In order to investigate charge ordering phenomena under electric field, static nonequilibrium Hartree approximation (SNHA) method is formulated on the basis of the nonequilibrium Green's functions introduced by Keldysh. By applying the SNHA to the 3/4-filling extended Hubbard model on anisotropic triangular lattice, we study the stabilities and amplitudes of 3-fold and horizontal charge orders in $θ$ and $θ_d$-(BEDT-TTF)$_2X$ salts under the electric field. The obtained results show that the electric field stabilizes the 3-fold state in comparison to the horizontal state. The amplitude of the 3-fold state tends to decrease by the field, whereas that of the horizontal state does not change.
Even though organic conductors have complicated crystalline structure with low symmetry and large unit cell, band structure calculations predict multiband quasi-two dimensional electronic structure yielding very simple Fermi surface in most cases. Although few puzzling experimental results are observed, data of numerous compounds are in agreement with calculations which make them suitable systems for studying magnetic quantum oscillations in networks of orbits connected by magnetic breakdown. The state of the art of this problematics is reviewed.
On the basis of an analysis of a 3/4-filled two-dimensional (2D) extended Hubbard model under the fluctuation-exchange approximation, we find Coulomb frustrated phase separation (PS) in a region of nonzero temperature, where the quantum critical phenomenon of charge ordering (CO) dominates. In quasi-2D organic conductors on the verge of CO, this frustrated PS provides a mechanism for generating spatial inhomogeneity, which is characterized by an extremely slow relaxation and an intermediate length scale.
Although the topological phases are difficult to be realized in organic molecular crystals, we demonstrate here that they can emerge in the τ-type organic layered conductors, τ-(EDO-S,S-DMEDT-TTF)_2X_{1+y} and τ-(P-S,S-DMEDT-TTF)_2X_{1+y} (X=AuBr_2, I_3, IBr_2), where EDO-S,S-DMEDT-TTF and P-S,S-DMEDT-TTF denote the planar donor molecules ethylenedioxy-S,S-dimethyl(ethylenedithio)tetrathiafulvalene and pyrazino-S,S-dimethyl(ethylenedithio)tetrathiafulvalene, respectively. The conducting layers of these conductors have a highly symmetric checkerboard structure, which can be regarded as a modifi…
Measurements and calculations of magnetotransport in the molecular organic conductor (DMET)2I3 detect and simulate all known angular magnetoresistance oscillation (AMRO) phenomena for quasi-one dimensional (Q1D) systems. Employing the true triclinic crystal structure in the calculations, these results address the mystery of the putative vanishing of the primary AMRO phenomenon, the Lebed magic angle effect, for orientations in which it was expected to be strongest. They also show a common origin for Lebed and so-called "LN" oscillations, and confirm the generalized nature of AMRO in Q1D system…
We investigate the metallic transport in the organic superconductor (TMTSF)2PF6 under pressure within the framework of the spin density wave theory in the proximity of a Peierls quantum critical point (QCP). We use a simple transport model of hot and cold regions around the Fermi surface, driven by the proximity to the QCP in order to provide a template to fit the experimental results. Successful agreement with the data comforts the interpretation of extended criticality around the antiferromagnetic QCP in the normal phase of quasi one-dimensional organic superconductors.
Comparison of experimental data and theoretical calculations for electrical resistivity and Hall coefficient in quasi-one-dimensional organic conductor (TMTSF)2PF6
最近由Moser等人测量的霍尔系数和电阻率的温度依赖性。84，2674（2000）]中的准一维有机导体（TMTSF）2 PF 6的计算结果与我们以前的理论计算[Synth. Met. 103，2202（1999）; Eur. J. B 11，385（1999）]。我们发现一个很好的协议，虽然不是一个完全一致的参数集的两个数量，没有呼吁Luttinger液体的概念。
Anomalous temperature dependence of the single-particle spectrum in the organic conductor TTF-TCNQ
有机导体TTF-TCNQ的角分辨光电子能谱在60 K <T<260 K的宽能量范围内表现出不寻常的光谱权重转移。为了研究这一发现的起源，在这里，我们报告的单粒子谱权A（k，ω）的一维（1D）哈伯德模型的数值结果，此外，为1D扩展哈伯德和1D哈伯德-荷尔斯泰因模型。与光电发射数据的比较表明，一维哈伯德模型是不足以解释不寻常的T依赖性，和库仑排斥的长程部分也需要包括在内。
Shubnikov-de Haas and angular dependent magnetoresistance oscillations have been used to explore the role of anion size, magnetic moment, and disorder in the organic conductors kappa-(BETS)_2GaBr_{4} and kappa-(BETS)_2FeCl_{2}_Br_{2} in the isomorphic class kappa-(BETS)_2Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}. The results, combined with previous work, show correlations between the anion composition (Ga_{1-x}Fe_{x}Cl_{4-y}_Br_{y}) and the superconducting transition temperature, effective mass, Fermi surface topology, and the mean free path.
We have demonstrated transient charge localization effects with a driving high-frequency field of 7-fs, 1.5-cycle near infrared light in correlated organic conductors. In a layered organic conductor alpha-(BEDT-TTF)2I3 (BEDT-TTF: bis[ethylenedithio]-tetrathiafulvalene), a transient short-range charge order (CO) state is induced in a metallic phase. In contrast to such drastic change in the electronic state from the metal to the transient CO in alpha-(BEDT-TTF)2I3, dynamics of a field-induced reduction of a transfer integral are captured as a red shift of the plasma-like reflectivity edge in a …
We theoretically discuss the mechanism for the peculiar nonlinear conduction in quasi-two-dimensional organic conductors θ-(BEDT-TTF)2X [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] through the melting of stripe-type charge order. An extended Peierls-Hubbard model attached to metallic electrodes is investigated by a nonequilibrium Green's function technique. A novel current-voltage characteristic appears in a coexistent state of stripe-type and nonstripe 3-fold charge orders, where the applied bias melts mainly the stripe-type charge order through the reduction of lattice distortion, wherea…
To verify the effect of geometrical frustration, we artificially distort the triangular lattice of quasi-two-dimensional organic conductor $κ$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ [BEDT-TTF: bis(ethylenedithio)terathiofulvalene] by analogous-molecular substitution and apply $^{13}$C NMR of bulk and substituted sites, electric conductivity, and static magnetic susceptibility measurements. The results indicate that the magnetic characteristics of the substituted sample are quantitatively similar to those of the pure sample. Moreover the magnetic characteristics at the substituted sites are also the same…
A complex study of magnetic properties including dc magnetization, 1H NMR and magnetic torque measurements has been performed for the organic conductor kappa-(BETS)2Mn[N(CN)2]3 which undergoes a metal-insulator transition at T_MI~25K. NMR and the magnetization data indicate a transition in the manganese subsystem from paramagnetic to a frozen state at T_MI, which is, however, not a simple Neel type order. Further, a magnetic field induced transition resembling a spin flop has been detected in the torque measurements at temperatures below T_MI. This transition is most likely related to the spin…
An inductive method is used to follow the magnetic field-dependent susceptibility of the coupled charge density wave (CDW) and spin-Peierls (SP) ordered state behavior in the dual chain organic conductor Perylene$_2$[Pt(mnt)$_2$]. In addition to the coexisting SP-CDW state phase below 8 K and 20 T, the measurements show that a second spin-gapped phase appears above 20 T that coincides with a field-induced insulating phase. The results support a strong coupling of the CDW and SP order parameters even in high magnetic fields, and provide new insight into the nature of the magnetic susceptibility…
We study the continuous bandwidth-controlled Mott transition in the two-dimensional single-band Hubbard model with a focus on the critical scaling behavior of charge and spin degrees of freedom. Using plaquette cluster dynamical mean-field theory, we find charge and spin criticality consistent with experimental results for organic conductors. In particular, the charge degree of freedom measured via the local density of states at the Fermi level shows a smoother transition than expected for the Ising universality class and in single-site dynamical mean-field theory, revealing the importance of …
Superconductivity of quasi-one-dimensional organic conductors with a quarter-filled band is investigated using the two-loop renormalization group approach to the extended Hubbard model for which both the single electron hopping t_{\perp} and the repulsive interaction V_{\perp} perpendicular to the chains are included. For a four-patches Fermi surface with deviations to perfect nesting, we calculate the response functions for the dominant fluctuations and possible superconducting states. By increasing V_{\perp}, it is shown that a d-wave (singlet) to f-wave (triplet) superconducting state cross…
Angle dependent magnetoresistance experiments on organic conductors exhibit a wide range of angular oscillations associated with the dimensionality and symmetry of the crystal structure and electron energy dispersion. In particular, characteristics associated with 1, 2, and 3 dimensional electronic motion are separately revealed when a sample is rotated through different crystal planes in a magnetic field. Originally discovered in the TMTSF based conductors, these effects are particularly pronounced in the related system (DMET)2I3. Here, experimental and computational results for magnetoresist…
The quasi-two-dimensional organic semiconductor α-(BEDT-TTF)2I3 [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] has an anisotropic linear dispersion with a zero energy gap near the Fermi level. Owing to the vanishing density of states at the Fermi level, the Coulomb interaction is unscreened in this material. We theoretically study the effect of the long-range Coulomb interaction and the low-energy/long-wavelength behavior of α-(BEDT-TTF)2I3 using the renormalization group analysis. The nearly logarithmic enhancement of the velocity reshapes tilted Dirac cones, and changes the low-temperature…
Phase-change memory (PCM), a promising candidate for next-generation non-volatile memories, exploits quenched glassy and thermodynamically stable crystalline states as reversibly switchable state variables. We demonstrate PCM functions emerging from a charge-configuration degree of freedom in strongly correlated electron systems. Non-volatile reversible switching between a high-resistivity charge-crystalline (or charge-ordered) state and a low-resistivity quenched state, charge glass, is achieved experimentally via heat pulses supplied by optical or electrical means in organic conductors $θ$-(…
Role of Interlayer Electron Hopping for Spin Density Wave State in the Zero-Gap Organic Conductor
研究了准二维有机导体$α$ -（BEDT-TTF）$_2$ I $_3$盐在静水压力下零能隙态（ZGS）密度波的形成. ZGS的导带和价带在二维波矢处都呈现锥形色散，相互简并，$\pm\mib{k}_0$形成零带隙。通过使用扩展的哈伯德模型与排斥相互作用，我们计算的自旋密度波（SDW）的起始温度作为层间电子跳跃的函数，这本身并不打破锥状色散。结果表明，波数为$2\mib{k}_0$的SDW是由相互作用、带间激发和层间跃迁共同作用的结果。
We theoretically investigate charge order and nonlinear conduction in a quasi-two-dimensional organic conductor β-(meso-DMBEDT-TTF)2PF6 [DMBEDT-TTF=dimethylbis(ethylenedithio)tetrathiafulvalene]. Within the Hartree-Fock approximation, we study effects of structural distortion on the experimentally observed checkerboard charge order and its bias-induced melting by using an extended Hubbard model with Peierls- and Holstein-types of electron-lattice interactions. The structural distortion is important in realizing the charge order. The current-voltage characteristics obtained by a nonequilibrium …
Magnetic properties of the conduction pi-electron system of kappa-BETS)2Mn[N(CN)2]3 have been probed using 13C NMR. At ambient pressure, the metal-insulator transition observed in the resistivity measurements below T~23K is shown to be accompanied by ordering of the pi-spins in a long-range staggered structure. As the metal-insulator transition is suppressed by applying a small pressure of ~0.5 kbar, the pi-spin system maintains the properties of the metallic state down to 5K.
Interchain conductivity of coupled Luttinger liquids and organic conductors
我们重新考虑准一维系统中直流和交流链间电导率的理论。我们的计算结果与（TMTSF）_2{ClO}_4的c轴电导率的测量结果符合得很好，并表明（TMTSF）_2{PF}_6在150 K < T <300 Kd $范围内的c轴直流电导率主要是由Mott局域化的先驱效应所决定的。在动力学平均场论中，还讨论了从高能量的Luttinger液体到低能量的Fermi液体的交叉。链间电阻率和德鲁德重量的费米液体制度的影响进行了讨论。
A $^{13}$C NMR study of the normal and superconducting states of the all-organic charge-transfer salt $β"$-(BEDT-TTF)$_2$SF$_5$CH$_2$CF$_2$SO$_3$ is presented. We find that the normal state is a charge-ordered metal configured as vertical stripes, produced by a combination of 1/4-filling, correlations, and a polar counterion sublattice. The NMR properties associated with the superconducting state are consistent with gap nodes and singlet pairing, and therefore similar to other organic superconductors. Quite distinct, however, is the absence of evidence for low-energy antiferromagnetic spin flu…
The organic charge-transfer salt $κ$-(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 $κ$-(BEDT-TTF) salts, in particular the Cl-analogue, where a charge-order transition takes place a…
Dynamical localization, i.e., reduction of the intersite electronic transfer integral t by an alternating electric field, E(omega) , is a promising strategy for controlling strongly correlated systems with a competing energy balance between t and the Coulomb repulsion energy. Here we describe a charge localization induced by the 9.3 MV/cm instantaneous electric field of a 1.5 cycle (7 fs) infrared pulse in an organic conductor alpha-(bis[ethylenedithio]-tetrathiafulvelene)_2I_3. A large reflectivity change of > 25% and a coherent charge oscillation along the time axis reflect the opening of th…
We present a systematic investigation of the low-frequency charge carrier dynamics in different charge states of the organic conductors $θ$-(BEDT-TTF)$_2$$M$Zn(SCN)$_4$ with $M$=Rb,Tl, which result from quenching or relaxing the charge degrees of freedom on a geometrically frustrated triangular lattice. Due to strong electronic correlations these materials exhibit a charge-ordering transition, which can be kinetically avoided by rapid cooling resulting in a so-called charge-glass state without long-range order. The combination of fluctuation spectroscopy and a heat pulse method allows us to st…
The effects of electron correlation in the quasi-two-dimensional organic conductor α-(BEDT-TTF)2I3 are investigated theoretically by using an extended Hubbard model with on-site and nearest-neighbor Coulomb interactions. A variational Monte Carlo method is applied to study its ground-state properties. We show that there appears a nonmagnetic horizontal-stripe charge order in which nearest-neighbor correlation functions indicate a tendency toward a spin-singlet formation on the bonds with large transfer integrals along the charge-rich stripe. Under uniaxial pressure, a first-order transition fr…
