211 research outputs found
Magnetotransport studies of Superconducting PrFeAsTeO
We report a detailed study of the electrical transport properties of single
crystals of PrFeAsTeO, a recently discovered iron-based
superconductor. Resistivity, Hall effect and magnetoresistance are measured in
a broad temperature range revealing the role of electrons as dominant charge
carriers. The significant temperature dependence of the Hall coefficient and
the violation of Kohler's law indicate multiband effects in this compound. The
upper critical field and the magnetic anisotropy are investigated in fields up
to 16 T, applied parallel and perpendicular to the crystallographic c-axis.
Hydrostatic pressure up to 2 GPa linearly increases the critical temperature
and the resistivity residual ratio. A simple two-band model is used to describe
the transport and magnetic properties of PrFeAsTeO. The
model can successfully explain the strongly temperature dependent negative Hall
coefficient and the high magnetic anisotropy assuming that the mobility of
electrons is higher than that of holes
Charged particle display
An optical shutter based on charged particles is presented. The output light
intensity of the proposed device has an intrinsic dependence on the
interparticle spacing between charged particles, which can be controlled by
varying voltages applied to the control electrodes. The interparticle spacing
between charged particles can be varied continuously and this opens up the
possibility of particle based displays with continuous grayscale.Comment: typographic errors corrected in Eqs (37) and (39); published in
Journal of Applied Physics; doi:10.1063/1.317648
Upper critical field, pressure-dependent superconductivity and electronic anisotropy of SmFeAsTeOF
We present a detailed study of the electrical transport properties of a
recently discovered iron-based superconductor:
SmFeAsTeOF. We followed the temperature
dependence of the upper critical field by resistivity measurement of single
crystals in magnetic fields up to 16 T, oriented along the two main
crystallographic directions. This material exhibits a zero-temperature upper
critical field of 90 T and 65 T parallel and perpendicular to the FeAs
planes, respectively. An unprecedented superconducting magnetic anisotropy
is observed near Tc, and it decreases
at lower temperatures as expected in multiband superconductors. Direct
measurement of the electronic anisotropy was performed on microfabricated
samples, showing a value of that raises up to
19 near Tc. Finally, we have studied the pressure and temperature dependence of
the in-plane resistivity. The critical temperature decreases linearly upon
application of hydrostatic pressure (up to 2 GPa) similarly to overdoped
cuprate superconductors. The resistivity shows saturation at high temperatures,
suggesting that the material approaches the Mott-Ioffe-Regel limit for metallic
conduction. Indeed, we have successfully modelled the resistivity in the normal
state with a parallel resistor model that is widely accepted for this state.
All the measured quantities suggest strong pressure dependence of the density
of states
Role of the antisymmetric exchange in quantum spin liquids
The quantum critical state of organic quantum spin liquids (QSL) exhibits large sensitivity even to weak perturbations. For example, the antisymmetric exchange, the Dzyaloshinskii-Moriya (DM) interaction, which is present in all spin systems without inversion symmetry, could result in a phase transition from the quantum critical phase to an antiferromagnetic phase already at moderate magnetic fields. Using the combination of multi-frequency Electron Spin Resonance spectroscopy (ESR) in the 1-500 GHz frequency range and muon spin rotation (mSR), we studied the influence of the DM interaction in two-dimensional and quasi-one-dimensional organic QSL candidates.
In the triangular lattice QSL, k-(ET)2Ag2(CN)3 (J’/J=0.94, J=175 K), our ESR measurements found a static staggered moment of 6×10-3 mB at T=1.5 K and at B=15 T [1]. The magnetic field dependence of the ESR linewidth, which measures the spectral density of the antiferromagnetic fluctuations, proves that this staggered moment stems from the DM interaction (DM0=4 K) in a perfectly crystalline two-dimensional structure. In a new quasi-one-dimensional QSL candidate, (EDT-TTF-CONH2)2+BABCO-, which is a weak Mott insulator with a distorted triangular lattice (J’/J=3, J=360 K), our combined ESR and mSR study confirmed the absence of magnetic ordering down to 20 mK [2]. This remarkable observation is partially attributed to a unique structural motif of the (EDT-TTF-CONH2)2+BABCO- salt. Here, the (EDT-TTF-CONH2)2+ conducting layers are separated by the highly disordered BABCO- molecular rotors. Importantly, despite the presence of a sizable DM interaction (DM0=0.6 K), the staggered moment is smaller than 4×10-4 mB at T=1.5 K and B=15 T. The magnetic field dependence of the ESR linewidth does not show the effect of the DM interaction. Instead, the linear dependence is indicative of the presence of fast spin fluctuations, which is supported by longitudinal-field mSR measurements that reveal the spin excitations to possess one-dimensional diffusive character. The quenching of the effect of the DM interaction is explained by the strong disorder introduced by the anion layer.
Despite the fact that the magnitude of the DM interaction is 2 to 3 orders of magnitude weaker than the symmetric exchange, it can substantially alter the phase diagram of QSLs. Our work gives a novel explanation to the field-induced phase transitions, and it demonstrates that high-frequency ESR is a powerful technique to study the spin dynamics of QSLs
Insulating charge density wave for a half-filled SU(N) Hubbard model with an attractive on-site interaction in one dimension
We study a one-dimensional SU(N) Hubbard model with an attractive on-site
interaction and at half-filling on the bipartite lattice using
density-matrix renormalization-group method and a perturbation theory. We find
that the ground state of the SU(N) Hubbard model is a charge density wave state
with two-fold degeneracy. All the excitations are found to be gapful, resulting
in an insulating ground state, on contrary to that in the SU(2) case. Moreover,
the charge gap is equal to the Cooperon gap, which behaves as
in the strong coupling regime. However, the spin gap and the
quasiparticle gap as well open exponentially in the weak coupling
region, while in the strong coupling region, they linearly depend on such
that and .Comment: 7 pages, 7 figure
Properties of excitations in systems with a spinor Bose-Einstein condensate
General theory in case of homogenous Bose-Einstein condensed systems with
spinor condensate is presented for the correlation functions of density and
spin fluctuations and for the one-particle propagators as well. The random
phase approximation is investigated and the damping of the modes is given in
the intermediate temperature region. It is shown that the collective and the
one-particle excitation spectra do not coincide fully.Comment: 5 pages, 1 figur
Energies and damping rates of elementary excitations in spin-1 Bose-Einstein condensed gases
Finite temperature Green's function technique is used to calculate the
energies and damping rates of elementary excitations of the homogeneous,
dilute, spin-1 Bose gases below the Bose-Einstein condensation temperature both
in the density and spin channels. For this purpose the self-consistent
dynamical Hartree-Fock model is formulated, which takes into account the direct
and exchange processes on equal footing by summing up certain classes of
Feynman diagrams. The model is shown to fulfil the Goldstone theorem and to
exhibit the hybridization of one-particle and collective excitations correctly.
The results are applied to the gases of ^{23}Na and ^{87}Rb atoms.Comment: 26 pages, 21 figures. Added 2 new figures, detailed discussio
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