32 research outputs found
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
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
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, 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
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 LaSrFeO
We have measured the temperature dependence of the photoemission and x-ray
absorption spectra of LaSrFeO (LSFO) epitaxial thin films with
, where charge disproportionation () resulting in long-range spin and charge ordering is known to occur
below K. With decreasing temperature we observed gradual changes
of the spectra with spectral weight transfer over a wide energy range of eV. Above the intensity at the Fermi level () was relatively
high compared to that below but still much lower than that in
conventional metals. We also found a similar temperature dependence for
, and to a lesser extent for . These observations suggest that a
local charge disproportionation occurs not only in the sample below
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
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
Development of Diamond Tracking Detectors for High Luminosity Experiments at LHC
During 2006 detectors based on new polycrystalline CVD (pCVD) material were produced as candidates for use in LHC experiments. The first full size diamond pixel module with ATLAS specifications using a cm pCVD sample was characterized in the 2006 CERN test beam. Radiation damage studies performed outside of CERN corroborate the radiation hardness of this material. Radiation hardness studies at CERN using the highest quality diamond were deferred until 2007 due to the PS magnet problem. ATLAS, CMS, ALICE and LHCb are planning to use diamond for their beam conditions monitoring systems. Construction of the BCM system for ATLAS was completed in 2006 and the BCM modules were characterized in 2006 CERN test beams. Similar devices are under construction for the CMS, ALICE and LHCb experiments. Single-crystal CVD (scCVD) samples were produced and made available to RD42 institutes. The first scCVD diamond pixel device was constructed and tested in the 2006 CERN test beams. In this report we present the progress and work done by the RD42 collaboration on the development of CVD diamond material for radiation detectors