Discoveries of ratios whose values are constant within broad classes of materials have led to many deep physical insights. The Kadowaki-Woods ratio (KWR) 1,2 compares the temperature dependence of a metals resistivity to that of its heat capacity; thereby probing the relationship between the electronelectron scattering rate and the renormalisation of the electron mass. However, the KWR takes very different values in different materials 3,4 . Here we introduce a ratio, closely related to the KWR, that includes the effects of carrier density and spatial dimensionality and takes the same (predicted) value in organic charge transfer salts, transition metal oxides, heavy fermions and transition metalsdespite the numerator and denominator varying by ten orders of magnitude.Hence, in these materials, the same emergent physics is responsible for the mass enhancement and the quadratic temperature dependence of the resistivity and no exotic explanations of their KWRs are required.In a Fermi liquid the temperature dependence of the electronic contribution to the heat capacity is linear, i.e., C el (T ) = γT . Another prediction of Fermi liquid theory 5 is that, at low temperatures, the resistivity varies as ρ(T ) = ρ 0 + AT 2 . This is observed experimentally when electron-electron scattering, which gives rise to the quadratic term, dominates over electron-phonon scattering.Rice observed 1 that in the transition metals A/γ 2 ≈ a T M = 0.4 µΩ cm mol 2 K 2 /J 2 (Fig. 1), even though γ 2 varies by an order of magnitude across the materials he studied. Later, Kadowaki and Woods 2 found that in many heavy fermion compounds A/γ 2 ≈ a HF = 10 µΩ cm mol 2 K 2 /J 2 (Fig. 1), despite the large mass renormalisation which causes γ 2 to vary by more than two orders of magnitude in these materials. Because of this remarkable

We report density functional theory calculations for Mo 3 S 7 (dmit) 3 . We derive an ab initio tight-binding model from overlaps of Wannier orbitals; finding a layered model with interlayer hopping terms ∼3/4 the size of the in-plane terms. The in-plane Hamiltonian interpolates the kagomé and honeycomb lattices. It supports states localized to dodecahedral rings within the plane, which populate one-dimensional (1D) bands and lead to a quasi-1D spin-one model on a layered honeycomb lattice once interactions are included. Two lines of Dirac cones also cross the Fermi energy.

We offer an explanation for the recently observed pressure-induced magnetic state in the iron-chalcogenide FeSe based on \textit{ab initio} estimates for the pressure evolution of the most important Coulomb interaction parameters. We find that an increase of pressure leads to an overall decrease mostly in the nearest-neighbor Coulomb repulsion, which in turn leads to a reduction of the nematic order and the generation of magnetic stripe order. We treat the concomitant effects of band renormalization and the induced interplay of nematic and magnetic order in a self-consistent way and determine the generic topology of the temperature-pressure phase diagram, and find qualitative agreement with the experimentally determined phase diagram.Comment: 13 pages, 6 fig

Using density functional theory, we determine parameters of tight-binding Hamiltonians for a variety of Fabre charge transfer salts, focusing, in particular, on the effects of temperature and pressure. Besides relying on previously published crystal structures, we experimentally determine two new sets of structures: (TMTTF) 2 SbF 6 at different temperatures and (TMTTF) 2 PF 6 under various hydrostatic pressures. We find that a few trends in the electronic behavior can be connected to the complex phase diagram shown by these materials. Decreasing temperature and increasing pressure cause the systems to become more two dimensional. We analyze the importance of correlations by considering an extended Hubbard model parameterized using Wannier orbital overlaps and show that while charge order is strongly activated by the intersite Coulomb interaction, the magnetic order is only weakly enhanced. Both orders are suppressed when the effective pressure is increased.

We report the in-plane microwave surface impedance of a high-quality single crystal of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br. In the superconducting state, we find three independent signatures of d-wave pairing: (i) a strong, linear temperature dependence of superfluid density; (ii) deep in the superconducting state the quasiparticle scattering rate ∼ T 3 ; and (iii) no BCS coherence peak is observed in the quasiparticle conductivity. Above T c , the Kadowaki-Woods ratio and the temperature dependence of the in-plane conductivity show that the normal state is a Fermi liquid below 23 K, yet resilient quasiparticles dominate the transport up to 50 K. It has been widely argued that the doped Mott insulator describes the essential physics of the cuprates.1 Similarly, the physics of the κ-(ET) 2 X salts (ET is an abbreviation of BEDT-TTF) appears to be connected to the bandwidth-controlled Mott transition.2 Thus, it is essential to identify and understand the important similarities and differences between these two classes of quasi-two-dimensional superconductor. In both the cuprates and the κ-(ET) 2 X salts, the superconducting critical temperature is only two orders of magnitude smaller than the Fermi temperature; in this sense, both are high-temperature superconductors.A broad consensus that the cuprates are d-wave superconductors was quickly reached.3-6 However, the nature of the pairing state of the κ-(ET) 2 X salts has taken longer to understand due to the lack of a "smoking gun" experiment. 7,8 Early on there was clear evidence for singlet pairing. [9][10][11][12] This, and the low symmetry of the organics, limits the pairing symmetry to be either s-wave (A 1g representation of the D 2h point group) or d-wave (B 2g ).13 Early heat capacity experiments suggested s-wave pairing, 14,15 but more recent low-temperature data point to d-wave pairing. 16 Measurements of the NMR relaxation rate support unconventional pairing. [9][10][11][12] Disorder studies show a reduction in T c with increasing scattering 17,18 but, for larger scattering rates, the suppression of T c is less than expected for non-s-wave superconductors.Attempts to locate the nodes expected in a d-wave superconductor have not yet yielded a simple picture. The in-plane thermal conductivity shows a fourfold angular variation with minima at 45• to the crystal axes, 19 whereas when a magnetic field is rotated in the plane both the heat capacity 20 and the millimeter wave absorption 21 have minima when the field is aligned with the crystal axes. At first sight these results seem contradictory, but both experiments are extremely difficult to interpret 22 and a complicated phase diagram could occur as a function of field strength and temperature. 20,22 Nevertheless, as this has not yet been observed, these measurements have not yet settled the pairing symmetry. There have also been attempts to directly image the gap via scanning tunneling microscopy (STM).23 Some care is needed with the interpretation of these experiments as the coherence peaks, the key feature of ...