Transition between Heavy-Fermion-Strange-Metal and Quantum Spin Liquid in a 4d-Electron Trimer Lattice

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Heavy fermion systems typically involve f-electron orbitals.
• Quantum spin liquids and strange metals are exotic states of matter with unique electronic properties.
• Understanding the interplay between spin, charge, and lattice in correlated electron systems is a key challenge.

Purpose of the Study:

• To experimentally investigate the underlying mechanism for heavy-fermion-strange-metal and quantum-spin-liquid states in a 4d-electron system.
• To explore the role of spinons in these exotic electronic phases.
• To establish a unified framework for understanding these phenomena in Ba_{4}Nb_{1-x}Ru_{3+x}O_{12}.

Main Methods:

• Experimental synthesis and characterization of Ba_{4}Nb_{1-x}Ru_{3+x}O_{12} with varying Nb concentration.
• Measurements of thermodynamic properties (entropy, heat capacity) down to milli-Kelvin temperatures.
• Thermal conductivity measurements to probe charge and spin transport.

Main Results:

• Evidence for a heavy Fermi surface composed of itinerant, charge-neutral spinons in both heavy-fermion-strange-metal and quantum-spin-liquid states.
• Both states exhibit large entropy, linear heat capacity, and linear thermal conductivity.
• The insulating spin liquid shows superior thermal conductivity compared to the heavy-fermion-strange-metal state, which violates the Wiedemann-Franz law.

Conclusions:

• A universal heavy spinon Fermi surface provides a unified explanation for the observed exotic phenomena.
• The variable Nb concentration offers a new route to control and study these correlated quantum states.
• This work presents a new paradigm for exploring correlated quantum matter without f electrons.