Destruction of the Kondo effect in the cubic heavy-fermion compound Ce3Pd20Si6

Abstract

How ground states of quantum matter transform between one another reveals deep insights into the mechanisms stabilizing them. Correspondingly, quantum phase transitions are explored in numerous materials classes, with heavy fermion compounds being among the most prominent ones. Recent studies in an anisotropic heavy fermion compound have shown that different types of transitions are induced by variations of chemical or external pressure 1-3 , raising the question of the extent to which heavy fermion quantum criticality is universal.To make progress, it is essential to broaden both the materials basis and the microscopic parameter variety. Here, we identify a cubic heavy fermion material as exhibiting a field-induced quantum phase transition, and show how the material can be used to explore one extreme of the dimensionality axis. The transition between two different ordered phases is accompanied by an abrupt change of Fermi surface, reminiscent of what happens across the field-induced antiferromagnetic to paramagnetic transition in the anisotropic YbRh 2 Si 2 . This finding leads to a materials-based global phase diagram -a precondition for a unified theoretical description.1 Quantum phase transitions arise in matter at zero temperature due to competing interactions. When they are continuous, the associated quantum critical points (QCPs) give rise to collective excitations which influence the physical properties over a wide range of parameters. As such, they are being explored in a variety of electronic materials, ranging from high T c cuprates to insulating magnets and quantum Hall systems 4,5 .Heavy fermion compounds are prototype materials to study quantum phase transitions. Their low energy scales allow to induce such transitions deliberately, by the variation of external parameters such as pressure or magnetic field. Microscopically, electrons in partiallyfilled f shells behave as localized magnetic moments. They interact with conduction electrons through a Kondo exchange interaction, which favors a non-magnetic ground state that entangles the local moments and the spins of the conduction electrons. They also interact among themselves through an RKKY exchange interaction, which typically induces antiferromagnetic order. It has been known that tuning external parameters changes the ratio of the Kondo coupling to the RKKY interaction. Recently, the importance of a second microscopic quantity has been suggested. This is the degree of quantum fluctuations of the local moments, parameterized by G: magnetic order weakens with increasing G, as it would with enhancing the Kondo coupling J K . These two quantities define a two-dimensional parameter space, which allows the consideration of a global phase diagram 10 . This global phase diagram is most clearly specified via the energy scale T * associated with the breakdown of the Kondo entanglement between the local moments and conduction electrons. So far T * has only been identified in tetragonal YbRh 2 Si 2 (refs. 8,11,12 ). It is believed that this energy scale no...

Antiferromagnetism in metals: from the cuprate superconductors to the heavy fermion materials

“…We reproduce in Fig. 12 a phase diagram of Custers et al [50,51], which combines our Figs. 10 and 11 with additional experimental information.…”

Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

“…4c). As in the spherically symmetric case, the parameter I 21 ) could be added, but the good agreement between our model using the basis of eigenstates from the crystal field Hamiltonian and the experimental data suggests that these terms are not dominant.…”

SCES2013 Summary: Experiment

“…Strongly correlated electron systems, however, are providing an increasing number of examples suggesting that this model is insufficient and that fermionic degrees of freedom cannot be ignored. [31,32,33,34] These examples have motivated new theoretical models of quantum criticality that explicitly include criticality of fermions and that appear to account for observations not captured in the conventional model. [35,36,37,38,39,40] Pressure, magnetic field and chemical composition are three non-thermal control parameters that commonly are used to access a quantum-phase transition.…”

“…1, that there are other routes to a quantum-critical state. Though not easily tunable, spatial dimensionality [34], geometrical frustration of magnetic ions [41,42,43,44] and, interestingly, the lack of periodicity in quasi-crystals [45,46] lead to physical properties that are consistent with expectations of quantum criticality. Whether it will be possible to understand properties of these materials within the context of the conventional model of criticality remains to be seen, but it seems unlikely.…”