We calculate the effective Coulomb interactions between holes in dimers of the organic molecule BEDT-TTF in vacuo. We use density functional theory (DFT) to parameterise Hubbard models for beta and kappa phase organic charge transfer salts. We focus on the intra-dimer Coulomb repulsion, U_d, and the inter-monomer Coulomb repulsion, V_m. We find that U_d = 3.22 \pm 0.09 eV and V_m = 2.71 \pm 0.10 eV for 23 experimental geometries taken from a range of materials in both polymorphs. The quoted error is one standard deviation over the set of conformations studied. We conclude that U_d and V_m are essentially the same for an isolated dimer with the geometries present in all of the compounds studied. We highlight the disagreement between our parameterisation of the Hubbard model and previous results from both DFT and Huckel methods and show that this is caused by the failure of an assumption made in previous calculations (that U_m >> V_m, where U_m is the effective intra-monomer Coulomb repulsion). We discuss the implications of our calculations for theories of the BEDT-TTF salts based on the Hubbard model on the 2D anisotropic triangular lattice and explore the role of conformational disorder in these materials.
Absence of charge order in the dimerized κ-phase BEDT-TTF salts
利用红外振动光谱，我们研究了二聚二维有机盐：量子自旋液体κ-（BEDT-TTF）2 Cu 2（CN）3，反铁磁莫特绝缘体κ-（BEDT-TTF）2 $Cu[N(CN)2]Cl, and the superconductor κ-(BEDT-TTF)2$ Cu[N（CN）2]Br.在冷却至低温时，它们都没有表现出任何电荷沉淀的迹象。在T = 6 K附近没有观察到电荷分布的改变，其中已经报道了自旋液体κ-（BEDT-TTF）2$Cu2（CN）3的低温异常。在该化合物中，面内光学响应和振动耦合是相当各向异性的，表明BEDT-TTF分子在c方向上的倾斜以及它们与阴离子层的耦合在解释电磁性质时必须考虑。
Superconducting Fluctuations and the Reduced Dimensionality of the Organic Superconductor $κ$- (BEDT-TTF)$_{2}$Cu(NCS)$_{2}$ as Observed through Measurements of the de Haas-van Alphen Effect
In the most studied family of organic superconductors kappa-(BEDT-TTF)_2X, the BEDT-TTF molecules that make up the conducting planes are coupled as dimers. For some anions X, an antiferromagnetic insulator is found at low temperatures adjacent to superconductivity. With an average of one hole carrier per dimer, the BEDT-TTF band is effectively 1/2-filled. Numerous theories have suggested that fluctuations of the magnetic order can drive superconducting pairing in these models, even as direct calculations of superconducting pairing in monomer 1/2-filled band models find no superconductivity. He…
Evidence of the superconducting energy gap in the optical spectra of $α_t$-(BEDT-TTF)$_{2}$I$_{3}$
测量有机超导体$α_t$ -（BEDT-TTF）$_{2}$/$_{3}$的远红外面内反射率，直到10 cm $^{-1}$的频率;通过Kramers-Kronig程序获得光学电导率。在超导状态下，能隙在25 cm $^{-1}$处打开，其对应于与中等耦合一致的$2Δ/k_BT_c = 4.4$。即使远低于$T_c=8$ K，$\hbarω<2Δ$仍有相当大的吸收。我们讨论不同的可能性来解释这种行为。
The pressure dependence of electron-phonon coupling in the organic superconductor $κ$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$: A comparison of high pressure infrared reflectivity and Raman scattering experiments
Fermi-surface topology and the effects of intrinsic disorder in a class of charge-transfer salts containing magnetic ions, β''-(BEDT-TTF)_4[(H_3O)M(C_2O_4)_3]Y
We show that the anisotropy of the effective spin model for the dimer Mott insulator phase of $κ$-(BEDT-TTF)$_2X$ salts is dramatically different from that of the underlying tight-binding model. Intra-dimer quantum interference results in a model of coupled spin chains, where frustrated interchain interactions suppress long-range magnetic order. Thus, we argue, the "spin liquid" phase observed in some of these materials is a remnant of the Tomonaga-Luttinger physics of a single chain. This is consistent with previous experiments and resolves some outstanding puzzles. An erratum [Phys. Rev. Let…
The electron paramagnetic resonance study for an organic superconductor $β''$-(BEDT-TTF)$_{4}$[(H$_3$O)Ga(C$_2$O$_4$)$_3$]$\cdot$C$_6$H$_5$NO$_2$ reveals that superconductivity coexists uniformly with the charge ordered state in one material. In the charge ordered state, the interplane spin exchange is gapped, while the in-plane conductivity is not significantly modified. This anisotropic behavior is explained by the exotic charge ordered state, in which molecular-site selective carrier localization coexists with conducting carriers on other molecules. Relationship between superconductivity an…
Cyclotron resonance harmonics in the organic superconductor $β^{\prime\prime}$-(BEDT-TTF)$_2$SF$_5$CH$_2$CF$_2$SO$_3$; observation of a new kind of effective mass renormalization
在准二维有机超导体$β^{\prime\prime}$ -（BEDT-TTF）$_2$ SF $_5$ CH $_2$ CF $_2$ SO $_3$中观察到了回旋共振及其二次和三次谐波。谐波含量是丰富的角度依赖性，并解释在层间翘曲的费米表面引起的回旋共振。与科恩定理不同，但与最近的理论预测一致，从回旋共振测量中推导出的有效质量大于从磁量子振荡中确定的有效质量。
Different superconducting percolation regimes in the layered organic Mott system $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl -- evidence from fluctuation spectroscopy
We theoretically study the competition among different electronic phases in molecular conductors $κ$-(BEDT-TTF)$_2$X. The ground-state properties of a 3/4-filled extended Hubbard model with the $κ$-type geometry are investigated by a variational Monte Carlo method. We find various competing phases: dimer-Mott insulator, polar charge-ordered insulator, 3-fold charge-ordered metal, and superconductivity, whose pairing symmetry is an "extended-$s$+$d_{x^2-y^2}$"-wave type. Our results show that the superconducting phase is stabilized not on the verge of the Mott metal-insulator transition but nea…
Comparison of the normal state properties of $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$ and its deuterated analogue in high magnetic fields and under high hydrostatic pressures
In-plane superfluid density and microwave conductivity of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br: evidence for d-wave pairing and resilient quasiparticles
We report the effect of Dirac cone tilting on interlayer magnetoresistance in α-(BEDT-TTF)$_2$I$_3$, which is a Dirac semimetal under pressure. Fitting of the experimental data by the theoretical formula suggests that the system is close to a type-II Dirac semimetal.
We present the results of precise correlated-electron calculations on the monomer lattices of the organic charge-transfer solids $κ$-(BEDT-TTF)$_2$X for 32 and 64 molecular sites. Our calculations are for band parameters corresponding to X = Cu[N(CN)$_2$]Cl and Cu$_2$(CN)$_3$, which are semiconducting antiferromagnetic and quantum spin liquid, respectively, at ambient pressure. We have performed our calculations for variable electron densities $ρ$ per BEDT-TTF molecule, with $ρ$ ranging from 1 to 2. We find that $d$-wave superconducting pair-pair correlations are enhanced by electron-electron …
We investigated the interlayer magnetoresistance in an organic massless Dirac electron system $α$-(BEDT-TTF)$_2$I$_3$ under pressure. We experimentally demonstrate that the width of the zero mode owing to carrier scattering is much narrower than that of the other Landau levels.
We investigate the spin-orbit coupling (SOC) effects in $α$- and $κ$-phase BEDT-TTF and BEDT-TSF organic salts. Contrary to the assumption that SOC in organics is negligible due to light C, S, H atoms, we show the relevance of such an interaction in a few representative cases. In the weakly correlated regime, SOC manifests primarily in the opening of energy gaps at degenerate band touching points. This effect becomes especially important for Dirac semimetals such as $α$-(ET)$_2$I$_3$. Furthermore, in the magnetic insulating phase, SOC results in additional anisotropic exchange interactions, wh…
