626 research outputs found
Electronic Transport Properties of Pentacene Single Crystals upon Exposure to Air
We report the effect of air exposure on the electronic properties of
pentacene single crystals. Air can diffuse reversibly in and out of the
crystals and controls the physical properties. We discern two competing
mechanisms that modulate the electronic transport. The presence of oxygen
increases the hole conduction, as in dark four O2 molecules introduce one
charge carrier. This effect is enhanced by the presence of visible light.
Contrarily, water, present in ambient air, is incorporated in the crystal
lattice and forms trapping sites for injected charges.Comment: 16 pages, 3 figure
Inversion symmetry in the spin-Peierls compound NaV2O5
At room-temperature NaV2O5 was found to have the centrosymmetric space group
Pmmn. This space group implies the presence of only one kind of V site in
contrast with previous reports of the non-centrosymmetric counterpart P21mn.
This indicates a non-integer valence state of vanadium.
Furthermore, this symmetry has consequences for the interpretation of the
transition at 34 K, which was ascribed to a spin-Peierls transition of one
dimensional chains of V4+.Comment: Revtex, 3 pages, 2 postscript pictures embedded in the text.
Corrected a mistake in one pictur
Evidence for differentiation in the iron-helicoidal-chain in GdFe(BO)
We report on a single-crystal X-ray structure study of
at room temperature and at T=90 K. At room temperature
crystallizes in a trigonal space group R32 (No. 155), the same as found for
other members of iron-borate family . At 90 K the
structure of has transformed to the space group
(No. 152). The low-temperature structure determination gives new
insight into the weakly first-order structural phase transition at 156 K and
into the related Raman phonon anomalies. The discovery of two inequivalent iron
chains in the low temperature structure provide new point of view on the
low-temperature magnetic properties.Comment: Subm. to Acta Cryst.
Inducing ferromagnetism and Kondo effect in platinum by paramagnetic ionic gating
Electrically controllable magnetism, which requires the field-effect
manipulation of both charge and spin degrees of freedom, has attracted growing
interests since the emergence of spintronics. In this work, we report the
reversible electrical switching of ferromagnetic (FM) states in platinum (Pt)
thin films by introducing paramagnetic ionic liquid (PIL) as the gating media.
The paramagnetic ionic gating controls the movement of ions with magnetic
moments, which induces itinerant ferromagnetism on the surface of Pt films with
large coercivity and perpendicular anisotropy mimicking the ideal
two-dimensional Ising-type FM state. The electrical transport of the induced FM
state shows Kondo effect at low temperature suggesting spatially separated
coexistence of Kondo scattering beneath the FM interface. The tunable FM state
indicates that paramagnetic ionic gating could serve as a versatile method to
induce rich transport phenomena combining field effect and magnetism at
PIL-gated interfaces.Comment: 17 pages, 4 figure
Electron-Phonon Interactions in C-derived Molecular Solids
We present {\it ab initio} density-functional calculations of molecular
solids formed from C-derived closed-shell fullerenes. Solid
CH is found to bind weakly and exhibits many of the electronic
structure features of solid C with an enhanced electron-phonon
interaction potential. We show that chemical doping of this structure is
feasible, albeit more restrictive than its C counterpart, with an
estimated superconducting transition temperature exceeding those of the
alkali-doped C solids.Comment: Lower quality postscript file for Figure 1 is used in the manuscript
in order to meet submission quota for pre-print server. Higher quality
postscript file available from author: [email protected] This article has
been updated to reflect changes incorporated during the peer review process.
It is published in PRB 70, 140504(R) 200
Ferroelectric displacements in multiferroic Y(Mn,Ga)O-3
We have studied the effects of substitution of Mn3+ by Ga3+ on the crystal structure of YMnO3. Y(Mn,Ga)O-3 is a magnetoferroelectric in which the ferroelectric displacements from the YO7 polyhedra are associated with buckling and tilting of the MnO5 bipyramids. The differences in ionic radius and orbital occupation between Mn3+ and Ga3+ result in an increase of the c/a lattice parameter ratio. This dilation is not associated with the displacements of MnO5 bipyramids, but with the elongation of the YO6 antiprisms. The magnitude of the local YO6 dipoles decrease with Ga substitution
- …