We consider an effectively one-dimensional periodic atomic chain subjected to a weak static electric field transverse to the chain axis. The intrinsic lattice is represented in reciprocal space by a harmonically weighted periodic pseudopotential, while the transverse field produces a weak elastic and polarizable response whose minimum-energy distribution is approximated by a periodically repeated catenary profile. Bloch reduction places both contributions in a common reciprocal-space Hamiltonian. The intrinsic lattice produces a \ (|r-s|^ {-1} \) hierarchy, whereas the catenary contribution is a symmetric Toeplitz correction with coefficients proportional to \((1+π^2(r-2) ^ {-1} \) and therefore asymptotically to \ (|r-s|^ {-2} \). The complete nonzero reciprocal weight of the catenary contribution is absolutely convergent and sums to \ (|V_ {\rm c} |/e \). At the unit-cell level, the lowest intrinsic harmonic together with the catenary term gives a Mathieu equation containing both cosine and hyperbolic-cosine modulations. A first-Brillouin-zone reduction then yields the field-dependent band energies and the corresponding hierarchy of Bragg gaps. The model isolates a simple mechanism by which a transverse electric field can reorganize the Bloch spectrum of a low-dimensional periodic system.
Keywords: Bloch theory; transverse electric field; catenary potential; Mathieu equation; Brillouin zone; band structure.
Comments
A revised formulation based on an explicit lattice energy-balance model is in preparation
We consider an effectively one-dimensional periodic atomic chain subjected to a weak static electric field transverse to the chain axis. The intrinsic lattice is represented in reciprocal space by a harmonically weighted periodic pseudopotential, while the transverse field produces a weak elastic and polarizable response whose minimum-energy distribution is approximated by a periodically repeated catenary profile. Bloch reduction places both contributions in a common reciprocal-space Hamiltonian. The intrinsic lattice produces a \ (|r-s|^ {-1} ) hierarchy, whereas the catenary contribution is a symmetric Toeplitz correction with coefficients proportional to ((1+π^2(r-2) ^ {-1} ) and therefore asymptotically to \ (|r-s|^ {-2} ). The complete nonzero reciprocal weight of the catenary contribution is absolutely convergent and sums to \ (|V_ {\rm c} |/e ). At the unit-cell level, the lowest intrinsic harmonic together with the catenary term gives a Mathieu equation containing both cosine and hyperbolic-cosine modulations. A first-Brillouin-zone reduction then yields the field-dependent band energies and the corresponding hierarchy of Bragg gaps. The model isolates a simple mechanism by which a transverse electric field can reorganize the Bloch spectrum of a low-dimensional periodic system.
Keywords: Bloch theory; transverse electric field; catenary potential; Mathieu equation; Brillouin zone; band structure.
We develop the Floquet-Bloch theory of noninteracting fermions on a periodic lattice in the presence of a constant electric field. As long as the field lies along a reciprocal-lattice vector, time periodicity of the Bloch Hamiltonian is inherited from the evolution of momentum in the Brillouin zone. The corresponding Floquet quasienergies yield the Wannier-Stark ladder with interband couplings included to all orders. These results are compared to perturbative results where the lowest-order interband correction gives the field-induced polarization shift in terms of the electric susceptibility. Additionally, we investigate electronic transport by coupling the system to a bath within the Floquet-Keldysh formalism. We then study the breakdown of the band-projected theory from the onset of interband contributions and Landau-Zener resonances in the band-resolved currents. In particular, we consider the transverse quantum-geometric response in two spatial dimensions due to the Berry curvature. In the strong-field regime, the semiclassical theory predicts a plateau of the geometric response as a function of field strength. Here, we scrutinize the conditions under which the semiclassical results continue to hold in the quantum theory.
The early quantum theory of electrical conductivity in crystal lattices by Bloch and Zener [1,2] led to the striking prediction that a homogeneous static electric field induces an oscillatory rather than uniform motion of the electrons. These so-called Bloch oscillations have never been observed in natural crystals because the scattering time of the electrons by the lattice defects is much shorter than the Bloch period. In semiconductor superlattices the larger spatial period leads to a much shorter Bloch period (,600 fs) and Bloch oscillations have recently been observed through the emission of THz radiation by the electrons [3]. Here we present Bloch oscillations of atoms in the fundamental energy band of a periodic optical potential. We directly measure the atomic momentum distribution evolving in time under the influence of a constant inertial force for various potential depths. We experimentally observe oscillation periods in the millisecond range as well as positive and negative effective masses. Bloch oscillations are a pure quantum effect which can be explained in a simple one-dimensional model. The periodicity of the lattice (period d) leads to a band structure (Fig. 1) of the energy spectrum of the particle and the corresponding eigenenergies Ensqd and eigenstates jn, ql (Bloch states) are labeled by the discrete band index n and the continuous quasimomentum q; Ensqd and jn, ql are periodic functions of q with period 2pyd and q is conventionally restricted to the first Brillouin zone g2pyd, pydg [4]. Under the influence of a constant external force F, weak enough not to induce interband transitions, a given Bloch state jn, qs0dl evolves (up to a phase factor) into the state jn, qstdl according to qstd qs0d 1 Ftyh . (1) This evolution is periodic with a period tB hyjFjd corresponding to the time required for the quasimomentum to scan a full Brillouin zone. The mean velocity in jn, qstdl
An exactly solvable lattice with periodic inverse-square singularities exhibits two physically distinct mechanisms of spectral-gap closure. The model arises from the generalized trigonometric Pöschl-Teller potential in the coupling range where both local solutions at each singularity are square-integrable. A transmitting, current-preserving self-adjoint matching condition connects neighboring cells and generates a nontrivial Bloch spectrum. For a generic lattice with two inequivalent singular sublattices, the spectrum contains two alternating families of gaps, and the band edges reproduce the scale-invariant spectra of the associated finite singular system. One gap family closes when the two sublattices become equivalent. In this symmetric limit, however, the primitive period halves, so the apparent band crossing results from Brillouin-zone folding. A different family closes at a critical but genuinely asymmetric configuration. Because the primitive period is preserved, adjacent bands then meet at the center of the original Brillouin zone in a genuine massless Dirac-like cone. Near either critical limit, a small finite gap acts as an effective Dirac mass: the dispersion remains quadratic near a band edge but crosses over to a massive Dirac-like form beyond that narrow region. The band curvatures define effective electron and hole masses. Exact Bloch eigenfunctions further reveal that isospectral lattices can display different single-particle probability densities. This model therefore provides an analytically controlled one-dimensional setting in which conventional quadratic carriers, massive Dirac-like band dispersions, and a tunable massless contact coexist within the same singular lattice.
Strongly correlated materials exhibit some of the most complex and technologically useful phenomena in condensed matter. We use the world line and determinant quantum Monte Carlo techniques to explore the phases of the Hubbard Hamiltonian, a model describing strong interactions, in a number of different contexts. We first consider the spin, charge, and bond order correlations of the one-dimensional extended fermion Hubbard model in the presence of a coupling to the lattice. A static alternating lattice distortion leads to enhanced charge density wave correlations at the expense of antiferromagnetic order. When the lattice degrees of freedom are dynamic, we show that a similar effect occurs even though the charge asymmetry must arise spontaneously. Although the evolution of the total energy with lattice coupling is smooth, the individual components exhibit sharp crossovers at the phase boundaries. Finally, we observe a tendency for bond order in the region between the charge and spin density wave phases. Second, we examine mixtures of bosons and fermions in one-dimensional optical lattices. We evaluate the density profiles and bosonic visibility [special characters omitted] resolving the discrepancy between theory and experiment by identifying parameter regimes where [special characters omitted] is reduced and increased. We present a simple qualitative picture of the different response to the fermion admixture in terms of the superfluid and Mott-insulating domains before and after the fermions are included. Finally, we show that [special characters omitted] exhibits kinks which are tied to the domain evolution present in the pure bosonic case, and also additional structure arising from the formation of boson-fermion molecules, a prediction for future experiments. Third, we report large scale calculations of the effective bandwidth, momentum distribution, and magnetic correlations of the square lattice fermion Hubbard Hamiltonian. The sharp Fermi surface of the non-interacting limit is significantly broadened by the electronic correlations, but retains signatures of the approach to the edges of the first Brillouin zone as the density increases. Finite size scaling of simulations on large lattices allows us to extract the interaction dependence of the antiferromagnetic order parameter, exhibiting its evolution from weak-coupling to the strong-coupling Heisenberg limit. Our lattices provide improved resolution of the momentum distribution, allowing a more quantitative comparison with time-of-flight optical lattice experiments.
The properties of resonant two-electron pairs are examined in three-dimensional simple cubic extended Hubbard tUW model, in sand dsymmetry channels, in the limit of empty lattice.Lattice Green function technique is applied to calculate the scattering amplitude by means of T matrix for any energy in the band on Γ R line within the Brillouin zone.The analysis shows the persistence of resonant states even for Coulomb interactions so weak that the equation for the resonant states is not formally fullled.The dierence in behavior of resonances controlled by on-site and intersite Coulomb interactions is found.The ranges of applicability of approximate formula for the actual position of resonant peak and its width are shown.
Understanding strongly correlated systems driven out of equilibrium is a challenging task necessitating the simultaneous treatment of quantum mechanics, dynamical constraints, and strong interactions. A Mott insulator subjected to a uniform and static electric field is prototypical, raising key questions such as the fate of Bloch oscillations with increasing correlation strength, the approach to a steady-state DC transport regime and the role of dissipation in it, and electric-field-driven phase transitions. Despite tremendous efforts over the past decade employing various numerical and analytical approaches, the manner in which a nonequilibrium steady state gets established has remained an unresolved problem. We develop here an effective large-N Keldysh field theory for studying nonequilibrium transport in a regular one-dimensional dissipative Mott insulator system subjected to a uniform electric field. Upon abruptly turning on the electric field (a quench), a transient oscillatory current response reminiscent of Bloch oscillations is found. In the regime of small tunneling conductance the amplitude of these oscillations, over a large time window, decreases as an inverse square power law in time, ultimately going over to an exponential decay beyond a large characteristic time ${\ensuremath{\tau}}_{d}$ that increases with N. Such a relaxation to a steady-state DC response is absent in the dissipation-free Hubbard chain at half filling. The steady-state current at small fields is governed by large-distance cotunneling, a process absent in the equilibrium counterpart. The low-field DC current has a Landau-Zener-Schwinger form but qualitatively differs from the expression for pair-production probability for the dissipation-free counterpart. The breakdown of perturbation theory in the Mott phase possibly signals a nonequilibrium phase transition to a metallic phase. Our study sheds light on the approach of a driven, dissipative strongly correlated system to a nonequilibrium steady state and also provides a general analytic microscopic framework for understanding other nonequilibrium phenomena in these systems.