Spontaneous Spin Textures in Multiorbital Mott Systems

Abstract

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...

LDA+DMFT approach to ordering phenomena and the structural stability of correlated materials

“…Nevertheless, the primed and unprimed phases have distinct properties. The primed phases were shown to host spin textures in the reciprocal space [62]. In particular, textures with odd k-parity are interesting since they do not break time reversal symmetry and give rise to an effective Hamiltonian similar to RashbaDresselhaus spin-orbit coupling.…”

“…At low temperatures the transition is of first order and is accompanied by charge separation, while at higher temperatures it proceeds via two continuous phase transitions. The microscopic origin of the FMEC phase has been explained in terms of a generalized double-exchange mechanism [62]. The spin of the doped carrier couples to the net spin polarization of the condensate.…”

“…Second, a continuous phase 2 at the indicated points of the phase diagrams. After reference [62]. (This figure is subject to copyright protection and is not covered by a Creative Commons License.)…”

“…The European Physical Journal Special Topics as spin-state ordered states or excitonic condensates [59][60][61][62][63]. An exciton is a bound state between an electron and a hole with total charge zero.…”

Excitonic Insulator State of the Extended Falicov–Kimball Model in the Cluster Dynamical Impurity Approximation

“…[33][34][35][36][37][38][39][40][41] The multiband Hubbard model, taking into account the spin de- * ohta@faculty.chiba-u.jp grees of freedom, has also been used to discuss, for example, the relative stability of the spin-singlet and spintriplet excitonic phases. [42][43][44][45][46][47][48][49] We have so far studied the excitonic phases of the EFKM and multiband Hubbard models using the variational cluster approximation (VCA) based on the exact diagonalization of small clusters. 50,51) However, some difficulty arises in such a small-cluster approach, particularly when we calculate physical quantities as a function of the model parameters.…”