One-dimensional Correlated Electron Systems Research Articles

Frustration-driven singlet superconductivity in the one-dimensional [formula omitted] model with positive interactions

Motivated by the discovery of iron-based superconductors, we analytically investigate the one-dimensional correlated electron system described by the t−U−J1−J2 model at weak coupling and at half filling. The low-energy field theory analysis combining the bosonization and renormalization-group scenario helps us to derive the quantum phase diagram, which includes a spin density wave phase, a bond order wave phase and a superconducting phase characterized by the coexistence of singlet superconductivity and charge density wave instabilities. The frustration J2 accounts for the realization of the superconductivity in the regime of positive interactions.

Evolution of dimerized phase in a one-dimensional correlated electron system

The one-dimensional half-filled correlated electron system with on-site (U), nearest-neighbor (V) and pair hopping (Y) repulsions is studied analytically at weak coupling, combined the Abelian bosonization with renormalization group methods. The corresponding ground-state phase diagram consists of three insulating phases, a charge-density-wave (CDW) phase for U − 2V 2Y, and a bond-charge-density-wave (BOW) phase for | U − 2V | < 2Y. The pair hopping, which breaks an accident symmetry and splits the frustrating line U − 2V = 0, provides a possibility for the dimerized BOW phase between the CDW and SDW phases. In the phenomenological parameter regime, the superconducting (SC) and bond-spin-density-wave (BSDW) phases are briefly discussed.

Persistent current and Drude weight for the one-dimensional Hubbard model from current lattice density functional theory

The Bethe ansatz local density approximation (LDA) to lattice density functional theory (LDFT) for the one-dimensional repulsive Hubbard model is extended to current-LDFT (CLDFT). The transport properties of mesoscopic Hubbard rings threaded by a magnetic flux are then systematically investigated by this scheme. In particular we present calculations of ground state energies, persistent currents and Drude weights for both a repulsive homogeneous and a single impurity Hubbard model. Our results for the ground state energies in the metallic phase compare favorably well with those obtained with numerically accurate many-body techniques. Also the dependence of the persistent currents on the Coulomb and the impurity interaction strength, and on the ring size are all well captured by LDA-CLDFT. Our study demonstrates the value of CLDFT in describing the transport properties of one-dimensional correlated electron systems. As its computational overheads are rather modest, we propose this method as a tool for studying problems where both disorder and interaction are present.

Renormalization-group study of Luttinger liquids with boundaries

We use Wilsons weak coupling ``momentum'' shell renormalization group method to show that two-particle interaction terms commonly neglected in bosonization of one-dimensional correlated electron systems with open boundaries are indeed irrelevant in the renormalization group sense. Our study provides a more solid ground for many investigations of Luttinger liquids with open boundaries.

Coexisting Ground State of Ferromagnetic and Charge Orderings in the Doped Extended Hubbard Ladder with Intersite Repulsions

The origin of metallic ferromagnetism is a long-standing problem in condensed matter physics, because it is a strong coupling phenomenon essentially. It was also known that one dimensional systems have a lesser chance of showing ferromagnetism in the ground states. In fact, for a class of one-dimensional correlated electron systems including the simple Hubbard chain, the ground state was proved to be nonmagnetic. Several authors have been studied whether ferromagnetism is stabilized or not by taking neglected terms in the simple Hubbard chain into account. It was shown that a positive next-nearest neighbor hopping leads to ferromagnetism for less-than-half filled systems in strong correlation regime on the basis of DMRG calculations. We call this model the railroad–trestle-lattice Hubbard model below. The railroad–trestle lattice is graphically shown in Fig. 1. In this article, we treat the problem of ferromagnetism of the nearly half-filled extended Hubbard ladder with an additional intersite repulsion V . The Hamiltonian is H 1⁄4 t P hi; ji; ðc y i cj þ c y j ci Þ þU P i nini# þV P hi; ji ninj, where ci represent electron creation operators, ni 1⁄4 P c y i ci , and hi; ji denotes nearest-neighbor pairs of the sites on the two-leg ladder. Vojta et al. made a DMRG study of this model in strong coupling region. Tsuchiizu and Suzumura recently studied this model by using the weakcoupling bosonization method, motivated by the experimental observation of a charge-density-wave in the selfdoped ladder compound Sr14 xCaxCu24O41. 7,8) We first mention the half-filled case, i.e., electron density n 1⁄4 1. When U < 3V , the ground state has the checkerboard-type charge-ordering shown in Fig. 2 due to the intersite repulsion. (The sublattice consisting of doubly occupied sites is defined as A-sublattice.) Our main concern is what happens when holes are doped into this chargeordered insulating state. By using the DMRG method, Vojta et al. calculated the checkerboard-type charge-ordering correlation function from quarter-filling to half-filling, 1=2 n 1, where U 1⁄4 8t was chosen. They confirmed that the long-range charge-order correlation is obtained for V VcðnÞ ’ U=3. They also found that the total spin of the doped charge-ordering state is not zero, i.e., the charge ordering coexists with ferromagnetism. However, the origin of this ferromagnetism was not clarified. The main purpose of this paper is to get intuitive understanding of the ferromagnetism in the doped charge-ordered state. In order to attack this issue, we assume t U, V and use strong coupling expansion. Then, we calculate the effective Hamiltonian for holes doped into the charge-ordered state at half-filling. When holes are introduced, they enter the A-sublattice sites [see Fig. 3(a)]. If we totally neglect the bare hopping term in H, then we have the ground state degeneracy concerned with the way of arrangement of doped holes. The introduction of the bare hopping term resolves this degeneracy and is expected to induce an ordering of the doped holes. In order to write down the second-order effective Hamiltonian with respect to t, it is convenient to carry out the particle–hole transformation for the A-sublattice according to c‘ 1⁄4 a‘ , where a y ‘ are the creation operators of the A-sublattice holes. Within the two-hole approximation, we obtain the following effective Hamiltonian:

Spin-charge separation in transport through Luttinger liquid rings

We investigate how the different velocities characterizing the low-energy spectral properties and the low-temperature thermodynamics of one-dimensional correlated electron systems (Luttinger liquids) affect the transport properties of ringlike conductors. The Luttinger liquid ring is coupled to two noninteracting leads and pierced by a magnetic flux. We study the flux dependence of the linear conductance. It shows a dip structure that is governed by the interaction dependent velocities. Our work extends an earlier study that was restricted to rather specific choices of the interaction parameters. We show that for generic repulsive two-particle interactions, the number of dips can be estimated from the ratio of the charge current velocity and the spin velocity. In addition, we clarify the range of validity of the central approximation underlying the earlier study.

Ac Josephson current and supercurrent noise through one-dimensional correlated electron systems

ac Josephson effect in one-dimensional Tomonaga-Luttinger liquid (TLL) adiabatically connected to superconducting electrodes is theoretically investigated. It is found that density fluctuations due to repulsive electron-electron interactions in TLL inhibit Josephson oscillations, whereas they do not affect time-independent current part. We also show that the fluctuations reduce supercurrent noise caused by multiple Andreev reflections. This indicates that the quantum fluctuations in TLL disturb the superconducting phase coherence spreading across the junction.

Charging of a quantum dot coupled to Luttinger-liquid leads

Luttinger-liquid behavior of one-dimensional correlated electron systems is characterized by power-law scaling of a variety of physical observables with exponents determined by a single interaction dependent parameter $K$. We suggest a setup to study Luttinger-liquid behavior in quantum wires which allows us to determine $K$ from two independent measurements: transport through a quantum dot embedded in the wire and the charge on the dot. Consistency of the two $K$'s for a single probe would provide strong experimental evidence for the Luttinger-liquid paradigm.

Ultrafast Phase Control in One-Dimensional Correlated Electron Systems

One-dimensional (1D) correlated electron systems are good targets for the exploration of photoinduced phase transitions (PIPTs). This is because photocarrier generations and/or charge transfer (CT) excitations by lights can stimulate instabilities inherent to the 1D nature of electronic states through strong electron–electron interactions and electron(spin)–lattice interactions. In this paper, we review the ultrafast dynamics of three typical PIPTs observed in 1D correlated electron systems: 1) a photoinduced transition from a Mott insulator to a metal in a halogen-bridged Ni-chain compound, [Ni(chxn) 2 Br]Br 2 (chxn = cyclohexanediamine); 2) a photoinduced melting of a spin-Peierls phase in an organic CT compound, K-tetracyanoquinodimethane (TCNQ); 3) a photoinduced transition between neutral (N) and ionic (I) states in an organic CT compound, tetrathiafulvalene- p -chloranil (TTF-CA). The primary dynamics of these PIPTs are discussed on the basis of the results of femtosecond pump–probe spectroscopy.

Mechanism of Ambipolar Field-Effect Carrier Injections in One-Dimensional Mott Insulators

To clarify the mechanism of recently reported, ambipolar carrier injections into quasi-one-dimensional Mott insulators on which field-effect transistors are fabricated, we employ the one-dimensional Hubbard model attached to a tight-binding model for source and drain electrodes. To take account of the formation of Schottky barriers, we add scalar and vector potentials, which satisfy the Poisson equation with boundary values depending on the drain voltage, the gate bias, and the work-function difference. The current-voltage characteristics are obtained by solving the time-dependent Schr\"odinger equation in the unrestricted Hartree-Fock approximation. Its validity is discussed with the help of the Lanczos method applied to small systems. We find generally ambipolar carrier injections in Mott insulators even if the work function of the crystal is quite different from that of the electrodes. They result from balancing the correlation effect with the barrier effect. For the gate-bias polarity with higher Schottky barriers, the correlation effect is weakened accordingly, owing to collective transport in the one-dimensional correlated electron systems.

To the theory of spin–charge separation in one-dimensional correlated electron systems

Spin–charge separation is considered to be one of the key properties that distinguish low-dimensional electron systems from others. Three-dimensional correlated electron systems are described by the Fermi liquid theory. There, low-energy excitations (quasiparticles) are reminiscent of noninteracting electrons: They carry charges −e and spins 1/2. It is believed that for any one-dimensional correlated electron system, low-lying electron excitations carry either only spin and no charge, or only charge without spin. That is why recent experiments looked for such low-lying collective electron excitations, one of which carries only spin, and the other carries only charge. Here we show that despite the fact that for exactly solvable one-dimensional correlated electron models there exist excitations which carry only spin and only charge, in all these models with short-range interactions the low-energy physics is described by low-lying collective excitations, one of which carries both spin and charge.

Transition from band insulator to Mott insulator in one dimension: Critical behavior and phase diagram

We report a systematic study of the transition from a band insulator (BI) to a Mott insulator (MI) in a one-dimensional Hubbard model at half-filling with an on-site Coulomb interaction U and an alternating periodic site potential V. We employ both the zero-temperature density matrix renormalization group (DMRG) method to determine the gap and critical behavior of the system and the finite-temperature transfer matrix renormalization group method to evaluate the thermodynamic properties. We find two critical points at U = $U_c$ and U = $U_s$ that separate the BI and MI phases for a given V. A charge-neutral spin-singlet exciton band develops in the BI phase (U<$U_c$) and drops below the band gap when U exceeds a special point Ue. The exciton gap closes at the first critical point $U_c$ while the charge and spin gaps persist and coincide between $U_c$<U<$U_s$ where the system is dimerized. Both the charge and spin gaps collapse at U = $U_s$ when the transition to the MI phase occurs. In the MI phase (U>$U_s$) the charge gap increases almost linearly with U while the spin gap remains zero. These findings clarify earlier published results on the same model, and offer insights into several important issues regarding an appropriate scaling analysis of DMRG data and a full physical picture of the delicate nature of the phase transitions driven by electron correlation. The present work provides a comprehensive understanding for the critical behavior and phase diagram for the transition from BI to MI in one-dimensional correlated electron systems with a periodic alternating site potential.

Topological Excitations of One-Dimensional Correlated Electron Systems

Properties of low-energy excitations in one-dimensional superconductors and density-wave systems are examined by the bosonization technique. In addition to the usual spin and charge quantum numbers, a new, independently measurable attribute is introduced to describe elementary, low-energy excitations. It can be defined as a number w which determines, in multiple of $\pi$, how many times the phase of the order parameter winds as an excitation is transposed from far left to far right. The winding number is zero for electrons and holes with conventional quantum numbers, but it acquires a nontrivial value w=1 for neutral spin-1/2 excitations and for spinless excitations with a unit electron charge. It may even be irrational, if the charge is irrational. Thus, these excitations are topological, and they can be viewed as composite particles made of spin or charge degrees of freedom and dressed by kinks in the order parameter.

Mobile impurity in one-dimensional correlated electron systems

Critical properties of one-dimensional (1D) correlated electron systems with a mobile impurity are investigated. By applying the finite-size scaling method to a Bethe-ansatz solvable model, we derive the conformal dimensions related to the orthogonality catastrophe. We then apply the results to the Fermi-edge singularity in quantum wires, and clarify how the critical exponent for X-ray absorption depends on the mass of the core-hole created. A generalization to SU(\(\)) electron systems is outlined based on the g-on description of 1D electron systems.

A Kondo Impurity in One-Dimensional Correlated Conduction Electrons

A spin-1/2 magnetic impurity coupled to a one-dimensional correlated electron system have been studied by applying the density renormalization group method. The Kondo temperature is substantially enhanced by strong repulsive interactions in the chain, but it changes non-monotonically in the case of electron attraction. The magnetization of the impurity at zero-temperature shows local Fermi liquid behavior.

Effect of electron-phonon interaction on a one-dimensional correlated electron system.

The effect of an on-site electron-phonon (e-ph) interaction is studied within the framework of an extended Hubbard model in one dimension. We have eliminated the local phonon coordinates using a modified Lang-Firsov transformation and diagonalized the effective electronic Hamiltonian by a real space renormalization group technique to determine the transition from a charge density wave (CDW) state to a spin density wave (SDW) state. It turns out that the CDW phase is favored by the e-ph coupling with an appreciable band-narrowing effect. In the SDW phase the distortions produced at nearest neighbor sites due to the e-ph interaction become comparable to the on-site distortions while this retardation effect is negligible in the CDW phase. \textcopyright{} 1996 The American Physical Society.

Charge susceptibility of the one-dimensional Hubbard model

The charge susceptibility of the one-dimensional correlated electron system is calculated by means of the exact solution of the Hubbard model at zero temperature. It is pointed out that the charge susceptibility and the specific-heat coefficient become very large and then diverge as the electron concentration approaches the half-filled case in which the system shows the Mott-type insulator. The exact relation is derived between the specific-heat coefficient, the magnetic susceptibility and the charge susceptibility.