). mRNA quantification of TREM-2 (MSU:PBS at 9 h = 0.2:0.9), granzyme D (MSU:PBS = 0.5:0.8), leukemia/lymphoma-related factor (LRF; MSU:PBS = 1.8:1.7), and Nab2 (MSU:PBS = 0.8:0.9).<p><b>Copyright information:</b></p><p>Taken from "Identification of novel monosodium urate crystal regulated mRNAs by transcript profiling of dissected murine air pouch membranes"</p><p>http://arthritis-research.com/content/10/3/R64</p><p>Arthritis Research & Therapy 2008;10(3):R64-R64.</p><p>Published online 3 Jun 2008</p><p>PMCID:PMC2483455.</p><p></p