Origin of Gap Anisotropy in Spin Fluctuation Models of the Fe-pnictides (2009)
Maier, T. A., Graser, S., Scalapino, D. J., Hirschfeld, P. J.
We discuss the large gap anisotropy found for the A1g (s-wave) state in RPA spin-fluctuation and functional renormalization group calculations and show how the simple arguments leading to isotropic...
Neutron Scattering Resonance and the Fe-pnictide Superconducting Gap (2009)
Maier, T. A., Graser, S., Scalapino, D. J., Hirschfeld, P.
The existence of a neutron scattering resonance at a wavevector q* implies a sign change of the gap between two Fermi surface regions separated by wavevector q* . For the Fe pnictides, a resonance...
Mishra, V., Boyd, G., Graser, S., Maier, T., Hirschfeld, P. J., Scalapino, D. J.
We show, using a simple model, how ordinary disorder can gap an extended-$s$ ($A_{1g}$) symmetry superconducting state with nodes. The concommitant crossover of thermodynamic properties, particularly...
Near-degeneracy of several pairing channels in multiorbital models for the Fe-pnictides (2008)
Graser, S., Maier, T. A., Hirschfeld, P. J., Scalapino, D. J.
Weak-coupling approaches to the pairing problem in the iron pnictide superconductors have predicted a wide variety of superconducting ground states. We argue here that this is due both to the...
Andersen, Brian M., Graser, S., Hirschfeld, P. J.
Impurity resonances observed by scanning tunneling spectroscopy in the superconducting state have been used to deduce properties of the underlying pure state. Here we study a longstanding puzzle...
Graser, S., Boyd, G. R., Cao, Chao, Cheng, Hai-Ping, Hirschfeld, P. J., Scalapino, D. J.
Since the discovery of high-Tc LaO_1-xF_xFeAs, and other such systems based on FeAs layers, several proposals have been made for the superconducting order parameter Delta_k, on both phenomenological...
Local quasiparticle lifetimes in a d-wave superconductor (2007)
Graser, S., Hirschfeld, P. J., Scalapino, D. J.
Scanning tunnelling spectroscopy (STS) measurements find that the surface of Bi-2212 is characterized by nanoscale sized regions, "gap patches," which have different magnitudes for the d-wave energy...
Wagenknecht, M., Koelle, D., Kleiner, R., Graser, S., Schopohl, N., Chesca, B., ...
We investigate in-plane quasiparticle tunneling across thin film grain boundary junctions (GBJs) of the electron-doped cuprate La$_{2-x}$Ce$_{x}$CuO$_4$ in magnetic fields up to $B=16 $T,...
Structure of BSCCO supermodulation from ab initio calculations (2007)
He, Y., Graser, S., Hirschfeld, P. J.
We present results of density functional theory (DFT) calculation of the structural supermodulation in BSCCO-2212 structure, and show that the supermodulation is indeed a spontaneous symmetry...
Novel Josephson Effects in d-wave Superconductor Junctions with Antiferromagnetic Interlayers (2007)
Andersen, Brian M., Barash, Yu. S., Graser, S., Hirschfeld, P. J.
We calculate the dc supercurrent through a Josephson tunnel junction consisting of an antiferromagnetic (AF) interlayer sandwiched between two d-wave superconductors (d). Such d/AF/d junctions...
Tc suppression and resistivity in cuprates with out of plane defects (2007)
Graser, S., Dahm, T., Hirschfeld, P. J.
Recent experiments introducing controlled disorder into optimally doped cuprate superconductors by both electron irradiation and chemical substitution have found unusual behavior in the rate of...
Cep164, a novel centriole appendage protein required for primary cilium formation (2007)
Graser, S., Stierhof, Y. D., Lavoie, S. B., Gassner, O. S., Lamla, S., Le Clech, M., ...
Transfer-matrix approach to multiband Josephson junctions (2006)
We study the influence of multiple bands on the properties of Josephson junctions. In particular we focus on the two gap superconductor magnesium diboride. We present a formalism to describe...
Vortex core shrinkage in a two gap superconductor: application to MgB2 (2006)
Graser, S., Gumann, A., Dahm, T., Schopohl, N.
As a model for the vortex core in MgB2 we study a two band model with a clean sigma band and a dirty pi band. We present calculations of the vortex core size in both bands as a function of...
Induced Kramer-Pesch-Effect in a Two Gap Superconductor: Application to MgB2 (2005)
Gumann, A., Graser, S., Dahm, T., Schopohl, N.
The size of the vortex core in a clean superconductor is strongly temperature dependent and shrinks with decreasing temperature, decreasing to zero for T -> 0. We study this so-called Kramer-Pesch...
Local density of states at polygonal boundaries of d-wave superconductors (2005)
Iniotakis, C., Graser, S., Dahm, T., Schopohl, N.
Besides the well-known existence of Andreev bound states, the zero-energy local density of states at the boundary of a d-wave superconductor strongly depends on the boundary geometry itself. In this...
Shadow on the wall cast by an Abrikosov vortex (2004)
Graser, S., Iniotakis, C., Dahm, T., Schopohl, N.
At the surface of a d-wave superconductor, a zero-energy peak in the quasiparticle spectrum can be observed. This peak appears due to Andreev bound states and is maximal if the nodal direction of the...
Influence of Fermi surface topology on the quasiparticle spectrum in the vortex state (2003)
Graser, S., Dahm, T., Schopohl, N.
We study the influence of Fermi surface topology on the quasiparticle density of states in the vortex state of type II superconductors. We observe that the field dependence and the shape of the...
Fermi surface topology and vortex state in MgB2 (2003)
Dahm, T., Graser, S., Schopohl, N.
Based on a detailed modeling of the Fermi surface topology of MgB2 we calculated the anisotropy of the upper critical field Bc2 within the two gap model. The sigma-band is modeled as a distorted...
Dahm, T., Graser, S., Iniotakis, C., Schopohl, N.
We present a detailed comparison of numerical solutions of the quasiclassical Eilenberger equations with several approximation schemes for the density of states of s- and d-wave superconductors in...
Integration of IP-Packet Data Transfers Within UHF DAMA (1998)
Huckell, Gary, Clinesmith, G., Graser, S., Chandler, Edward W.
The Navy is planning to update its operational Information Exchange Subsystems to incorporate Internet Protocols (IP) to create a more robust and flexible networking environment. There is also a...