Fermi level density of states modulation without charge transfer in nickelate superlattices

Han, Myung Joon; Veenendaal, Michel van

doi:10.1088/0953-8984/26/14/145501

Cited by 4 publications

(4 citation statements)

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“…The predominant Ni d 8 electronic configuration is likely to arise primarily from charge transfer effects, as unlike some other perovskites, the 3d levels in LaTiO 3 lie near to the Fermi level of LaNiO 3 -heterostructures [60,61]. Ti L-edge XAS showed that the Ti charge state changes from 3+ to close to 4+ upon heterostructuring indicating that a large fraction of the one electron per Ti has been transferred to other layers in the heterostruc- ture [17] driving Ni towards a d 8 state.…”

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confidence: 99%

Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels

et al. 2016

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Resonant inelastic x-ray scattering is used to investigate the electronic origin of orbital polarization in nickelate heterostructures taking LaTiO3 − LaNiO3 − 3x(LaAlO3), a system with exceptionally large polarization, as a model system. We find that heterostructuring generates only minor changes in the Ni 3d orbital energy levels, contradicting the often-invoked picture in which changes in orbital energy levels generate orbital polarization. Instead, O K-edge x-ray absorption spectroscopy demonstrates that orbital polarization is caused by an anisotropic reconstruction of the oxygen ligand hole states. This provides an explanation for the limited success of theoretical predictions based on tuning orbital energy levels and implies that future theories should focus on anisotropic hybridization as the most effective means to drive large changes in electronic structure and realize novel emergent phenomena.The electronic structure of transition metal oxides (TMOs) is dominated by the active 3d TM orbitals and how these hybridize with the neighboring oxygen 2p ligand orbitals. Building heterostructures from one-unitcell-thick layers of different TMOs offers the opportunity of tuning the TM 3d states configuration and potentially realizing emergent phenomena with new or improved properties [1][2][3][4][5][6]. LaNiO 3 based heterostructures are a prototypical example of such an endeavor [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], motivated by several predictions of novel superconducting, magnetic and topological states [21][22][23][24]. Bulk LaNiO 3 has nominally Ni 3+ ions with filled t 2g states and one e g electron. Efforts to realize the predicted novel states are crucially dependent on inducing orbital polarization in the Ni e g level [25], i.e. breaking its degeneracy and pushing the system towards a half filled x 2 − y 2 (or 3z 2 − r 2 ) configuration ( Fig. 1(b)). Initial efforts to realize strong orbital polarization in heterostructures reported up to ∼ 20% change in orbital occupancy compared to the bulk [7-12, 14, 19], corresponding to ∼ 0.3 eV splitting of the e g states as inferred from cluster calculations of x-ray absorption spectra [14], in fact first principle calculations indicate that ∼ 10% strain is needed to drive ∼ 40% change in orbital polarization (see supplemental material of Ref. 17). Novel trilayer LaTiO 3 − LaNiO 3 − 3x(LaAlO 3 ) (LTNAO) superlattices were recently produced obtaining ∼ 50% change in orbital polarization via charge transfer, polar charge and electronic confinement effects [15][16][17][18]. To date, changes in orbital polarization have been conceptualized as a consequence of tuning the 3d orbital energy level through crystal field engineering. However, this approach has led to a dramatic mismatch between theoretical predictions and experimental results [14,[21][22][23]26], raising questions about the precise electronic character, and the driving mechanism behind, orbital polarization in these materials.We apply resonant inelastic x-ray scattering (RIXS) [27,28] ...

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confidence: 99%

Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels

et al. 2016

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“…8 Electrical transport measurements showed an enhanced sheet conductivity for LNO/SrTiO 3 (001) SLs on (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT), 13,14 whereas standing-wave excited photoemission experiments and ab initio calculations reported a reduction of the electronic density of states (DOS) at the Fermi energy on LSAT and SrTiO 3 (STO). [15][16][17] The LNO/STO(001) SLs bear two major differences to commonly studied oxide interfaces. Unlike the nonpolar LNO/LAO(001) SLs, in LNO/STO(001) SLs there is a charge discontinuity at the interface depending on the layer stacking that can lead to either n-type [(LaO) + /(TiO 2 ) 0 ] or p-type [(NiO 2 ) − /(SrO) 0 ] δ-doping.…”

Section: Introductionmentioning

confidence: 99%

Design of $n$- and $p$-type oxide thermoelectrics in LaNiO$_3$/SrTiO$_3(001)$ superlattices exploiting interface polarity

Geisler,

Blanca-Romero,

Pentcheva

2017

Preprint

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We investigate the structural, electronic, transport, and thermoelectric properties of LaNiO3/SrTiO3(001) superlattices containing either exclusively n-or p-type interfaces or coupled interfaces of opposite polarity by using density functional theory calculations with an on-site Coulomb repulsion term. The results show that significant octahedral tilts are induced in the SrTiO3 part of the superlattice. Moreover, the La-Sr distances and Ni-O out-of-plane bond lengths at the interfaces exhibit a distinct variation by about 7 % with the sign of the electrostatic doping. In contrast to the much studied LaAlO3/SrTiO3 system, the charge mismatch at the interfaces is exclusively accommodated within the LaNiO3 layers, whereas the interface polarity leads to a band offset and to the formation of an electric field within the coupled superlattice. Features of the electronic structure indicate an orbital-selective quantization of quantum well states. The potential-and confinementinduced multiband splitting results in complex cylindrical Fermi surfaces with a tendency towards nesting that depends on the interface polarity. The analysis of the thermoelectric response reveals a particularly large positive Seebeck coefficient (135 µV/K) and a high figure of merit (0.35) for room-temperature cross-plane transport in the p-type superlattice that is attributed to the participation of the SrTiO3 valence band. Superlattices with either n-or p-type interfaces show cross-plane Seebeck coefficients of opposite sign and thus emerge as a platform to construct an oxide-based thermoelectric generator with structurally and electronically compatible n-and p-type oxide thermoelectrics.

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“…Indeed, it has recently been reported that LaNiO 3 , which is a paramagnetic metal in the bulk phase, shows insulating behavior with magnetic order in a superlattice 21,22 . There have been a number of subsequent studies about nickelate heterostructures [22][23][24][25][26][27][28][29][30][31][32][33] , which show a potential for rich physics, but there has not been systematic studies about the effect of doping in these systems yet.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we examine the effect of doping on the nickelate superlattice by taking (LaNiO 3 ) 1 /(SrTiO 3 ) 1 as a prototype example [31][32][33][34] . We employed first-principles density functional theory (DFT) calculations augmented with mean-field treatment of on-site Coulomb interaction, the so-called DFT+U methodology, to consider the role of electron correlations inherent in the Ni e g orbitals.…”

Section: Introductionmentioning

confidence: 99%

Effect of charge doping on the electronic structure, orbital polarization, and structural distortion in nickelate superlattice

Kim

Han

2015

Phys. Rev. B

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Using first-principles density functional theory calculations, we investigated the effect of charge doping in a LaNiO3/SrTiO3 superlattice. The detailed analysis based on two different doping simulation methods clearly shows that the electronic and structural properties change in a systematic way, and that the orbital polarization (i.e. relative occupation of two Ni-eg orbitals) is reduced and the Ni to apical oxygen distance is enlarged as the number of doped electrons increases. Also, the rotation angles of the NiO6/TiO6 octahedra strongly and systematically depend on the doping. Our results not only suggest a possible way to control the orbital and structural properties by means of charge doping, but also provide useful information for understanding experiments under various doping situations such as oxygen vacancy.

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Fermi level density of states modulation without charge transfer in nickelate superlattices

Cited by 4 publications

References 35 publications

Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels

Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels

Design of $n$- and $p$-type oxide thermoelectrics in LaNiO$_3$/SrTiO$_3(001)$ superlattices exploiting interface polarity

Effect of charge doping on the electronic structure, orbital polarization, and structural distortion in nickelate superlattice

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