595 research outputs found
Kondo Lattice without Nozieres Exhaustion Effect
We discuss the properties of layered Anderson/Kondo lattices with metallic
electrons confined in 2D xy planes and local spins in insulating layers forming
chains in z direction. Each spin in this model possesses its own 2D Kondo
cloud, so that the Nozieres' exhaustion problem does not occur. The excitation
spectrum of the model is gapless both in charge and spin sectors. The
disordered phases and possible experimental realizations of the model are
briefly discussed.Comment: 4 pages, 3 figure
Signatures of electron-electron correlations in the optical spectra of -(BEDT-TTF)Hg(SCN) (=NH and Rb)
We interpret the optical spectra of -(BEDT-TTF)Hg(SCN)
(M=NH and Rb) in terms of a 1/4 filled metallic system close to charge
ordering and show that in the conductivity spectra of these compounds a
fraction of the spectral weight is shifted from the Drude-peak to higher
frequencies due to strong electronic correlations. Analyzing the temperature
dependence of the electronic parameters, we distinguish between different
aspects of the influence of electronic correlations on optical properties. We
conclude, that the correlation effects are slightly weaker in the NH
compound compared to the Rb one.Comment: Proceedings ISCOM0
Upper critical field study in the organic superconductor -(ET)SFCHCFSO : Possibility of Fulde-Ferrell-Larkin-Ovchinnikov state
We report upper critical field measurements in the metal-free-all-organic
superconductor -(ET)SFCHCFSO obtained
from measuring the in-plane penetration depth using the tunnel diode oscillator
technique. For magnetic field applied parallel to the conducting planes the low
temperature upper critical fields are found to exceed the Pauli limiting field
calculated by using a semi-empirical method. Furthermore, we found a signature
that could be the phase transition between the superconducting vortex state and
the Fulde-Ferrell-Larkin-Ovchinnikov state in the form of a kink just below the
upper critical field and only at temperatures below 1.23 K.Comment: 4 pages, 6 figure
Test for interlayer coherence in a quasi-two-dimensional superconductor
Peaks in the magnetoresistivity of the layered superconductor
-(BEDT-TTF)Cu(NCS), measured in fields T applied
within the layers, show that the Fermi surface is extended in the interlayer
direction and enable the interlayer transfer integral (
meV) to be deduced. However, the quasiparticle scattering rate is
such that , implying that
-(BEDT-TTF)Cu(NCS) meets the criterion used to identify
interlayer incoherence. The applicability of this criterion to anisotropic
materials is thus shown to be questionable.Comment: 5 pages, 4 figure
Comparison of the Fermi-surface topologies of kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated analogue
We have measured details of the quasi one-dimensional Fermi-surface sections
in the organic superconductor kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated
analogue using angle-dependent millimetre-wave techniques. There are
significant differences in the corrugations of the Fermi surfaces in the
deuterated and undeuterated salts. We suggest that this is important in
understanding the inverse isotope effect, where the superconducting transition
temperature rises on deuteration. The data support models for superconductivity
which invoke electron-electron interactions depending on the topological
properties of the Fermi surface
Electronic properties of correlated metals in the vicinity of a charge order transition: optical spectroscopy of -(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl)
The infrared spectra of the quasi-two-dimensional organic conductors
-(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl) were measured in
the range from 50 to 7000 \cm down to low temperatures in order to explore the
influence of electronic correlations in quarter-filled metals. The
interpretation of electronic spectra was confirmed by measurements of pressure
dependant reflectance of -(BEDT-TTF)KHg(SCN) at T=300 K. The
signatures of charge order fluctuations become more pronounced when going from
the NH salt to Rb and further to Tl compounds. On reducing the temperature,
the metallic character of the optical response in the NH and Rb salts
increases, and the effective mass diminishes. For the Tl compound, clear
signatures of charge order are found albeit the metallic properties still
dominate. From the temperature dependence of the electronic scattering rate the
crossover temperature is estimated below which the coherent charge-carriers
response sets in. The observations are in excellent agreement with recent
theoretical predictions for a quarter-filled metallic system close to charge
order
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