Heavy Fermion Metals’ Phase Diagram Enables Insights into Strange Metal Physics

Strange metals present a long-standing challenge in condensed matter physics, and heavy fermion systems offer a crucial environment for developing a broader understanding of these materials. Yiming Wang, Shouvik Sur, and Chia-Chuan Liu, all from Rice University, along with Qimiao Si, investigate the competition between the Kondo effect, a quantum mechanical process influencing electron behaviour, and the emergence of local magnetism. Their work establishes a comprehensive theoretical framework to analyse this interplay, starting from the perspective of magnetically ordered materials, and reveals a critical point where the Kondo effect transitions from being suppressed to becoming the dominant influence. This discovery not only clarifies the nature of Kondo destruction criticality but also maps out the complete phase diagram for heavy fermion metals, offering new insights into their complex behaviour.

Their work establishes a theoretical framework to analyse this competition, beginning with magnetically ordered materials, and identifies a critical point where the Kondo effect shifts from being suppressed to becoming the dominant influence. This discovery clarifies the nature of Kondo destruction criticality and provides a complete phase diagram for heavy fermion metals, offering new insights into their complex behaviour.,.

Strange metals represent a fundamental problem in quantum condensed matter physics, and heavy fermion systems provide an ideal setting for developing a broader understanding of these materials. The research team developed a unified theoretical approach, analysing the competition between the Kondo effect and local-moment magnetism from a perspective where the Kondo effect is initially suppressed, leading to a new mechanism for Kondo destruction. The results demonstrate that the global phase diagram of heavy fermion metals exhibits a rich structure, including regions where the Kondo effect and local-moment magnetism coexist, regions of pure Kondo destruction, and regions dominated by local-moment magnetism.,.

The analysis predicts a new quantum critical point separating the Kondo destruction region from the local-moment magnetism region, characterised by a change in the universality class, and elucidates the Kondo destruction quantum criticality. This work establishes a comprehensive framework for understanding the interplay between the Kondo effect and local-moment magnetism in heavy fermion metals, providing insights into the origin of strange metal behaviour, and is anchored by the magnetically ordered side of the system. The findings reveal, for the first time within a renormalization group framework, a quantum critical point where the Kondo effect transitions from being destroyed to dominating.,.

Kondo Impurity Renormalization Group Flows Calculated

Detailed calculations explore a quantum nonlinear sigma model (QNLSM) coupled to a Kondo impurity, aiming to understand how parameters change with energy scale. This is crucial for determining the stability of the system at low energies, and the calculations are performed to one-loop order, including quantum corrections up to the level of diagrams with one closed loop. The model incorporates a QNLSM, describing fluctuations of a manifold, and a Kondo impurity, representing a magnetic impurity in a metal, with the parameters g representing the stiffness of the manifold and λ representing the Kondo coupling strength.,.

The calculations meticulously detail loop integrals contributing to beta functions, including the boson self-energy, fermion self-energy, and vertex corrections, utilising techniques like dimensional regularization to handle ultraviolet divergences. The results reveal ultraviolet divergences in the boson self-energy and vertex corrections, which are handled using dimensional regularization, and confirm the stability of the non-linear sigma model side. The document provides a comprehensive and rigorous analysis, with clear notation and useful integral formulas, making it a valuable resource for researchers in the field.,.

Kondo Effect Drives Heavy Fermion Phase Diagram

Scientists have developed a new theoretical understanding of heavy fermion metals, materials exhibiting strong interactions between electrons and magnetism. They have created a comprehensive framework, based on a renormalization group approach, to analyse the competition between the Kondo effect, where electrons align their spins with localized magnetic moments, and the tendency towards local-moment magnetism. Their analysis identifies a critical point at which the Kondo effect transitions from being suppressed to becoming the dominant influence, providing a key insight into the behaviour of these complex materials.,.

The team’s work successfully maps out the global phase diagram of heavy fermion metals, encompassing various phases including antiferromagnetic, paramagnetic, and a puzzling “strange metal” phase, representing the first complete theoretical description of this phase diagram, validated by experimental observations in materials like CePdAl. Beyond its immediate application to understanding these materials, the established theoretical framework holds promise for the design and study of quantum simulators and flat-band systems, offering new avenues for exploring quantum criticality and Kondo destruction in highly controlled environments.