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Dagotto, Elbio R

Publications and source records attributed to Dagotto, Elbio R.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Magnetic phase diagram of a five-orbital Hubbard model in the real-space Hartree-Fock approximation varying the electronic density

Usingthereal-spaceHartree-Fockapproximation,themagneticphasediagramofa ve-orbitalHubbardmodelfortheiron-basedsuperconductorsisstudiedvaryingtheelectronicdensitynintherangefrom vetosevenelectronspertransitionmetalatom.TheHubbardinteractionUisalsovaried,ata xedHundcouplingJ/U=0.25.Severalqualitativetrendsandavarietyofcompetingmagneticstatesareobserved.Atn=5,arobustG-typeantiferromagneticinsulatorisfound,inagreementwithexperimentalresultsforBaMn2As2.Asnincreasesawayfrom5,magneticstateswithanincreasingnumberofnearest-neighborsferromagneticlinksbecomeenergeticallystable.Thisincludesthewell-knownC-typeantiferromagneticstateatn=6,theE-phaseknowntoexistinFeTe,andalsoavarietyofnovelstatesnotfoundyetexperimentally,someoftheminvolvingblocksofferromagneticallyorientedspins.Regionsofphaseseparation,asinMnoxides,havealsobeendetected.Comparisontoprevioustheoreticalinvestigationsindicatethatthesequalitativetrendsmaybegenericcharacteristicsofphasediagramsofmulti-orbitalHubbardmodels.

Luo, Qinlong↗
DOE OSTI2014

Exotic Magnetic Order in the Orbital-Selective Mott Regime of Multiorbital Systems

The orbital-selective Mott phase of multiorbital Hubbard models has been extensively analyzed before using static and dynamical mean-field approximations. In parallel, the properties of block states (antiferromagnetically coupled ferromagnetic spin clusters) in Fe-based superconductors have also been much discussed. The present effort uses numerically exact techniques in one-dimensional systems to report the observation of block states within the orbital-selective Mott phase regime, connecting two seemingly independent areas of research, and providing analogies with the physics of double-exchange models.

Rincon, Julian↗
DOE OSTI2014

Ab initio quantum Monte Carlo calculations of spin superexchange in cuprates: the benchmarking case of Ca2CuO3

In view of the continuous theoretical efforts aimed at an accurate microscopic description of the strongly correlated transition metal oxides and related materials, we show that with continuum quantum Monte Carlo (QMC) calculations it is possible to obtain the value of the spin superexchange coupling constant of a copper oxide in a quantitatively excellent agreement with experiment. The variational nature of the QMC total energy allows us to identify the best trial wave function out of the available pool of wave functions, which makes the approach essentially free from adjustable parameters and thus truly ab initio. The present results on magnetic interactions suggest that QMC is capable of accurately describing ground state properties of strongly correlated materials.

magnetism↗
DOE OSTI2013

Electron Doping by Charge Transfer at LaFeO 3 /Sm 2 CuO 4 Epitaxial Interfaces

The breakdown of the lattice translational invariance symmetry that occurs at complex oxide interfaces may profoundly modify their electronic structure, leading to interfacial states with properties drastically different from those of the superlattice individual components. The appearance of a conducting two dimensional (2D) electron gas at the interface between two insulating oxides and induced magnetism in a non-magnetic material are just two among many fascinating examples. [ 1 8 ] One of the key factors underlying novel properties is the modifi cation of the doping and orbital occupancy near those interfaces, which may result from charge transfer processes. [ 3 , 9 11 ] If materials used in heterostructures have different work functions, a non-equilibrium situation will be created at the interface and charge will be transferred until the chemical potential levels off. [ 12 ] The use of such phenomena to modify doping in heterostructures has been proposed theoretically as a new route to avoid the quenched disorder that inevitably accompanies the chemical doping. At the interface between a Mott insulating parent compound of the high critical temperature superconductor (HTSC) family and a suitable material that would act as the charge donor, electron doped phases could be stabilized which would eventually turn metallic and perhaps superconducting. [ 12 , 13 ] Such charge transfer processes have been observed at interfaces involving copper oxides such as La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7 , [ 14 ] La 2 x Sr x CuO 4 /La 2 CuO 4 [ 15 ] and SrTi 1 x Nb x O 3 / Sm 2 CuO 4 . [ 16 ] While a novel 2D superconducting state was found at the La 2-x Sr x CuO 4 /La 2 CuO 4 interface, [ 17 ] the effect of doping by charge transfer could not be examined in the other two cases due to the detrimental effect on the YBa 2 Cu 3 O 7 superconductivity of the spin polarized electrons from La 0.7 Ca 0.3 MnO 3 in one case and due to the conducting nature of the SrTi 1 x Nb x O 3 in the other case, which obscures changes in the conducting properties of the interface layer. In this paper, the structural and

Bruno, Flavio Y.↗
DOE OSTI2013

Charge Excitations in Two-Leg Ladders: A tDMRG Approach

Abstract We study the dynamics of holon doublon pairs in two-leg Hubbard ladders with the time-dependent Density Matrix Renormalization-Group approach. Benchmark results show that the Krylov algorithm is well suited to calculate the time dependence of observables in these systems. Furthermore, we show that the dynamics of the holon doublon depend strongly on the coupling asymmetry within the ladder, indicating that the ladder geometry plays a role in the decay of these elementary charge excitations.

Dias da Silva, Luis↗
DOE OSTI2013

Quantum confinement induced magnetism in LaNiO3-LaMnO3 superlattices

The emergence of magnetic reconstructions at the interfaces of oxide heterostructures are often explained via subtle modifications in the electronic densities, exchange couplings, or strain. Here, an additional possible route for induced magnetism is studied in the context of the (LaNiO3)n/(LaMnO3)n superlattices using a hybrid tightbinding model. In the LaNiO3 region, the induced magnetizations decouple from the intensity of charge leakage from Mn to Ni, but originate from the spin-filtered quantum confinement present in these nanostructures. In general, the induced magnetization is the largest for the (111)-stacking and the weakest for the (001)-stacking superlattices; results compatible with the exchange bias effects reported byGibert et al. [Nat.Mater. 11, 195 (2012)].

Dong, Shuai↗
DOE OSTI2013

Full control of magnetism in a manganite bilayer by ferroelectric polarization

An oxide heterostructure made of manganite bilayers and ferroelectric perovskites is predicted to lead to the full control of magnetism when switching the ferroelectric polarizations. By using asymmetric polar interfaces in the superlattices, more electrons occupy the Mn layer at the n-type interface side than at the p-type side. This charge disproportionation can be enhanced or suppressed by the ferroelectric polarization. Quantum model and density functional theory calculations reach the same conclusion: a ferromagnetic-ferrimagnetic phase transition with maximal change >90% of the total magnetization can be achieved by switching the polarization s direction. This function is robust and provides full control of the magnetization s magnitude, not only its direction, via electrical methods.

Dong, Shuai↗
DOE OSTI2013

The unexpected properties of alkali metal iron selenide superconductors

The iron-based superconductors that contain FeAs layers as the fundamental building block in the crystal structures have been rationalized in the past using ideas based on the Fermi surface nesting of hole and electron pockets when in the presence of weak Hubbard U interactions. This approach seemed appropriate considering the small values of the magnetic moments in the parent compounds and the clear evidence based on photoemission experiments of the required electron and hole pockets. However, recent results in the context of alkali metal iron selenides, with generic chemical composition AxFe2ySe2 (A alkali metal element), have challenged those previous ideas since at particular compositions y the low-temperature ground states are insulating and display antiferromagnetic order with large iron magnetic moments. Moreover, angle-resolved photoemission studies have revealed the absence of hole pockets at the Fermi level in these materials. The present status of this exciting area of research, with the potential to alter conceptually our understanding of the ironbased superconductors, is here reviewed, covering both experimental and theoretical investigations. Other recent related developments are also briefly reviewed, such as the study of selenide two-leg ladders and the discovery of superconductivity in a single layer of FeSe. The conceptual issues considered established for the alkali metal iron selenides, as well as several issues that still require further work, are discussed.

Dagotto, Elbio R↗
DOE OSTI2012

Magnetismanditsmicroscopicorigininiron-basedhigh-temperaturesuperconductors

High-temperaturesuperconductivityintheiron-basedmaterialsemergesfrom,orsometimescoexistswith,theirmetallicorinsulatingparentcompoundstates.Thisissurprising,astheseundopedstatesexhibitdramaticallydifferentantiferromagneticspinarrangementsandN eltemperatures.Althoughthereisageneralconsensusthatmagneticinteractionsareimportantforsuperconductivity,muchremainsunknownconcerningthemicroscopicoriginofthemagneticstates.Inthisreview,wesummarizetheprogressinthisarea,focusingonrecentexperimentalandtheoreticalresults,andtheirmicroscopicimplications.WeconcludethattheparentcompoundsareinastatethatismorecomplexthanthatimpliedbyasimpleFermisurfacenestingscenario,andadualdescriptionincludingbothitinerantandlocalizeddegreesoffreedomisneededtoproperlydescribethesefascinatingmaterials.

Dai, Pengcheng↗
DOE OSTI2012

Multifunctional Oxide Heterostructures

This book is devoted to the rapidly developing field of oxide thin-films and heterostructures. Oxide materials combined with atomic-scale precision in a heterostructure exhibit an abundance of macroscopic physical properties involving the strong coupling between the electronic, spin, and structural degrees of freedom, and the interplay between magnetism, ferroelectricity, and conductivity. Recent advances in thin-film deposition and characterization techniques made possible the experimental realization of such oxide heterostructures, promising novel functionalities and device concepts.

Tsymbal, E Y↗
DOE OSTI2012

Pairing symmetries of a hole-doped extended two-orbital model for the pnictides

The hole-doped ground state of a recently introduced extended t-U-J two-orbital Hubbard model for the Fe-based superconductors is studied via exact diagonalization methods on small clusters. Similarly as in the previously studied case of electron doping [A. Nicholson et al., Phys. Rev. Lett. 106, 217002 (2011)], upon hole doping it is observed that there are several competing pairing symmetries, including A1g , B1g , and B2g . However, contrary to the electron-doped case, the ground state of the hole-doped state has pseudocrystal momentum k = ( , ) in the unfolded Brillouin zone. In the two Fe-atom per unit cell representation, this indicates that the ground state involves antibonding, rather than bonding, combinations of the orbitals of the two Fe atoms in the unit cell. The lowest state with k = (0,0) has only a slightly higher energy. These results indicate that this simple two-orbital model may be useful to capture some subtle aspects of the hole-doped pnictides, since calculations for the five-orbital model have unveiled a hole pocket centered at M [k = ( , )] in the unfolded Brillouin zone.

99 GENERAL AND MISCELLANEOUS↗