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Register a new userRole of Interchain Hopping in the Magnetic Susceptibility of Quasi-One-Dimensional Electron Systems
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The role of interchain hopping in quasi-one-dimensional (Q-1D) electron systems is investigated by extending the Kadanoff-Wilson renormalization group of one-dimensional (1D) systems to Q-1D systems. This scheme is applied to the extended Hubbard model to calculate the temperature ($T$) dependence of the magnetic susceptibility, $chi (T)$. The calculation is performed by taking into account not only the logarithmic Cooper and Peierls channels, but also the non-logarithmic Landau and finite momentum Cooper channels, which give relevant contributions to the uniform response at finite temperatures. It is shown that the interchain hopping, $t_perp$, reduces $chi (T)$ at low temperatures, while it enhances $chi(T)$ at high temperatures. This notable $t_perp$ dependence is ascribed to the fact that $t_perp$ enhances the antiferromagnetic spin fluctuation at low temperatures, while it suppresses the 1D fluctuation at high temperatures. The result is at variance with the random-phase-approximation approach, which predicts an enhancement of $chi (T)$ by $t_perp$ over the whole temperature range. The influence of both the long-range repulsion and the nesting deviations on $chi (T)$ is further investigated. We discuss the present results in connection with the data of $chi (T)$ in the (TMTTF)$_2X$ and (TMTSF)$_2X$ series of Q-1D organic conductors, and propose a theoretical prediction for the effect of pressure on magnetic susceptibility.
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We suggest a theory of internal coherent tunneling in the pseudogap region, when the applied voltage U is below the free electron gap 2Delta_0. We address quasi 1D systems, where the gap is originated by spontaneous lattice distortions of the Incommensurate Charge Density Wave (ICDW) type. Results can be adjusted also to quasi-1D superconductors. The instanton approach allows to calculate the interchain tunneling current both in single electron (amplitude solitons, i.e. spinons) and bi-electron (phase slips) channels. Transition rates are governed by a dissipative dynamics originated by emission of gapless phase excitations in the course of the instanton process. We find that the single-electron tunneling is allowed below the nominal gap 2Delta_0 down to the true pair-breaking threshold at 2W_as<2Delta, where W_as=2Delta/pi is the amplitude soliton energy. Most importantly, the bi-electronic tunneling stretches down to U=0 (in the 1D regime). In both cases, the threshold behavior is given by power laws J (U-U_c)^beta, where the exponent beta v_F/u is large as the ratio of the Fermi velocity v_F and the phase one u. In the 2D or 3D ordered phases, at temperature T<T_c, the one-electron tunneling current does not vanish at the threshold U_c anymore, but saturates above it at U-U_c T_c<<Delta. Also the bi-particle channel acquires a finite threshold U_c=W_ph T_c<<Delta at the energy W_ph of the 2pi phase soliton.
The temperature dependence of the magnetic susceptibility, chi (T), is investigated for one-dimensional interacting electron systems at quarter-filling within the Kadanoff-Wilson renormalization-group method. The forward scattering on the same branch (the g_4-process) is examined together with the backward (g_1) and forward (g_2) scattering amplitudes on opposite branches. In connection with lattice models, we show that chi (T) is strongly enhanced by the nearest-neighbor interaction, an enhancement that surpasses one of the next-nearest-neighbor interaction. A connection between our predictions for chi (T) and experimental results for chi (T) in quasi-one-dimensional organic conductors is presented.
High resolution resonant inelastic x-ray scattering has been performed to reveal the role of lattice-coupling in a family of quasi-1D insulating cuprates, Ca$_{2+5x}$Y$_{2-5x}$Cu$_5$O$_{10}$. Site-dependent low energy excitations arising from progressive emissions of a 70 meV lattice vibrational mode are resolved for the first time, providing a direct measurement of electron-lattice coupling strength. We show that such electron-lattice coupling causes doping-dependent distortions of the Cu-O-Cu bond angle, which sets the intra-chain spin exchange interactions. Our results indicate that the lattice degrees of freedom are fully integrated into the electronic behavior in low dimensional systems.
We study a question of presence of Kohn points, yielding at low temperatures non-analytic momentum dependence of magnetic susceptibility near its maximum, in electronic spectum of some three-dimensional systems. In particular, we consider one-band model on face centered cubic lattice with hopping between nearest and next-nearest neighbors, which models some aspects of the dispersion of ZrZn$_2$, and the two-band model on body centered cubic lattice, modeling the dispersion of chromium. For the former model it is shown that Kohn points yielding maxima of susceptibility exist in a certain (sufficiently wide) region of electronic concentrations; the dependence of the wave vectors, corresponding to the maxima, on the chemical potential is investigated. For the two-band model we show existence of the lines of Kohn points, yielding maximum of the susceptibility, which position agrees with the results of band structure calculations and experimental data on the wave vector of antiferromagnetism of chromium.
The dynamical properties of free and bound domain-wall excitations in Ising-chain materials have recently become the focus of intense research interest. New materials and spectrometers have made it possible to control the environment of coupled Ising chains by both effective internal and applied external fields, which can be both longitudinal and transverse, and thus to demonstrate how the resulting magnetic phase transitions and the nature of the associated excited states obey fundamental symmetry properties. In RbCoCl$_3$, the weakly coupled Ising chains form a triangular lattice whose frustrated geometry and magnetic ordering transitions at low temperature open new possibilities for the Ising-chain environment. We have investigated the structure and magnetism in RbCoCl$_3$ by high-resolution x-ray diffraction and neutron scattering measurements on powder and single crystal samples between 1.5 K and 300 K. Upon cooling, the Co$^{2+}$ spins develop one-dimensional antiferromagnetic correlations along the chain axis ($c$-axis) below 90 K. Below the first Neel temperature, $T_{N1}$ = 28 K, a partial 3D magnetic order sets in, with propagation vector ${vec k}_1$ = (1/3,1/3,1), the moments aligned along the $c$-axis and every third chain uncorrelated from its neighbours. Only below a second magnetic phase transition at $T_{N2}$ = 13 K does the system achieve a fully ordered state, with two additional propagation vectors: ${vec k}_2$ = (0,0,1) establishes a honeycomb $c$-axis order, in which 1/3 of the chains are subject to a strong effective mean field due to their neighbours whereas 2/3 experience no net field, while ${vec k}_3$ = (1/2,0,1) governs a small, staggered in-plane ordered moment. We conclude that RbCoCl$_3$ is an excellent material to study the physics of Ising chains in a wide variety of temperature-controlled environments.
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