When an electronic system has strong correlations and a large spin-orbit interaction, it often exhibits a plethora of mutually competing quantum phases. How a particular quantum ground state is selected out of several possibilities is a very interesting question. However, equally fascinating is how such a quantum entangled state breaks up due to perturbation. This important question has relevance in very diverse fields of science from strongly correlated electron physics to quantum information. Here we report that a quantum entangled dimerized state or valence bond crystal (VBC) phase of Li2RuO3 shows nontrivial doping dependence as we perturb the Ru honeycomb lattice by replacing Ru with Li. Through extensive experimental studies, we demonstrate that the VBC phase melts into a valence bond liquid phase of the RVB (resonating valence bond) type. This system offers an interesting playground where one can test and refine our current understanding of the quantum competing phases in a single compound.

The electronic structure of Li 2 RuO 3 was investigated using x-ray emission and absorption spectroscopy and by theoretical calculations employing two approaches: the local density approximation (LDA) and a combination of LDA with the cluster extension of dynamical mean-field theory (LDA+DMFT). The evolution of the spectral properties with the strength of electronic correlations is analyzed. We show that for moderate values of on-site Coulomb repulsion U and intra-atomic Hund's rule exchange J H , Li 2 RuO 3 is in an orbital-selective strongly correlated state in the sense that a part of the t 2g manifold (i.e., xz/yz) behaves as local atomic orbitals susceptible to Hubbard correlations, while the remaining (xy) orbitals must be described as bond-centered molecular orbitals. Both theoretical approaches succeed in explaining the x-ray data, and a comparison of the theoretical and experimental spectra provides a reasonable estimate of the possible correlation strength (U ) and Hund's coupling (J H ) in Li 2 RuO 3 .

The mixed-valence manganite Sr 0.65 Pr 0.35 MnO 3 has been prepared and its crystal and magnetic structure investigated between 7 and 1200 K using high-resolution powder neutron diffraction. The structural and lattice parameter data have been used to determine the octahedral tilting and spontaneous strains associated with the structural, electronic, and magnetic phase transitions. At room temperature, the structure is tetragonal and is characterized by cooperative out-of-phase tilts of the MnO 6 octahedra about the c axis and a large Jahn-Teller-type distortion due to the presence of Mn 3+ . The sample exhibits a reversible phase transition from the cubic P m3m perovskite to a tetragonal I 4/mcm structure at 750 K. The P m3m ↔ I4/mcm phase transition is continuous, and the tetragonal strain, which is dominated by the Jahn-Teller-type distortion of the MnO 6 octahedra, exhibits an unusual e t 0.5 ∝ (T c − T ) temperature dependence. At low temperatures, a C-type antiferromagnetic structure develops with a Neel temperature T N of 250 K. The Mn magnetic moment at 7 K is 2.99(2) μ B /Mn. The magnetic ordering introduces additional tetragonal strain, and this strain shows the expected quadratic dependence on the magnetic moment at low temperatures. An increase in the octahedral tilt angle at T N demonstrates an effective coupling between the magnetic ordering process and octahedral tilting.

No abstract

No abstract