Electronic correlation and strain effects at the interfaces between polar and nonpolar complex oxides

Annadi, Anil; Putra, Andi Sudjana; Liu, Z. Q.; Wang, X.; Gopinadhan, K.; Huang, Zhen; Dhar, S.; Venkatesan, T.; Ariando, Ariando

doi:10.1103/physrevb.86.085450

Cited by 77 publications

(80 citation statements)

References 23 publications

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“…1(a) must be due to the electrons at the LaAlO 3 /SrTiO 3 interface. This insulating SrTiO 3 /NdGaO 3 interface is different from the conducting one, found when NdGaO 3 is grown on a SrTiO 3 substrate [33]. In the former case, there is no observable conductivity, similar to the insulating interface, where the SrTiO 3 layers are grown on a LaAlO 3 substrate [34].…”

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confidence: 89%

Conducting channel at the LaAlO3/SrTiO3interface

et al. 2013

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Localization of electrons in the two-dimensional electron gas at the LaAlO) [10] and fabrication of millions of transistors on a single chip [11] have highlighted the importance of these oxide interfaces both from fundamental and applied perspectives. The 2DEG is thought to result from an electron transfer to the interface between the polar oxide (LaAlO 3 ) and the nonpolar oxide (SrTiO 3 ), which is necessary to avoid a divergence of the energy associated with the electric field [12]. A charge transfer of 0.5 electron per interface unit cell (uc) or 3.310 14 cm -2 should be required to compensate the electric field in polar LaAlO 3 and avert the polar catastrophe [12].However, a major puzzle is that the experimentally-observed carrier densities at low temperatures for the 2DEG in fully oxidized samples [3,5,13] are an order of magnitude lower than expected.Furthermore, it is unclear where exactly at the interface the conduction electrons are located, since the LaAlO 3 is usually grown on a SrTiO 3 substrate. One proposed explanation is that these 'disappearing' electrons are localized within the first SrTiO 3 layers that are closest to the interface, where Ti 3d xy sub-bands have lower energy than the other Ti 3d orbitals [14][15][16]. According to the theoretical calculations, the mobile electrons responsible for the transport properties of the 2DEG are farther away (≥ 4 uc) from the interface [15]. While experimental results [12,[17][18][19] The results on temperature-dependent sheet resistance (R S -T) are shown in Fig , an upturn of sheet resistance invariably occurs below a temperature T min (where R S is minimum). This upturn in R S -T has been also reported at the LaAlO 3 /SrTiO 3 interfaces grown on other substrates [21,23,24], and it depends on the stoichiometry of the LaAlO 3 [30]. Reducing the thickness of the SrTiO 3 layer raises T min and R S at the same time. For the samples with 3, 4, and 6 uc SrTiO 3 layers, the R S at 2 K is far above the quantum of resistance (12.9 k, including spin degeneracy). The R S -T curves for these samples diverge as the temperature is decreased, and they can be well fitted to R S  exp[(T 0 /T) The temperature dependence of sheet carrier density (n S ) and mobility (μ H ) are plotted in Fig. 2 , which corresponds to 0.5 electrons per unit cell at the interface . It can be argued that the reason for the temperature independence is the clamping effect of the NdGaO 3 substrate, which prevents the SrTiO 3 layer from undergoing the structural transitions that occur at low temperatures [5,38], thus avoiding the strong localization of carriers at low temperatures, which is widely observed in the 2DEG on SrTiO 3 substrates. This result supports the view that the SrTiO 3 phase transitions are important for determining the low temperature 2DEG properties, carrier localization in particular [39]. Also the absence of temperature dependence in mobility when the free carrier concentration is high suggests that electron-electron scattering is dominant. The main point here is t...

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Conducting channel at the LaAlO3/SrTiO3interface

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“…Following the seminal work by Ohtomo and Hwang1, insulator-to-metal transitions have been found in other heterostructures in which SrTiO 3 is coupled to a polar band insulator, such as LaGaO 3 , NdGaO 3 67, and NdAlO 3 8. LaGaO 3 /SrTiO 3 and NdGaO 3 /SrTiO 3 share with LaAlO 3 /SrTiO 3 the same critical overlayer thickness of n = 4 unit cells (u.c.…”

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Universal electronic structure of polar oxide hetero-interfaces

Treske

Heming

Knupfer

et al. 2015

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The electronic properties of NdGaO3/SrTiO3, LaGaO3/SrTiO3, and LaAlO3/SrTiO3 interfaces, all showing an insulator-to-metal transition as a function of the overlayer-thickness, are addressed in a comparative study based on x-ray absorption, x-ray photoemission and resonant photoemission spectroscopy. The nature of the charge carriers, their concentration and spatial distribution as well as the interface band alignments and the overall interface band diagrams are studied and quantitatively evaluated. The behavior of the three analyzed heterostructures is found to be remarkably similar. The valence band edge of all the three overlayers aligns to that of bulk SrTiO3. The near-interface SrTiO3 layer is affected, at increasing overlayer thickness, by the building-up of a confining potential. This potential bends both the valence and the conduction band downwards. The latter one crossing the Fermi energy in the proximity of the interface and determines the formation of an interfacial band offset growing as a function of thickness. Quite remarkably, but in agreement with previous reports for LaAlO3/SrTiO3, no electric field is detected inside any of the polar overlayers. The essential phenomenology emerging from our findings is discussed on the base of different alternative scenarios regarding the origin of interface carriers and their interaction with an intense photon beam.

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“…Sharing a similar ionic structure with LAO (A 3þ B 3þ O 3 ), NGO generally causes a similar interface reconstruction as LAO when grown on f100g STO [32][33][34]. However, NGO possesses Nd 3þ ions carrying a magnetic moment that is not present in LAO.…”

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confidence: 98%

Defect Control of Conventional and Anomalous Electron Transport at Complex Oxide Interfaces

et al. 2016

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Using low-temperature electrical measurements, the interrelation between electron transport, magnetic properties, and ionic defect structure in complex oxide interface systems is investigated, focusing on NdGaO 3 =SrTiO 3 (100) interfaces. Field-dependent Hall characteristics (2-300 K) are obtained for samples grown at various growth pressures. In addition to multiple electron transport, interfacial magnetism is tracked exploiting the anomalous Hall effect (AHE). These two properties both contribute to a nonlinearity in the field dependence of the Hall resistance, with multiple carrier conduction evident below 30 K and AHE at temperatures ≲10 K. Considering these two sources of nonlinearity, we suggest a phenomenological model capturing the complex field dependence of the Hall characteristics in the low-temperature regime. Our model allows the extraction of the conventional transport parameters and a qualitative analysis of the magnetization. The electron mobility is found to decrease systematically with increasing growth pressure. This suggests dominant electron scattering by acceptor-type strontium vacancies incorporated during growth. The AHE scales with growth pressure. The most pronounced AHE is found at increased growth pressure and, thus, in the most defective, low-mobility samples, indicating a correlation between transport, magnetism, and cation defect concentration.

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Electronic correlation and strain effects at the interfaces between polar and nonpolar complex oxides

Cited by 77 publications

References 23 publications

Conducting channel at the LaAlO3/SrTiO3interface

Conducting channel at the LaAlO3/SrTiO3interface

Universal electronic structure of polar oxide hetero-interfaces

Defect Control of Conventional and Anomalous Electron Transport at Complex Oxide Interfaces

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