PUSHING THE BOUNDARIES OF SOLID-STATE NMR IN PHYSICS: FROM FUNDAMENTAL UNDERSTANDING TO PRACTICAL APPLICATIONS

In this talk, I will explore the multifaceted behavior of an important class of superconductors: the heavy fermion materials such as Ce(Co, Rh, Ir)In₅. The investigations used solid-state Nuclear Magnetic Resonance as a powerful local tool to unravel the complex interactions between superconductivity, magnetism, and quantum criticality, moving from fundamental understanding to practical applications.

Our journey begins by briefly discussing the nature of the low-temperature phase transition in CeCoIn₅ under high magnetic fields, where NMR revealed a first-order transition from the normal to the superconducting state and the presence of static spin moments in the vortex cores.(1) Furthermore, we demonstrated that doping with cadmium (Cd) induces a microscopic coexistence of superconductivity and antiferromagnetic order and the formation of impurity-induced “spin droplets”,(2) which persist even under applied pressure, highlighting electronic heterogeneity and the need for caution when interpreting the effects of tuning a correlated system by chemical substitution.(3)

Deepening our understanding, we also used NMR to probe the magnetic behavior in CeRhIn₅ and showed that a high magnetic field induces an abrupt reconstruction of the Fermi surface with no structural changes, but rather modifies the Ce 4f orbitals, which intensifies hybridization and leads to an itinerant quantum critical point.(4) The versatility of NMR allowed us to go even further and demonstrate how this technique can be used to quantify anisotropic orbital hybridization in materials such as CeRh_1-xIr_xIn₅. By measuring the hyperfine coupling, we were able to determine the directionality of the interaction between the 4f electrons and the nuclear spins.(5)

Finally, we may ask what happens to these heavy fermion materials when their properties are confined to a single dimension. In this talk I will also dive into the world of CeIn₃ nanowires, where magnetic order behaves in an unexpected way. Our recent NMR, specific heat, and magnetic susceptibility data revealed that the magnetic transition is drastically suppressed — an effect we attribute to dimensionality-induced magnetic order frustration.(6) This discovery not only reveals new physical behavior but also paves the way for developing materials with tunable magnetic properties, showing that dimensionality can be the key to unlocking new frontiers in materials physics.

In summary, our research demonstrates how NMR, combined with other techniques, offers unprecedented insight into the physics of heavy fermion superconductors, revealing the complexity of their phases and the potential for developing materials with tunable magnetic and superconducting properties.

REFERENCES

1. B.-L. Young, R. R. Urbano, N. J. Curro, J. D. Thompson, J. L. Sarrao, A. B. Vorontsov, M. J. Graf, Phys. Rev. Lett., 2007, 98, 036402. https://doi.org/10.1103/PhysRevLett.98.036402
2. R. R. Urbano, B.-L. Young, N. J. Curro, J. D. Thompson, L. D. Pham and Z. Fisk, Phys. Rev. Lett., 2007, 99, 146402. https://doi.org/10.1103/PhysRevLett.99.146402
3. S. Seo, Xin Lu, J-X. Zhu, R. R. Urbano, N. Curro, E. D. Bauer, V. A. Sidorov, L. D. Pham, Tuson Park, Z. Fisk and J. D. Thompson, Nature Physics, 2014, 10, 120-125. https://doi.org/10.1038/nphys2820
4. G. G. Lesseux, H. Sakai, T. Hattori, Y. Tokunaga, S. Kambe, P. L. Kuhns, A. P. Reyes, J. D. Thompson, P. G. Pagliuso, and R. R. Urbano, Phys. Rev. B, 2020, 101, 165111. https://doi.org/10.1103/PhysRevB.101.165111
5. P. Menegasso, J. C. Souza, I. Vinograd, Z. Wang, S. P. Edwards, P. G. Pagliuso, N. J. Curro, and R. R. Urbano, Phys. Rev. B, 2021, 104, 035154. https://doi.org/10.1103/PhysRevB.104.035154.
6. M. H. Carvalho, D. Zau, A. P. Reyes, R. Cong, S. D. House, H. P. Pizzi, A. M. Caffer, D. S. Passos, R. C. Santos, G. S. Freitas, K. R. Pirota, R. R. Urbano, P. J. G. Pagliuso, arXiv:2507.04477 [cond-mat.str-el] 2025.

Acknowledgements: This work was supported by the Brazilian funding agencies Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP 2012/05903-6, 2017/10581-1) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 309483/2018-2 and 314587/2021-7). The work at the National High Magnetic Field Laboratory was supported by the National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida. We are grateful for the electronic microscopy support from the LNNano – Brazilian Nanotechnology National Laboratory (LNNano/CNPEM/MCTIC), the Center for Integrated Nanotechnology (CINT) and all co-authors listed in the references herein.