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Long-range electronic reconstruction to a dxz,yz-dominated Fermi surface below the LaAlO₃/SrTiO₃ interface.

Petrović AP, Paré A, Paudel TR, Lee K, Holmes S, Barnes CH, David A, Wu T, Tsymbal EY, Panagopoulos C - Sci Rep (2014)

Bottom Line: However, the spatial extent of such reconstructions - i.e. the interfacial "depth" - remains unclear.Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO₃ emerge simultaneously at higher n(2D).We distinguish three areas in doped perovskite heterostructures: narrow (<20 nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far (>120 nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.

View Article: PubMed Central - PubMed

Affiliation: School of Physical and Mathematical Sciences, Division of Physics and Applied Physics, Nanyang Technological University, 637371 Singapore.

ABSTRACT
Low dimensionality, broken symmetry and easily-modulated carrier concentrations provoke novel electronic phase emergence at oxide interfaces. However, the spatial extent of such reconstructions - i.e. the interfacial "depth" - remains unclear. Examining LaAlO₃/SrTiO₃ heterostructures at previously unexplored carrier densities n(2D) ≥ 6.9 × 10(14) cm(-2), we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic of an anisotropic 3D Fermi surface with preferential dxz,yz orbital occupancy extending over at least 100 nm perpendicular to the interface. Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO₃ emerge simultaneously at higher n(2D). We distinguish three areas in doped perovskite heterostructures: narrow (<20 nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far (>120 nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.

No MeSH data available.


Related in: MedlinePlus

Evolution of the Shubnikov-de Haas oscillations and carrier density with increasing gate voltage.(a), Variation of the oscillating component of Rxx(H//) for sample B (left panel) at Vg ≥ 0, with FFTs of the raw data (right panel). For Vg < 0 the noise level rises and it is not possible to identify oscillations: this is a well-known phenomenon and has been attributed to emergent inhomogeneity6. (b), Oscillating components of Rxx(H⊥) for Vg ≥ −100 V in sample B (left panel) with associated FFTs (right panel). The two peaks in the FFTs are indicated by grey and red arrows; for Vg = −100 V, the peaks merge. (c), Vg dependence of various properties of sample B, including Tc (above), SdH frequencies F//,2⊥ and n2D (below). Tc is measured from Rxx(T) data (see Supplementary Fig. S2) and the errors in F//,2⊥ correspond to the FFT peak widths at 80% of their maximum height (from (a),(b)). n2D(Vg) obtained from the Hall coefficient follows the values expected from the sample capacitance C(Vg) (see Supplementary Figs. S1b,S3b for raw capacitance and Hall data). We attribute the fall in n2D above Vg = 350 V to charge-trapping deep within the SrTiO3. Tc(Vg) forms a dome: since d = 19 nm at Vg = 350 V and SrTiO3 is SC for 5.5 × 1017 cm−3 ≤ n3D ≤ 5 × 1020 cm−32324, we estimate a maximum conducting channel thickness W ~ 20 μm due to the combination of carrier injection and electron gas decompression6. In practice, we anticipate  due to the extremely high n2D at the interface which will locally suppress SC: even at Vg = 350 V, every carrier in sample B could be accommodated in merely 3 nm of SrTiO3 doped at 0.5e−/unit cell.
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f2: Evolution of the Shubnikov-de Haas oscillations and carrier density with increasing gate voltage.(a), Variation of the oscillating component of Rxx(H//) for sample B (left panel) at Vg ≥ 0, with FFTs of the raw data (right panel). For Vg < 0 the noise level rises and it is not possible to identify oscillations: this is a well-known phenomenon and has been attributed to emergent inhomogeneity6. (b), Oscillating components of Rxx(H⊥) for Vg ≥ −100 V in sample B (left panel) with associated FFTs (right panel). The two peaks in the FFTs are indicated by grey and red arrows; for Vg = −100 V, the peaks merge. (c), Vg dependence of various properties of sample B, including Tc (above), SdH frequencies F//,2⊥ and n2D (below). Tc is measured from Rxx(T) data (see Supplementary Fig. S2) and the errors in F//,2⊥ correspond to the FFT peak widths at 80% of their maximum height (from (a),(b)). n2D(Vg) obtained from the Hall coefficient follows the values expected from the sample capacitance C(Vg) (see Supplementary Figs. S1b,S3b for raw capacitance and Hall data). We attribute the fall in n2D above Vg = 350 V to charge-trapping deep within the SrTiO3. Tc(Vg) forms a dome: since d = 19 nm at Vg = 350 V and SrTiO3 is SC for 5.5 × 1017 cm−3 ≤ n3D ≤ 5 × 1020 cm−32324, we estimate a maximum conducting channel thickness W ~ 20 μm due to the combination of carrier injection and electron gas decompression6. In practice, we anticipate due to the extremely high n2D at the interface which will locally suppress SC: even at Vg = 350 V, every carrier in sample B could be accommodated in merely 3 nm of SrTiO3 doped at 0.5e−/unit cell.

Mentions: The fact that our measured TD is lower than than those reported for the LaAlO3/SrTiO3 2DEG78 also suggests that the band whose FS generates the in-plane oscillations lies within an extremely clean region of our heterostructures, far from the cation defects and magnetic scattering expected at oxygen-deficient PLD-grown LaAlO3/SrTiO3 interfaces. To determine the location of these high-mobility carriers more precisely, we examine the evolution of the SdH oscillation frequencies with field-effect doping, obtained from the peaks in fast Fourier transforms (FFTs) of Rxx(H//,⊥) (Fig. 2a,b). The Onsager relation links the peak frequency F with the extremal area S of the FS normal to the applied field via : since the size of the FS should be proportional to the carrier density, it is useful to compare F(Vg) with our experimentally-determined total n2D as well as the superconducting critical temperature Tc (which varies strongly with the local three-dimensional carrier density n3D2324). Once the interfacial carrier density exceeds n3D ~ 1020 cm−3, we expect a gradual suppression of SC leading to a dome in Tc(Vg)56; this is indeed observed (Fig. 2c). However, the in-plane oscillation frequency F// is independent of Vg, implying that the FS area S ⊥ [110] responsible for these oscillations remains roughly constant upon field-effect doping. Furthermore, F//(Vg) displays no correlation with Tc(Vg) or n2D(Vg): the FS (and hence the density of states) of the SC band(s) is being influenced by field-effect doping, but the FS of the high-mobility band is not. Field-effect doping should have a similar effect on all occupied bands within the same spatial region. Therefore, the only possible explanation for this decoupling between Tc(Vg) and F//(Vg) is that the SdH-oscillating electron gas must be spatially separated from superconductivity, i.e. the high-mobility carriers lie below the SC channel.


Long-range electronic reconstruction to a dxz,yz-dominated Fermi surface below the LaAlO₃/SrTiO₃ interface.

Petrović AP, Paré A, Paudel TR, Lee K, Holmes S, Barnes CH, David A, Wu T, Tsymbal EY, Panagopoulos C - Sci Rep (2014)

Evolution of the Shubnikov-de Haas oscillations and carrier density with increasing gate voltage.(a), Variation of the oscillating component of Rxx(H//) for sample B (left panel) at Vg ≥ 0, with FFTs of the raw data (right panel). For Vg < 0 the noise level rises and it is not possible to identify oscillations: this is a well-known phenomenon and has been attributed to emergent inhomogeneity6. (b), Oscillating components of Rxx(H⊥) for Vg ≥ −100 V in sample B (left panel) with associated FFTs (right panel). The two peaks in the FFTs are indicated by grey and red arrows; for Vg = −100 V, the peaks merge. (c), Vg dependence of various properties of sample B, including Tc (above), SdH frequencies F//,2⊥ and n2D (below). Tc is measured from Rxx(T) data (see Supplementary Fig. S2) and the errors in F//,2⊥ correspond to the FFT peak widths at 80% of their maximum height (from (a),(b)). n2D(Vg) obtained from the Hall coefficient follows the values expected from the sample capacitance C(Vg) (see Supplementary Figs. S1b,S3b for raw capacitance and Hall data). We attribute the fall in n2D above Vg = 350 V to charge-trapping deep within the SrTiO3. Tc(Vg) forms a dome: since d = 19 nm at Vg = 350 V and SrTiO3 is SC for 5.5 × 1017 cm−3 ≤ n3D ≤ 5 × 1020 cm−32324, we estimate a maximum conducting channel thickness W ~ 20 μm due to the combination of carrier injection and electron gas decompression6. In practice, we anticipate  due to the extremely high n2D at the interface which will locally suppress SC: even at Vg = 350 V, every carrier in sample B could be accommodated in merely 3 nm of SrTiO3 doped at 0.5e−/unit cell.
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Related In: Results  -  Collection

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Show All Figures
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f2: Evolution of the Shubnikov-de Haas oscillations and carrier density with increasing gate voltage.(a), Variation of the oscillating component of Rxx(H//) for sample B (left panel) at Vg ≥ 0, with FFTs of the raw data (right panel). For Vg < 0 the noise level rises and it is not possible to identify oscillations: this is a well-known phenomenon and has been attributed to emergent inhomogeneity6. (b), Oscillating components of Rxx(H⊥) for Vg ≥ −100 V in sample B (left panel) with associated FFTs (right panel). The two peaks in the FFTs are indicated by grey and red arrows; for Vg = −100 V, the peaks merge. (c), Vg dependence of various properties of sample B, including Tc (above), SdH frequencies F//,2⊥ and n2D (below). Tc is measured from Rxx(T) data (see Supplementary Fig. S2) and the errors in F//,2⊥ correspond to the FFT peak widths at 80% of their maximum height (from (a),(b)). n2D(Vg) obtained from the Hall coefficient follows the values expected from the sample capacitance C(Vg) (see Supplementary Figs. S1b,S3b for raw capacitance and Hall data). We attribute the fall in n2D above Vg = 350 V to charge-trapping deep within the SrTiO3. Tc(Vg) forms a dome: since d = 19 nm at Vg = 350 V and SrTiO3 is SC for 5.5 × 1017 cm−3 ≤ n3D ≤ 5 × 1020 cm−32324, we estimate a maximum conducting channel thickness W ~ 20 μm due to the combination of carrier injection and electron gas decompression6. In practice, we anticipate due to the extremely high n2D at the interface which will locally suppress SC: even at Vg = 350 V, every carrier in sample B could be accommodated in merely 3 nm of SrTiO3 doped at 0.5e−/unit cell.
Mentions: The fact that our measured TD is lower than than those reported for the LaAlO3/SrTiO3 2DEG78 also suggests that the band whose FS generates the in-plane oscillations lies within an extremely clean region of our heterostructures, far from the cation defects and magnetic scattering expected at oxygen-deficient PLD-grown LaAlO3/SrTiO3 interfaces. To determine the location of these high-mobility carriers more precisely, we examine the evolution of the SdH oscillation frequencies with field-effect doping, obtained from the peaks in fast Fourier transforms (FFTs) of Rxx(H//,⊥) (Fig. 2a,b). The Onsager relation links the peak frequency F with the extremal area S of the FS normal to the applied field via : since the size of the FS should be proportional to the carrier density, it is useful to compare F(Vg) with our experimentally-determined total n2D as well as the superconducting critical temperature Tc (which varies strongly with the local three-dimensional carrier density n3D2324). Once the interfacial carrier density exceeds n3D ~ 1020 cm−3, we expect a gradual suppression of SC leading to a dome in Tc(Vg)56; this is indeed observed (Fig. 2c). However, the in-plane oscillation frequency F// is independent of Vg, implying that the FS area S ⊥ [110] responsible for these oscillations remains roughly constant upon field-effect doping. Furthermore, F//(Vg) displays no correlation with Tc(Vg) or n2D(Vg): the FS (and hence the density of states) of the SC band(s) is being influenced by field-effect doping, but the FS of the high-mobility band is not. Field-effect doping should have a similar effect on all occupied bands within the same spatial region. Therefore, the only possible explanation for this decoupling between Tc(Vg) and F//(Vg) is that the SdH-oscillating electron gas must be spatially separated from superconductivity, i.e. the high-mobility carriers lie below the SC channel.

Bottom Line: However, the spatial extent of such reconstructions - i.e. the interfacial "depth" - remains unclear.Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO₃ emerge simultaneously at higher n(2D).We distinguish three areas in doped perovskite heterostructures: narrow (<20 nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far (>120 nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.

View Article: PubMed Central - PubMed

Affiliation: School of Physical and Mathematical Sciences, Division of Physics and Applied Physics, Nanyang Technological University, 637371 Singapore.

ABSTRACT
Low dimensionality, broken symmetry and easily-modulated carrier concentrations provoke novel electronic phase emergence at oxide interfaces. However, the spatial extent of such reconstructions - i.e. the interfacial "depth" - remains unclear. Examining LaAlO₃/SrTiO₃ heterostructures at previously unexplored carrier densities n(2D) ≥ 6.9 × 10(14) cm(-2), we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic of an anisotropic 3D Fermi surface with preferential dxz,yz orbital occupancy extending over at least 100 nm perpendicular to the interface. Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO₃ emerge simultaneously at higher n(2D). We distinguish three areas in doped perovskite heterostructures: narrow (<20 nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far (>120 nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.

No MeSH data available.


Related in: MedlinePlus