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T. Giamarchi

Publications and source records attributed to T. Giamarchi.

At least 127 records · Page 7Linked to original sources

Spinless fermions ladders at half filling

We study a half filled ladder of spinless fermions. We show that contrarily to a single chain, the ladder becomes a Mott insulator for arbitrarily small repulsive interactions. We obtain the full phase diagram and physical quantities such as the charge gap. We show that there is only a single insulating phase for repulsive interactions, regardless of the stength of the interchain hopping and single chain Mott gap. There is thus no confinement-deconfinement transition in this system but a simple crossover. We show that upon doping the system becomes a Luttinger liquid with a universal parameter $K=1/2$ different from the one of the single chain ($K=1/4$).

cond-mat.str-el↗

NMR properties of a one-dimesional Cu-O model

We obtain the Knight shifts and the relaxation rates related to the Fermi contact interaction term for a one-dimensional Cu-O model using bosonization technique. We consider the small interaction limit at half-filling and away from half-filling. In this framework we predict that the antiferromagnetic contribution to the relaxation rate of the nuclear oxygen spin is completely suppressed even away from half-filling, when the temperature is low enough. In the strong interaction limit at half-filling we compute the effective Fermi contact interaction performing a Gutzwiller projection. Both limits suggest that the one-dimensional versions of the Mila-Rice and of the Shastry scenarios of transferred hyperfine couplings which were proposed to explain the NMR measurements for High-T_c cuprates fail in a one-dimensional situation.

cond-mat.str-el↗

Role of interchain hopping in two disordered chains of spinless fermions

The effect of interchain hopping and interaction on Anderson localization has been investigated for two coupled chains of spinless fermions with nearest neighbor interaction. Using the renormalization group method, we find that interchain hopping plays a significant role when the correlation gap induced by the interplay of interchain hopping and intrachain interaction becomes larger than the Anderson localization energy scale induced by impurities. The strong competition between localization and delocalization is examined for attractive interaction.

cond-mat.str-el↗

Disordered Quantum Solids

Due to the peculiar non-fermi liquid of one dimensional systems, disorder has particularly strong effects. We show that such systems belong to the more general class of disordered quantum solids. We discuss the physics of such disordered interacting systems and the methods that allows to treat them. In addition to, by now standard renormalization group methods, We explain how a simple variational approach allows to treat these problems even in case when the RG fails. We discuss various physical realizations of such disordered quantum solids both in one and higher dimensions (Wigner crystal, Bose glass). We investigate in details the interesting example of a disordered Mott insulator and argue that intermediate disorder can lead to a novel phase, the Mott glass, intermediate between a Mott and and Anderson insulator.

cond-mat.str-el↗

Correlated Fermions in a one-dimensional quasiperiodic potential

We study analytically one-dimensional interacting spinless fermions in a Fibonacci potential. We show that the effects of the quasiperiodic modulation are intermediate between those of a commensurate potential and a disordered one. The system exhibits a metal-insulator transition whose position depends both on the strength of the correlations and on the position of the Fermi level. Consequently, the conductivity displays a power law like size and frequency behaviour characterized by a non trivial exponent.

cond-mat↗

A possible new phase of commensurate insulators with disorder: the Mott Glass

A new thermodynamic phase resulting from the competition between a commensurate potential and disorder in interacting fermionic or bosonic systems is predicted. It requires interactions of finite extent. This phase, intermediate between the Mott insulator and the Anderson insulator, is both incompressible and has no gap in the conductivity. The corresponding phase is also predicted for commensurate classical elastic systems in presence of correlated disorder.

cond-mat.str-el↗

Coupled Ladders in a Magnetic Field

We investigate the phase transitions in two-leg ladders systems in the incommensurate phase, for which the gap is destroyed by a magnetic field ($h_{c1}< h$) and the ladder is not yet totally saturated ($h < h_{c2}$). We compute quantitatively the correlation functions as a function of the magnetic field for an isolated strong coupling ladder $J_\perp \gg J_\parallel$ and use it to study the phase transition occuring in a three dimensional array of antiferromagnetically coupled ladders. The three dimensional ordering is in the universality class of Bose condensation of hard core bosons. We compute the critical temperature $T_c(h)$ as well as various physical quantities such as the NMR relaxations rate. $T_c$ has an unusual camel-like shape with a local minimum at $h=(h_{c1}+h_{c2})/2$ and behaves as $T_c \sim (h-h_{c1})^{2/3}$ for $h\sim h_{c1}$. We discuss the experimental consequences for compounds such as Cu_2(C_5H_{12}N_2)_2Cl_4

cond-mat.str-el↗

Disordered periodic systems at the upper critical dimension

The effects of weak point-like disorder on periodic systems at their upper critical dimension D_c for disorder are studied. The systems studied range from simple elastic systems with D_c=4 to systems with long range interactions with D_c=2 and systems with D_c=3 such as the vortex lattice with dispersive elastic constants. These problems are studied using the Gaussian Variational method and the Functional Renormalisation Group. In all the cases studied we find a typical ultra-slow loglog(x) growth of the asymptotic displacement correlation function, resulting in nearly perfect translational order. Consequences for the Bragg glass phase of vortex lattices are discussed.

cond-mat.dis-nn↗

Anderson localization in Hubbard ladders

The effect of a weak random potential on two-leg Hubbard ladders is investigated. The random potential is shown to induce Anderson localization except for attractive enough interactions, supressing completely d-wave superconductivity. These localization effects remain very strong even for many ladders coupled by Josephson coupling. Both dc and ac conductivities and localization lengths are obtained. Consequences for the superconducting ladder compound Sr$_x$Ca$_{14-x}$Cu$_{24}$O$_{41+δ}$ are discussed.

cond-mat.str-el↗

On-chain electrodynamics of metallic (TMTSF)_2 X salts: Observation of Tomonaga-Luttinger liquid response

We have measured the electrodynamic response in the metallic state of three highly anisotropic conductors, (TMTSF)_2 X, where X=PF_6, AsF_6, or ClO_4, and TMTSF is the organic molecule tetramethyltetraselenofulvalene. In all three cases we find dramatic deviations from a simple Drude response. The optical conductivity has two features: a narrow mode at zero frequency, with a small spectral weight, and a mode centered around 200 cm^{-1}, with nearly all of the spectral weight expected for the relevant number of carriers and single particle bandmass. We argue that these features are characteristic of a nearly one-dimensional half- or quarter-filled band with Coulomb correlations, and evaluate the finite energy mode in terms of a one-dimensional Mott insulator. At high frequencies (\hbarω> t_\perp, the transfer integral perpendicular to the chains), the frequency dependence of the optical conductivity σ_1(ω) is in agreement with calculations based on an interacting Tomonaga-Luttinger liquid, and is different from what is expected for an uncorrelated one-dimensional semiconductor. The zero frequency mode shows deviations from a simple Drude response, and can be adequately described with a frequency dependent mass and relaxation rate.

cond-mat.str-el↗

Creep via dynamical functional renormalization group

We study a D-dimensional interface driven in a disordered medium. We derive finite temperature and velocity functional renormalization group (FRG) equations, valid in a 4-D expansion. These equations allow in principle for a complete study of the the velocity versus applied force characteristics. We focus here on the creep regime at finite temperature and small velocity. We show how our FRG approach gives the form of the v-f characteristics in this regime, and in particular the creep exponent, obtained previously only through phenomenological scaling arguments.

cond-mat↗

Vortices in coupled planes with columnar disorder and bosonic ladders

We consider two coupled strongly correlated bosonic chains. We derive the phase diagram of the pure system and obtain an antisymmetric charge density wave, a 4k_F charge density wave, a superfluid phase and a second superfluid phase which is a condensate of boson pairs. We consider the effect of a weak disorder on that system and show that the superfluid phase is less localized than in the one chain case. On the other hand, the pinning length of the antisymmetric charge density wave is shorter than in the one chain case. We discuss the consequences of these results for two coupled vortex planes with columnar disorder. We show that in the vortex system there is a conventional pinned solid phase for 0 T_L. We obtain the critical currents by a modified Larkin-Ovchinnikov argument and prove that there is a strong reduction of critical current for T=T_m.

cond-mat.str-el↗

Weakly disordered spin ladders

We analyze an anisotropic spin 1/2 two legs ladder in the presence of various type of random perturbations. The generic phase diagram for the pure system, in a way similar to spin one chains, consists of four phases: an Antiferromagnet, a Haldane gap or a Singlet phase (depending on the sign of interchain coupling) and two XY phases designated by XY1 and XY2. The effects of disorder depend crucially on whether it preserves XY symmetry (random field along z and random exchange) or not (random anisotropy or random XY fields). The singlet phases and the massless XY1 phase are totally unaffected by disorder in stark contrast with the single chain case. On the other hand the XY2 phase is very strongly suppressed. Disorder breaking XY symmetry has much stronger effects and most of the phases at the exception of the singlet one are destroyed. Interestingly, the disordered XY1 phase has a much shorter correlation length than the disordered XY2 phase contrarily with the case of perturbations preserving the rotation symmetry around the z axis.

cond-mat.str-el↗

Dynamical properties of the pinned Wigner crystal

We study various dynamical properties of the weakly pinned Wigner crystal in a high magnetic field. Using a Gaussian variational method we can compute the full frequency and field dependence of the real and imaginary parts of the diagonal and Hall conductivities. The zero temperature Hall resistivity is independent of frequency and remains unaffected by disorder at its classical value. We show that, depending on the inherent length scales of the system, the pinning peak and the threshold electric field exhibit strikingly different magnetic field dependences.

cond-mat↗

Effects of disorder on two strongly correlated coupled chains

We study the effects of disorder on a system of two coupled chain of strongly correlated fermions (ladder system), using renormalization group. The stability of the phases of the pure system is investigated as a function of interactions both for fermions with spin and spinless fermions. For spinless fermions the repulsive side is strongly localized whereas the system with attractive interactions is stable with respect to disorder, at variance with the single chain case. For fermions with spins, the repulsive side is also localized, and in particular the d-wave superconducting phase found for the pure system is totally destroyed by an arbitrarily small amount of disorder. On the other hand the attractive side is again remarkably stable with respect to localization. We have also computed the charge stiffness, the localization length and the temperature dependence of the conductivity for the various phases. In the range of parameter where d-wave superconductivity would occur for the pure system the conductivity is found to decrease monotonically with temperature, even at high temperature, and we discuss this surprising result. For a model with one site repulsion and nearest neighbor attraction, the most stable phase is an orbital antiferromagnet . Although this phase has no divergent superconducting fluctuation it can have a divergent conductivity at low temperature. We argue based on our results that the superconductivity observed in some two chain compounds cannot be a simple stabilization of the d-wave phase found for a pure single ladder. Applications to quantum wires are discussed.

cond-mat.str-el↗

Bragg- and Moving-glasses: a theory of disordered vortex lattices

We study periodic lattices, such as vortex lattices in type II superconductors in a random pinning potential. For the static case we review the prediction that the phase diagram of such systems consists of a topologically ordered Bragg glass phase, with quasi long range translational order, at low fields. This Bragg glass phase undergoes a transition at higher fields into another glassy phase, with dislocations, or a liquid. This proposition is compatible with a large number of experimental results on BSCCO or Thalium compounds. Further experimental consequences of our results and relevance to other systems will be discussed. When such vortex systems are driven by an external force, we show that, due to periodicity in the direction transverse to motion, the effects of static disorder persist even at large velocity. In $d=3$, at weak disorder, or large velocity the lattice forms a topologically ordered glass state, the ``moving Bragg glass'', an anisotropic version of the static Bragg glass. The lattice flows through well-defined, elastically coupled, static channels. We determine the roughness of the manifold of channels and the positional correlation functions. The channel structure also provides a natural starting point to study the influence of topological defects such as dislocations. In $d=2$ or at strong disorder the channels can decouple along the direction of motion leading to a ``smectic'' like flow. We also show that such a structure exhibits an effective transverse critical pinning force due to barriers to transverse motion, and discuss the experimental consequences of this effect.

cond-mat.supr-con↗

Critical Properties of gapped spin-1/2 chains and ladders in a magnetic field

An interesting feature of spin-1/2 chains with a gap is that they undergo a commensurate-incommensurate transition in the presence of an external magnetic field $H$. The system is in a gapless incommensurate regime for all values of the magnetic field between the lower critical field $H_{c1}$ and an upper critical field $H_{c2}$, where it is gapless and has power law correlations. We calculate the critical exponents for such a generic gapped system in the incommensurate regime at the critical field $H_{c1}$ and in its vicinity. Our analysis also applies to the spin-1/2 ladder. We compute the full dynamical susceptibilities at finite temperature. We use the same to discuss the thermal broadening of various modes and obtain the low temperature behaviour of the nuclear spin relaxation rate $T_1^{-1}$. We discuss the results obtained here for the special cases of the dimerised chain, frustrated chain and the spin-1/2 ladder.

cond-mat.stat-mech↗

Mott transition in one dimension

I review some of the results on the Mott transition in one dimensional systems. In particular I discuss the phase diagram and critical properties of both Mott transitions at fixed filling and upon doping, as well as the dc and ac conductivity. Application of these results to organic conductors is discussed.

cond-mat↗