5,318 research outputs found
Test Experiment for Time-Reversal Symmetry Breaking Superconductivity
A new experiment is proposed to probe the time-reversal symmetry of a
superconductor. It is shown that a time-reversal symmetry breaking
superconductor can be identified by the observation of a fractional flux in
connection with a Josephson junction in a special geometry.Comment: 4 pages, 2 figures available upon request, Revtex, MIT-CMT-OC
Metamagnetism of itinerant electrons in multi-layer ruthenates
The problem of quantum criticality in the context of itinerant ferro- or
metamagnetism has received considerable attention [S. A. Grigera et. al.,
Science 294, 329 (2001); C. Pfleiderer et. al., Nature, 414, 427 (2001)]. It
has been proposed that a new kind of quantum criticality is realised in
materials such as MnSi or Sr_3Ru_2O_7. We show based on a mean-field theory
that the low-temperature behaviour of the n-layer ruthenates
Sr_{n+1}Ru_nO_{3n+1} can be understood as a result of a Van Hove singularity
(VHS). We consider a single band whose Fermi energy, E_F, is close to the VHS
and deduce a complex phase diagram for the magnetism as a function of
temperature, magnetic field and E_F. The location of E_F with respect to the
VHS depends on the number of layers or can be tuned by pressure. We find that
the ferromagnetic quantum phase transition in this case is not of second but of
first order, with a metamagnetic quantum critical endpoint at high magnetic
field. Despite its simplicity this model describes well the properties of the
uniform magnetism in the single, double and triple layer ruthenates. We would
like to emphasise that the origin of this behaviour lies in the band structure.Comment: 7 pages, 3 figures, typos corrected and acknowledgement added, to
appear in the Europhysics Letter
Superconducting order parameter of SrRuO: a microscopic perspective
The character of the superconducting phase of SrRuO, is topic of a
longstanding discussion. The classification of the symmetry allowed order
parameters has relied on the tetragonal symmetry of the lattice and on
cylindrical Fermi surfaces, usually taken to be featureless, not including the
non-trivial symmetry aspects related to their orbital content. Here we show how
the careful account of the orbital degree of freedom in SrRuO, leads to
a much richer classification of order parameters. We analyse the stability and
degeneracy of these new order parameters from the perspective of the concept of
superconducting fitness and propose a new best order parameter candidate.Comment: 13 page
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