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Abstract Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr 3 Si 7 reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr 3 Si 7 is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300โmK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.more » « less
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Abstract. Let ๐ be a real semisimple algebraic Lie group and ๐ a real reductive algebraic subgroup. We describe the pairs (๐,๐) for which the representation of ๐ in Lยฒ(๐/๐) is tempered. The proof gives the complete list of pairs (๐,๐) for which Lยฒ(๐/๐) is not tempered. When ๐ and ๐ are complex Lie groups, the temperedness condition is characterized by the fact that ๐ต๐ฉ๐ฆ ๐ด๐ต๐ข๐ฃ๐ช๐ญ๐ช๐ป๐ฆ๐ณ ๐ช๐ฏ ๐ ๐ฐ๐ง ๐ข ๐จ๐ฆ๐ฏ๐ฆ๐ณ๐ช๐ค ๐ฑ๐ฐ๐ช๐ฏ๐ต ๐ฐ๐ฏ ๐/๐ ๐ช๐ด ๐ท๐ช๐ณ๐ต๐ถ๐ข๐ญ๐ญ๐บ ๐ข๐ฃ๐ฆ๐ญ๐ช๐ข๐ฏ. ๐๐ข๐ต๐ฉ๐ฆ๐ฎ๐ข๐ต๐ช๐ค๐ด ๐๐ถ๐ฃ๐ซ๐ฆ๐ค๐ต ๐๐ญ๐ข๐ด๐ด๐ช๐ง๐ช๐ค๐ข๐ต๐ช๐ฐ๐ฏ: Primary 22๐46; secondary 43๐85, 22๐ 30. ๐๐ฆ๐บ ๐๐ฐ๐ณ๐ฅ๐ด: Lie groups, homogeneous spaces, tempered representations, unitary representations, matrix coefficients, symmetric spaces.more » « less
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