Influence of the electronic structure on tunneling through ferroelectric insulators: Application to BaTiO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and PbTiO3<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Wortmann, Daniel; Blügel, Stefan

doi:10.1103/physrevb.83.155114

Cited by 18 publications

(13 citation statements)

References 29 publications

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“…The much larger area of the 2DBZ outside those sections contributes to the darker cluster of imaginary bands at q ∼ 0.2. Similar results have been previously reported for other perovskites [11,17,23,24]. The main messages that can be drawn might be summarized as follows: (i) the most penetrating bands (the most important for tunneling, especially in thick films) come from high-symmetry points or lines in the 2DBZ whose relative weight is small.…”

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confidence: 85%

First-principles study of metal-induced gap states in metal/oxide interfaces and their relation with the complex band structure

Aguado‐Puente

Junquera

2013

MRS Communications

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We develop a simple model to compute the energy-dependent decay factors of metal-induced gap states in metal/insulator interfaces considering the collective behaviour of all the bulk complex bands in the gap of the insulator. The agreement between the penetration length obtained from the model (considering only bulk properties) and full first-principles simulations of the interface (including explicitly the interfaces) is good. The influence of the electrodes and the polarization of the insulator is analyzed. The method simplifies the process of screening materials to be used in Schootky barriers or in the design of giant tunneling electroresistance and magnetoresistance devices. PACS numbers: 73.40.Gk, 73.30.+y, 77.80.Fm,Interfaces between different oxide materials exhibit a fantastic variety of functional properties, some of them intrinsic to the boundary between the constituent compounds [1]. A ubiquitous type of interface is that formed between a metal and an insulator or semiconductor, since the presence of electrodes is required for the application of electric fields in solid state devices. At any metal/insulator interface, bulk Bloch states in the metal side of the junction with eigenvalues below the Fermi energy and within the energy gap of the insulator cannot propagate into the insulating side. These states do not vanish right at the interface either, but they decay exponentially as they penetrate into the insulator [2]. Indeed, the tails of the metal Bloch states might have a significant amplitude for a few layers from the interface, creating a continuum of gap states [the so-called metal-induced gap states (MIGS)] [2]. These MIGS are essential to determine many interfacial properties. The transfer of charge associated to them contribute to the interfacial dipole, which enter into most of the models describing the formation of Schottky barriers. For this reason, theory of MIGS were deeply studied in semiconductor heterostructures [3, 4]. More recently, the attention has turned to metal/oxide interfaces, mostly due to several works that have first predicted [5, 6] and later demonstrated giant tunnel electroresistance [7-10] and magnetoresistance [11][12][13] in ferroelectric/metal junctions, where the decay length of the MIGS plays a major role.The eigenstates of the Hamiltonian for the interface can be described as the matching at the junction of two wave functions: an ordinary bulk Bloch state on the metal side, and an exponentially decaying function on the insulator side. Assuming that the interface is periodic in the plane parallel to the boundary [referred to as the (x, y) plane], then the components of the wave vectors parallel to the interface, k , are real and have to be preserved when the electron crosses the junction [14]. Therefore, the previous matching is possible only if the two wave functions do have the same associated energy, symmetry, and k [15].The exponential tails within the insulator decay only in the direction perpendicular to the junction (referred to as the z-direction), and ca...

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supporting

confidence: 85%

First-principles study of metal-induced gap states in metal/oxide interfaces and their relation with the complex band structure

Aguado‐Puente

Junquera

2013

MRS Communications

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“…54,57,58 In the case of ferroelectrics, the CBS has been calculated for BTO 20,23,52,59 and PTO. [60][61][62][63] The results show that there are multiple decay rates in the barrier for propagating states with different symmetry. The largest contribution to the transmission is expected from the bands that have lowest decay rates.…”

Section: Mechanisms Of Ter and Their Experimental Manifestationmentioning

confidence: 93%

Predictive modelling of ferroelectric tunnel junctions

et al. 2016

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Ferroelectric tunnel junctions combine the phenomena of quantum-mechanical tunnelling and switchable spontaneous polarisation of a nanometre-thick ferroelectric film into novel device functionality. Switching the ferroelectric barrier polarisation direction produces a sizable change in resistance of the junction-a phenomenon known as the tunnelling electroresistance effect. From a fundamental perspective, ferroelectric tunnel junctions and their version with ferromagnetic electrodes, i.e., multiferroic tunnel junctions, are testbeds for studying the underlying mechanisms of tunnelling electroresistance as well as the interplay between electric and magnetic degrees of freedom and their effect on transport. From a practical perspective, ferroelectric tunnel junctions hold promise for disruptive device applications. In a very short time, they have traversed the path from basic model predictions to prototypes for novel non-volatile ferroelectric random access memories with non-destructive readout. This remarkable progress is to a large extent driven by a productive cycle of predictive modelling and innovative experimental effort. In this review article, we outline the development of the ferroelectric tunnel junction concept and the role of theoretical modelling in guiding experimental work. We discuss a wide range of physical phenomena that control the functional properties of ferroelectric tunnel junctions and summarise the state-of-the-art achievements in the field.Predictive modelling of FTJs JP Velev et al

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“…In contrast, it is known that tunneling through insulators can be understood in terms of the evanescent states 17 and the method to investigate them is the complex band structure in the energy gap region. [18][19][20][21] So far, however, this approach has not been applied to spin-filter materials such as EuO. It has recently been shown, both theoretically using reliable GW calculations 22 and experimentally using angle-resolved photoemission experiments, 23 that the band gap in EuO is indirect, with the conduction-band minimum being located at the X point in the Brillouin zone.…”

Section: Introductionmentioning

confidence: 99%

Spin filtering with EuO: Insight from the complex band structure

et al. 2012

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Spin-filter tunneling is a promising way to create highly-spin-polarized currents. So far the understanding of the spin-filtering effect has been limited to a free-electron description based on the spin-dependent tunneling barrier height. In this work we explore the complex of EuO as a representative ferromagnetic insulator used in spin-filter tunneling experiments and show that the mechanism of spin filtering is more intricate than it has been previously thought. We demonstrate the importance of the multiorbital band structure with an indirect band gap for spin-filter tunneling. By analyzing the symmetry of the complex bands and the decay rates for different wave vectors and energies we draw conclusions about spin-filter efficiency of EuO. Our results provide guidelines for the design of spin-filter tunnel junctions with enhanced spin polarization.

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Influence of the electronic structure on tunneling through ferroelectric insulators: Application to BaTiO3and PbTiO33

Cited by 18 publications

References 29 publications

First-principles study of metal-induced gap states in metal/oxide interfaces and their relation with the complex band structure

First-principles study of metal-induced gap states in metal/oxide interfaces and their relation with the complex band structure

Predictive modelling of ferroelectric tunnel junctions

Spin filtering with EuO: Insight from the complex band structure

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