In this work we study theoretically and experimentally the multi-particle structure of the so-called type-II quantum dots with spatially separated electrons and holes. Our calculations based on customarily developed full configuration interaction ap- proach reveal that exciton complexes containing holes interacting with two or more electrons exhibit fairly large antibinding energies. This effect is found to be the hallmark of the type-II confinement. In addition, an approximate self-consistent solution of the multi-exciton problem allows us to explain two pronounced phenomena: the blue-shift of the emission with pumping and the large inhomogeneous spectral broadening, both of those eluding explanation so far. The results are confirmed by detailed intensity and polarization resolved photoluminescence measurements on a number of type-II samples.

We present a dynamical mean-field study of dynamical susceptibilities in two-band Hubbard model. Varying the model parameters we analyze the two-particle excitations in the normal as well as in the ordered phase, an excitonic condensate. The two-particle DMFT spectra in the ordered phase reveal the gapless Goldstone modes arising from spontaneous breaking of continuous symmetries. We also observe gapped Higgs mode, characterized by vanishing of the gap at the phase boundary. Qualitative changes observed in the spin susceptibility can be used as an experimental probe to identify the excitonic condensation. arXiv:1808.08046v2 [cond-mat.str-el]

Spin textures in k-space arising from spin-orbit coupling in non-centrosymmetric crystals find numerous applications in spintronics. We present a mechanism that leads to appearance of kspace spin texture due to spontaneous symmetry breaking driven by electronic correlations. Using dynamical mean-field theory we show that doping a spin-triplet excitonic insulator provides a means of creating new thermodynamic phases with unique properties. The numerical results are interpreted using analytic calculations within a generalized double-exchange framework.PACS numbers: 71.70. Ej,71.27.+a,75.40.Gb Manipulation of spin polarization by controlling charge currents and vice versa has attracted considerable attention due to applications in spintronic devices. A major role is played by spin-orbit (SO) coupling in non-centrosymmetric systems. As originally realized by Dresselhaus 1 and Rashba 2 , SO coupling in a noncentrosymmetric crystal lifts the degeneracy of the Bloch states at a given k-point and locks their momenta and spin polarizations together giving rise to a spin texture in reciprocal space. This leads to a number of phenomena 3 such as spin-torques in ferro-4,5 and anti-ferromagnets 6,7 , topological states of matter, or spin textures in the reciprocal space that are the basis of the spin galvanic effect. 8 Electronic correlations alone can provide coupling between spin polarization and charge currents, e.g., via effective magnetic fields acting on electrons moving through a non-coplanar spin background. 9,10 Wu and Zhang 11 proposed that SO coupling can be generated dynamically in analogy to the breaking of relative spin-orbit symmetry in 3 He 12 . Subsequently, an effective field theory of spin-triplet Fermi surface instabilities with high orbital partial wave was developed in Ref. 13.Here, we present a spontaneous formation of a k-space spin texture, similar to the effect of Rashba-Dresselhaus SO coupling, in centrosymmetric bulk systems with no intrinsic SO coupling. The spin texture is a manifestation of excitonic magnetism that has been proposed to take place in some strongly correlated materials. 14,15 The basic ingredient is a crystal built of atoms with quasidegenerate singlet/triplet ground states. Under suitable conditions a spin-triplet exciton condensate 16,17 is formed, which may adopt a variety of thermodynamic phases with diverse properties 18 . Several experimental realizations of excitonic magnetism have already been discussed in the literature. [19][20][21][22][23] Model. We use the dynamical mean-field theory (DMFT) to study the minimal model of an excitonic magnet -the two-orbital Hubbard Hamiltonian at half- fillingThe local part of the Hamiltonian contains the crystalfield splitting ∆ between the orbitals labeled a and b and the Coulomb interaction with ferromagnetic Hund's exchange J. The kinetic part H t describes the nearestneighbor hopping on the square lattice between the same orbital flavors t a , t b as well as cross-hopping between the different orbital flavors V 1 , V 2 , see Fi...

Many-body calculations at the two-particle level require a compact representation of two-particle Green’s functions. In this paper, we introduce a sparse sampling scheme in the Matsubara frequency domain as well as a tensor network representation for two-particle Green’s functions. The sparse sampling is based on the intermediate representation basis and allows an accurate extraction of the generalized susceptibility from a reduced set of Matsubara frequencies. The tensor network representation provides a system independent way to compress the information carried by two-particle Green’s functions. We demonstrate efficiency of the present scheme for calculations of static and dynamic susceptibilities in single- and two-band Hubbard models in the framework of dynamical mean-field theory.