T. Saha-Dasgupta

Electronic structure, phonons, and dielectric anomaly in ferromagnetic insulating double pervoskite La2NiMnO6.

Using first-principles density functional calculations, we study the electronic and magnetic properties of the ferromagnetic insulating double perovskite compound La2NiMnO6, which has been reported to exhibit an interesting magnetic field sensitive dielectric anomaly as a function of temperature. Our study reveals the existence of very soft infrared active phonons that couple strongly with spins at the Ni and Mn sites through modification of the superexchange interaction. We suggest that these modes are the origin for the observed dielectric anomaly in La2NiMnO6.

Proposed Orbital Ordering inMnV2O4from First-Principles Calculations

Based on density functional calculations, we propose a possible orbital ordering in MnV2O4 which consists of orbital chains running along crystallographic a and b directions with orbitals rotated alternatively by about 45 degrees within each chain. We show that the consideration of correlation effects as implemented in the local spin density approximation +U approach is crucial for a correct description of the space group symmetry. This implies that the correlation-driven orbital ordering has a strong influence on the structural transitions in this system. Inclusion of spin-orbit effects does not seem to influence the orbital ordering pattern. We further find that the proposed orbital arrangement favors a noncollinear magnetic ordering of V spins, as observed experimentally. Exchange couplings among V spins are also calculated and discussed.

Combined density functional and dynamical cluster quantum Monte Carlo calculations of the three-band Hubbard model for hole-doped cuprate superconductors

Using a combined local density functional theory (DFT-LDA) and quantum Monte Carlo (QMC) dynamic cluster approximation approach, the parameter dependence of the superconducting transition temperature T c of several single-layer hole-doped cuprate superconductors with experimentally very different T cmax is investigated. The parameters of two different three-band Hubbard models are obtained using the LDA and the downfolding Nth-order muffin-tin orbital technique with N=0 and 1, respectively. QMC calculations on four-site clusters show that the d-wave transition temperature T c depends sensitively on the parameters. While the N=1 MTO basis set which reproduces all three pds bands leads to a d-wave transition, the N=0 set which merely reproduces the LDA Fermi surface and velocities does not.

Halogen-mediated exchange in the coupled-tetrahedra quantum spin systemsCu2Te2O5X2(X=Br,Cl)

Motivated by recent discussion on possible quantum critical behavior in the coupled Cu-tetrahedra system Cu 2 Te 2 O 5 Br 2 , we present a comparative ab initio study of the electronic properties of Cu 2 Te 2 O 5 Br 2 and the isostructural Cu 2 Te 2 O 5 Cl 2 . A detailed investigation of the copper-copper interaction paths reveals that the halogen ions play an important role in the inter-tetrahedral couplings via X 4 rings (X=Br, Cl). We find that, contrary to initial indications, both systems show a similar electronic behavior with long range exchange paths mediated by the X 4 rings.

Negative temperature coefficient of resistance in a crystalline compound

Resistivity measurements and temperature-dependent X-ray structural analyses are reported for the crystalline compounds GdPd3BxC1- x. We show that a controlled tuning of the temperature coefficient of resistance (TCR) can be done by modifying the structural parameters and chemical environment of the compounds. We have achieved the result of negative TCR in an ordered, non-Kondo crystalline compound. Electronic-structure calculations have been carried out to elucidate some of our observations.

Effective magnetic correlations in hole-doped graphene nanoflakes

The magnetic properties of zigzag graphene nanoflakes (ZGNFs) are investigated within the framework of inhomogeneous dynamical mean-field theory. At half-filling and for realistic values of the local interaction, the ZGNF is in a fully compensated antiferromagnetic (AF) state, which is found to be robust against temperature fluctuations. Introducing charge carriers in the AF background drives the ZGNF metallic and stabilizes a magnetic state with a net uncompensated moment at low temperatures. The change in magnetism is ascribed to the delocalization of the doped holes in the proximity of the edges, which mediate ferromagnetic correlations between the localized magnetic moments. Depending on the hole concentration, the magnetic transition may display a pronounced hysteresis over a wide range of temperatures, indicating the coexistence of magnetic states with different symmetries. This suggests the possibility of achieving electrostatic control of the magnetic state of ZGNFs to realize a switchable spintronic device.

Tunable site- and orbital-selective Mott transition and quantum confinement effects in La 0.5 Ca 0.5 MnO 3 nanoclusters

We present a dynamical mean-field theory (DMFT) study of the charge and orbital correlations in finite-size La

Anomalous breakdown of Bloch's rule in the Mott-Hubbard insulator MnTe2

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Evolution of electronic and magnetic properties in four polytypes of BaRuO3: a?first-principles study

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Spectral properties of the Mott Hubbard insulator (Cr0.011V0.989)2O3 calculated by LDA+DMFT

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