Exploring heavy fermions from macroscopic to microscopic length scales

  • A Corrigendum to this article was published on 01 January 2016

Abstract

Strongly correlated systems present fundamental challenges, especially in materials in which electronic correlations cause a strong increase of the effective mass of the charge carriers. Heavy fermion metals — intermetallic compounds of rare earth metals (such as Ce, Sm and Yb) and actinides (such as U, Np and Pu) — are prototype systems for complex and collective quantum states; they exhibit both a lattice Kondo effect and antiferromagnetic correlations. These materials show unexpected phenomena; for example, they display unconventional superconductivity (beyond Bardeen–Cooper–Schrieffer (BCS) theory) and unconventional quantum criticality (beyond the Landau framework). In this Review, we focus on systems in which Landau's Fermi-liquid theory does not apply. Heavy fermion metals and semiconductors are well suited for the study of strong electronic correlations, because the relevant energy scales (for charge carriers, magnetic excitations and lattice dynamics) are well separated from each other, allowing the exploration of concomitant physical phenomena almost independently. Thus, the study of these materials also provides valuable insight for the understanding — and tailoring — of other correlated systems.

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Figure 1: Doniach phase diagram and its realization in CePd2Si2.
Figure 2: Electronic structure of a Kondo lattice.
Figure 3: Comparison of quantum criticality in the spin-density wave and in the locally critical scenario.
Figure 4: Evidence for conventional quantum critical points in CeNi2Ge2 and CeCu2Si2.
Figure 5: Evidence for unconventional QCPs in CeCu5.9Au0.1 and in CeRhIn5 under pressure.
Figure 6: Phase diagram of YbRh2Si2.
Figure 7: Violation of the Wiedemann–Franz law at the QCP.
Figure 8: Evolution of the temperature–magnetic field (TB) phase diagram upon isoelectronic substitution.
Figure 9: Generalized phase diagram at T = 0.
Figure 10: Kondo temperatures TKhigh and TKlow = TK and development of Kondo-lattice coherence below Tcoh.
Figure 11: Tunnelling conductance of SmB6.

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Acknowledgements

The authors thank E. Abrahams, J. W. Allen, J. Arndt, P. Coleman, Z. Fisk, S. Friedemann, P. Gegenwart, C. Geibel, S. Kirchner, S. Lausberg, S. Paschen, H. Pfau, A. P. Pikul, S. Rößler, S. Seiro, Q. Si, O. Stockert, U. Stockert, P. Sun, L. H. Tjeng, H. Q. Yuan and G. Zwicknagl for enlightening discussions and/or providing data. They also acknowledge partial financial support by DFG Research Unit 960.

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Wirth, S., Steglich, F. Exploring heavy fermions from macroscopic to microscopic length scales. Nat Rev Mater 1, 16051 (2016). https://doi.org/10.1038/natrevmats.2016.51

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