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 $\beta$"-(ET)$_4$(H$_3$O)[Fe(C$_2$O$_4$)$_3$]$\cdot$C$_6$H$_4$Cl$_2$ have been investigated in pulsed magnetic fields up to 54 T. The data reveal three basic frequencies F$_a$, F$_b$ and F$_{b - a}$, 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$_b$, 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 $\rm Pr_{2-x}Ce_{x}CuO_{4+\delta}$ and $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ have been successfully grown by the container-free traveling solvent floating zone technique. The optimally doped $\rm Pr_{2-x}Ce_{x}CuO_{4+\delta}$ and $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ crystals have transition temperatures $T_{\rm c}$ of $25$\,K and $23.5$\,K, respectively, with a transition width of less than $1$\,K. We found a strong dependence of the optimal growth parameters on the Ce content $x$. 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 $\ge 4.0$. 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$_{2}$ layers. The very high crystal quality of $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ 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 $d_{z^2}$ 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 Tomonaga–Luttinger liquids, quasiparticles are replaced by distinct collective excitations of spin and charge that propagate independently with different velocities. Although evidence for spin–charge separation exists, no bulk low-energy probe has yet been able to distinguish successfully between Tomonaga–Luttinger 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 Tomonaga–Luttinger liquid theory. Such a dramatic manifestation of spin–charge 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 : 133179.pdf (publisher's version ) (Open Access

The effect of magnetic ions and disorder on superconducting β′′\beta{''}-(BEDT-TTF)4{_4}[ (H3{_3}O)M(C2{_2}O4{_4})3{_3}] ⋅\cdot C6{_6}H5_5NO2{_2} salts, where M = Ga and Cr

We report magnetotransport measurements performed in magnetic fields of up to 33 T and at low temperatures (0.45 K$<$T$<$4.2 K) on two iso-structural superconducting charge-transfer salts, $\beta^{''}$-(BEDT-TTF)$_4$[ (H$_3$O)$M$(C$_2$O$_4$)$_3$] $\cdot$ C$_6$H$_5$NO$_2$, where the 3d metal ion $M$ is either non-magnetic Ga$^{3+}$ or magnetic Cr$^{3+}$. Quantum oscillations suggest that the salt with $M$ = Ga has two two-dimensional Fermi surface pockets (45 T and 230 T) whereas when $M$ = Cr only one pocket (230 T) is observed. Replacing Ga with Cr has the effect of enhancing the effective mass of the 230 T pocket from $1.2 \pm 0.2~m_{e}$ to $2.2 \pm 0.3~m_{e}$ and reducing the superconducting critical temperature from $T_{c}$ $\approx$ 8 K to $T_{c}$ $\approx$ 5 K. Key words. organic superconductors-quantum oscillations

Fermiology of new charge-transfer salts, β′′{\beta''}-(BEDT-TTF)4_4[ (H3_3O)M(C2_2O4_4)3_3] ⋅\cdot solvent where M = Ga, Cr and Fe

We report high-field magnetotransport measurements on $\beta''$-(BEDT-TTF)$_4$[ (H$_3$O)M(C$_2$O$_4$)$_3$] $\cdot$ $solvent$, where M=Ga$^{3+}$, Cr$^{3+}$ and Fe$^{3+}$ and $solvent$=C$_5$H$_5$N. 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 $m_{\rm eff} \approx 0.5-1.1~m_e$ whereas the Dingle temperatures varies between $T_{\rm D} \approx 1.4-4$ 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 (0≤x≤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