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We point out that particle-hole asymmetry induced by doping or pressure
leads to patterns of triplets of order parameters that necessarilly coexist whenever
two of the order parameters are present. As a result, in any antiferromagnetic
superconductor, there is coexistence of singlet and staggered triplet superconducting
components. we have found a systematic way to predict all such patetrns
of unconventional superconducting and particle-hole condensates and we have
explored the new qualitative insight that we gain knowing that all order
parameters should be treated on the same footing in particular under the influence of
a Zeeman magnetic field. We will discuss our results
in connection with some controversial issues on novel unconventional superconductors.
In particular, we observe novel magnetic field induced transitions that may show
the thermodynamic characteristics of Fulde-Ferrel phases.
For example, above a given field, in a particle-hole symmetric system
we report a transition from d-wave singlet SC to a
state in which d-wave singlet SC coexists with staggered triplet SC and SDW.
We will argue based on experiments on CeCoIn_5 that this may correspond to the
high field state observed in this material.
In the same context we will also discuss issues related with the pseudogap
in high-T_c cuprates, the parity of the order parameter in organic compounds
as well as the possibility for staggered superconductivity in ferromagnetic superconductors.
This work has been done partly in collaboration with P. Thalmeier and partly in collaboration with P.B. Littlewood. Related Refs. arxiv:0804.2450 arxiv:0804.2460 arxiv:0802.4093 arxiv:0709.1025 arxiv:0802.4080 |
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