Conduction States with Vanishing Dimerization in Pt Nanowires on Ge(001) Observed with Scanning Tunneling Microscopy

The low-energy electronic properties of one-dimensional nanowires formed by Pt atoms on Ge(001) are studied with scanning tunneling microscopy down to the millivolt-regime. The chain structure exhibits various dimerized elements at high tunneling bias, indicative of a substrate bonding origin rather than a charge density wave. Unexpectedly, this dimerization becomes vanishingly small when imaging energy windows close to the Fermi level with adequately low tunneling currents. Evenly spaced nanowire atoms emerge which are found to represent conduction states. Implications for the metallicity of the chains are discussed.Comment: 4 pages, 4 figure

Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy

The optical properties of magnetite at room temperature were studied by infrared reflectivity measurements as a function of pressure up to 8 GPa. The optical conductivity spectrum consists of a Drude term, two sharp phonon modes, a far-infrared band at around 600 cm$^{-1}$, and a pronounced mid-infrared absorption band. With increasing pressure both absorption bands shift to lower frequencies and the phonon modes harden in a linear fashion. Based on the shape of the MIR band, the temperature dependence of the dc transport data, and the occurrence of the far-infrared band in the optical conductivity spectrum the polaronic coupling strength in magnetite at room temperature should be classified as intermediate. For the lower-energy phonon mode an abrupt increase of the linear pressure coefficient occurs at around 6 GPa, which could be attributed to minor alterations of the charge distribution among the different Fe sites.Comment: 7 pages, 7 figure

The Nature of a Quartz Pebble Conglomerate Unit as Understood through Large-Scale Mapping and Thin Section Analysis

The Shelburne, New Hampshire 7.5’ quadrangle contains a relatively narrow but distinct quartz pebble conglomerate unit (Srqpc). This unit is located on the western face of Mt. Carlo and is constrained by numerous varying rock units including interbedded gray schist quartzite, granitic pegmatite, micaceous quartzite, biotite granofels, and two mica granite. Conglomerate rocks have complex formations because they contain both clasts and a matrix of two different ages and origins. This Srqpc unit has never been studied in thin sections. Moreover, the analysis of the composition of its clasts and matrix at a microscopic level provides valuable insights into its formational relationship with the surrounding interbedded units and original tectonic deposition. Through large-scale mapping of this area and thin section analysis of numerous rock sites, this study provides new interpretations of the unique marine sedimentary processes required to create a medium grained metasedimentary rock with quartz pebble inclusions. It also sheds light on its constraining relationship to the surrounding interbedded units and the tectonic history of the greater Mahoosuc Range. Although its existence and location were first documented in 1975, this unit has never actually been published in a bedrock map because of its narrow shape and the scale at which those areas were mapped. This study aims to further detail the description of this unit and map its existence onto a 1:500 large-scale map. The large-scale detailed bedrock map comprehensively represents the complicated bedrock variation of the study area and is accompanied by an exposed bedrock outcrop map. Together, these maps give non-mappers a glimpse into the nature and methodology of bedrock mapping by showing what the physical features were and by providing surficial geologic data. Together, the maps of this study improve upon traditional mapping techniques by representing and communicating complex spatial information in a meaningful and accessible manner. Additionally, the large-scale bedrock maps of this study lend insights into the orogeny and formation of this unit, something small-scale maps do not have the resolution to provide

High-energy photoemission on Fe3O4: Small polaron physics and the Verwey transition

We have studied the electronic structure and charge ordering (Verwey) transition of magnetite (Fe3O4) by soft x-ray photoemission. Due to the enhanced probing depth and the use of different surface preparations we are able to distinguish surface and volume effects in the spectra. The pseudogap behavior of the intrinsic spectra and its temperature dependence give evidence for the existence of strongly bound small polarons consistent with both dc and optical conductivity. Together with other recent structural and theoretical results our findings support a picture in which the Verwey transition contains elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb interaction

Temperature-dependent soft x-ray photoemission and absorption studies of charge disproportionation in La1−x_{1-x}Srx_xFeO3_3

We have measured the temperature dependence of the photoemission and x-ray absorption spectra of La$_{1-x}$Sr$_x$FeO$_3$ (LSFO) epitaxial thin films with $x=0.67$, where charge disproportionation ($3{Fe}^{3.67+}\to 2{Fe}^{3+}+ {Fe}^{5+}$) resulting in long-range spin and charge ordering is known to occur below $T_{CD}=190$ K. With decreasing temperature we observed gradual changes of the spectra with spectral weight transfer over a wide energy range of $\sim 5$ eV. Above $T_{CD}$ the intensity at the Fermi level ($E_F$) was relatively high compared to that below $T_{CD}$ but still much lower than that in conventional metals. We also found a similar temperature dependence for $x=0.4$, and to a lesser extent for $x=0.2$. These observations suggest that a local charge disproportionation occurs not only in the $x=0.67$ sample below $T_{CD}$ but also over a wider temperature and composition range in LSFO. This implies that the tendency toward charge disproportionation may be the origin of the unusually wide insulating region of the LSFO phase diagram.Comment: 6 pages, 8 figure

Terahertz Conductivity at the Verwey Transition in Magnetite

The complex conductivity at the (Verwey) metal-insulator transition in Fe_3O_4 has been investigated at THz and infrared frequencies. In the insulating state, both the dynamic conductivity and the dielectric constant reveal a power-law frequency dependence, the characteristic feature of hopping conduction of localized charge carriers. The hopping process is limited to low frequencies only, and a cutoff frequency nu_1 ~ 8 meV must be introduced for a self-consistent description. On heating through the Verwey transition the low-frequency dielectric constant abruptly decreases and becomes negative. Together with the conductivity spectra this indicates a formation of a narrow Drude-peak with a characteristic scattering rate of about 5 meV containing only a small fraction of the available charge carriers. The spectra can be explained assuming the transformation of the spectral weight from the hopping process to the free-carrier conductivity. These results support an interpretation of Verwey transition in magnetite as an insulator-semiconductor transition with structure-induced changes in activation energy.Comment: 6 Pages, 3 Figure

Hidden Amongst the Crowd: Experiences of Students from Underrepresented Religions and Denominations

This research addresses the lived experiences of students from underrepresented religions and denominations at a small Catholic college. There has been increased interest in promoting inclusive practices in higher education around race, ethnicity, gender. An article published in 2012 by Bowman and Smedley, outlines the dissatisfaction of college students from marginalized religions on campuses where they do not identify with the majority religion. This research seeks to expand the research to include religion, particularly at institutions with religious affiliation.Using ethnographic research methods, including participant observations and semi-structured interviews, this research explores student understandings, experiences and practices of religion as well as the institutional involvement, support and perspective religious inclusivity. Adapting an applied framework, this research, seeks make suggestions regarding fostering a more inclusive campus environment

Complex-Orbital Order in Fe_3O_4 and Mechanism of the Verwey Transition

Electronic state and the Verwey transition in magnetite (Fe_3O_4) are studied using a spinless three-band Hubbard model for 3d electrons on the B sites with the Hartree-Fock approximation and the exact diagonalisation method. Complex-orbital, e.g., 1/sqrt(2)[|zx> + i |yz>], ordered (COO) states having noncollinear orbital moments ~ 0.4 mu_B on the B sites are obtained with the cubic lattice structure of the high-temperature phase. The COO state is a novel form of magnetic ordering within the orbital degree of freedom. It arises from the formation of Hund's second rule states of spinless pseudo-d molecular orbitals in the Fe_4 tetrahedral units of the B sites and ferromagnetic alignment of their fictitious orbital moments. A COO state with longer periodicity is obtained with pseudo-orthorhombic Pmca and Pmc2_1 structures for the low-temperature phase. The state spontaneously lowers the crystal symmetry to the monoclinic and explains experimentally observed rhombohedral cell deformation and Jahn-Teller like distortion. From these findings, we consider that at the Verwey transition temperature, the COO state remaining to be short-range order impeded by dynamical lattice distortion in high temperature is developed into that with long-range order coupled with the monoclinic lattice distortion.Comment: 16 pages, 13 figures, 6 tables, accepted for publication in J. Phys. Soc. Jp