Systematic Study of Short Range Antiferromagnetic Order and The Spin-Glass State in Lightly Doped La2-xSrxCuO4

Systematic measurements of the magnetic susceptibility were performed on single crystals of lightly doped La2-xSrxCuO4 (x=0.03, 0.04 and 0.05). For all samples the temperature dependence of the in-plane magnetic susceptibility shows typical spin-glass features with spin-glass transition temperatures Tg of 6.3K, 5.5K and 5.0K for x=0.03, 0.04 and 0.05, respectively. The canonical spin-glass order parameter extracted from the in-plane susceptibility of all the samples follows a universal scaling curve. On the other hand, the out-of-plane magnetic susceptibility deviates from Curie law below a temperature Tdv, higher than Tg. Comparing with previous neutron scattering results with an instrumental energy resolution of 0.25 meV from Wakimoto et al., the x-dependence of Tdv is qualitatively the same as that of Tel, the temperature below which the elastic magnetic scattering develops around (pi, pi). Thus, a revised magnetic phase diagram in the lightly doped region of La2-xSrxCuO4 is proposed. The Curie constants calculated from the in-plane susceptibility are independent of the Sr concentration. On the basis of the cluster spin-glass model, this fact might reflect an inhomogeneous distribution of doped holes in the CuO2 plane, such as in a stripe structure.Comment: 7 pages, 6 figure

Complex regulation and multiple developmental functions of misfire, the Drosophila melanogaster ferlin gene

BACKGROUND: Ferlins are membrane proteins with multiple C2 domains and proposed functions in Ca(2+ )mediated membrane-membrane interactions in animals. Caenorhabditis elegans has two ferlin genes, one of which is required for sperm function. Mammals have several ferlin genes and mutations in the human dysferlin (DYSF) and otoferlin (OTOF) genes result in muscular dystrophy and hearing loss, respectively. Drosophila melanogaster has a single ferlin gene called misfire (mfr). A previous study showed that a mfr mutation caused male sterility because of defects in fertilization. Here we analyze the expression and structure of the mfr gene and the consequences of multiple mutations to better understand the developmental function of ferlins. RESULTS: We show that mfr is expressed in the testis and ovaries of adult flies, has tissue-specific promoters, and expresses alternatively spliced transcripts that are predicted to encode distinct protein isoforms. Studies of 11 male sterile mutations indicate that a predicted Mfr testis isoform with five C2 domains and a transmembrane (TM) domain is required for sperm plasma membrane breakdown (PMBD) and completion of sperm activation during fertilization. We demonstrate that Mfr is not required for localization of Sneaky, another membrane protein necessary for PMBD. The mfr mutations vary in their effects in females, with a subset disrupting egg patterning and causing a maternal effect delay in early embryonic development. Locations of these mutations indicate that a short Mfr protein isoform carries out ferlin activities during oogenesis. CONCLUSION: The mfr gene exhibits complex transcriptional and post-transcriptional regulation and functions in three developmental processes: sperm activation, egg patterning, and early embryogenesis. These functions are in part due to the production of protein isoforms that vary in the number of C2 domains. These findings help establish D. melanogaster as model system for understanding ferlin function and dysfunction in animals, including humans

Archivist as activist: lessons from three queer community archives in California

California is home to multiple queer community archives created by community members outside of government, academic, and public archives. These archives are maintained by the communities and are important spaces not only for the preservation of records, but also as safe spaces to study, gather, and learn about the communities' histories. This article describes the histories of three such queer community archives (Gay, Lesbian, Bisexual, Transgender Historical Society Lavender Library, Archives, and Cultural Exchange of Sacramento, Inc.; and ONE National Gay & Lesbian Archives) in order to discuss the role of activism in the community archives and implications for re-examining the role of activism to incorporate communities into the heart of archival professional work. By understanding the impetus for creating and maintaining queer community archives, archivists can use this knowledge to foster more reflective practices to be more inclusive in their archival practices through outreach, collaboration, and descriptive practices. This article extends our knowledge of community archives and provides evidence for the need to include communities in archival professional practice

Static magnetic correlations near the insulating-superconducting phase boundary in La2−x_{2-x}Srx_{x}CuO4_{4}

An elastic neutron scattering study has been performed on several single crystals of La$_{2-x}$Sr$_{x}$CuO$_{4}$ for {\it x} near the lower critical concentration {\it x$_{c}$} for superconductivity. % In the insulating spin-glass phase ({\it x} = 0.04 and 0.053), the previously reported one-dimensional spin modulation along the orthorhombic {\it b}-axis is confirmed. % Just inside the superconducting phase ({\it x} = 0.06), however, two pairs of incommensurate magnetic peaks are additionally observed corresponding to the spin modulation parallel to the tetragonal axes. % These two types of spin modulations with similar incommensurabilities coexist near the boundary. % The peak-width $\kappa$ along spin-modulation direction exhibits an anomalous maximum in the superconducting phase near {\it x$_{c}$}, where the incommensurability $\delta$ monotonically increases upon doping across the phase boundary. % These results are discussed in connection with the doping-induced superconducting phase transition.Comment: 9pages, 9figure

Neutron scattering studies of Zn-doped La2-xSrxCuO4

This paper reviews studies of the spatial modulation of spin in La2-xSrxCuO4 (LSCO) through neutron-scattering measurements of the elastic magnetic peaks, with emphasis on Zn-doped LSCO. The elastic incommensurate magnetic peaks can be categorized in two classes with respect to the temperature dependence. Nd-doped LSCO, La2CuO4+y and LSCO with x ~ 1/8 exhibit an ordinary power law behavior. On the other hand, Zn-doped LSCO and LSCO with x = 0.02-0.07 show an exponential temperature dependence, and the correlation lengths stay short. This discrepancy can be attributed to the difference in the mechanism of pinning spin fluctuations. The former systems have pinning centers which is coherent to the lattice. In the latter, however, pinning centers are randomly scattered in the CuO2 planes, thus incoherent. The incoherent pinning model is discussed with referring to recent mu-SR studies.Comment: 6 pages, including 4 figures and 1 table. Proceedings for ISS2000 (Tokyo, October 2000

Inelastic neutron scattering study on the resonance mode in an optimally doped superconductor LaFeAsO0.92_{0.92}F0.08_{0.08}

An optimally doped iron-based superconductor LaFeAsO$_{0.92}$F$_{0.08}$ with $T_c = 29$ K has been studied by inelastic powder neutron scattering. The magnetic excitation at $Q=1.15$ \AA$^{-1}$ is enhanced below $T_c$, leading to a peak at $E_{res}\sim13$ meV as the resonance mode, in addition to the formation of a gap at low energy below the crossover energy $\Delta_{c}\sim10 meV$. The peak energy at $Q=1.15$ \AA$^{-1}$ corresponds to $5.2 k_B T_c$ in good agreement with the other values of resonance mode observed in the various iron-based superconductors, even in the high-$T_c$ cuprates. Although the phonon density of states has a peak at the same energy as the resonance mode in the present superconductor, the $Q$-dependence is consistent with the resonance being of predominately magnetic origin.Comment: 4 pages, 5 Postscript figure

Resonant inelastic X-ray scattering study of overdoped La2−x_{2-x}Srx_{x}CuO4_{4}

Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge has been performed for heavily overdoped samples of La$_{2-x}$Sr$_{x}$CuO$_{4}$ with $x= 0.25$ and 0.30. We have observed the charge transfer and molecular-orbital excitations which exhibit resonances at incident energies of $E_i= 8.992$ and 8.998 keV, respectively. From a comparison with previous results on undoped and optimally-doped samples, we determine that the charge-transfer excitation energy increases monotonically as doping increases. In addition, the $E_i$-dependences of the RIXS spectral weight and absorption spectrum exhibit no clear peak at $E_i = 8.998$ keV in contrast to results in the underdoped samples. The low-energy ($\leq 3$ eV) continuum excitation intensity has been studied utilizing the high energy resolution of 0.13 eV (FWHM). A comparison of the RIXS profiles at $(\pi ~0)$ and $(\pi ~\pi)$ indicates that the continuum intensity exists even at $(\pi ~\pi)$ in the overdoped samples, whereas it has been reported only at $(0 ~0)$ and $(\pi ~0)$ for the $x=0.17$ sample. Furthermore, we also found an additional excitation on top of the continuum intensity at the $(\pi ~\pi)$ and $(\pi ~0)$ positions.Comment: 7 pages, 7 figure