The High Magnetic Field Phase Diagram of a Quasi-One Dimensional Metal

We present a unique high magnetic field phase of the quasi-one dimensional organic conductor (TMTSF)$_2$ClO$_4$. This phase, termed "Q-ClO$_4$", is obtained by rapid thermal quenching to avoid ordering of the ClO$_4$ anion. The magnetic field dependent phase of Q-ClO$_4$ is distinctly different from that in the extensively studied annealed material. Q-ClO$_4$ exhibits a spin density wave (SDW) transition at $\approx$ 5 K which is strongly magnetic field dependent. This dependence is well described by the theoretical treatment of Bjelis and Maki. We show that Q-ClO$_4$ provides a new B-T phase diagram in the hierarchy of low-dimensional organic metals (one-dimensional towards two-dimensional), and describe the temperature dependence of the of the quantum oscillations observed in the SDW phase.Comment: 10 pages, 4 figures, preprin

XY ring-exchange model on the triangular lattice

We study ring-exchange models for bosons or XY-spins on the triangular lattice. A four-spin exchange leads to a manifold of ground states with gapless excitations and critical power-law correlations. With a nearest-neighbour exchange, fluctuations select a four-fold ferrimagnetically ordered ground state with a small spin/superfluid stiffness which breaks the global U(1) and translational symmetry. We explore consequences for phase transitions at finite temperature and in an in-plane magnetic field.Comment: 9 pgs (RevTeX), 4 fig

Ring exchange, the Bose metal, and bosonization in two dimensions

Motivated by the high-T_c cuprates, we consider a model of bosonic Cooper pairs moving on a square lattice via ring exchange. We show that this model offers a natural middle ground between a conventional antiferromagnetic Mott insulator and the fully deconfined fractionalized phase which underlies the spin-charge separation scenario for high-T_c superconductivity. We show that such ring models sustain a stable critical phase in two dimensions, the *Bose metal*. The Bose metal is a compressible state, with gapless but uncondensed boson and ``vortex'' excitations, power-law superconducting and charge-ordering correlations, and broad spectral functions. We characterize the Bose metal with the aid of an exact plaquette duality transformation, which motivates a universal low energy description of the Bose metal. This description is in terms of a pair of dual bosonic phase fields, and is a direct analog of the well-known one-dimensional bosonization approach. We verify the validity of the low energy description by numerical simulations of the ring model in its exact dual form. The relevance to the high-T_c superconductors and a variety of extensions to other systems are discussed, including the bosonization of a two dimensional fermionic ring model

Properties of the Ideal Ginzburg-Landau Vortex Lattice

The magnetization curves M(H) for ideal type-II superconductors and the maximum, minimum, and saddle point magnetic fields of the vortex lattice are calculated from Ginzburg-Landau theory for the entire ranges of applied magnetic fields Hc1 <= H < Hc2 or inductions 0 <= B < Hc2 and Ginzburg-Landau parameters sqrt(1/2) <= kappa <= 1000. Results for the triangular and square flux-line lattices are compared with the results of the circular cell approximation. The exact magnetic field B(x,y) and magnetization M(H, kappa) are compared with often used approximate expressions, some of which deviate considerably or have limited validity. Useful limiting expressions and analytical interpolation formulas are presented.Comment: 11 pages, 8 figure

A Two-dimensional Superconductor in a Tilted Magnetic Field - new states with finite Cooper-pair momentum

Varying the angle Theta between applied field and the conducting planes of a layered superconductor in a small interval close to the plane-parallel field direction, a large number of superconducting states with unusual properties may be produced. For these states, the pair breaking effect of the magnetic field affects both the orbital and the spin degree of freedom. This leads to pair wave functions with finite momentum, which are labeled by Landau quantum numbers 0<n<\infty. The stable order parameter structure and magnetic field distribution for these states is found by minimizing the quasiclassical free energy near H_{c2} including nonlinear terms. One finds states with coexisting line-like and point-like order parameter zeros and states with coexisting vortices and antivortices. The magnetic response may be diamagnetic or paramagnetic depending on the position within the unit cell. The structure of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states at Theta=0 is reconsidered. The transition n->\infty of the paramagnetic vortex states to the FFLO-limit is analyzed and the physical reason for the occupation of higher Landau levels is pointed out.Comment: 24 pages, 11 figure

Orbital hydrodynamics of the anisotropic a phase of 3He for large angles of rotation of the orbital momentum

A linear hydrodynamic theory of the orbital order parameter rotations and mass transport in the A phase of superfluid 3He is proposed which is free of the problems related to the definition of the phase ϕ, and thus, to describe large angle rotations of the order parameter orbital symmetry axis Î, is simpler and more adequate than the locally equivalent theory of Graham.On présente une théorie de l'hydrodynamique linéaire décrivant les rotations du paramètre d'ordre et les courants de masses dans la phase A de l'hélium trois superfluide. Elle ne présente aucune des ambiguïtés liées à l'utilisation de la phase ϕ. Ainsi cette théorie permet de décrire sur des distances macroscopiques toutes les rotations de l'axe orbital Î, quel que soit leur angle, beaucoup plus simplement que la théorie localement équivalente de Graham

Effet d'un champ électrique dans l'hélium 3 superfluide

An electric field can, in principle, produce a single domain in the A-phase of superfluid helium 3 and, because of its small effect in the B phase, test the orbital isotropy of the B phase.Un champ électrique peut permettre de réaliser un monodomaine dans la phase A de l'hélium 3 superfluide, et l'absence d'effet important dans la phase B donne un moyen de vérifier que cette phase est isotrope pour les variables orbitales

Errata : Effet d'un champ électrique dans l'hélium 3 superfluide

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PHYSICAL ORIGIN OF A LARGE FOUR SPIN EXCHANGE IN b.c.c. SOLID 3He

Une méthode de calcul de l'échange est présentée, en utilisant un potentiel effectif pour corriger la fonction d'onde variationnelle. L'étude géométrique des configurations les plus probables, qui tient compte de la répulsion des coeurs durs, explique l'origine d'un échange 4 spins du même ordre que l'échange 2 spins.A method of calculating the exchange is presented, using an effective potential to correct the variationnal wave function. The geometrical study of the most likely configurations, taking account of hard core repulsion, explains the origin of four spin exchange of the same order as two spin exchange

Self diffusion in solid 3He at very low temperature

Multiple spin echoes in solid 3He, which are due to the demagnetizing field effect, have been reconsidered by taking into account the spin diffusion. The analysis is applied to the experimental results obtained earlier at very low temperature. The spin diffusion coefficient D remains constant in the whole temperature range 10.5 mK-1.07 mK, even close to the spin ordering temperature of solid 3He. The susceptibility values χ obtained have a higher precision than those previously published [3].Les échos multiples dans l'3He solide, dus à l'effet du champ démagnétisant, ont été recalculés en tenant compte de la diffusion de spin et nous avons appliqué cette analyse à des résultats expérimentaux antérieurs obtenus à très basse température. Le coefficient de diffusion de spin D reste constant dans tout le domaine de température 10,5 mK-1,07 mK, même au voisinage de la température d'ordre des spins de l'3He solide. On détermine les valeurs de la susceptibilité magnétique χ avec une précision améliorée par rapport aux valeurs précédemment publiées [3]