We report on a Monte-Carlo study of two-dimensional Ginzburg-Landau superconductors in a magnetic field which finds clear evidence for a firstorder phase transition characterized by broken translational symmetry of the superfluid density. A key aspect of our study is the introduction of a quantity proportional to the Fourier transform of the superfluid density which can be sampled efficiently i...

The equilibrium statistical mechanics of the energy-enstrophy theory for the barotropic vorticity equation is solved exactly in the sense that a explicitly non-Gaussian configurational integral is calculated in closed form. A family of lattice vortex gas models for the barotropic vorticity equation (BVE) is derived and shown to have a well-defined nonextensive continuum limit as the coarse-grai...

Competition with magnetism is at the heart of high-temperature superconductivity, most intensely felt near a vortex core. To investigate vortex magnetism we have developed a spatially resolved probe based upon NMR spin-lattice-relaxation spectroscopy. With this approach we have found a spin-density wave associated with the vortex core in Bi(2)Sr(2)CaCu(2)O(8+y), similar to checkerboard patterns...

The spin-transfer effect is investigated for the vortex state of a magnetic nanodot. A spin current is shown to act similarly to an effective magnetic field perpendicular to the nanodot. Then a vortex with magnetization (polarity) parallel to the current polarization is energetically favorable. Following a simple energy analysis and using direct spin-lattice simulations, we predict the polarity...

We carry out Monte Carlo simulations of the uniformly frustrated three dimensional XY model, as a model for vortex line fluctuations in high temperature superconductors in an applied magnetic field. We show, comparing systems of different size, that there are two distinct phase transitions. At a lower Tc⊥, the vortex lattice melts, and coherence is lost in planes perpendicular to the magnetic f...

We found a novel dimensional transition in the vortex lattice of a finite-sized superconductor. The low-field dependence (with field applied parallel to the film plane) of the magnetization exhibits two maxima, which signal the transition from one to two dimensions. In one dimension the vortices line up along the film, and with increasing field their arrangement changes into a two-dimensional a...

We present an atomic resolution scanning tunneling spectroscopy study of superconducting BaFe1.8Co0.2As2 single crystals in magnetic fields up to 9 T. At zero field, a single gap with coherence peaks at Delta=6.25 meV is observed in the density of states. At 9 and 6 T, we image a disordered vortex lattice, consistent with isotropic, single flux quantum vortices. Vortex locations are uncorrelate...

From muon spin rotation measurements on under-to overdoped Bi-2212 crystals we obtain evidence for a two-stage transition of the vortex matter as a function of temperature. The first transition is well known and related to the irreversibility line (IL). The second one is located below the IL and has not been previously observed. It occurs for all three sets of crystals and is unrelated to the v...

Vortex tilt response in a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex lattice is studied as a probe reflecting the spatial structure of this state. In quasi 2D materials under a parallel magnetic field, the tilt modulus E2 of the nodal planes in the FFLO state modulating along the field decreases as the paramagnetic effect is effectively enhanced, and this reduction of E2 in turn reduces the...