Hidden fluctuations close to a quantum bicritical point

TL;DR

This paper investigates the physical properties near two coupled quantum phase transitions, revealing that their susceptibilities may behave similarly at low temperatures due to biquadratic coupling, despite differences without it.

Contribution

It introduces a phenomenological model of two coupled quantum phase transitions and analyzes how biquadratic coupling influences susceptibility behavior at low temperatures.

Findings

Susceptibilities of coupled order parameters can have similar forms at low temperature.

Biquadratic coupling affects the qualitative behavior of susceptibilities.

Limitations of the self-consistent approach are discussed.

Abstract

In this paper we describe physical properties arising in the vicinity of two coupled quantum phase transitions. We consider a phenomenological model based on two scalar order parameter fields locally coupled biquadratically and having a common quantum critical point as a function of a quantum tuning parameter such as pressure or magnetic field. A self-consistent treatment suggests that the uniform static susceptibilities of the two order parameter fields may have the same qualitative form at low temperature even where the forms differ sharply in the absence of the biquadratic coupling. The possible limitations of the self-consistent analysis leading to this prediction are considered.