# Large positive correlation between the effective electron mass and the multipolar fluctuation in the heavy-fermion metal Ce$_{1-x}$La$_x$B$_6$

## TL;DR

This study maps the complex phase diagrams of Ce$_{1-x}$La$_x$B$_6$, revealing a strong link between multipolar fluctuations and increased effective electron mass near quantum critical points.

## Contribution

It provides comprehensive phase diagrams and experimental analysis showing a positive correlation between multipolar fluctuations and electron mass in Ce$_{1-x}$La$_x$B$_6$, highlighting new quantum critical phenomena.

## Key findings

- Increase in Sommerfeld coefficient with La substitution
- Identification of a high-entropy region in phase diagram
- Evidence of a quantum critical point at x>0.75

## Abstract

For the last few decades, researchers have been intrigued by multipolar ordering phenomena while looking for the related quantum criticality in the heavy-fermion Kondo system Ce$_{1-x}$La$_{x}$B$_6$. However, critical phenomena induced by substitution level ($x$), temperature ($T$), and magnetic field ($B$) are poorly understood despite a large collection of experimental results is available. In this work, we present $T$-$B$, $x$-$T$, and $x$-$B$ phase diagrams of Ce$_{1-x}$La$_x$B$_6$ ($\mathbf{B}\parallel[110]$). These are completed by analyzing heat capacity, magnetocaloric effect (MCE), and elastic neutron scattering. A drastic increase of the Sommerfeld coefficient $\gamma_0$, which is estimated from the heat capacity down to 0.05 K, is observed with increasing $x$. The precise $T$-$B$ phase diagram which includes an unforeseen high-entropy region is drawn by analyzing the MCE for the first time in Ce$_{1-x}$La$_x$B$_6$. The $x$-$B$ phase diagram, which supports the existence of a QCP at $x>0.75$, is obtained by the same analysis. A detailed interpretation of phase diagrams strongly indicates positive correlation between the fluctuating multipoles and the effective electron mass.