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Engineering two-dimensional superconductivity and Rashba spin-orbit coupling in LaAlO₃/SrTiO₃ quantum wells by selective orbital occupancy.

Herranz G, Singh G, Bergeal N, Jouan A, Lesueur J, Gázquez J, Varela M, Scigaj M, Dix N, Sánchez F, Fontcuberta J - Nat Commun (2015)

Bottom Line: The discovery of two-dimensional electron gases (2DEGs) at oxide interfaces-involving electrons in narrow d-bands-has broken new ground, enabling the access to correlated states that are unreachable in conventional semiconductors based on s- and p- electrons.There is a growing consensus that emerging properties at these novel quantum wells-such as 2D superconductivity and magnetism-are intimately connected to specific orbital symmetries in the 2DEG sub-band structure.Such an orientational tuning expands the possibilities for electronic engineering of 2DEGs at LaAlO3/SrTiO3 interfaces.

View Article: PubMed Central - PubMed

Affiliation: Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain.

ABSTRACT
The discovery of two-dimensional electron gases (2DEGs) at oxide interfaces-involving electrons in narrow d-bands-has broken new ground, enabling the access to correlated states that are unreachable in conventional semiconductors based on s- and p- electrons. There is a growing consensus that emerging properties at these novel quantum wells-such as 2D superconductivity and magnetism-are intimately connected to specific orbital symmetries in the 2DEG sub-band structure. Here we show that crystal orientation allows selective orbital occupancy, disclosing unprecedented ways to tailor the 2DEG properties. By carrying out electrostatic gating experiments in LaAlO3/SrTiO3 wells of different crystal orientations, we show that the spatial extension and anisotropy of the 2D superconductivity and the Rashba spin-orbit field can be largely modulated by controlling the 2DEG sub-band filling. Such an orientational tuning expands the possibilities for electronic engineering of 2DEGs at LaAlO3/SrTiO3 interfaces.

No MeSH data available.


Related in: MedlinePlus

Atomic-resolution STEM characterization.(a) HAADF-STEM images of the LaAlO3/SrTiO3 (001) interface. The left and right panels are magnified views of the interface observed from [100] and [1–10] zone axes, respectively. (b) HAADF-STEM images of the LaAlO3/SrTiO3 (110) interface. Left and right panels are magnified views of the interface observed from [001] and [1–10] directions, respectively. Both LaAlO3 layers are continuous within the analysed region (of the order of 1 μm). The images in the central panels a and b have been Fourier filtered to reduce background noise. The positions of La and Sr are indicated by green and orange circles, whereas Al and Ti are shown in red and light green. Note that for both orientations the interfaces are atomically flat and that the (110) interface does not show any local (100) microfacet.
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f1: Atomic-resolution STEM characterization.(a) HAADF-STEM images of the LaAlO3/SrTiO3 (001) interface. The left and right panels are magnified views of the interface observed from [100] and [1–10] zone axes, respectively. (b) HAADF-STEM images of the LaAlO3/SrTiO3 (110) interface. Left and right panels are magnified views of the interface observed from [001] and [1–10] directions, respectively. Both LaAlO3 layers are continuous within the analysed region (of the order of 1 μm). The images in the central panels a and b have been Fourier filtered to reduce background noise. The positions of La and Sr are indicated by green and orange circles, whereas Al and Ti are shown in red and light green. Note that for both orientations the interfaces are atomically flat and that the (110) interface does not show any local (100) microfacet.

Mentions: The samples analysed here were obtained by pulsed laser deposition of LaAlO3 thin films on TiO2-terminated (001)-SrTiO3 substrates (LaAlO3 thickness t=10 monolayers (MLs), corresponding to t~3.8 nm) as well as on thermally treated (110)-oriented SrTiO3 substrates (t=7–14 MLs, t~1.9–3.8 nm), see details in Methods and (refs 22, 26, 27). We carried out cross-sectional scanning transmission electron microscopy (STEM) in the high-angle annular dark field (HAADF) imaging mode, in which, to a good approximation, the intensity of an atomic column is proportional to the square of the atomic number (Z), so elements can be deduced by tracking column intensities28. Brighter atomic columns correspond to the heavier elements, La and Sr, whereas fainter columns correspond to Ti and Al. Atomic-scale structural characterization shows a coherent and epitaxial growth of both heterostructures and atomically flat interfaces—Fig. 1a,b for (001) and (110), respectively— Besides, regarding the (110)-oriented sample, along the [001] zone axis the (110) ionic stacking across the interface can be readily appreciated, see Fig. 1b. Therefore, in spite of the higher surface energies of (110)-planes with respect to (001), the STEM-HAADF study rules out altogether the formation of (100) microfacets at the (110)-interface232930.


Engineering two-dimensional superconductivity and Rashba spin-orbit coupling in LaAlO₃/SrTiO₃ quantum wells by selective orbital occupancy.

Herranz G, Singh G, Bergeal N, Jouan A, Lesueur J, Gázquez J, Varela M, Scigaj M, Dix N, Sánchez F, Fontcuberta J - Nat Commun (2015)

Atomic-resolution STEM characterization.(a) HAADF-STEM images of the LaAlO3/SrTiO3 (001) interface. The left and right panels are magnified views of the interface observed from [100] and [1–10] zone axes, respectively. (b) HAADF-STEM images of the LaAlO3/SrTiO3 (110) interface. Left and right panels are magnified views of the interface observed from [001] and [1–10] directions, respectively. Both LaAlO3 layers are continuous within the analysed region (of the order of 1 μm). The images in the central panels a and b have been Fourier filtered to reduce background noise. The positions of La and Sr are indicated by green and orange circles, whereas Al and Ti are shown in red and light green. Note that for both orientations the interfaces are atomically flat and that the (110) interface does not show any local (100) microfacet.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308716&req=5

f1: Atomic-resolution STEM characterization.(a) HAADF-STEM images of the LaAlO3/SrTiO3 (001) interface. The left and right panels are magnified views of the interface observed from [100] and [1–10] zone axes, respectively. (b) HAADF-STEM images of the LaAlO3/SrTiO3 (110) interface. Left and right panels are magnified views of the interface observed from [001] and [1–10] directions, respectively. Both LaAlO3 layers are continuous within the analysed region (of the order of 1 μm). The images in the central panels a and b have been Fourier filtered to reduce background noise. The positions of La and Sr are indicated by green and orange circles, whereas Al and Ti are shown in red and light green. Note that for both orientations the interfaces are atomically flat and that the (110) interface does not show any local (100) microfacet.
Mentions: The samples analysed here were obtained by pulsed laser deposition of LaAlO3 thin films on TiO2-terminated (001)-SrTiO3 substrates (LaAlO3 thickness t=10 monolayers (MLs), corresponding to t~3.8 nm) as well as on thermally treated (110)-oriented SrTiO3 substrates (t=7–14 MLs, t~1.9–3.8 nm), see details in Methods and (refs 22, 26, 27). We carried out cross-sectional scanning transmission electron microscopy (STEM) in the high-angle annular dark field (HAADF) imaging mode, in which, to a good approximation, the intensity of an atomic column is proportional to the square of the atomic number (Z), so elements can be deduced by tracking column intensities28. Brighter atomic columns correspond to the heavier elements, La and Sr, whereas fainter columns correspond to Ti and Al. Atomic-scale structural characterization shows a coherent and epitaxial growth of both heterostructures and atomically flat interfaces—Fig. 1a,b for (001) and (110), respectively— Besides, regarding the (110)-oriented sample, along the [001] zone axis the (110) ionic stacking across the interface can be readily appreciated, see Fig. 1b. Therefore, in spite of the higher surface energies of (110)-planes with respect to (001), the STEM-HAADF study rules out altogether the formation of (100) microfacets at the (110)-interface232930.

Bottom Line: The discovery of two-dimensional electron gases (2DEGs) at oxide interfaces-involving electrons in narrow d-bands-has broken new ground, enabling the access to correlated states that are unreachable in conventional semiconductors based on s- and p- electrons.There is a growing consensus that emerging properties at these novel quantum wells-such as 2D superconductivity and magnetism-are intimately connected to specific orbital symmetries in the 2DEG sub-band structure.Such an orientational tuning expands the possibilities for electronic engineering of 2DEGs at LaAlO3/SrTiO3 interfaces.

View Article: PubMed Central - PubMed

Affiliation: Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain.

ABSTRACT
The discovery of two-dimensional electron gases (2DEGs) at oxide interfaces-involving electrons in narrow d-bands-has broken new ground, enabling the access to correlated states that are unreachable in conventional semiconductors based on s- and p- electrons. There is a growing consensus that emerging properties at these novel quantum wells-such as 2D superconductivity and magnetism-are intimately connected to specific orbital symmetries in the 2DEG sub-band structure. Here we show that crystal orientation allows selective orbital occupancy, disclosing unprecedented ways to tailor the 2DEG properties. By carrying out electrostatic gating experiments in LaAlO3/SrTiO3 wells of different crystal orientations, we show that the spatial extension and anisotropy of the 2D superconductivity and the Rashba spin-orbit field can be largely modulated by controlling the 2DEG sub-band filling. Such an orientational tuning expands the possibilities for electronic engineering of 2DEGs at LaAlO3/SrTiO3 interfaces.

No MeSH data available.


Related in: MedlinePlus