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Register a new userFermi surface properties of the bifunctional organic metal $kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$ near the metal--insulator transition
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We present detailed studies of the high-field magnetoresistance of the layered organic metal $kappa$-(BETS)$_2$-Mn-[N(CN)$_2$]$_3$ under a pressure slightly above the insulator-metal transition. The experimental data are analysed in terms of the Fermi surface properties and compared with the results of first-principles band structure calculations. The calculated size and shape of the inplane Fermi surface are in very good agreement with those derived from Shubnikov-de Haas oscillations as well as the classical angle-dependent magnetoresistance oscillations. A comparison of the experimentally obtained effective cyclotron masses with the calculated band masses reveals electron correlations significantly dependent on the electron momentum. The momentum- or band-dependent mobility is also reflected in the behavior of the classical magnetoresistance anisotropy in a magnetic field parallel to layers. Other characteristics of the conducting system related to interlayer charge transfer and scattering mechanisms are discussed based on the experimental data. Besides the known high-field effects associated with the Fermi surface geometry, new pronounced features have been found in the angle-dependent magnetoresistance, which might be caused by coupling of the metallic charge transport to a magnetic instability in proximity to the metal-insulator phase boundary.
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We present magnetoresistance studies of the quasi-two-dimensional organic conductor $kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, where BETS stands for bis-(ethylene-dithio)-tetra-selena-fulvalene. Under a moderate pressure of 1.4,kbar, required for stabilizing the metallic ground state, Shubnikov - de Haas oscillations, associated with a classical and a magnetic-breakdown cyclotron orbits on the cylindrical Fermi surface, have been found at fields above 10,T. The effective cyclotron masses evaluated from the temperature dependence of the oscillation amplitudes reveal strong renormalization due to many-body interactions. The analysis of the relative strength of the oscillations corresponding to the different orbits and its dependence on magnetic field suggests an enhanced role of electron-electron interactions on flat parts of the Fermi surface.
The organic charge-transfer salt $kappa$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Br is a quasi two-dimensional metal with a half-filled conduction band at ambient conditions. When cooled below $T=80$ K it undergoes a pronounced transition to an insulating phase where the resistivity increases many orders of magnitude. In order to elucidate the nature of this metal-insulator transition we have performed comprehensive transport, dielectric and optical investigations. The findings are compared with other dimerized $kappa$-(BEDT-TTF) salts, in particular the Cl-analogue, where a charge-order transition takes place at $T_{rm CO}=30$ K.
We report the magnetic diffraction pattern and spin wave excitations in (CD$_3$)$_2$ND$_2$[Mn(DCO$_2$)$_3$] measured using elastic and inelastic neutron scattering. The magnetic structure is shown to be a G-type antiferromagnet with moments pointing along the $b$ axis. By comparison with simulations based on linear spin wave theory, we have developed a model for the magnetic interactions in this multiferroic metal-organic framework material. The interactions form a three-dimensional network with antiferromagnetic nearest-neighbour interactions along three directions of $J_1=-0.103(8)$~meV, $J_2=-0.032(8)$~meV and $J_3=-0.035(8)$~meV.
The electronic structure of Me[N(CN)$_2$]$_2$ (Me=Mn, Fe, Co, Ni, Cu) molecular magnets has been investigated using x-ray emission spectroscopy (XES) and x-ray photoelectron spectroscopy (XPS) as well as theoretical density-functional-based methods. Both theory and experiments show that the top of the valence band is dominated by Me 3d bands, while a strong hybridization between C 2p and N 2p states determines the valence band electronic structure away from the top. The 2p contributions from non-equivalent nitrogen sites have been identified using resonant inelastic x-ray scattering spectroscopy with the excitation energy tuned near the N 1s threshold. The binding energy of the Me 3d bands and the hybridization between N 2p and Me 3d states both increase in going across the row from Me = Mn to Me = Cu. Localization of the Cu 3d states also leads to weak screening of Cu 2p and 3s states, which accounts for shifts in the core 2p and 3s spectra of the transition metal atoms. Calculations indicate that the ground-state magnetic ordering, which varies across the series is largely dependent on the occupation of the metal 3d shell and that structural differences in the superexchange pathways for different compounds play a secondary role.
The density of states of the organic superconductor $kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br, measured by scanning tunneling spectroscopy on textit{in-situ} cleaved surfaces, reveals a logarithmic suppression near the Fermi edge persisting above the critical temperature $T_mathrm{c}$. A soft Hubbard gap as predicted by the Anderson-Hubbard model for systems with disorder exactly describes the experimentally observed suppression. The electronic disorder also explains the diminished coherence peaks of the quasiparticle density of states below $T_mathrm{c}$.
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