Nodes vs. minima in the energy gap of iron-pnictides from field-induced anisotropy

We develop the formalism for computing the oscillations of the specific heat and thermal transport under rotated magnetic field in multiband superconductors with anisotropic gap and apply it to iron-pnictides. We show that these oscillations change sign at low temperatures and fields, which strongly influences the conclusions about the gap structure based on experiment. We find that recent measurements of the specific heat oscillations indicate that the iron-based superconductors possess an anisotropic gap with deep minima or nodes close to the line connecting electron and hole pockets. We make predictions for the behavior of the thermal conductivity that will help distinguish between these cases.Comment: 4+3 pages, published version with supplemen

Crystalline order in superfluid 3He films

We predict an inhomogeneous phase of superfluid 3He films in which translational symmetry is spontaneously broken in the plane of the film. This phase is energetically favored over a range of film thicknesses, $D_{c_2}(T)<D<D_{c_1}(T)$, separating distinct homogeneous superfluid phases. The instability at the critical film thickness, $D_{c_2}\approx 9 \xi(T)$, is a single-mode instability generating striped phase order in the film. Numerical calculations of the order parameter and free energy indicate a second-order instability to a periodic lattice of degenerate B-like phases separated by domain walls at $D_{c_1}\approx 12 \xi(T)$. The striped phase should be identifiable in transport and nuclear magnetic resonance experiments.Comment: 4 pages, 4 figure

Specific heat jump at superconducting transition in the presence of Spin-Density-Wave in iron-pnictides

We analyze the magnitude of the specific heat jump \Delta C at the superconducting transition temperature T_c in the situation when superconductivity develops in the pre-existing antiferromagnetic phase. We show that \Delta C/T_c differs from the BCS value and is peaked at the tri-critical point where this coexistence phase first emerges. Deeper in the magnetic phase, the onset of coexistence, T_c, drops and \Delta C/T_c decreases, roughly as \Delta C/T_c \propto T^2_c at intermediate T_c and exponentially at the lowest T_c, in agreement with the observed behavior of \Delta C/T_c in iron-based superconductors.Comment: 4+ pages, 3 figure

Spontaneously broken translational symmetry at edges of high-temperature superconductors: thermodynamics in magnetic field

We investigate equilibrium properties, including structure of the order parameter, superflow patterns, and thermodynamics of low-temperature surface phases of layered d_{x^2-y^2}-wave superconductors in magnetic field. At zero external magnetic field, time-reversal symmetry and continuous translational symmetry along the edge are broken spontaneously in a second order phase transition at a temperature $T^*\approx 0.18 T_c$, where $T_c$ is the superconducting transition temperature. At the phase transition there is a jump in the specific heat that scales with the ratio between the edge length $D$ and layer area ${\cal A}$ as $(D\xi_0/{\cal A})\Delta C_d$, where $\Delta C_d$ is the jump in the specific heat at the d-wave superconducting transition and $\xi_0$ is the superconducting coherence length. The phase with broken symmetry is characterized by a gauge invariant superfluid momentum ${\bf p}_s$ that forms a non-trivial planar vector field with a chain of sources and sinks along the edges with a period of approximately $12\xi_0$, and saddle point disclinations in the interior. To find out the relative importance of time-reversal and translational symmetry breaking we apply an external field that breaks time-reversal symmetry explicitly. We find that the phase transition into the state with the non-trivial ${\bf p}_s$ vector field keeps its main signatures, and is still of second order. In the external field, the saddle point disclinations are pushed towards the edges, and thereby a chain of edge motifs are formed, where each motif contains a source, a sink, and a saddle point. Due to a competing paramagnetic response at the edges, the phase transition temperature $T^*$ is slowly suppressed with increasing magnetic field strength, but the phase with broken symmetry survives into the mixed state.Comment: 12 pages, 9 figure

Supercomputer Simulations of Disk Galaxies

The time evolution of models for an isolated disk of highly flattened galaxies of stars is investigated by direct integration of the Newtonian equations of motion of N=30,000 identical stars over a time span of many galactic rotations. Certain astronomical implications of the simulations to actual disk-shaped (i.e. rapidly rotating) galaxies are explored as well.Comment: 3 pages, 2 figure Aat.sty, Aattable.sty, presented by E. Griv at the JENAM 2000, S02, Moscow, Russia, 200

Reduced effect of impurities on the universal pairing scale in the cuprates

We consider the effect of non-magnetic impurities on the onset temperature $T^*$ for the $d-$wave pairing in spin-fluctuation scenario for the cuprates. We analyze intermediate coupling regime when the magnetic correlation length $\xi/a >1$ and the dimensionless coupling $u$ is O(1). In the clean limit, $T^* \approx 0.02 v_f/a$ in this parameter range, and weakly depends on $\xi$ and $u$. We found numerically that this universal pairing scale is also quite robust with respect to impurities: the scattering rate $\Gamma_{cr}$ needed to bring $T^*$ down to zero is about 4 times larger than in weak coupling, in good quantitative agreement with experiments. We provide analytical reasoning for this result.Comment: 4 pages, 2 fig, submitted to PR

Microscopic evidence for field-induced magnetism in CeCoIn5_5

We present NMR data in the normal and superconducting states of CeCoIn$_5$ for fields close to $H_{\rm c2}(0)=11.8$ T in the $ab$ plane. Recent experiments identified a first-order transition from the normal to superconducting state for $H> 10.5$ T, and a new thermodynamic phase below 290 mK within the superconducting state. We find that the Knight shifts of the In(1), In(2) and the Co are discontinuous across the first-order transition and the magnetic linewidths increase dramatically. The broadening differs for the three sites, unlike the expectation for an Abrikosov vortex lattice, and suggests the presence of static spin moments in the vortex cores. In the low-temperature and high-field phase the broad NMR lineshapes suggest ordered local moments, rather than a long wavelength quasiparticle spin density modulation expected for an FFLO phase.Comment: 4 pages, 4 figures. to appear in Phys. Rev. Let