Vortex tilt modulus in Fulde-Ferrell-Larkin-Ovchinnikov state

Vortex tilt response in Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex lattice is theoretically examined as a probe reflecting the spatial structure of this state. In the FFLO state with nodal planes perpendicular to the magnetic field in a quasi 2D material under a parallel field, the tilt modulus E_{2} {\it of the nodal planes} decreases as the paramagnetic effect is effectively enhanced, and this reduction of E_{2} in turn reduces the vortex tilt modulus. This reduction of vortex tilt modulus, more remarkable in more anisotropic systems, accompanying the FFLO transition may be an origin of the monotonous reduction of sound velocity detected upon cooling in a ultrasound measurement for CeCoIn5.Comment: 14 pages, 5 figures. Accepted for publication in Phys. Rev.

AKSZ-BV Formalism and Courant Algebroid-induced Topological Field Theories

We give a detailed exposition of the Alexandrov-Kontsevich-Schwarz- Zaboronsky superfield formalism using the language of graded manifolds. As a main illustarting example, to every Courant algebroid structure we associate canonically a three-dimensional topological sigma-model. Using the AKSZ formalism, we construct the Batalin-Vilkovisky master action for the model.Comment: 13 pages, based on lectures at Rencontres mathematiques de Glanon 200

Comment on "Constant stress and pressure rheology of colloidal suspensions"

This is a comment on the recent letter by Wang and Brady on "Constant stress and pressure rheology of colloidal suspensions", Phys. Rev. Lett. 115, 158301 (2015).Comment: 1 page; under review -> v2: publishe

Effect of in-plane line defects on field-tuned superconductor-insulator transition behavior in homogeneous thin film

Field-tuned superconductor-insulator transition (FSIT) behavior in 2D isotropic and homogeneous thin films is usually accompanied by a nonvanishing critical resistance at low $T$. It is shown that, in a 2D film including line defects paralle to each other but with random positions perpendicular to them, the (apparent) critical resistance in low $T$ limit vanishes, as in the 1D quantum superconducting (SC) transition, under a current parallel to the line defects. This 1D-like critical resistive behavior is more clearly seen in systems with weaker point disorder and may be useful in clarifying whether the true origin of FSIT behavior in the parent superconductor is the glass fluctuation or the quantum SC fluctuation. As a by-product of the present calculation, it is also pointed out that, in 2D films with line-like defects with a long but {\it finite} correlation length parallel to the lines, a quantum metallic behavior intervening the insulating and SC ones appears in the resistivity curves.Comment: 16 pages, 14 figure

High field superconducting phase diagrams including Fulde-Ferrell-Larkin-Ovchinnikov vortex states

Motivated by a striking observation of a Fulde-Ferell-Larkin-Ovchinnikov (FFLO) vortex state in the heavy fermion material CeCoIn5 in fields {\it perpendicular} to the superconducting planes (${\bf H} \parallel c$), superconducting phase diagrams including an FFLO state of quasi two-dimensional (Q2D) superconductors are systematically studied. In the clean {\it limit}, the high field superconducting state in the low temperature limit should be not the FFLO state modulating along ${\bf H}$, appeared in CeCoIn5 in both ${\bf H} \parallel c$ and ${\bf H} \perp c$, but a different vortex state with a modulation, induced by the paramagnetism, perpendicular to the field. It is found that the presence of weak impurities is the origin of the absence in CeCoIn5 of the latter state and leads to the ${\bf H} \parallel c$ phase diagram, as seen in CeCoIn5, {\it apparently} different in character from that in ${\bf H} \perp c$.Comment: A reference was updated. To appear in Phys. Rev.

Theoretical Description of Resistive Behavior near a Quantum Vortex-Glass Transition

Resistive behaviors at nonzero temperatures (T > 0) reflecting a quantum vortex-glass (VG) transition (the so-called field-tuned superconductor-insulator transition at T=0) are studied based on a quantum Ginzburg-Landau (GL) action for a s-wave pairing case containing microscopic details. The ordinary dissipative dynamics of the pair-field is assumed on the basis of a consistency between the fluctuation conductance terms excluded from GL approach and an observed negative magnetoresistance. It is shown that the VG contribution, G_{vg}(B=B_{vg}, T \to 0),to 2D fluctuation conductance at the VG transition field B_{vg} depends on the strength of a repulsive-interaction between electrons and takes a universal value only in the ordinary dirty limit neglecting the electron-repulsion. Available resistivity data near B_{vg} are discussed based on our results, and extensions to the cases of a d-wave pairing and of 3D systems are briefly commented on.Comment: Explanation of data in strongly disordered case, as well as Fig.2 and 3, was renewed, and comments on recent publications were added. To appear in J.Phys.Soc. Jp

Modulated Vortex Lattice in High Fields and Gap Nodes

The mean field vortex phase diagram of a quasi two dimensional superconductor with a nodal d-wave pairing and with strong Pauli spin depairing is examined in the parallel field case in order to examine an effect of gap nodes (or minima) on the stability of a FFLO-like vortex lattice. We find through a heuristic argument and a model calculation with a four-fold anisotropic Fermi velocity that the FFLO-like state is relatively suppressed as the field approaches a nodal direction. When taking account of a couple of experimental results altogether, the present result strongly suggests that a node or gap minimum of the pairing function of CeCoIn$_5$ is located along the [100]-direction.Comment: 5 pages, 2 figures, References were added. To appear in Phys. Rev.

Theoretical Description of Nearly Discontinuous Transition in Superconductors with Paramagnetic Depairing

Based on a theoretical argument and Monte Carlo simulations of a Ginzburg-Landau model derived microscopically, it is argued that, in type-II superconductors where {\it both} the paramagnetic {\it and} orbital depairings are important, a strong first-order transition (FOT) at $H_{c2}$ expected in the mean field (MF) approximation never occurs in real systems and changes due to the fluctuation into a crossover. The present result explains why a {\it nearly} discontinuous crossover at $H_{c2}$ with {\it no} intrinsic hysteresis is observed only in a clean superconducting material with a singlet pairing and a high condensation energy such as CeCoIn$_5$.Comment: Publication version. See cond-mat/0306060 regarding a corresponding long pape

Evaluation of true interlamellar spacing from microstructural observations

A method for evaluating true interlamellar spacing from micrographs is proposed for a multidomained lamellar structure. The microstructure of these materials is assumed to be composed of many domains with the lamellae aligned roughly parallel to each other within each domain and with the domains themselves randomly oriented relative to one another. An explicit expression for the distribution of apparent interlamellar spacing is derived assuming that the distribution of the true interlamellar spacing is Gaussian. The average interlamellar spacing is close to the peak interlamellar spacing observed in the distribution. The theoretical distributions are compared with experimental ones obtained by analyzing micrographs of PbTe–Sb2Te3 lamellar composites

Microscopic Study of Quantum Vortex-Glass Transition Field in Two-Dimensional Superconductors

The position of a field-tuned superconductor-insulator quantum transition occuring in disordered thin films is examined within the mean field approximation. Our calculation shows that the microscopic disorder-induced reduction of the quantum transition point found experimentally cannot be explained if the interplay between the disorder and an electron-electron repulsive interaction is ignored. This work is presented as a microscopic basis of an explanation (cond-mat/0105122) of resistive phenomena near the transition field.Comment: 16 pages, 5 figures. To appear in J.Phys.Soc.Jp