Magnetic-field dependence of phase correlation length in spin- and charge-density waves

Within a simple quasi-two-dimensional model, we study the phason propagator in both spin- and charge-density waves in the presence of a magnetic field perpendicular to the conducting plane. We find, though the magnetic field has little effect in the longitudinal correlation length (i.e., the correlation length in the chain direction), the magnetic field reduces significantly the transverse correlation length. This effect is most easily observable as increases in the fluctuation-induced specific heat and the resistivity in the chain direction in magnetic fields

Pauli coupling of the external magnetic field to spin-density waves

The effects of the external magnetic field on the spin-density-wave (SDW) order and on accompanying fluctuations are calculated within the random-phase approximation for the extended Hubbard model with imperfectly nested quasi-one-dimenisonal Fermi surfaces. Both Pauli and orbital mechanisms are treated in parallel. It is shown that the Pauli coupling leads to a finite hybridization of the SDW component in the direction of the external field and the charge-density wave. The mean value of this SDW component remains zero below the critical temperature in the isotropic system, but may be activated in systems with an internal spin anisotropy. The mean-field expression for the corresponding spin-flop field is derived. Furthermore, the Pauli coupling renormalizes two of six fluctuative SDW modes. In order to establish ways of qualitative and quantitative comparison between effects belonging to the Pauli and orbital couplings, we analyze the characteristic parameters for these two modes as well as for the other four modes affected only by the orbital coupling. In particular we evaluate the field dependence of longwavelength gaps, correlation lengths, and attenuation coefficients

Magnetic-field influence on the collective properties of charge- and spin-density waves

Taking account of a quasi-one-dimensional electron band with an imperfect nesting, we consider the orbital effects of a transverse magnetic field on systems with a charge- or spin-density-wave ground state. Assuming that the cyclotron frequency is small with respect to the critical temperature, we analyze the effects of magnetic field on the quasiparticle Green’s function, the equilibrium value of the order parameter, and the density of collective carriers (i.e., the condensate density). It is shown that the order parameter decreases, while the condensate density increases in the magnetic field at low temperatures

Dinamičke dislokacione linije u sistemima s valovima gustoće naboja

The topological aspects of the conversion of collective charge density wave transport into the ohmic one in front of extended barriers are discussed in the frame of Gor’kov’s model. It is shown that simultaneous phase slips form a family of dislocation lines. The shape and dynamics of these lines depend on the morphology of the barrier. They influence the amplitude of the narrow band noise, but do not modify its fundamental frequency.Razmatrana su topološka svojstva konverzije kolektivne struje nošene valom gustoće naboja u omsku struju ispred barijere koja u potpunosti zaustavlja kolektivni transport. U okviru Gor’kovljevog modela se pokazuje da centri istovremenih proklizavanja faze formiraju familiju dislokacionih linija. Oblik i dinamika dislokacionih linija ovise o morfologiji barijere. Takva ovisnost odražava se u amplitudi uskopojasnog šuma, ali ne utječe na njegovu frekvenciju

Dinamičke dislokacione linije u sistemima s valovima gustoće naboja

The topological aspects of the conversion of collective charge density wave transport into the ohmic one in front of extended barriers are discussed in the frame of Gor’kov’s model. It is shown that simultaneous phase slips form a family of dislocation lines. The shape and dynamics of these lines depend on the morphology of the barrier. They influence the amplitude of the narrow band noise, but do not modify its fundamental frequency.Razmatrana su topološka svojstva konverzije kolektivne struje nošene valom gustoće naboja u omsku struju ispred barijere koja u potpunosti zaustavlja kolektivni transport. U okviru Gor’kovljevog modela se pokazuje da centri istovremenih proklizavanja faze formiraju familiju dislokacionih linija. Oblik i dinamika dislokacionih linija ovise o morfologiji barijere. Takva ovisnost odražava se u amplitudi uskopojasnog šuma, ali ne utječe na njegovu frekvenciju

Dynamical dislocation lines in the charge density wave systems

The topological aspects of the conversion of collective charge density wave transport into the Ohmic one in front of extended barriers are discussed in the frame of Gor'kov's model. It is shown that simultaneous phase slips form a family of dislocation lines. The shape and dynamics of these lines depend on the morphology of the barrier. They influence the amplitude of the narrow band noise, but do not modify its fundamental frequency

Domain patterns in incommensurate systems with the uniaxial real order parameter

The basic Landau model for the incommensurate-commensurate transition to the uniform or dimerized uniaxial ordering is critically reexamined. The previous analyses identified only sinusoidal and homogeneous solutions as thermodynamically stable and proposed a simple phase diagram with the first-order phase transition between these configurations. By performing the numerical analysis of the free-energy and the Euler-Lagrange equation we show that the phase diagram is more complex. It also contains a set of metastable solutions present in the range of coexistence of homogeneous and sinusoidal solutions. These new configurations are periodic patterns of homogeneous domains connected by sinusoidal segments. They are Lyapunov unstable, very probably due to the nonintegrability of the free-energy functional. We also discuss some other mathematical aspects of the model and compare it with the essentially simpler sine-Gordon model for the transitions to the states with higher commensurabilities. We argue that the present results might be a basis for the explanation of phenomena such as thermal hystereses, cascades of phase transitions, and memory effects

Discrete approach to incoherent excitations in conductors

While keeping the discreteness of the reciprocal space, we calculate the spectrum of incoherent electron-hole excitations in the conducting Fermi liquids. The method is illustrated on the well-known jellium model within the random phase approximation. It also leads to the formulation of a sum rule from which we get the details of the dispersion curve for the collective plasmon mode. The notion of time averaging in the discrete approach is briefly recalled