Quantum phase transitions and non-Fermi liquid regime in the heavy fermion
Ce1-xYbxCoIn5
Carmen C. Almasan1, Yogesh P. Singh1, Tao Hu1, Ivy K. Lum2, Benjamin D. White2, Maxim
Dzero1, and M. Brian Maple2
1
Kent State University, Kent, USA
University of California, San Diego, USA
2
One of the greatest challenges to Landau’s Fermi liquid theory – the standard theory
of metals - is presented by complex materials with strong electronic correlations.
The non-Fermi liquid (NFL) transport and thermodynamic properties of these
materials are often explained by the presence of strong quantum critical
fluctuations associated with a quantum phase transition that happens at a quantum
critical point (QCP). A QCP can be revealed by applying pressure, magnetic field, or
changing the chemical composition. The heavy-fermion CeCoIn5 is a prototypical
system for which its pronounced NFL behavior in the normal state and
unconventional superconductivity are thought to arise from the proximity of this
system to a QCP. Previous experiments address the physics of this QCP by
extrapolating results obtained in the normal state, i.e., there were no direct probes
of antiferromagnetism and quantum criticality in the superconducting state. This
motivated us to study the transport in the mixed state, thus revealing the physics of
antiferromagnetism and quantum criticality of the underlying normal state [1]. We
will present the results obtained in these studies by measuring the vortex core
dissipation under applied hydrostatic pressure (P) and magnetic field (H). Using our
experimental results, we obtained an explicit equation for the antiferromagnetic
boundary inside the superconducting dome and constructed an H-T-P phase
diagram, hence, a quantum critical line inside the superconducting phase.
Furthermore, we will also show that the full suppression of the QCP in CeCoIn5 by
doping with Yb has surprisingly little impact on both superconductivity and the
NFL behavior [2-4]. The robustness of superconductivity against substitutioninduced disorder points towards an alternative microscopic origin of
superconductivity in this system, while the robustness of the NFL behavior implies
that this behavior could be a new state of matter in its own right rather than a
consequence of the underlying quantum phase transition.
[1] T. Hu et al., Phys. Rev. Lett. 108, 056401 (2012).
[2] T. Hu et al., PNAS 110, 7160 (2013).
[3] Y. Singh et al., Phys. Rev. B 89, 115106 (2014).
[4] Y. Singh et al, to be published.