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Quantum criticality and superconducting pairing in Ce(1-x)Yb(x)CoIn5 alloys

In this paper we review some of our recent experimental and theoretical results on transport and thermodynamic properties of heavy-fermion alloys Ce(1-x)Yb(x)CoIn5. Charge transport measurements under magnetic field and pressure on these single crystalline alloys revealed that: (i) relatively small Yb substitution suppresses the field induced quantum critical point, with a complete suppression for nominal Yb doping x>0.20; (ii) the superconducting transition temperature Tc and Kondo lattice coherence temperature T* decrease with x, yet they remain finite over the wide range of Yb concentrations; (iii) both Tc and T* increase with pressure; (iv) there are two contributions to resistivity, which show different temperature and pressure dependences, implying that both heavy and light quasiparticles contribute to inelastic scattering. We also analyzed theoretically the pressure dependence of both T* and Tc within the composite pairing theory. In the purely static limit, when we ignore the lattice dynamics, we find that the composite pairing mechanism necessarily causes opposite behaviors of T* and Tc with pressure: if T* grows with pressure, Tc must decrease with pressure and vice versa.