University of Connecticut

Events Calendar

Condensed Matter Physics Seminar

Tuesday, April 10, 2018
2:00pm – 3:00pm

Storrs Campus
Physics Building, P121

Dr. Daniel Mazzone, National Synchrotron Light Source II, Brookhaven National Laboratory

Intertwined degrees of freedom in the series Nd1-xCexCoIn5

Strongly correlated electron systems are quantum materials that reveal a deep intertwining between different electronic charge, orbital, spin and lattice degrees of freedom. The interaction among them can stabilize ground states that feature novel collective phenomena. Particular complex phases occur in systems containing rare earth elements, where the conduction electrons either screen or couple the magnetic moments of partially filled electronic f-states. The subtle balance between these energy scales yields strong electronic fluctuations that trigger a rich diversity of states including unconventional superconductivity, antiferromagnetism or correlated insulating, metallic and topological protected states.

It is an open question how magnetic order is affected when the local f-electrons become itinerant. While the prevailing theory predicts the possibility of two separated critical points, it is unknown whether they have an impact on the magnetic structure. I will present our recent results on the evolution of magnetic order in the series Nd1-xCexCoIn5 that features a Kondo breakdown within an antiferromagnetic phase. We find a transition between two distinct magnetic phases that is detached from the emergence of heavy-bands, demonstrating that the magnetism and the Kondo coupling can be governed by different energy scales. The observation of two magnetic structures with different symmetry is evidence that the magnetic interactions change with increasing electronic itineracy. This opens novel perspectives for the fundamental understanding of the microscopic mechanism controlling the various quantum phases in this class of materials.

We further investigated the intertwined degrees of freedom in the itinerant limit of the series. CeCoIn5 is a paramagnetic heavy-fermion with a d-wave superconducting ground state that is believed to be mediated by magnetic fluctuations. The superconducting condensate features an additional phase at very low temperatures and large magnetic fields. This so-called Q-phase reveals magnetic order that only survives inside the superconducting condensate and directly couples to it. I will show that the Q-phase is stable under a perturbation 5% Nd doping, and that the high-field phase is separated from a low-field antiferromagnetic state via a magnetic instability that may origin from a field-induced quantum phase transition. Intriguingly, both phases display an identical magnetic symmetry, which prevents the emergence of a primary order parameter of magnetic nature in the Q-phase. We suggest the presence of an auxiliary superconducting order parameter in the Q-phase that couples magnetic order with d-wave superconductivity. This is in contrast to the behavior in the low-field phase, where we believe that superconductivity and magnetism remain decoupled.

Contact:

Prof. J. Hancock

Physics Department (primary)

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