The ground state of a quantum critical system

TL;DR

This paper investigates the ground state of quantum critical systems, revealing that residual electron interactions lead to incommensurate order, but quantum fluctuations prevent long-range magnetic order.

Contribution

It provides experimental evidence that residual conduction electron interactions determine the ground state in quantum critical systems, highlighting the role of quantum fluctuations.

Findings

Residual interactions cause incommensurate intermediate-range order.

Quantum fluctuations prevent the establishment of long-range magnetic order.

The ground state is characterized by local destruction of magnetic moments.

Abstract

The competition between the tendency of magnetic moments to order at low temperatures, and the tendency of conduction electrons to shield these moments, can result in a phase transition that takes place at zero Kelvin, the quantum critical point (QCP). So far, the ground state of these types of systems has remained unresolved. We present neutron scattering experiments that show that the ground state of a sample representative of a class of QCP-systems is determined by the residual interactions between the conduction electrons, resulting in a state with incommensurate intermediate-range order. However, long-range order is thwarted by quantum fluctuations that locally destroy magnetic moments, leaving the system with too few moments to achieve long-range order.