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NCN PRELUDIUM 2: 2011/03/N/ST3/02989

Magnetic-field-induced reconstruction of a Fermi surface in strongly correlated electron systems

leader: Dr. Ł. Bochenek

Description

Research project “Magnetic-field-induced reconstruction of a Fermi surface in strongly correlated electron systems” concerns strongly correlated electron phenomena which are at the heart of modern condensed-matter physics. The main scientific objective is to study the relation between Fermi-surface reconstruction and quantum criticality, metal–insulator transitions, as well as unconventional superconductivity. Heavy-fermion compounds, being a prominent example of strongly correlated systems, are exceptionally predisposed for studying the interplay between these phenomena due to a strongly renormalized energy scale resulting from the Kondo effect.

The research material will consist of high-quality single crystals of selected f-electron compounds. Experiments determining the impact of a magnetic field on their ground-state properties are planned, with the main focus on angular-dependent magnetoresistivity measurements at very low temperatures (down to 80 mK) and magnetic fields up to 14 T, utilizing self-made equipment.

A striking resemblance of magnetic/superconducting phase diagrams for cuprates, iron pnictides, organic charge-transfer salts, alkali-doped fullerenes, and heavy fermions remains a major challenge for condensed-matter physicists. The origin of superconductivity in these strongly correlated materials is likely different from electron–phonon interactions governing conventional superconductivity. It is actively debated whether superconductivity is mediated by quantum critical fluctuations; however, the nature of the underlying quantum critical point remains unclear.

Heavy-fermion superconductors are ideally suited for studying the interplay between quantum criticality, electronic localization, and unconventional superconductivity. The recent discovery of a new energy scale associated with the breakdown of heavy quasiparticles and the resulting reconstruction of a Fermi surface is an intriguing issue that may go beyond the Landau paradigm of classical phase transitions.

Quantum mechanics not only governs the subatomic world but also dictates the organization of microscopic particles in bulk matter at low temperatures. A prominent example is the concept of the Fermi surface, which provides a precise explanation of the basic physical properties of metals. At absolute zero, electrons occupy the lowest energy states up to the Fermi energy. In momentum space, defined by the wave vector, this creates a Fermi surface enclosing a Fermi volume in which all states are occupied.

The goal of this project is not to determine Fermi surfaces themselves, but rather to detect their changes caused by strongly correlated phenomena. To this end, we propose measurements of angular-dependent electrical resistivity at constant temperature and magnetic field to reveal changes in the geometry of the Fermi surface. In strongly correlated systems, magnetic fields may induce a reconstruction of the Fermi surface via enhancement or suppression of field-dependent phenomena.

It should be emphasized that field-induced Fermi-surface reconstruction is qualitatively different from the commonly observed magnetic breakdown, which leads to higher-frequency Shubnikov–de Haas oscillations at the highest fields.

The project consists of two main objectives: (1) fundamental research on heavy fermions and (2) development of an experimental setup for angular-dependent magnetoresistivity measurements under extreme conditions. A substantial part of the research will focus on the Kondo insulator CeOs4As12 and the unconventional superconductor Ce2PdIn8, both discovered and studied at the Institute of Low Temperature and Structure Research, Polish Academy of Sciences (Wrocław).

Scientific objectives include: (a) quantum criticality and the search for Kondo breakdown behavior in PrOs4Sb12, URhGe, and UCoGe; (b) magnetic-field-driven metal–insulator transitions with emphasis on anisotropy effects in CeOs4As12 and CeOs4Sb12; and (c) symmetry of the order parameter investigated via anisotropy of the upper critical field in Ce2PdIn8. All systems will be studied using angular-dependent magnetoresistivity.

Most samples are already available thanks to collaboration with Prof. Dr. Zygmunt Henkie (CeOs4As12, CeOs4Sb12), Prof. Dr. Vin Hung Tran (URhGe), and Prof. Dr. Dariusz Kaczorowski (Ce2PdIn8). Single crystals of PrOs4Sb12 and UCoGe will be synthesized.

The impact of the project is twofold: (1) it introduces a new experimental approach to studying field-induced Fermi-surface reconstruction, and (2) it provides new results for various heavy-fermion systems, contributing to understanding quantum criticality, electron localization, and unconventional superconductivity.

The expected impact on natural sciences is significant due to the global interest in strongly correlated f-electron systems. For example, in 2010–2011 alone, hundreds of papers on heavy fermions were published, including works in Nature, Science, and Physical Review Letters.

A measurable outcome will also be the development of an experimental setup for angular-dependent magnetoresistivity under extreme conditions (0.08–4.2 K and magnetic fields up to 14 T). A 3He–4He dilution refrigerator at the Low Temperature Laboratory (ILT&SR PAS, group led by Prof. T. Cichorek) will be utilized.

The project is closely related to the PhD thesis “Low-temperature physical properties of selected arsenic compounds” and further academic development of the project leader. The results will contribute both to the thesis and to future research directions, as well as to student training programs.

Publications