Anomalous quantum criticality in an itinerant ferromagnet

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Magnetism

Background:

• Continuous phase transitions are governed by dynamic scaling exponents.
• At quantum phase transitions (QPTs), static and dynamic properties are intertwined due to the uncertainty principle.
• Thermodynamic scaling equations for QPTs explicitly include the dynamic exponent.

Purpose of the Study:

• To investigate the thermodynamic properties and quantum critical dynamics of the itinerant ferromagnet Sr1-xCaxRuO3.
• To determine the dynamic scaling exponent at the quantum phase transition where the transition temperature approaches zero.

Main Methods:

• Thermodynamic measurements of magnetization and specific heat as a function of temperature and magnetic field.
• Analysis of dynamic scaling behavior near the quantum critical point.

Main Results:

• Observed dynamic scaling in magnetization and specific heat for Sr1-xCaxRuO3 at x=0.7.
• Identified a small dynamic scaling exponent of 1.76, deviating significantly from established models of ferromagnetic quantum criticality.
• The observed dynamics suggest the influence of strong disorder and strong electron-electron coupling.

Conclusions:

• The itinerant ferromagnet Sr1-xCaxRuO3 exhibits unusual quantum critical dynamics.
• The small dynamic scaling exponent indicates that current theoretical models may not fully capture the complexity of this system.
• Strong disorder and electron-electron interactions are likely key factors governing the observed quantum critical behavior.