arXiv subjects

T. Giamarchi

Publications and source records attributed to T. Giamarchi.

At least 73 records · Page 4Linked to original sources

arXiv2008

Doping dependence of the vortex-core energy in bilayer films of cuprates

The energy needed to create a vortex core is the basic ingredient to address the physics of thermal vortex fluctuations in underdoped cuprates. Here we theoretically investigate its role on the occurrence of the Beresinskii-Kosterlitz-Thouless transition in a bilayer film with inhomogeneity. From the comparison with recent measurements of the penetration depth in two-unit cell thin films of Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-\d}$ (YBCO) by Hetel et al. [Nat. Phys. 3, 700 (2007)] we can extract the value of the vortex-core energy $μ$, and show that $μ$ scales linearly with $T_c$ at low doping.

cond-mat.supr-con↗

arXiv2008

Dipolar bosons in a planar array of one-dimensional tubes

We investigate bosonic atoms or molecules interacting via dipolar interactions in a planar array of one-dimensional tubes. We consider the situation in which the dipoles are oriented perpendicular to the tubes by an external field. We find various quantum phases reaching from a `sliding Luttinger liquid' phase in which the tubes remain Luttinger liquids to a two-dimensional charge density wave ordered phase. Two different kinds of charge density wave order occur: a stripe phase in which the bosons in different tubes are aligned and a checkerboard phase. We further point out how to distinguish the occurring phases experimentally.

cond-mat.other↗

arXiv2007

Bose-Einstein Condensation in Magnetic Insulators

The elementary excitations in antiferromagnets are magnons, quasiparticles with integer spin and Bose statistics. In an experiment their density is controlled efficiently by an applied magnetic field and can be made finite to cause the formation of a Bose-Einstein condensate (BEC). Studies of magnon condensation in a growing number of magnetic materials provide a unique window into an exciting world of quantum phase transitions (QPT) and exotic quantum states.

cond-mat.str-el↗

arXiv2007

Spin dynamics in a one-dimensional ferromagnetic Bose gas

We investigate the propagation of spin excitations in a one-dimensional (1D) ferromagnetic Bose gas. While the spectrum of longitudinal spin waves in this system is sound-like, the dispersion of transverse spin excitations is quadratic making a direct application of the Luttinger Liquid (LL) theory impossible. By using a combination of different analytic methods we derive the large time asymptotic behavior of the spin-spin dynamical correlation function for strong interparticle repulsion. The result has an unusual structure associated with a crossover from the regime of trapped spin wave to an open regime and does not have analogues in known low-energy universality classes of quantum 1D systems.

cond-mat.other↗

arXiv2007

Sine-Gordon description of Beresinskii-Kosterlitz-Thouless physics at finite magnetic field

The Beresinskii-Kosterlitz-Thouless (BKT) physics of vortices in two-dimensional superconductors at finite magnetic field is investigated by means of a field-theoretical approach based on the sine-Gordon model. This description leads to a straightforward definition of the field-induced magnetization and shows that the persistence of non-linear effects at low fields above the transition is a typical signature of the fast divergence of the correlation length within the BKT theory.

cond-mat.supr-con↗

arXiv2007

Phase diagram of hole doped two-leg Cu-O ladders

In the weak coupling limit, we establish the phase diagram of a two-leg ladder with a unit cell containing both Cu and O atoms, as a function of doping. We use bosonization and design a specific RG procedure to handle the additional degrees of freedom. Significant differences are found with the single orbital case; for purely repulsive interactions, a completely massless quantum critical region is obtained at intermediate carrier concentrations (well inside the bands) where the ground state consists of an incommensurate pattern of orbital currents plus a spin density wave (SDW) structure.

cond-mat.str-el↗

arXiv2007

Thermal rounding of the depinning transition

We study thermal effects at the depinning transition by numerical simulations of driven one-dimensional elastic interfaces in a disordered medium. We find that the velocity of the interface, evaluated at the critical depinning force, can be correctly described with the power law $v\sim T^ψ$, where $ψ$ is the thermal exponent. Using the sample-dependent value of the critical force, we precisely evaluate the value of $ψ$ directly from the temperature dependence of the velocity, obtaining the value $ψ= 0.15 \pm 0.01$. By measuring the structure factor of the interface we show that both the thermally-rounded and the T=0 depinning, display the same large-scale geometry, described by an identical divergence of a characteristic length with the velocity $ξ\propto v^{-ν/β}$, where $ν$ and $β$ are respectively the T=0 correlation and depinning exponents. We discuss the comparison of our results with previous estimates of the thermal exponent and the direct consequences for recent experiments on magnetic domain wall motion in ferromagnetic thin films.

cond-mat.stat-mech↗

arXiv2007

New aspects in the Bragg Glass-Disordered phase transition: an analysis based on the 3rd harmonics of the AC magnetic susceptibility

We analyse the phase transition between the Bragg Glass and the Disordered phase in the vortex lattice in type-II superconductors, both by analytical computations and experimental investigations. It is known that if the Peak Effect can be detected, a Bragg Glass/Disordered phase transition takes place. We show that, in some conditions, this transition can occur without the observation of the Peak Effect Phenomenon. We introduce a method based on the 3rd harmonics of the AC magnetic susceptibility to detect the transition also in these cases. Using this method, we obtain an experimental confirmation of the theoretical predictions on sphere shaped V3Si single crystals, in the high fields/low temperatures range too, where previous experimental studies failed to detect the Bragg/Disordered phase transition.

cond-mat.supr-con↗

arXiv2007

Spin-charge separation in two-component Bose-gases

We show that one of the key characteristics of interacting one-dimensional electronic quantum systems, the separation of spin and charge, can be observed in a two-component system of bosonic ultracold atoms even close to a competing phase separation regime. To this purpose we determine the real-time evolution of a single particle excitation and the single-particle spectral function using density-matrix renormalization group techniques. Due to efficient bosonic cooling and good tunability this setup exhibits very good conditions for observing this strong correlation effect. In anticipation of experimental realizations we calculate the velocities for spin and charge perturbations for a wide range of parameters.

cond-mat.other↗

arXiv2007

Fourier transform of the $2k_F$ Luttinger liquid density correlation function with different spin and charge velocities

We obtain a closed-form analytical expression for the zero temperature Fourier transform of the $2k_F$ component of the density-density correlation function in a Luttinger liquid with different spin and charge velocities. For frequencies near the spin and charge singularities approximate analytical forms are given and compared with the exact result. We find power law like singularities leading to either divergence or cusps, depending on the values of the Luttinger parameters and compute the corresponding exponents. Exact integral expressions and numerical results are given for the finite temperature case as well. We show in particular how the temperature rounds the singularities in the correlation function.

cond-mat.str-el↗

arXiv2007

Hall effect in strongly correlated low dimensional systems

We investigate the Hall effect in a quasi one-dimensional system made of weakly coupled Luttinger Liquids at half filling. Using a memory function approach, we compute the Hall coefficient as a function of temperature and frequency in the presence of umklapp scattering. We find a power-law correction to the free-fermion value (band value), with an exponent depending on the Luttinger parameter $K_ρ$. At high enough temperature or frequency the Hall coefficient approaches the band value.

cond-mat.str-el↗

arXiv2007

From Luttinger to Fermi liquids in organic conductors

This chapter reviews the effects of interactions in quasi-one dimensional systems, such as the Bechgaard and Fabre salts, and in particular the Luttinger liquid physics. It discusses in details how transport measurements both d.c. and a.c. allow to probe such a physics. It also examine the dimensional crossover and deconfinement transition occurring between the one dimensional case and the higher dimensional one resulting from the hopping of electrons between chains in the quasi-one dimensional structure.

cond-mat.str-el↗

arXiv2007

Kosterlitz-Thouless behavior in layered superconductors: the role of the vortex-core energy

In layered superconductors with small interlayer Josephson coupling vortex-antivortex phase fluctuations characteristic of quasi two-dimensional (2D) Kosterlitz-Thouless (KT) behavior are expected to be observable at some energy scale $T_d$. While in the 2D case $T_d$ is uniquely identified by the KT temperature $T_{KT}$ where the universal value of the superfluid density is reached, we show that in a generic anisotropic 3D system $T_d$ is controlled by the vortex-core energy, and can be significantly larger than the 2D scale $T_{KT}$. These results are discussed in relation to recent experiments in cuprate superconductors, which represent a typical experimental realization of layered anisotropic superconductors.

cond-mat.supr-con↗

arXiv2007

Competition between Vortex Unbinding and Tunneling in an Optical Lattice

We study a system of two-dimensional Bose gases trapped in minima of a deep one-dimensional optical lattice potential. Increasing the tunneling amplitude between adjacent gases drives a deconfinement transition to a phase where coherence is established between neighboring two-dimensional gases. We compute the signature of this transition in the interference pattern of the system as well as in its rotational response, which provides a direct measurement of the superfluidity in the system.

cond-mat.stat-mech↗

arXiv2007

Critical properties and Bose Einstein Condensation in dimer spin systems

We analyze the spin relaxation time $1/T_1$ for a system made of weakly coupled one dimensional ladders.This system allows to probe the dimensional crossover between a Luttinger liquid and a Bose-Einstein condensateof magnons. We obtain the temperature dependence of $1/T_1$ in the various dimensional regimes, and discuss the experimental consequences.

cond-mat.str-el↗

arXiv2006

Energy absorption of a Bose gas in a periodically modulated optical lattice

We compute the energy absorbed by a one dimensional system of cold bosonic atoms in an optical lattice subjected to lattice amplitude modulation periodic with time. We perform the calculation for the superfluid and the Mott insulator created by a weak lattice, and the Mott insulator in a strong lattice potential. For the latter case we show results for 3D systems as well. Our calculations, based on bosonization techniques and strong coupling methods, go beyond standard Bogoliubov theory. We show that the energy absorption rate exhibits distinctive features of low dimensional systems and Luttinger liquid physics. We compare our results with experiments and find good agreement.

cond-mat.mes-hall↗

arXiv2006

Modulation spectroscopy with ultracold fermions in an optical lattice

We propose an experimental setup of ultracold fermions in an optical lattice to determine the pairing gap in a superfluid state and the spin ordering in a Mott-insulating state. The idea is to apply a periodic modulation of the lattice potential and to use the thereby induced double occupancy to probe the system. We show by full time-dependent calculation using the adaptive time dependent density-matrix renormalization group method that the position of the peak in the spectrum of the induced double occupancy gives the pairing energy in a superfluid and the interaction energy in a Mott-insulator, respectively. In the Mott-insulator we relate the spectral weight of the peak to the spin ordering at finite temperature using perturbative calculations.

cond-mat.supr-con↗

arXiv2006

Spectroscopy of ultracold atoms by periodic lattice modulations

We present a non-perturbative analysis of a new experimental technique for probing ultracold bosons in an optical lattice by periodic lattice depth modulations. This is done using the time-dependent density-matrix renormalization group method. We find that sharp energy absorption peaks are not unique to the Mott insulating phase at commensurate filling, but also exist for superfluids at incommensurate filling. For strong interactions the peak structure provides an experimental measure of the interaction strength. Moreover, the peak height of the second peak can be employed as a measure of the incommensurability of the system.

cond-mat.other↗