Magnetic ordering in GdNi2B2C revisited by resonant x-ray scattering: evidence for the double-q model

Recent theoretical efforts aimed at understanding the nature of antiferromagnetic ordering in GdNi2B2C predicted double-q ordering. Here we employ resonant elastic x-ray scattering to test this theory against the formerly proposed, single-q ordering scenario. Our study reveals a satellite reflection associated with a mixed-order component propagation wave vector, viz., (q_a,2q_b,0) with q_b = q_a approx= 0.55 reciprocal lattice units, the presence of which is incompatible with single-q ordering but is expected from the double-q model. A (3q_a,0,0) wave vector (i.e., third-order) satellite is also observed, again in line with the double-q model. The temperature dependencies of these along with that of a first-order satellite are compared with calculations based on the double-q model and reasonable qualitative agreement is found. By examining the azimuthal dependence of first-order satellite scattering, we show the magnetic order to be, as predicted, elliptically polarized at base temperature and find the temperature dependence of the "out of a-b plane" moment component to be in fairly good agreement with calculation. Our results provide qualitative support for the double-q model and thus in turn corroborate the explanation for the "magnetoelastic paradox" offered by this model.Comment: 8 pages, 5 figures. Submitted to Phys. Rev.

Scanning Tunneling Microscopy in the superconductor LaSb2

We present very low temperature (0.15 K) scanning tunneling microscopy and spectroscopy experiments in the layered superconductor LaSb$_2$. We obtain topographic microscopy images with surfaces showing hexagonal and square atomic size patterns, and observe in the tunneling conductance a superconducting gap. We find well defined quasiparticle peaks located at a bias voltage comparable to the weak coupling s-wave BCS expected gap value (0.17 meV). The amount of states at the Fermi level is however large and the curves are significantly broadened. We find T$_c$ of 1.2 K by following the tunneling conductance with temperature.Comment: 5 pages, 4 figure

The biogeochemistry of microbial mats, stromatolites and the ancient biosphere

Stromatolites offer an unparalleled geologic record of early life, because they constitute the oldest and most abundant recognizable remains of microbial ecosystems. Microbial mats are living homologs of stromatolites; thus, the physiology of the microbiota as well as the processes which create those features of mats (e.g., biomarker organic compounds, elemental and stable isotopic compositions) which are preserved in the ancient record. Observations of the carbon isotopic composition (delta C-13) of stromatolites and microbial mats were made and are consistent with the hypothesis that atmospheric CO2 concentrations have declined by at least one to two orders of magnitude during the past 2.5 Ga. Whereas delta C-13 values of carbonate carbon average about 0 permil during both the early and mid-Proterozoic, the delta C-13 values of stromatolitic organic matter increase from an average of -35 between 2.0 and 2.6 Ga ago to an average of about -28 about 1.0 Ga ago. Modern microbial mats in hypersaline environments have delta C-13 values typically in the range of -5 to -9, relative to an inorganic bicarbonate source at 0 permil. Both microbial mats and pur cultures of cyanobacteria grown in waters in near equilibrium with current atmospheric CO2 levels exhibit minimal discrimination against C-13. In contrast, hot spring cyanobacterial mats or cyanobacterial cultures grown under higher CO2 levels exhibit substantially greater discrimination. If care is taken to compare modern mats with stromatolites from comparable environments, it might be possible to estimate ancient levels of atmospheric CO2. In modern microbial mats, a tight coupling exists between photosynthetic organic carbon production and subsequent carbon oxidation, mostly by sulfate reduction. The rate of one process fuels a high rate of the other, with much of the sulfate reduction occurring within the same depth interval as oxygenic photosynthesis. Other aspects of this study are presented

Damping of dHvA oscillations and vortex-lattice disorder in the peak-effect region of strong type-II superconductors

The phenomenon of magnetic quantum oscillations in the superconducting state poses several questions that still defy satisfactory answers. A key controversial issue concerns the additional damping observed in the vortex state. Here, we show results of \mu SR, dHvA, and SQUID magnetization measurements on borocarbide superconductors, indicating that a sharp drop observed in the dHvA amplitude just below H_{c2} is correlated with enhanced disorder of the vortex lattice in the peak-effect region, which significantly enhances quasiparticle scattering by the pair potential.Comment: 4 pages 4 figure

Local superconducting density of states of ErNi2B2C

We present local tunnelling microscopy and spectroscopy measurements at low temperatures in single crystalline samples of the magnetic superconductor ErNi2B2C. The electronic local density of states shows a striking departure from s-wave BCS theory with a finite value at the Fermi level, which amounts to half of the normal phase density of states.Comment: 9 pages, 3 figure

Alternating magnetic anisotropy of Li2_2(Li1−xTx_{1-x}T_x)N with TT = Mn, Fe, Co, and Ni

Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy-plane $\rightarrow$ easy-axis $\rightarrow$ easy-plane $\rightarrow$ easy-axis when progressing from $T$ = Mn $\rightarrow$ Fe $\rightarrow$ Co $\rightarrow$ Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show a surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.Comment: 5 pages, 3 figures, published as PRB Rapid Communication, Fig. 3 update

Mavericks on the Border: The Early Southwest in Historical Fiction and Film

Twentieth-century authors and filmmakers have created a pantheon of mavericks—some macho, others angst-ridden—who often cross a metaphorical boundary among the literal ones of Anglo, Native American, and Hispanic cultures. Douglas Canfield examines the concept of borders, defining them as the space between states and cultures and ideologies, and focuses on these border crossings as a key feature of novels and films about the region. Canfield begins in the Old Southwest of Faulkner’s Mississippi, addressing the problem of slavery; travels west to North Texas and the infamous Gainesville Hanging of Unionists during the Civil War; and then follows scalpers into the Southwest Borderlands. He then turns to the area of the Gadsden Purchase, known for its outlaws and Indian wars, before heading south of the border for the Yaqui persecution and the Mexican Revolution. Alongside such well-known works as Go Down Moses, The Wild Bunch, Broken Arrow, Gringo Viejo, and Blood Meridian, Canfield discusses novels and films that tell equally compelling stories of the region. Protagonists face various identity crises as they attempt border crossings into other cultures or mindsets—some complete successful crossings, some go native, and some fail. He analyzes figures such as Geronimo, Doc Holliday, and Billy the Kid alongside less familiar mavericks as they struggle for identity, purpose, and justice. J. Douglas Canfield, Regents Professor of English at the University of Arizona, is the author of Tricksters and Estates and Heroes and States, a two-volume cultural history of English Restoration drama. Praiseworthy for its ambitious effort to bring together works written in Spanish and in English, as well as canonical literature, popular literature, and film. —American Literature Locates itself—brilliantly and originally—at the intersection of a geography in the making and a quest for identity, offering the classic Southwest—more an event than a place—as the moral and spiritual region wherein the protagonists attempt a crossing, the shift of identity located in the shifting borderlands. —Armando J. Prats Wise, urbane, persuasive, and comprehensive. . . . Canfield does it all and extremely well. —Choice A fascinating subject and a timely one, dealing as it does with multicultural traditions and with versions of the Western. —John G. Caweltihttps://uknowledge.uky.edu/upk_english_language_and_literature_north_america/1064/thumbnail.jp

Crossing Laterally into Solidarity in Montserrat Fontes\u27s Dreams of the Centaur

Fontes\u27s novel begins with a corrido announcing typical themes of murder and revenge. But the novel has from the outset been interimplicated in a history of the persecution of the Yoeme (Yaquis) at the turn into the twentieth century. Its three main protagonists become mavericks on the border, as they cross ultimately not only into safety in Arizona but into solidarity with the oppressed. Such crossings are existential, resulting in new identities that eschew racial or ethnic purity but instead embrace mixed ethnicity, or mestizaje (to borrow key concepts from Anzaldúa). Such crossings are lateral, non-hierarchic. But Fontes does not allow refuge in some romantic vision: even as one crosses over, one retains one\u27s membership in the group that oppresses. Instead, Fontes\u27s mavericks—and Fontes herself— become tellers of a story too little known, too horrible to be obliterated. United in a kinán of spiritual force, they become potential drops of water that penetrate and soften the land, leaving prints for others to follow

Tricksters and Estates: On the Ideology of Restoration Comedy

If the Renaissance was the Golden Age of English comedy, the Restoration was the Silver. These comedies are full of tricksters attempting to gain estates, the emblem and the reality of power in late feudal England. The tricksters appear in a number of guises, such as heroines landing their men, younger brothers seeking estates, or Cavaliers threatened with dispossession. The hybrid nature of these plays has long posed problems for critics, and few studies have attempted to deal with their diversity in a comprehensive way. Now one of the leading scholars of Restoration drama offers a cultural history of the period’s comedy that puts the plays in perspective and reveals the ideological function they performed in England during the latter half of the seventeenth century. To explain this function, J. Douglas Canfield groups the plays into three categories: social comedy, which underwrites Stuart ideology; subversive comedy, which undercuts it; and comical satire, which challenges it as fundamentally immoral or amoral. Through play-by-play analysis, he demonstrates how most of the comedies support the ideology of the Stuart monarchs and the aristocracy, upholding what they regarded as their natural right to rule because of an innate superiority over all other classes. A significant minority of comedies, however, reveal cracks in class solidarity, portray witty heroines who inhabit the margins of society, or give voice to folk tricksters who embody a democratic force nearly capable of overwhelming class hierarchy. A smaller yet but still significant minority end in no resolution, no restoration, but, at their most radical, playfully portray Stuart ideology as empty rhetoric. Tricksters and Estates is a truly comprehensive work, offering serious critical readings of many plays that have never before received close attention and fresh insights into more familiar works. By juxtaposing the comedies of such lesser-known playwrights as Orrery, Lacy, and Rawlins with those of more familiar figures like Behn, Wycherley, and Dryden, the author invites a greater appreciation than has previously been possible of the meaning and function of Restoration comedy. This intelligent and wide-ranging study promises is a standard work in its field. J. Douglas Canfield, Regents\u27 Professor of English at the University of Arizona, is the author of Word as Bond in English Literature from the Middle Ages to the Restoration and coeditor of Cultural Readings of Restoration and Eighteenth-Century Theater. Canfield’s use of genre, admirably, never seems like pigeonholing. He shows that these plays perform different sorts of cultural work, and his study uses the work each play does to locate it generically. —1650-1850 This ambitious book explores the relationship between Restoration comedy and concepts of power and cultural hegemony in late seventeenth-century England. —Albion A book which displays an incisive grasp of what is really at state in Restoration comic plots and which soundly seeks to overturn the negligence of much of what was popularly performed during the Stuart reign. —British Journal for Eighteenth-Century Studies By not relying on generic and formalist perspectives, Canfield enriches understanding of social, economic, political, and religious currents and countercurrents of cultural history and their presence in drama. A model of interdisciplinary interpretation. —Choice Canfield has produced an important and impressive book, both in depth and in coverage. —Kritikon Litterarum Sharpens the focus with which we view the official comedies. —Modern Philology An excellent survey of the comedy of the period and serves a useful role in reminding us to keep our eyes not only on the money but on who gets the land. —Seventeenth-Century News A Choice Outstanding Academic Bookhttps://uknowledge.uky.edu/upk_english_language_and_literature_british_isles/1067/thumbnail.jp