Kondo Insulator to Semimetal Transformation Tuned by Spin-Orbit Coupling

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Topologically nontrivial electronic states in Kondo insulators are theoretically linked to spin-orbit coupling (SOC).
• Experimental tuning of SOC in Kondo insulators is challenging due to concurrent changes in Kondo coupling (J_K) and chemical potential (μ).

Purpose of the Study:

• To experimentally investigate the role of SOC in Kondo insulators by systematically tuning it.
• To explore the electronic phase transitions induced by varying SOC in a Kondo insulator system.

Main Methods:

• Growth of the substitution series Ce_{3}Bi_{4}(Pt_{1-x}Pd_{x})_{3} (0≤x≤1) to tune SOC.
• Utilizing Pt-Pd substitution for its isostructural, isoelectronic, and isosize properties, minimizing changes in J_K and μ.
• Thermodynamic measurements to characterize the electronic properties of the synthesized compounds.

Main Results:

• Successful synthesis of a complete Pt-Pd substitution series in the archetypal Kondo insulator Ce_{3}Bi_{4}Pt_{3}.
• Demonstration that Pt-Pd substitution effectively tunes SOC while keeping J_K and μ largely constant.
• Observation of a Kondo insulator to semimetal transition with increasing Pd content (decreasing SOC).
• Identification of the end compound Ce_{3}Bi_{4}Pd_{3} exhibiting characteristics of a predicted Weyl-Kondo semimetal.

Conclusions:

• Spin-orbit coupling plays a dominant and previously underestimated role in determining the electronic ground state of Kondo insulators.
• The study provides the first experimental evidence for a tunable SOC parameter in Kondo insulators, enabling the exploration of topological electronic states.
• The findings open new avenues for designing and discovering novel topological quantum materials, including Weyl-Kondo semimetals.