Nonlocal correlations induced by Hund's coupling: A cluster DMFT study

Nomura, Yusuke; Sakai, Shiro; Arita, Ryotaro

doi:10.1103/physrevb.91.235107

Cited by 31 publications

(31 citation statements)

References 36 publications

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“…The best known example is the single orbital case at half-filling for which antiferromagnetic (Heisenberg-like) correlations between the local electrons in neighboring sites emerge. In multi-orbital systems the inter-site correlations involve both magnetic and orbital degrees of freedom, and depend on J H [40,41] and the filling. For a two-orbital system with x=1/4 positive (negative) Hund's coupling promotes ferromagnetic and antiferroorbital (AFM and ferroorbital) correlations [42,43] while for J H =0 correlations are AFM and antiferroorbital [44].…”

Section: Effect Of Inter-site Correlationsmentioning

confidence: 99%

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The nature of correlations in the insulating states of twisted bilayer graphene

Pizarro¹,

Calderón²,

Bascones³

2019

J. Phys. Commun.

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The recently observed superconductivity in twisted bilayer graphene emerges from insulating states believed to arise from electronic correlations. While there have been many proposals to explain the insulating behaviour, the commensurability at which these states appear suggests that they are Mott insulators. Here we focus on the insulating states with ±2 electrons or holes with respect to the charge neutrality point. We show that the theoretical expectations for the Mott insulating states are not compatible with the experimentally observed dependence on temperature and magnetic field if, as frequently assumed, only the correlations between electrons on the same site are included. We argue that the inclusion of non-local (inter-site) correlations in the treatment of the Hubbard model can bring the predictions for the magnetic and temperature dependencies of the Mott transition to an agreement with experiments and have consequences for the critical interactions, the size of the gap, and possible pseudogap physics. The importance of the inter-site correlations to explain the experimental observations indicates that the observed insulating gap is not the one between the Hubbard bands and that antiferromagnetic-like correlations play a key role in the Mott transition.

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Section: Effect Of Inter-site Correlationsmentioning

confidence: 99%

“…Cluster treatments of multi-orbital models are computationally challenging and very scarce [40,41,44,46,47]. To our knowledge there are no studies which include these non-local correlations in the twoorbital honeycomb lattice.…”

Section: Effect Of Inter-site Correlationsmentioning

confidence: 99%

The nature of correlations in the insulating states of twisted bilayer graphene

Pizarro¹,

Calderón²,

Bascones³

2019

J. Phys. Commun.

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“…Recently a three band Hamiltonian with nearest neighbors on the square lattice and strong Hunds and Hubbard interactions was studied. [53] Strong momentum space differentiation was found for much larger values of the Hunds coupling and the Hubbard U.…”

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confidence: 94%

Validity of the local approximation in iron pnictides and chalcogenides

2017

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We introduce a cluster DMFT (Dynamical Mean Field Theory) approach to study the normal state of the iron pnictides and chalcogenides. In the regime of moderate mass renormalizations, the self-energy is very local, justifying the success of single site DMFT for these materials and for other Hunds metals. We solve the corresponding impurity model with CTQMC (Continuous Time Quantum Monte-Carlo) and find that the minus sign problem is not severe in regimes of moderate mass renormalization.The unexpected discovery of superconductivity in the iron pnictide based materials has opened a new era of research in the field of condensed matter physics.[1] Multiple approaches, starting from weak coupling such as the random phase approximation (RPA) and strong coupling approaches using lessons learned from the t-J model, have been proposed, but there is not yet consensus in the community of what constitutes the proper theoretical framework for describing these systems.[2] It has been proposed that iron pnictides and chalcogenides are important not only because of their high temperature superconductivity, but because their normal state properties represent a new class of strongly correlated systems, the Hunds metals. They are distinct from doped Mott Hubbard systems, in that correlations effects in their physical properties derive from the Hunds rule coupling J, rather than the Hubbard U. [3,4] Many other interesting Hunds metals have been recognized, as for example Ruthenates [5] and numerous 3d and 4d compounds [6].Dynamical Mean Field Theory [7](DMFT) and its cluster extensions [8,9] have provided a good starting point for the description of Mott Hubbard physics. It is now established that it describes many puzzling properties of three dimensional materials such as Vanadium oxides near their finite temperature Mott transition. [10] In materials such as cuprates, as the temperature is lowered, the description in terms of single site DMFT gradually breaks down. New phenomena such as momentum space differentiation and the opening of a pseudogap takes place, and cluster DFMT is essential. How different cluster sizes and methods captures these effects has been explored intensively. [14,29,[36][37][38][39][40][41] The iron pnictides and chalcogenides have been extensively studied using LDA+DMFT by several groups. [3,4,[42][43][44] It has been argued using the GW method, that the frequency dependence of low order diagrams in perturbation theory in these materials is very local.[45] However, because of the difficulties posed by the multiorbital nature of these compounds, the accuracy of the local approximation beyond the GW level has not been examined and is the main goal of this paper.Building on the work of Ref. 46, we introduce a cluster extension for the treatment of iron pinctides, which is numerically tractable using CTQMC. By comparing single site and cluster DMFT, we establish that in a broad range of parameters where the mass renormalizations are of the order of 2 to 3, which corresponds to the experimental situation in...

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“…Orbitally degenerate models have so far been investigated by means of a variety of analytical approaches, among which we only mention for brevity variational methods [6][7][8], Gutzwiller [9][10][11] and slave-boson methods [12][13][14], the dynamical mean-field theory [15][16][17][18][19][20][21][22]. As far as numerical methods are concerned, though some information on the ground state properties has been obtained via Lanczos diagonalization on finite-size clusters [23], a fully reliable approach to treat multi-band degenerate Hubbard models is still lacking, since severe limitations are imposed by the procedures usually needed to derive the excitation spectrum.…”

Section: Introductionmentioning

confidence: 99%