17 research outputs found
Indication for the coexistence of closed orbit and quantum interferometer with the same cross section in the organic metal (ET)4(H3O)[Fe(C2O4)3].C6H4Cl2: Persistence of SdH oscillations above 30 K
Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) oscillations spectra of
the quasi-two dimensional charge transfer salt
"-(ET)(HO)[Fe(CO)]CHCl have been
investigated in pulsed magnetic fields up to 54 T. The data reveal three basic
frequencies F, F and F, which can be interpreted on the basis
of three compensated closed orbits at low temperature. However a very weak
thermal damping of the Fourier component F, with the highest amplitude, is
evidenced for SdH spectra above about 6 K. As a result, magnetoresistance
oscillations are observed at temperatures higher than 30 K. This feature, which
is not observed for dHvA oscillations, is in line with quantum interference,
pointing to a Fermi surface reconstruction in this compound.Comment: published in Eur. Phys. J. B 71 203 (2009
Advances in single crystal growth and annealing treatment of electron-doped HTSC
High quality electron-doped HTSC single crystals of and have been
successfully grown by the container-free traveling solvent floating zone
technique. The optimally doped and crystals have transition temperatures
of \,K and \,K, respectively, with a transition width of less than
\,K. We found a strong dependence of the optimal growth parameters on the Ce
content . We discuss the optimization of the post-growth annealing treatment
of the samples, the doping extension of the superconducting dome for both
compounds as well as the role of excess oxygen. The absolute oxygen content of
the as-grown crystals is determined from thermogravimetric experiments and is
found to be . This oxygen surplus is nearly completely removed by a
post-growth annealing treatment. The reduction process is reversible as
demonstrated by magnetization measurements. In as-grown samples the excess
oxygen resides on the apical site O(3). This apical oxygen has nearly no doping
effect, but rather influences the evolution of superconductivity by inducing
additional disorder in the CuO layers. The very high crystal quality of
is particularly manifest in magnetic quantum
oscillations observed on several samples at different doping levels. They
provide a unique opportunity of studying the Fermi surface and its dependence
on the carrier concentration in the bulk of the crystals.Comment: 19 pages, 7 figures, submitted to Eur. Phys. J.
Quantum Oscillation Studies of the Fermi Surface of LaFePO
We review recent experimental measurements of the Fermi surface of the
iron-pnictide superconductor LaFePO using quantum oscillation techniques. These
studies show that the Fermi surface topology is close to that predicted by
first principles density functional theory calculations, consisting of
quasi-two-dimensional electron-like and hole-like sheets. The total volume of
the two hole sheets is almost equal to that of the two electron sheets, and the
hole and electron Fermi surface sheets are close to a nesting condition. No
evidence for the predicted three dimensional pocket arising from the Fe
band is found. Measurements of the effective mass suggest a
renormalisation of around two, close to the value for the overall band
renormalisation found in recent angle resolved photoemission measurements.Comment: Submitted to Physica C special issue on iron-pnictide superconductor
The wiedemann-franz law in the putative one-dimensional metallic phase of prba2cu4o8
The nature of the electronic state of a metal depends strongly on its dimensionality. In a system of isolated conducting chains, the Fermi-liquid (quasiparticle) description appropriate for higher dimensions is replaced by the so-called Tomonaga-Luttinger liquid picture characterized by collective excitations of spin and charge. Temperature is often regarded as a viable tuning parameter between states of different dimensionality, but what happens once thermal broadening becomes comparable to the interchain hopping energy remains an unresolved issue, one that is central to many organic and inorganic conductors. Here we use the ratio of the thermal to electrical conductivities to probe the nature of the electronic state in PrBa(2)Cu(4)O(8) as a function of temperature. We find that despite the interchain transport becoming non-metallic, the charge carriers within the CuO chains appear to retain their quasiparticle nature. This implies that temperature alone cannot induce a crossover from Fermi-liquid to Tomonaga-Luttinger-liquid behaviour in quasi-one-dimensional metals
Gross violation of the Wiedemann-Franz law in a quasi-one-dimensional conductor
When charge carriers are spatially confined to one dimension, conventional Fermi-liquid theory breaks down. In such TomonagaâLuttinger liquids, quasiparticles are replaced by distinct collective excitations of spin and charge that propagate independently with different velocities. Although evidence for spinâcharge separation exists, no bulk low-energy probe has yet been able to distinguish successfully between TomonagaâLuttinger and Fermi-liquid physics. Here we show experimentally that the ratio of the thermal and electrical Hall conductivities in the metallic phase of quasi-one-dimensional Li(0.9)Mo(6)O(17) diverges with decreasing temperature, reaching a value five orders of magnitude larger than that found in conventional metals. Both the temperature dependence and magnitude of this ratio are consistent with TomonagaâLuttinger liquid theory. Such a dramatic manifestation of spinâcharge separation in a bulk three-dimensional solid offers a unique opportunity to explore how the fermionic quasiparticle picture recovers, and over what time scale, when coupling to a second or third dimension is restored
Cascade of field-induced magnetic transitions in a frustrated antiferromagnetic metal
Contains fulltext :
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The effect of magnetic ions and disorder on superconducting -(BEDT-TTF)[ (HO)M(CO)] CHNO salts, where M = Ga and Cr
We report magnetotransport measurements
performed in magnetic fields of up to 33Â T and at low temperatures (0.45
KT4.2 K) on two iso-structural superconducting charge-transfer salts,
-(BEDT-TTF)[ (HO)(CO)]
CHNO, where the 3d metal ion is either non-magnetic Ga
or magnetic Cr. Quantum oscillations suggest that the salt with  = Ga
has two two-dimensional Fermi surface pockets (45Â T and 230Â T) whereas when
 = Cr only one pocket (230 T) is observed. Replacing Ga with Cr has the
effect of enhancing the effective mass of the 230Â T pocket from to and reducing the superconducting critical
temperature from   8 K to   5 K.
Key words. organic superconductors-quantum oscillations
Fermiology of new charge-transfer salts, -(BEDT-TTF)[ (HO)M(CO)] solvent where Mâ=âGa, Cr and Fe
We report high-field magnetotransport measurements on
-(BEDT-TTF)[ (HO)M(CO)] , where
M=Ga, Cr and Fe and =CHN. In spite
of their differing transition metal-ions, M, the three compounds exhibit
similar magnetic quantum oscillation spectra superimposed on a positive
magnetoresistance. At least four independent quantum oscillation frequencies
have been identified, corresponding to two different hole and electron pockets
of the Fermi surface which follow the rules of a compensated metal. Observation
of the small pockets could be the result of the Fermi surface reconstruction
induced by a possible density wave. The effective masses are very similar for
different samples and for different pockets range between whereas the Dingle temperatures varies between  K. At low temperature, the longitudinal magnetoresistance violates
Kohler's rule, suggesting that the interlayer transport in these quasi-2D
systems cannot be related to a single scattering time and that the disorder
plays an important role.
Key words. Magnetoresistance-quantum oscillations
Persistent Paramagnons Deep in the Metallic Phase of Sr2-xLaxIrO4
We have studied the magnetic excitations of electron-doped Sr2-xLaxIrO4 (0â€xâ€0.10) using resonant inelastic x-ray scattering at the Ir L3 edge. The long-range magnetic order is rapidly lost with increasing x, but two-dimensional short-range order (SRO) and dispersive magnon excitations with nearly undiminished spectral weight persist well into the metallic part of the phase diagram. The magnons in the SRO phase are heavily damped and exhibit anisotropic softening. Their dispersions are well described by a pseudospin-1/2 Heisenberg model with exchange interactions whose spatial range increases with doping. We also find a doping-independent high-energy magnetic continuum, which is not described by this model. The spin-orbit excitons arising from the pseudospin-3/2 manifold of the Ir ions broaden substantially in the SRO phase, but remain largely separated from the low-energy magnons. Pseudospin-1/2 models are therefore a good starting point for the theoretical description of the low-energy magnetic dynamics of doped iridates. © 2016 American Physical Society119191sciescopu