arXiv subjects

D. F. Agterberg

Publications and source records attributed to D. F. Agterberg.

62 records · Page 4Linked to original sources

arXiv1999

Conventional mechanisms for "exotic" superconductivity

We consider the pairing state due to the usual BCS mechanism in substances of cubic and hexagonal symmetry where the Fermi surface forms pockets around several points of high symmetry. We find that the symmetry imposed on the multiple pocket positions could give rise to a multidimensional nontrivial superconducting order parameter. The time reversal symmetry in the pairing state is broken. We suggest several candidate substances where such ordering may appear, and discuss means by which such a phase may be identified.

cond-mat.supr-con↗

arXiv1998

On possible superconductivity in the doped ladder compound La_(1-x)Sr_xCuO_2.5

LaCuO_2.5 is a system of coupled, two-chain, cuprate ladders which may be doped systematically by Sr substitution. Motivated by the recent synthesis of single crystals, we investigate theoretically the possibility of superconductivity in this compound. We use a model of spin fluctuation-mediated superconductivity, where the pairing potential is strongly peaked at πin the ladder direction. We solve the coupled gap equations on the bonding and antibonding ladder bands to find superconducting solutions across the range of doping, and discuss their relevance to the real material.

cond-mat.str-el↗

arXiv1998

Ginzburg-Landau Theory for a p-Wave Sr_2RuO_4 Superconductor: Vortex Core Structure and Extended London Theory

Based on a two dimensional odd-parity superconducting order parameter for Sr_2RuO_4 with p-wave symmetry, we investigate the single vortex and vortex lattice structure of the mixed phase near H_{c1}. Ginzburg-Landau calculations for a single vortex show a fourfold structure with an orientation depending on the microscopic Fermi surface properties. The corresponding extended London theory is developed to determine the vortex lattice structure and we find near H_{c1} a centered rectangular vortex lattice. As the field is increased from H_{c1} this lattice continuously deforms until a square vortex lattice is achieved. In the centered rectangular phase the field distribution, as measurable through μ-SR experiments, exhibits a characteristic two peak structure (similar to that predicted in high temperature and borocarbide superconductors).

cond-mat.supr-con↗

arXiv1998

Square vortex lattices for two component superconducting order parameters

I investigate the vortex lattice structure of the Ginzburg Landau free energy for a two component order parameter in the weak-coupling clean-limit when the field is along the high symmetry axis in a tetragonal crystal. It is shown that the vortex lattice phase diagram as a function of the Ginzburg Landau free energy parameters includes phases with a hexagonal, centered rectangular, rectangular, and square unit cells. It is also shown that the square vortex lattice has the largest region of stability. The field distribution of the square vortex lattice near $H_{c2}$ is determined and the application of this model to Sr$_2$RuO$_4$ is discussed.

cond-mat.supr-con↗

arXiv1998

Vortex lattice structures of Sr$_2$RuO$_4$

The vortex lattice structures of Sr$_2$RuO$_4$ for the odd parity representations of the superconducting state are examined for the magnetic field along the crystallographic directions. Particular emphasis is placed upon the two dimensional representation which is believed to be relevant to this material. It is shown that when the zero-field state breaks time reversal symmetry, there must exist two superconducting transitions when there is a finite field along a high symmetry direction in the basal plane. Also it is shown that a square vortex lattice is expected when the field is along the $c$-axis. The orientation of the square lattice with respect to the underlying ionic lattice yields information as to which Ru 4d orbitals are relevant to the superconducting state.

cond-mat.supr-con↗

arXiv1997

Orbital dependent superconductivity in Sr_2RuO_4

We show that for superconducting Sr_2RuO_4 any unconventional pairing in the part of the Fermi surface with Ru 4d-xy orbital character is weakly coupled to that with Ru 4d-xz, 4d-yz orbital character. This naturally gives rise to two disparate energy scales in the superconducting state which leads to novel low temperature properties in a variety of thermodynamic and transport properties and which would also account for the large residual density of states seen in specific heat and NQR measurements.

cond-mat.supr-con↗

arXiv1996

Effect of diffusive boundaries on surface superconductivity in unconventional superconductors

Boundary conditions for a superconducting order parameter at a diffusive scattering boundary are derived from microscopic theory. The results indicate that for all but isotropic gap functions the diffusive boundary almost completely suppresses surface superconductivity in the Ginzburg-Landau regime. This indicates that in anisotropic superconductors surface superconductivity can only be observed for surface normals along high symmetry directions where atomically clean surfaces can be cleaved.

cond-mat↗

arXiv1995

Surface superconductivity and order parameter suppression in UPt$_3$

We show that a recent measurement of surface superconductivity in UPt$_3$ (Keller {\it et. al.}, Phys. Rev. Lett. {\bf 73}, 2364 (1994)) can be understood if the superconducting pair wavefunction is suppressed anisotropically at a vacuum to superconductor interface. Further measurements of surface superconductivity can distinguish between the various phenomenological models of superconducting UPt$_3$.

cond-mat↗