Comment on "Spectroscopic Evidence for Multiple Order Parameters in the Heavy Fermion Superconductor CeCoIn5"

This is a comment on recent paper by Rourke et al. titled "Spectroscopic Evidence for Multiple Order Parameters in the Heavy Fermion Superconductor CeCoIn5" (cond-mat/0409562v1 22 Sep 2004). We argue that the features observed by Rourke etal. arise from their contact not being in the ballistic limit.Comment: 4 pages with figures (pdf

Andreev reflection near the Dirac point at Graphene - NbSe2 junction

Despite extensive search for about a decade, specular Andreev reflection is only recently realized in bilayer graphene-superconductor interface. However, the evolution from the typical retro type Andreev reflection to the unique specular Andreev reflection in single layer graphene has not yet been observed. We investigate this transition by measuring the differential conductance at the van der Walls interface of single layer graphene and NbSe2 superconductor. We find that the normalized conductance becomes suppressed as we pass through the Dirac cone via tuning the Fermi level and bias energy, which manifests the transition from retro to non-retro type Andreev reflection. The suppression indicates the blockage of Andreev reflection beyond a critical angle of the incident electron with respect to the normal between the single layer graphene and the superconductor junction. The results are compared with a theoretical model of the corresponding setup

Signatures of two-step impurity mediated vortex lattice melting in Bose-Einstein Condensates

We simulate a rotating 2D BEC to study the melting of a vortex lattice in presence of random impurities. Impurities are introduced either through a protocol in which vortex lattice is produced in an impurity potential or first creating the vortex lattice in the absence of random pinning and then cranking up the (co-rotating) impurity potential. We find that for a fixed strength, pinning of vortices at randomly distributed impurities leads to the new states of vortex lattice. It is unearthed that the vortex lattice follow a two-step melting via loss of positional and orientational order. Also, the comparisons between the states obtained in two protocols show that the vortex lattice states are metastable states when impurities are introduced after the formation of an ordered vortex lattice. We also show the existence of metastable states which depend on the history of how the vortex lattice is created.Comment: Accepted in Euro. Phys. Let

CeMnNi4: A soft ferromagnet with a high degree of transport spin polarization

In this letter we introduce a new soft ferromagnetic compound, i.e. CeMnNi4, which exhibits a large moment (~4.95mu_B/Mn) and high degree of spin polarization. The system has a ferromagnetic transition temperature of 148K. Isothermal magnetization measurements at 5K reveal that the material is a soft ferromagnet with a magnetization saturating at about 500Oe and a coercive field of < 5 Oe. We determine the transport spin polarization of this material from Point Contact Andreev Reflection measurements to be 66% thereby making this material potentially important for spintronic applications.Comment: pdf file with figures Revised Version submitted to AP

Magnetic field induced emergent inhomogeneity in a superconducting film with weak and homogeneous disorder

When a magnetic field is applied, the mixed state of a conventional Type II superconductor gets destroyed at the upper critical field Hc2, where the normal vortex cores overlap with each other. Here, we show that in the presence weak and homogeneous disorder the destruction of superconductivity with field follows a different route. Starting with a weakly disordered NbN thin film ( Tc ~ 9K ), we show that under the application of magnetic field the superconducting state becomes increasingly granular, where lines of vortices separate the superconducting islands. Consequently, phase fluctuations between these islands give rise to a field induced pseudogap phase, which has a gap in the electronic density of states but where the global zero resistance state is destroyed.Comment: New data added in this versio

A two-coil mutual inductance technique to study matching effect in disordered NbN thin films

Although matching effects in superconducting anti-dot arrays have been studied extensively through magneto-resistance oscillations, these investigations have been restricted to a very narrow temperature window close to the superconducting transition. Here we report a "two coil" mutual inductance technique, which allows the study of this phenomenon deep in the superconducting state, through a direct measurement of the magnetic field variation of the shielding response. We demonstrate how this technique can be used to resolve outstanding issues on the origin of matching effects in superconducting thin films with periodic array of holes grown on anodized alumina membranes

Origin of Matching Effect in Anti-dot Array of Superconducting NbN Thin Films

We investigate the origin of matching effect observed in disordered superconducting NbN thin films with periodic array of holes. In addition to the periodic variation in the electrical resistance just above the superconducting transition temperature, Tc0, we find pronounced periodic variations with magnetic field in all dynamical quantities which can be influenced by flux-line motion under an external drive such as the magnetic shielding response and the critical current which survive in some samples down to temperatures as low as 0.09Tc0. In contrast, the superconducting energy gap, D which is a true thermodynamic quantity does not show any periodic variation with magnetic fields for the same films. Our results show that commensurate pinning of the flux line lattice driven by vortex-vortex interaction is the dominant mechanism for the observed matching effects in these superconducting anti-dot films rather than Little-Parks like quantum interference effect.Comment: 18 pages, 6 figure