We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba 3 ZnIr 2 O 9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba 3 ZnIr 2 O 9 with Ir 5þ (5d 4 ) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J ¼ 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir 2 O 9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK. DOI: 10.1103/PhysRevLett.116.097205 5d transition metal compounds often exhibit unusual electronic and magnetic properties due to the presence of strong spin-orbit coupling (SOC), comparable to their onsite Coulomb (U) and crystal field (Δ CFE ) interactions [1,2]. In the strong spin-orbit coupling regime, M J ( P m j ) becomes the only valid quantum number instead of m l (orbital) and m s (spin), and the multiplets and their degeneracies are solely determined by the total angular momentum J. The electronic and magnetic responses of a system in such limits are not yet well understood and have generated significant curiosity in recent times. For example, the curious insulating state of the layered tetravalent iridates (Ir 4þ ; 5d 5 ) has recently been explained within single particle theories assuming splitting of t 2g bands into a set of fully filled quartet bands separated from another set of half-filled narrow doublet bands due to finite SOC. The half-filled doublet bands further split into fully occupied lower and empty upper Hubbard bands in the presence of relatively small Hubbard U [3-5].The pentavalent Iridates (Ir 5þ ; 5d 4 ) are more intriguing, where in the strong SOC limit all the spin-orbit entangled electrons will be confined to singlet J ¼ 0 (M J ¼ 0) ground state, with no net moment. The evolution of ground and excited states of a low spin 5d t 4 2g Ir 5þ ion as a function of SOC parameter λ 0 is illustrated in Fig. 1(a) and a J ¼ 0 ground state is realized in the strong SOC limit [6]. A possibility of excitonic magnetism has been predicted for these systems where the energy scale of the singlet-triplet splitting determined by SOC is comparable to superexchange interaction promoted by hopping [10]. The breakdown of the J ¼ 0 nonmagnetic state in d 4 systems can also be realized within a single electron picture primarily driven by band-structure effect that allows the hybridization between the quartet and the doublet redistributed orbitals (eigenstates of the spin-orbit coupled Hamiltonian). Overall, d 4 Ir compounds in the strong SOC limit may host weak magnetic moment unless the λ 0 becomes so large that any excitonic or hopping-assisted magnetism become...

We report magnetic susceptibility (χ) and heat capacity (C p ) measurements along with ab-initio electronic structure calculations on PbCuTe 2 O 6 , a compound made up of a three dimensional 3D network of corner-shared triangular units. The presence of antiferromagnetic interactions is inferred from a Curie-Weiss temperature (θ CW ) of about −22 K from the χ(T ) data. The magnetic heat capacity C m data show a broad maximum at T max ≃ 1.15 K (i.e.T max /θ CW ≃ 0.05), which is analogous to the the observed broad maximum in the C m /T data of a hyper-Kagome system, Na 4 Ir 3 O 8 . In addition, C m data exhibit a weak kink at T * ≃ 0.87 K. While the T max is nearly unchanged, the T * is systematically suppressed in an increasing magnetic field (H) up to 80 kOe. For H ≥ 80 kOe, the C m data at low temperatures exhibit a characteristic power-law (T α ) behavior with an exponent α slightly less than 2. Hopping integrals obtained from the electronic structure calculations show the presence of strongly frustrated 3D spin interactions along with non-negligible unfrustrated couplings. Our results suggest that PbCuTe 2 O 6 is a candidate material for realizing a 3D quantum spin liquid state at high magnetic fields.

We investigate magnetic, thermal, and dielectric properties of SrCuTe2O6, which is isostructural to PbCuTe2O6, a recently found, Cu-based 3D frustrated magnet with a corner-sharing triangular spin network having dominant first and second nearest neighbor (nn) couplings [B. Koteswararao, et al. Phys. Rev. B 90, 035141 (2014)]. Although SrCuTe2O6 has a structurally similar spin network, but the magnetic data exhibit the characteristic features of a typical quasi-one-dimensional magnet, which mainly resulted from the magnetically dominant third nn coupling, uniform chains. The magnetic properties of this system are studied via magnetization (M), heat capacity (Cp), dielectric constant (ε'), measurements along with ab-initio band structure calculations. Magnetic susceptibility (T) data show a broad maximum at 32 K and the system orders at low temperatures TN1  5.5 K and TN2  4.5 K, respectively. The analysis of (T) data gives an intra-chain coupling, J3/kB, to be about  -42 K with non-negligible frustrated inter-chain couplings (J1/kB and J2/kB). The hopping parameters obtained from LDA band structure calculations also suggest the presence of coupled uniform chains. The observation of simultaneous anomalies in ε'(T) at TN1 and TN2 suggests the presence of magneto-dielectric effect in SrCuTe2O6. A magnetic phase diagram is also built based on M, Cp, and ε' results.

Green and sustainable energy production through renewable sources is enormously an exciting field of research. Herein, we report A-site lanthanum doped oxygen excess ruthenate (predominantly Ru5+-ions) double perovskite system, CaLaScRuO6+δ...

NiS, exhibiting a text-book example of a first-order transition with many unusual properties at low temperatures, has been variously described in terms of conflicting descriptions of its ground state during the past several decades. We calculate these physical properties within first-principle approaches based on the density functional theory and conclusively establish that all experimental data can be understood in terms of a rather unusual ground state of NiS that is best described as a self-doped, nearly compensated, antiferromagnetic metal, resolving the age-old controversy. We trace the origin of this novel ground state to the specific details of the crystal structure, band dispersions and a sizable Coulomb interaction strength that is still sub-critical to drive the system in to an insulating state. We also show how the specific antiferromagnetic structure is a consequence of the less-discussed 90° and less than 90° superexchange interactions built in to such crystal structures.