Tailoring Tc by symmetry principles: The concept of superconducting fitness

Abstract

We propose a generalization of the concept of superconducting fitness, which allows us to make statements analogous to Anderson's theorems concerning the stability of different superconducting states. This concept can be applied to complex materials with several orbital, layer, sublattice or valley degrees of freedom. The superconducting fitness parameters FA(k) and FC (k) give a direct measure of the robustness of the weak coupling instability and of the presence of detrimental terms in the Hamiltonian, respectively. These two parameters can be employed as a guide to engineer normal state Hamiltonians in order to favour or suppress superconducting order parameters with different symmetries and topological properties. To illustrate the applicability and power of this concept we study three cases: the non-centrosymmetric heavy fermion CePt3Si, the hole doped iron pnictide KFe2As2 and the doped topological insulator CuxBi2Se3.

The Role of Odd‐Frequency Pairing in Multiband Superconductors

“…If the system under consideration is translation invariant we can Fourier‐transform from real‐space to momentum space and we find the following condition for odd‐ω pairing: This condition is in fact identical to a measure of “superconducting fitness” recently discussed by Ramires and Sigrist . In that work, it was demonstrated that whenever this quantity is non‐zero there is a reduction in the critical temperature.…”

“…In that work, it was demonstrated that whenever this quantity is non‐zero there is a reduction in the critical temperature. The authors, therefore, concluded that superconducting fitness can be a tool in the search for order parameters that are expected to be more thermodynamically stable . It is here interesting to note that, just one year prior to the publication of ref.…”

“…The authors, therefore, concluded that superconducting fitness can be a tool in the search for order parameters that are expected to be more thermodynamically stable. [117,118] It is here interesting to note that, just one year prior to the publication of ref. [117], a work by Asano and Sasaki [59] concluded that the emergence of oddpairing in two-band superconductors is linked to a suppression of the critical temperature.…”

“…This condition is in fact identical to a measure of "superconducting fitness" recently discussed by Ramires and Sigrist. [117,118] In that work, it was demonstrated that whenever this quantity is non-zero there is a reduction in the critical temperature. The authors, therefore, concluded that superconducting fitness can be a tool in the search for order parameters that are expected to be more thermodynamically stable.…”

Analog of the Anderson Theorem for the Polar Phase of Liquid 3He in a Nematic Aerogel

“…This property also holds exactly for all realizations of the idealized system but may not hold for real nafen. The unexpected reaction of some superconductors on addition of impurities was recently discussed in connection with multi-orbital superconductors [17,18,19]. The superfluid 3 He falls in this category.…”