7,770 research outputs found
Coexistence of Antiferromagnetism and Superconductivity in Electron-doped High-Tc Superconductors
We present magnetotransport evidence for antiferromagnetism in films of the
electron-doped cuprates PrCeCuO. Our results show clear
signature of static antiferromagnetism up to optimal doping x=0.15, with a
quantum phase transition close to x=0.16, and a coexistence of static
antiferromagnetism and superconductivity for 0.12x0.15
Evidence for Antiferromagnetic Order in LaCeCuO from Angular Magnetoresistance Measurements
We investigated the in-plane angular magnetoresistivity (AMR) of -phase LaCeCuO (LCCO) thin films () fabricated by a pulsed laser deposition technique. The in-plane
AMR with shows a twofold symmetry instead of the
fourfold behavior found in other electron-doped cuprates such as PrCeCuO and NdCeCuO. The twofold AMR
disappears above a certain temperature, . The is well above
for ( K), and decreases with increasing doping,
until it is no longer observed above at . This twofold AMR
below is suggested to originate from an antiferromagnetic or spin
density wave order.Comment: to be published in Phys. Rev. B, Vol. 80 (2009
On the resistivity at low temperatures in electron-doped cuprate superconductors
We measured the magnetoresistance as a function of temperature down to 20mK
and magnetic field for a set of underdoped PrCeCuO (x=0.12) thin films with
controlled oxygen content. This allows us to access the edge of the
superconducting dome on the underdoped side. The sheet resistance increases
with increasing oxygen content whereas the superconducting transition
temperature is steadily decreasing down to zero. Upon applying various magnetic
fields to suppress superconductivity we found that the sheet resistance
increases when the temperature is lowered. It saturates at very low
temperatures. These results, along with the magnetoresistance, cannot be
described in the context of zero temperature two dimensional
superconductor-to-insulator transition nor as a simple Kondo effect due to
scattering off spins in the copper-oxide planes. We conjecture that due to the
proximity to an antiferromagnetic phase magnetic droplets are induced. This
results in negative magnetoresistance and in an upturn in the resistivity.Comment: Accepted in Phys. Rev.
Tunneling magnetoresistance in devices based on epitaxial NiMnSb with uniaxial anisotropy
We demonstrate tunnel magnetoresistance (TMR) junctions based on a tri layer
system consisting of an epitaxial NiMnSb, aluminum oxide and CoFe tri layer.
The junctions show a tunnelling magnetoresistance of Delta R/R of 8.7% at room
temperature which increases to 14.7% at 4.2K. The layers show clear separate
switching and a small ferromagnetic coupling. A uniaxial in plane anisotropy in
the NiMnSb layer leads to different switching characteristics depending on the
direction in which the magnetic field is applied, an effect which can be used
for sensor applications.Comment: 8 pages, 3 figures, submitted to Appl. Phys. Let
Origin of the anomalous Hall Effect in overdoped n-type cuprates: current vertex corrections due to antiferromagnetic fluctuations
The anomalous magneto-transport properties in electron doped (n-type)
cuprates were investigated using Hall measurements at THz frequencies. The
complex Hall angle was measured in overdoped PrCeCuO samples (x=0.17 and 0.18) as a continuous function of
temperature above at excitation energies 5.24 and 10.5 meV. The results,
extrapolated to low temperatures, show that inelastic scattering introduces
electron-like contributions to the Hall response. First principle calculations
of the Hall angle that include current vertex corrections (CVC) induced by
electron interactions mediated by magnetic fluctuations in the Hall
conductivity reproduce the temperature, frequency, and doping dependence of the
experimental data. These results show that CVC effects are the source of the
anomalous Hall transport properties in overdoped ntype cuprates.Comment: 5 pages, 3 figure
Bromination of Graphene and Graphite
We present a density functional theory study of low density bromination of
graphene and graphite, finding significantly different behaviour in these two
materials. On graphene we find a new Br2 form where the molecule sits
perpendicular to the graphene sheet with an extremely strong molecular dipole.
The resultant Br+-Br- has an empty pz-orbital located in the graphene
electronic pi-cloud. Bromination opens a small (86meV) band gap and strongly
dopes the graphene. In contrast, in graphite we find Br2 is most stable
parallel to the carbon layers with a slightly weaker associated charge transfer
and no molecular dipole. We identify a minimum stable Br2 concentration in
graphite, finding low density bromination to be endothermic. Graphene may be a
useful substrate for stabilising normally unstable transient molecular states
Ground State and Resonances in the Standard Model of Non-relativistic QED
We prove existence of a ground state and resonances in the standard model of
the non-relativistic quantum electro-dynamics (QED). To this end we introduce a
new canonical transformation of QED Hamiltonians and use the spectral
renormalization group technique with a new choice of Banach spaces.Comment: 50 pages change
Seeing with sound? Exploring different characteristics of a visual-to-auditory sensory substitution device
Sensory substitution devices convert live visual images into auditory signals, for example with a web camera (to record the images), a computer (to perform the conversion) and headphones (to listen to the sounds). In a series of three experiments, the performance of one such device (‘The vOICe’) was assessed under various conditions on blindfolded sighted participants. The main task that we used involved identifying and locating objects placed on a table by holding a webcam (like a flashlight) or wearing it on the head (like a miner’s light). Identifying objects on a table was easier with a hand-held device, but locating the objects was easier with a head-mounted device. Brightness converted into loudness was less effective than the reverse contrast (dark being loud), suggesting that performance under these conditions (natural indoor lighting, novice users) is related more to the properties of the auditory signal (ie the amount of noise in it) than the cross-modal association between loudness and brightness. Individual differences in musical memory (detecting pitch changes in two sequences of notes) was related to the time taken to identify or recognise objects, but individual differences in self-reported vividness of visual imagery did not reliably predict performance across the experiments. In general, the results suggest that the auditory characteristics of the device may be more important for initial learning than visual associations
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