Superconducting Vortices in CeCoIn ₅ : Toward the Pauli-Limiting Field

Abstract

Many superconducting materials allow the penetration of magnetic fields in a mixed state in which the superfluid is threaded by a regular lattice of Abrikosov vortices, each carrying one quantum of magnetic flux. The phenomenological Ginzburg-Landau theory, based on the concept of characteristic length scales, has generally provided a good description of the Abrikosov vortex lattice state. We conducted neutron-scattering measurements of the vortex lattice form factor in the heavy-fermion superconductor cerium-cobalt-indium (CeCoIn 5 ) and found that this form factor increases with increasing field—opposite to the expectations within the Abrikosov-Ginzburg-Landau paradigm. We propose that the anomalous field dependence of the form factor arises from Pauli paramagnetic effects around the vortex cores and from the proximity of the superconducting state to a quantum critical point.

Visualizing nodal heavy fermion superconductivity in CeCoIn5

“…4a,b, STM conductance maps can be used to directly visualize the vortex lattice in this compound, which can have different structures depending on the magnetic field. Such structural changes of the vortex lattice (transition between rhombic and square lattices) have been previously studied in neutron scattering experiments 29 and various theoretical models 30 . Complementing these efforts, STM can be used to probe the electronic states within the vortex core directly, as shown in Fig.…”

“…An important next step in extending this phenomenology would be to explore how the competition between antiferromagnetism and superconductivity manifests itself on the atomic scale in STM measurements. Similarly, extending our studies of the electronic structure in magnetic vortices could be used to examine the competition between different types of ordering in the mixed LETTERS state, and the possible development of the Fulde-Ferrell-LarkinOvchinnikov state in this Pauli-limited superconductor 29,34,35 .…”

Quantum Critical Quasiparticle Scattering within the Superconducting State ofCeCoIn5

“…Together with large angle scattering evidence [32], the presence of similar critical behavior in the ordered antiferromagnet CeRhIn 5 under pressure [16] strongly suggests that the QCP for H c configuration in CeCoIn 5 is also magnetic in nature, although magnetic order was not observed in muon spin rotation [17] or neutron scattering measurements [18]. However, for H ab neutron scattering [19,20] and nuclear magnetic resonance [21] measurements have found field-induced antiferromagnetism in the vicinity of H c2 suggesting magnetism grows gradually with increasing field [22,23].…”

“…The pinning of H to H c2 was subsequently shown to hold regardless of field orientation [11] or suppression of the superconducting state by impurities [12], suggesting a novel form of quantum criticality closely linked with the superconducting state. Recent work has revealed other examples of systems that appear to have a field-tuned QCP pinned to H c2 , including cuprates [13,14] and iron pnictides [15].Together with large angle scattering evidence [32], the presence of similar critical behavior in the ordered antiferromagnet CeRhIn 5 under pressure [16] strongly suggests that the QCP for H c configuration in CeCoIn 5 is also magnetic in nature, although magnetic order was not observed in muon spin rotation [17] or neutron scattering measurements [18]. However, for H ab neutron scattering [19,20] and nuclear magnetic resonance [21] measurements have found field-induced antiferromagnetism in the vicinity of H c2 suggesting magnetism grows gradually with increasing field [22,23].…”

Fluctuations and order of antiferromagnetism induced by paramagnetic pair breaking in superconducting vortex lattices

“…the triangular lattice is used since, in the high field SC phase of CeCoIn 5 in H c, the square lattice characteristic of d-wave superconductors is deformed into nearly triangular ones due to the strong PPB effect [10,13]. By using the identity [23] exp iA…”