Possible Long-Range Order with Singlet Ground State in CeRu2Al10

TL;DR

This study explores the phase transition in CeRu2Al10, suggesting it originates from Ce ion singlet pair formation, representing a new type of transition during the crossover from dilute Kondo to Kondo semiconductor behavior.

Contribution

It proposes that the mysterious phase transition in CeRu2Al10 is due to Ce ion singlet pairing, offering a new perspective on Kondo-related phase transitions.

Findings

Transition temperature T0 decreases with La doping.

T0 is suppressed under magnetic field, indicating magnetic origin.

Transition linked to Ce ion singlet pair formation.

Abstract

We investigate the thermal and transport properties of CexLa1-xRu2Al10 to clarify the origin of the recently discovered mysterious phase below T0=27 K in CeRu2Al10 where a large magnetic entropy is released, however, the existence of an internal magnetic field is ruled out by 27Al-NQR measurement. We find that T0 decreases with decreasing x and disappears at x~0.45. T0 of CeRu2Al10 is suppressed down to 26 K under H=14.5 T along the a-axis. These results clearly indicate that the transition has a magnetic origin and is ascribed to the interaction between Ce ions. Considering the results of specific heat, magnetic susceptibility, thermal expansion, and electrical resistivity and also 27Al NQR, we propose that the transition originates from the singlet pair formation between Ce ions. Although its properties in a Ce dilute region is basically understood by the impurity Kondo effect, CeRu2Al10 shows a Kondo-semiconductor-like behavior. The phase transition at T0 may be characterized as a new type of phase transition that appears during the crossover from the dilute Kondo to the Kondo semiconductor.