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

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

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. Main scientific objective is to study a relation between a Fermi surface reconstruction andquantum criticality, metal-insulator transitionas well asunconventional superconductivity. Heavy-fermion compounds, being a prominent example of the strongly correlated systems,are exceptionally predisposedfor a study of the interplay between all these phenomena due to a strongly renormalized energy scaledue to the Kondo effect. Research material will be high-quality single crystals of certain f-electron compounds. Experimentsdetermining animpact of magnetic field on their ground-statepropertiesare planned, with the main focus on angular dependent magnetoresistivity measurementsat very lowtemperaturesdown to80mKand magnetic fields up to 14 T,utilizinga self-madeequipment.

Striking resemblance of magnetic/superconducting phase diagram for cuprates, iron pnictides, organics charge-transfer salts, alkali-doped fullerenes and, last but not least, heavy fermions is a difficult challenge for condensed-matter physicists. The source of the superconductivity inthese strongly correlated materials is likely different from the electron-phonon interactions which govern theconventional superconductivity. It is being actively debated that superconductivity is mediated by quantum critical fluctuations, but again, the nature of the underlying quantum critical point is still unclear. The heavy-fermion superconductors are ideally suitedfor a study of the interplay between quantum criticality, electronic localizationand unconventional superconductivity. Indeed, recent discovery of a new energy scale associated with the breakdown of the heavy quasiparticles and resultant reconstruction of a Fermi surfaceis an intriguing issue that can go beyondthe Landau paradigm of the classical phase transitions.

Quantum mechanics not only governs the subatomic world but also dictates the organization of the microscopic particles in bulk matter at low temperatures.A prominent example is the concept of the Fermi surfacethatprovides aprecise expalnation of the basicphysical properties of metals. At absolute zero, electrons occupy the states with the lowest energies, up to an energy referred to as the Fermi energy. In the momentum space defined by the wavevector, this defines a Fermi surface, enclosing a Fermivolume in which all the states are occupied. We would like, however,to emphasize that our goal is not to determine the Fermi surfaces, but to determine a Fermi-surface change due to various strongly correlated phenomena. To this aim we propose measurements ofan angular dependence of theelectrical resistivity takenin constant temperature and magnetic field to revealachange of thegeometryof the Fermi surface.In a strongly correlatedsystem, being much more complex than a simple metal, magnetic field may induce a reconstruction of the Fermi surfacevia either an enhancement or a suppression of field-dependent phenomena. It should be clearly state that the one-step effect of the field-induced Fermi-surface reconstruction is qualitatively different from frequentlyobserved magnetic breakdown which results in higher frequency Shubnikov-de Hass oscillations at the highest fields.

Research project “Magnetic-field-induced reconstruction of a Fermi surface in strongly correlated electron systems” consists oftwo main objectives: first is devoted to basic research on heavy fermions and second deals with developing of experimental station for an angular dependence of the magnetoresistivity under extreme conditions(task 1). We would also like toemphasize that a substantial part of research will be performed on the Kondo insulator CeOs4As12(task 2)and the unconventional superconductor Ce2PdIn8(task 7), both being a recentinput of Polish scientists to the field of strongly correlated electron phenomena. (Noteworthy that both systems were discovered, synthesized, and characterized at the Institute of Low Temperature and Structure ResearchPolish Academy of Sciencesin Wroclaw. Results of these recent studies were already presented in a couple of papers published in Preceedings of National Academy of Sciences, Physical Review Letters and Physical Review B.Scientificobjectives concern (a) quantum criticality and a search for the Kondo breakdown behaviorin PrOs4Sb12(task 4),URhGe(task 5) andUCoGe(task 6),(b) magnetic-field-driven metal insulator transition with particular emphasis onanisotropy effects caused byan appliedmagnetic fieldin CeOs4As12(task 2) and CeOs4Sb12(task 3),and (c) a symmetry of the order parameter investigated via anisotropy ofthe upper critical field in unconventional superconductorCe2PdIn8(task 7).All the systems will be investigated via the angular dependence of the magnetoresitivity.For selected orientations, studies of the temperature dependence of the resistivity in constant field are also planned.

Most of the samples are already availableby kind permission of Prof. Dr. Zygmunt Henkie(CeOs4As12, CeOs4Sb12), Prof. Dr. Vin Hung Tran(URhGe) and Prof. Dr. Dariusz Kaczorowski(Ce2PdIn5) form the ILT&SR PAS in Wroclaw. Single crystalsof two other systems (PrOs4Sb12and UCoGe) will be synthesized.

An impact of the project proposed to the field of strongly correlated systems appears to betwofold: First, a new experimental approach to the problem of a field-induced reconstruction of a Fermi surface is proposed. Its universality will allowto investigate different systems displaying different phenomena associated with the Fermi-surface change. Second, new experimental results for very differentheavy fermions are expected to reveal features towards our better understanding of the nature of quantum criticality, electron localization and unconventional superconductivity.

Expected impact of the research project „Magnetic-field-induced reconstruction of a Fermi surface in strongly correlated systems” on natural science is expected tobe significant -suchan assessment is based on an enormous word-wide interest in interdisciplinary studies of the f-electron systemsover last three decades.As an example, let us mention that onlyin 2010-2011appearedhundredsof paper regarding heavy fermion physics:among them3 papers were published in Nature, 4 in Science, 6 inNature Physics, 71 in Physical Review Lettersand 163 in Physical Review B(since the beginning of 2010).

Significant measurable outcome will bealso a position forangular dependence of the magnetoresistivityunder extreme conditions, i.e. in the temperature range0.08-4.2 Kand inmagnetic fieldsup to 14T. To this aim a 3He-4He dilution refrigerator operating in the Low Temperature Laboratory at the ILT&SR PAS(group leader Prof. Dr. Tomasz Cichorek)will be utilized. Such a word-wide unique position will serve new experimental possibilities for the Polish community in condensed-matter physics.

Chosen research subject creates connection between a topic ofPh.D Thesis „Low-temperature physical properties of selected arsenic compounds” and further academic career of the project leader. Part of the outcome about filled skutterudite will be mentioned in the Ph.D Thesis, and rest results become a beginning of a new chapter of my scientific research. It is also worth adding that the research performed will be an important part of a few student-practice programs.

Publications