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Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid (KSL) state. One of the front-runners is BaCo

The pyrochlore magnet ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ shows a lack of magnetic order to low temperatures and is considered to be a quantum spin liquid candidate. We perform time-domain THz spectroscopy on high-quality ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ crystals and study the low-energy excitations as a function of [111] magnetic field with high energy resolution. The low-energy crystal-field excitations change their energies anomalously under magnetic field. Despite several sharp field-dependent changes, we show that the material's spectrum can be described not by phase transitions but by field-dependent hybridization between the low-energy crystal-field levels. We highlight the strong coupling between spin and lattice degrees of freedom in ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ as evidenced by the magnetic-field tunable crystal-field environment. Calculations based on single ion physics with field-induced symmetry reduction of the crystal-field environment can reproduce our data.

Ferromagnetically interacting Ising spins on the pyrochlore lattice of corner-sharing tetrahedra form a highly degenerate manifold of low-energy states. A spin flip relative to this “spin-ice” manifold can fractionalize into two oppositely charged magnetic monopoles with effective Coulomb interactions. To understand this process, we have probed the low-temperature magnetic response of spin ice to time-varying magnetic fields through stroboscopic neutron scattering and SQUID magnetometry on a new class of ultrapure Ho_2Ti_2O_7 crystals. Covering almost 10 decades of time scales with atomic-scale spatial resolution, the experiments resolve apparent discrepancies between prior measurements on more disordered crystals and reveal a thermal crossover between distinct relaxation processes. Magnetic relaxation at low temperatures is associated with monopole motion through the spin-ice vacuum, while at elevated temperatures, relaxation occurs through reorientation of increasingly spin-like monopolar bound states. Spin fractionalization is thus directly manifest in the relaxation dynamics of spin ice., 論文

The crystal structure of Ba4NbRu3O12 is based on triangular planes of elongated Ru3O12 trimers oriented perpendicular to the plane. We report that it is semiconducting, that its Weiss temperature and effective magnetic moment are -155 K and 2.59 {\mu}B/f.u. respectively, and that magnetic susceptibility and specific heat data indicate that it exhibits magnetic ordering near 4 K. The presence of a high density of low energy states is evidenced by a substantial Sommerfeld-like T-linear term (gamma = 31(2) mJ/mole-K^2) in the specific heat. Electronic structure calculations reveal that the electronic states at the Fermi Energy reside on the Ru3O12 trimers and that the calculated density of electronic states is high and continuous around the Fermi Energy - in other words density functional theory calculates the material to be a metal. Our results imply that Ba4NbRu3O12 is a geometrically frustrated trimer-based Mott insulator., Comment: 25 pages, 10 figures "to be published in Physical Review Materials"

Deliver Us From Evil: The Slavery Question in the Old South, by Lacy K. Ford. New York: Oxford University Press, 2011,673 pp., $24.94, paperback.Deliver Us From Evil is a fine-grained analysis of the distinctive development of elite southern White opinion on the institution of slavery during the period between the drafting of the United States Constitution and the mid-1830s. This is not a history of slavery from 1787 to 1835, but a history of the southern discourse on slavery during that time from the perspective of the elite White southern male (although there are several elite White southern female voices included from time to time, and at least one Black voice). Written by Lacy Ford, a Professor of history at the University of South Carolina, this significant work will substantially influence the understanding of the development of the place of Black Americans in White southern political discourse.The tensions in southern opinions on slavery centered around issues of morality, the control of free and enslaved Blacks, and the economic impact of even the most subtle political decision made about the institution of slavery (although it was starkly apparent that morality was often subsumed in the attempt to balance control and economics) all placed within the context of an emerging Republic based on the principles of liberty and the increasingly unstable geopolitics of slaveholding-from major international insurrections, to forceftd domestic and international voices objecting to the institution, and the waning of the international slave trade. Ford emphasizes that there was not one southern view on slavery in the early Republic, but a broad array of views that changed geographically and over time in response to arguments about the future of slavery; the emancipation, diffusion, or colonization of Black populations; the proper methods for subduing enslaved populations and preventing insurrection; and the rhetorical justifications for slavery. Ford differentiates how the demographics and economics of broad regions-the Upper South and the Lower South-created broad coalitions of interest; how within the Upper South and Lower South the interests of individual states shifted with economic pressures and the need for control of enslaved populations; and how, within individual states, regional needs often created conflicting interests.Ford robustly and subtly treats an impressive number of themes, including the emergence of racial superiority as a justification for the treatment of Blacks, the burden placed on a slaveholder's ability to manumit, the waxing and waning of the interest in colonization, the degree to which free Blacks were allowed to participate in civil society, whether elite Whites viewed religion among the enslaved as a positive or a negative, the interest in expanding slaveholding territories, and, most importantly, the ever-present fear of insurrection that permeated White consciousness. …

Experiments investigated how vernier acuity for dot targets is affected by dot spatial separation and retinal eccentricity. Beck and Schwanz [ Vision Res . 19 , 313–319. 1979] found that the vernier thresholds increased linearly with interdot separation from 7.5 to 30 min arc. Experiment 1 showed that the vernier thresholds increased linearly with interdot separation from 0.5 to 8 deg arc. Experiments 2 and 3 showed that moving the dots into the periphery while keeping the interdot separation constant increased the threshold little if at all. The results are interpreted as supporting the hypothesis that there is (1) an encoding of dot positions in retinal coordinates, and (2) that the relative positions of the dots are made explicit in terms of the slope of the virtual line joining them. The increase in threshold with dot separation indicates that the visual system is unable to directly access and compare the retinal positions of the dots. The constancy of the threshold with eccentricity indicates that the visual system encodes the retinal positions of two well-separated dots as accurately in the periphery as in the fovea.