Geometric frustration produces long-sought Bose metal phase of quantum matter

Abstract

Two of the most prominent phases of bosonic matter are the superfluid with perfect flow and the insulator with no flow. A now decades-old mystery unexpectedly arose when experimental observations indicated that bosons could organize into the formation of an entirely different intervening third phase: the Bose metal with dissipative flow. The most viable theory for such a Bose metal to date invokes the use of the extrinsic property of impurity-based disorder; however, a generic intrinsic quantum Bose metal state is still lacking. We propose a universal homogeneous theory for a Bose metal in which geometric frustration confines the essential quantum coherence to a lower dimension. The result is a gapless insulator characterized by dissipative flow that vanishes in the low-energy limit. This failed insulator exemplifies a frustration-dominated regime that is only enhanced by additional scattering sources at low energy and therefore produces a Bose metal that thrives under realistic experimental conditions.

Probing a Bose metal via electrons: inescapable non-Fermi liquid scattering and pseudogap physics

“…Here we identify a robust paradigm where the exotic phenomena of non-Fermi liquid scattering rates and pseudogap formation inevitably result. The crucial component is an unconventional effective mean field derived from a recently proposed Bose metal [59]. The mean field studied here only exhibits lower-dimensional coherence leaving it a measure of incoherence, and it is this incoherence that defeats the conventional framework.…”

“…The latter by coupling to incomplete coherent structure. These conditions can be met by coupling to a recently proposed Bose metal [59]. This Bose metal is a stable phase of matter that is neither superfluid nor insulator and it is comprised of so-called type-I (real, conserved) bosons [61], so it is not confined to the vicinity of any critical transition as required by type-II bosons (excitations such as phonons, magnons, etc).…”

“…Our work exploits the unique imperfect phase coherence of the quantum Bose metal state. The bosons that scatter the electrons are not excitations of the system, but instead emerged particles (for example tightly bound state of two fermionic carriers) that constitute the Bose metal ground state [59]. The resulting exotic phenomena therefore persist to zero-temperature limit.…”

“…For those interested in the cuprates, our successful reproduction of NFL scattering, PG formation, and many related symptoms found in the cuprates leads one to wonder whether the pseudogap regime of the cuprate phase diagram below T * is actually contained within the finite temperature phase of a Bose metal below a higher temperature T BM . In fact, the Bose metal mean field used here directly results from the phase frustrated regime [59,71] of the emergent Bose liquid theory [62,72] of the cuprates, which has been demonstrated to describe many physical properties simultaneously with the same model and a single fixed set of parameters (cf appendix C). Within this EBL model, it is not surprising that the observations from single particle fermion probes such as ARPES and STM are so difficult to explain.…”

Infinite critical boson non-Fermi liquid

“…Experimentally, the relevance of critical boson surface has been implied by the neutron scattering in MnSi 41,42 where a nearly uniform intensity is measured on a sphere. Motivated by these developments, the investigation on the critical boson surface has received some attentions [43][44][45] . Here, we are neither dealing with nor relying on the stable phase of critical boson surfaces, instead we aim to improve our understanding of the critical boson surface-induced quantum criticality and its impact when it is coupled with gapless fermions.…”