Coexistence of metallic and nonmetallic properties in the pyrochlore Lu 2 Rh 2 O 7

Transition metal oxides of the 4 d and 5 d block have recently become the targets of materials discovery, largely due to their strong spin–orbit coupling that can generate exotic magnetic and electronic states. Here, we report the high-pressure synthesis of Lu 2 Rh 2 O 7 , a new cubic pyrochlore oxide based on 4 d 5 Rh 4+ , and characterizations via thermodynamic, electrical transport, and muon spin relaxation measurements. Magnetic susceptibility measurements reveal a large temperature-independent Pauli paramagnetic contribution, while heat capacity shows an enhanced Sommerfeld coefficient, γ = 21.8(1) mJ/mol-Rh K 2 . Muon spin relaxation measurements confirm that Lu 2 Rh 2 O 7 remains paramagnetic down to 2 K. Taken in combination, these three measurements suggest that Lu 2 Rh 2 O 7 is a correlated paramagnetic metal with a Wilson ratio of R W = 2.5. However, electric transport measurements present a striking contradiction as the resistivity of Lu 2 Rh 2 O 7 is observed to monotonically increase with decreasing temperature, indicative of a nonmetallic state. Furthermore, although the magnitude of the resistivity is that of a semiconductor, the temperature dependence does not obey any conventional form. Thus, we propose that Lu 2 Rh 2 O 7 may belong to the same novel class of non-Fermi liquids as the nonmetallic metal FeCrAs.