Sequential localization of a complex electron fluid

Abstract

Complex and correlated quantum systems with promise for new functionality often involve entwined electronic degrees of freedom. In such materials, highly unusual properties emerge and could be the result of electron localization. Here, a cubic heavy fermion metal governed by spins and orbitals is chosen as a model system for this physics. Its properties are found to originate from surprisingly simple low-energy behavior, with 2 distinct localization transitions driven by a single degree of freedom at a time. This result is unexpected, but we are able to understand it by advancing the notion of sequential destruction of an SU(4) spin–orbital-coupled Kondo entanglement. Our results implicate electron localization as a unified framework for strongly correlated materials and suggest ways to exploit multiple degrees of freedom for quantum engineering.

Evolution of the propagation vector of antiferroquadrupolar phases inCe3Pd20Si6under magnetic field

“…Another important observation of our present study is the destruction of coherent collective modes and the closing of the spin gap at the transition between phases II and II . This is fully consistent with the recently reported NFL behavior at this transition [17]. NFL behavior may result from the low-energy spin fluctuations in the proximity to a quantum critical point, when the spin gap in the excitation spectrum vanishes.…”

“…The cage compound Ce 3 Pd 20 Si 6 , which is the subject of this work, is remarkable in that it hosts two distinct types of hidden order that presumably originate from antiferroquadrupolar (AFQ) ordering of Ce 4 f moments [14][15][16][17]. In zero magnetic field, its ground state is antiferromagnetic (AFM), with a Néel temperature of T N ≈ 0.23 K [ [14][15][16][17][18] and a propagation vector 0 0 4 5 [19,20], which is referred to as phase III. In a narrow temperature range above T N , a hidden-order phase II sets in, which is further stabilized in moderate magnetic fields [14][15][16].…”

“…For the field directions [110] or [111], phase II persists up to rather high fields of at least 10 T. However, if the field is applied along the [001] cubic axis, phase II is only present up to about 2 T, where it gives way to another hidden-order phase known as II [14][15][16][17]. When phase II is suppressed, the field-induced magnetic Bragg peaks disappear, as we have previously demonstrated in Ref.…”

“…Then, in even stronger magnetic fields B [100] that are above 4 T, the AFQ order is suppressed completely, and a field-polarized paramagnetic phase (phase I) is stabilized. Remarkably, pronounced non-Fermi-liquid (NFL) behavior associated with quantum criticality has been observed in transport and thermodynamic measurements both at the III-II and II-II phase transitions, but not at the high-field boundary of phase II [17]. To understand these essential qualitative differences between the successive field-driven phase transitions, it is important to reveal the associated changes in Table I.…”

Quantum criticality and sequential destruction of spin-orbital Kondo entanglement

“…Of direct interest to us is Ce 3 Pd 20 Si 6 , which has re-cently been investigated as a function of a non-thermal control parameter (magnetic field) 41,42 . The results show two stages of Kondo-destruction quantum criticality.…”