Cross-over transitions and conductivity in coupled-chain models of correlated electron systems; applications to heavy-fermions and htcsuperconductors

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Project objective

Research objectives and content In the field of highly correlated electron systems, the focus of experimental and theoretical interest has turned to systems which can be grossly characterized by two interacting bands- These systems, and theoretical models, can be subdivided into two types: The first type has an interacffon between two inequivalent bands, In particular, one electronic band is made out of local 'core-like' orbitals which carry local magnetic moments, while the other is a wide conduction band of itinerant electrons. To this type belong, for example, heavy-fermion materials and high temperature superconductors. A econd type of systems is composed of coupling two identical bands To this second type belong systems of coupled spin- chains, organic conductors. While the most prevalent research in condensed matter has tradiffonally focussed on phase transitions associated with symmetry braking, some of the most interesting problems in the above menffoned systems are associated with quatitative cross-over phenomena associated with the development of strong interactlons I focus on three such cross-over phenomena: 1) The pseudo spin-gap phase, and its possible association with the 'stripe state' in underdoped high temperature superconductors. 2) Conductivity in coupled one dimensional organic conductors- 3) The qualitaffve disffncffon between Kondo latffce phase and mixed-valance phase in heavy fermion materials- In the proposal I describe my planed research in each of the above topics, which are related to each other in theoreffcal themes and the mathematical methods employed. Training content (objective, benefit and expected impact) The first nine months of my post-doc training (OCT-97 to JUNE-98) with professors Schulz and Giamarchi, at Orsay, are funded by a Chateaubriand fellowship from the French government (which cannot be extended!). I am thus applying for the TMR fellowship as the only mean available for funding the normal compleffon of my post doc research and training. In my previous work I gained proficiency with the Bosonizaffon technique, which is the core method of calculaffon in many of the proposed calculations. I have gained knowledge about heavy fermions and HTc superconducting materials. Yet, my working esperience with renormalization group calculations. the treatment of conducffvity in one dimension, and on spin ladder systems is not very exctensive. Prof. Schulz and Giamarchi are world experts on these subjects and thus I espect that my training as a post-doc with them will enable me to succeed in compleffng the research problems which I descride in my proposal. Links with industry / industrial relevance (22)

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Participants

• UNIVERSITE DE PARIS-SUD XI · ORSAYCoordinatorFrance

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