Electron-lattice and strain effects in manganite heterostructures: The case of a single interface

Abstract

A correlated inhomogeneous mean-field approach is proposed in order to study a tight-binding model of the manganite heterostructures (LaM nO3)2n/(SrM nO3)n with average hole doping x = 1/3. Phase diagrams, spectral and optical properties of large heterostructures (up to 48 sites along the growth direction) with a single interface are discussed analyzing the effects of electron-lattice anti-adiabatic fluctuations and strain. The formation of a metallic ferromagnetic interface is quite robust with varying the strength of electron-lattice coupling and strain, though the size of the interface region is strongly dependent on these interactions. The density of states never vanishes at the chemical potential due to the formation of the interface, but it shows a rapid suppression with increasing the electron-lattice coupling. The in-plane and out-of-plane optical conductivities show sharp differences since the in-plane response has metallic features, while the out-of-plane one is characterized by a transfer of spectral weight to high frequency. The in-plane response mainly comes from the region between the two insulating blocks, so that it provides a clear signature of the formation of the metallic ferromagnetic interface.

Effects of electron coupling to intramolecular and intermolecular vibrational modes on the transport properties of single-crystal organic semiconductors

“…The resulting inhomogeneous Holstein model can be accurately studied within the modified Lang-Firsov approach via a unitary transformation U , provided that the system is in the anti-adiabatic regime (ω Intra > t), where the quantum nature of phonons cannot be neglected. 27,28 The electron is renormalized by the coupling with local modes increasing its mass, and the oscillators are displaced from their equilibrium position to a distance proportional to the el-ph interaction. In our case, the new Hamiltonian H = U −1 HU is built through the varia-tional transformation:…”

“…where the variational parameters f i ({y j }), giving the new centers for the local oscillators at the sites i, have to be determined for each fixed configuration of non local displacements {y j }. Within our approach, 28,29 the solution of the full problem can be obtained by minimizing the free energy of the following inhomogeneous effective hamiltonian:…”

Strain-induced topological phase transition at (111) SrTiO$_3$-based heterostructures

“…A general property of heterostructures, among which LAO/STO, is the possibility of controlling strain at the interfaces by realizing superlattices or using micromembranes [23][24][25]. The presence of strain allows the manifestation of phenomena absent in the bulk structure [26][27][28][29]. Moreover, these phenomena can be tuned by manipulating the strain itself.…”

The Effects of Different Electron-Phonon Couplings on the Spectral and Transport Properties of Small Molecule Single-Crystal Organic Semiconductors

“…At a fixed configuration of non-local displacements, {y j }, Equation (10) is equivalent to a Holstein model with displacements {x i }, where the electron hopping depends on the specific nearest neighbor sites throughout the assigned {y j }. The resulting inhomogeneous Holstein model can be accurately studied within the modified variational Lang-Firsov approach via a unitary transformation, U ({y j }), depending on the non-local displacements, {y j }, and appropriate in the anti-adiabatic regime (ω Intra > t) [57,58]. The electron mass is renormalized by the coupling with local modes (polaronic effect), and the Holstein-coupled oscillators {x i } are displaced from their equilibrium position to a distance proportional to the electron-phonon interaction.…”