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NCN OPUS 1: 2011/01/B/ST3/05685

Emergent quantum phenomena in single crystals of filled arsenide skutterudites

leader: Prof. T. Cichorek

Description

Research project "Emergent quantum phenomena in single crystals of filled arsenide skutterudites” combines the study of a ground state of quantum matter with the search for new materials with promising thermoelectric applications. Emergent quantum phenomena in a macroscopic systems are of particular scientific interest, since they are not easily predicted from a microscopic description of the system’s constituent part and the rules that govern them.

On the other hand, a significance of studies, designed to obtain materials with high thermoelectric efficiency rapidly increases with ever increasing costs of energy production. Research material will be high-quality single crystals of filled skutterudite arsenides. These systems, despite significant technological advances in the preparation of arsenic compounds in the past few years, so far, only at the ILTSR PAS are obtained with great success. Experiments determining both the transport and the thermodynamic properties are planned, with the main focus on measurement at very low temperatures down to 30 mK and in high magnetic fields up to 14 T as well as with substantial impact of a new and self-produced equipment.

The main scientific objective of the project proposed is to investigate the impact of arsenic T4As12 matrix on low-temperature excitations of an electron gas in the filled skutterudites, i.e. in the MT4X12 type compounds, where M = alkali metals, alkaline earth metals, lanthanides or actinides, T = Fe, Ru or Os; X = P, As or Sb. Crystal structure of the filled skutterudites (the body centered cubic structure) is the basis of their intriguing physical properties. Indeed, a unique location of the M atom inside the icosahedron formed by 12 pnictogen atoms often leads to a simultaneous occurrence of additional, internal degrees of freedom (due to rattling motion) and enhanced hybridization effects. As a consequence, the filled skutterudites compounds (including recently discovered Ge-based ones) exhibit a large variety of interesting physical properties such as, e.g. a metal-insulator transition, a BCS-type superconductivity, magnetic ordering, quadru- and multipole ordering, and strong electron correlations resulting in unconventional superconductivity and the presence of a quantum critical point. An influence of higher electronic multipole moments on a ground state of complex systems is one of the most fascinating aspect of emergent behavior in the MT4X12 compounds. Indeed, these non-magnetic-in-origin phenomena distinctly differ the family of filled skutterudites from many other strongly electron correlated materials, especially from those based on a singular number of f-valence electrons (holes), i.e., Ce-, Yb- and U-based systems.

The main scientific objective of the project proposed is to investigate the impact of arsenic T4As12 matrix on low-temperature excitations of an electron gas in the The project is planned to extend a family of the MT4As12 type compounds on heavier lanthanides (especially Nd, Sm and Yb) and light actinides (Th and U) as well as on alkali and alkaline earth metal (being elements without d and f valence electrons). On the basis of hundreds reports in the best scientific journals regarding the phosphide and antimonide filled skutterudites, one could expect many exciting emergent phenomena also in their arsenide homologues. The second objective are detailed studies of selected compounds (M = La, Ce and Pr). It is very likely that an improvement of crystal-growth procedure, supported by experience collected in the years 2007-2010 during a realization of the research project NN 202 412933 "Intriguing physical properties of filled skutterudite arsenides: ground state and applications", will result in samples of a few millimeters in size. This will allow further studies of the ground state of selected filled skutterudite arsenides with particular emphasis on anisotropy effects caused by an applied magnetic field - often being indicative of contribution from electronic multipole moments.

The main scientific objective of the project proposed is to investigate the impact of arsenic T4As12 matrix on low-temperature excitations of an electron gas in the Due to a permanent underfunding of basic research in Poland, a realization of innovative research tasks must be based on additional funding resources. This hold especially true for a production of a new, world-wide unique, and not available commercially research position equipped with highly specialized instrumentation. Task No. 1 "Position for thermoelectric power measurements under extreme conditions, i.e. in the temperature range 0.03 - 4.2 K and in magnetic fields up to 7 T " is the most time consuming and costly task from all other ones. The fact that such experiments are made only in the most famous low-temperature laboratories additionally underlines the scale of its difficulty. On the other hand, 3He-4He dilution refrigerator with the base temperature about 0.03 K, being an equipment of the ILTSR PAS, is ideally suited for such an activity, since it possesses a large measuring space allowing for, e.g. a direct connection of the sample with a measuring instrument. It should be clearly stress that a knowledge of the magnetic-field effect on the low-temperature dependence of the thermoelectric power provides an important insight into a ground state of the systems investigated.

The main scientific objective of the project proposed is to investigate the impact of arsenic T4As12 matrix on low-temperature excitations of an electron gas in the In addition to their intriguing ground-state properties, certain filled skutterudites display promising thermoelectric parameters. It is because these materials combine strong electron correlations with a rattling motion. As a consequence, they appear to be exceptionally predisposed to an experimental implementation of the innovative concept: phonon glass - electron crystal, whose main objective is to obtain a thermoelectric material for temperature less then 300 K.

The main scientific objective of the project proposed is to investigate the impact of arsenic T4As12 matrix on low-temperature excitations of an electron gas in the Research project "Emergent quantum states in single crystals of filled skutterudite arsenides” will result in first-ever single crystals of new filled arsenide skutterudites. High-quality single-crystalline MT4As12 samples will give an opportunity for precise investigations of both their ground-states properties and promising thermoelectric parameters. Another aspect of the project proposed are detailed studies of the selected, in the course of the project NN 202 412 933 (2007-2009 ), filled skutterudite arsenides, including magnetic-field-induced anisotropy. In both cases, the expected impact on physical science is significant - such an assessment is based on an enormous interest over the world in interdisciplinary studies of the phosphide and antimonide filled skutterudite systems. Important measurable outcome will be also a position for thermoelectric power measurements under extreme conditions, i.e. in the temperature range 0.03 - 4.2 K and in magnetic fields up to 7 T. It is planned to disseminate the results obtained in the form of the publications in prestigious scientific journals as well as their presentations on international scientific conferences. It is worth adding that the results will form an important part of one doctoral dissertation, two master’s thesis and a few student-practice programs.

Publications