Quantum Criticality and Strong
Correlations in Low-dimensional Metals.
Meigan
Aronson
Stony Brook University & Brookhaven
National Lab.
T=0 phase transitions or `Quantum Critical
Points’ are found in virtually every class of correlated electron system,
including cuprates, heavy fermions, Fe-based pnictides, and organic conductors, and their presence
fundamentally changes the properties of the underlying metal from which these
ordered phases emerge. The associated critical modes can lead to the nucleation
of novel phases provide pairing for unconventional superconductors, and can
lead to the destruction of the metallic state via the localization of
electrons. There are two approaches to creating QCPs
in metals. In the first, an ordered phase, most often magnetic, is suppressed
by geometric frustration, dimerization, or simply by
low dimensionality, all of which strengthen quantum fluctuations at the expense
of order. Alternatively, increased hybridization of the moment bearing
electrons with conduction electrons diminishes correlations and leads to
conventional metallic states.
In this talk I will focus on the role of
dimensionality in stabilizing QCPs. I present the
results of high precision magnetic, thermal, and resistivity measurements in
the layered compound YFe2Al10 where a scaling analysis suggests proximity to a two-dimensional
ferromagnetic QCP. Even more dramatic evidence for low dimensionality comes
from our research on the Shastry-Sutherland lattice
(SSL) system Yb2Pt2Pb, where dimer formation competes with long range magnetic order. We
use inelastic neutron scattering measurements to argue that the in-plane
excitations are gapped by dimerization, but that the dispersion in the direction perpendicular to
the SSL planes reveals that here the fundamental excitations are spinons, strong evidence for the quasi-one dimensionality
of this system.
Host: Prof. P. Coleman