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Giant photoconductance at infinite-layer nickelate/SrTiO3 interfaces via an optically induced high-mobility electron gas

Nature Materials (2025)Cite this article

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Abstract

Two-dimensional electron gases (2DEGs) at oxide interfaces are promising for electronics because of desirable ingredients such as spin–orbit coupling and strong correlations that can be leveraged to bridge into spintronics or photonics. In this context, the ability to manipulate oxide 2DEGs via external knobs is particularly important. Here we show that a volatile high-mobility 2DEG can be photogenerated at the interface between SrTiO3 (001) and infinite-layer NdNiO2, where such an electronic state is otherwise absent. This allows us to optically switch the 2DEG between ON and OFF, leading to a giant, instantaneous conductivity variation. The key ingredients for this effect are the structural and electronic reconstructions at the NdNiO2//SrTiO3 interface, together with a built-in interfacial electric field that promotes the occupation of the Ti 3dxy band by the photogenerated carriers. By contributing to understanding photoconductance at complex-oxide interfaces, our results pave the way to engineer the photoresponse of strongly correlated electrons.

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Fig. 1: Phenomenology of giant photoconductivity in IL-NNO/STO under illumination.
Fig. 2: Illumination effects on resistance, carrier density and mobility.
Fig. 3: Illumination effects for several Sr doping, substrates and phase of nickelate thin films.
Fig. 4: Qualitative microscopic analysis of the NNO thin film on STO.
Fig. 5: STEM-EELS fine structure and qualitative analysis of the electric field and polar displacements at the interface at different temperatures.
Fig. 6: DFT + U calculations of the NNO/STO interface.

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Data availability

The data used in this paper are available via Zenodo at https://doi.org/10.5281/zenodo.16985730 (ref. 70).

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Acknowledgements

Work at Laboratoire Albert Fert was supported by ANR-22-CE30-00020-01 ‘SUPERFAST’, ANR-22-EXSP-0007 PEPR SPIN ‘SPINMAT’, the European Union’s Horizon 2020 research and innovation programme under the EIC pathfinder grant 101130224 ‘JOSEPHINE’, as well as the COST action ‘SUPERQUMAP’. Work at IPCMS was supported by the French National Research Agency (ANR) through the ANR-JCJC FOXIES ANR-21-CE08-0021. This work was also done as part of the Interdisciplinary Thematic Institute QMat, ITI 2021 2028 program of the University of Strasbourg, CNRS and Inserm, and supported by IdEx Unistra (ANR 10 IDEX 0002), and by SFRI STRAT’US project (ANR 20 SFRI 0012) and EUR QMAT ANR-17-EURE-0024 under the framework of the French Investments for the Future Program. A.R. and A.G. acknowledge Y. Auad, J.-D. Blazit and X. Li for experiments on LT atomically resolved STEM-EELS experiments with the time-resolved Timepix3 detector. Nion UltraSTEM—CHROMATEM at LPS Orsay and the focused ion beam at Centre de Nanosciences et de Nanotechnologies, University of Paris-Saclay, were accessed in the TEMPOS project framework (ANR 10-EQPX-0050). LT STEM was supported by a joint ANR-RGC ImagingQM project (ANR, ANR-23-CE42-0027). R.P. acknowledges funding through the German Research Foundation, CRC1242 (project number 278162697, subproject number C02). B.G. acknowledges support from the National Science Foundation, grant number NSF-DMR-2118718. R.P. and B.G. acknowledge computational time at magnitUDE of the Center of Computer Science and Simulation (DFG grants INST20876/209-1 FUGG and INST20876/243-1 FUGG).

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Author notes

  1. H. Sahib

    Present address: Department of Physics, College of Science, University of Halabja, Halabja, Iraq

Authors and Affiliations

  1. Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, Palaiseau, France

    David Sanchez-Manzano, V. Humbert, H. Jaffrès & Javier E. Villegas

  2. Institute of Physics and Chemistry of Materials of Strasbourg, CNRS, University of Strasbourg, Strasbourg, France

    G. Krieger, H. Sahib & D. Preziosi

  3. Laboratoire de Physique de Solides, CNRS, Université Paris-Saclay, Orsay, France

    A. Raji & A. Gloter

  4. Synchrotron SOLEIL, L’Orme des Merisiers, Gif sur Yvette, France

    A. Raji

  5. Department of Physics, University of Florida, Gainesville, FL, USA

    B. Geisler

  6. Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA

    B. Geisler

  7. Departamento de Física de Materiales, Universidad Complutense de Madrid, Madrid, Spain

    J. Santamaría

  8. Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, Duisburg, Germany

    R. Pentcheva

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Contributions

The study was conceived and designed by J.E.V., D.P., D.S.-M. and V.H. Sample fabrication was carried out by G.K. and D.P. Electron microscopy experiments were performed by A.R. and A.G. Transport experiments were carried out by D.S.-M. and V.H. DFT + U calculations were carried out by B.G. and R.P. The results were discussed and interpreted by all the authors together with H.J. and J.S. The paper was drafted by D.S.-M. and J.E.V. based on the contributions from all authors.

Corresponding authors

Correspondence to David Sanchez-Manzano or Javier E. Villegas.

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Extended data

Extended Data Fig. 1 On-off cycles.

(a) On-off cycles for different light powers. (b) Several on-off cycles for the same light power, 38 mW/cm2. In all cases we observe a high repeatability and reversibility, without signs of fatigue, nor degradation of the resistance levels.

Extended Data Fig. 2 Hall bar measurements.

(a) Sketch of the Hall bar geometry used. (b) R vs T of the for NNO//STO samples with a Hall bar, showing the same effect as the measurements done in VdP configuration, red with light on and black with light off. (c) 2D carrier density (in purple) and electron mobility (in blue) measured in the Hall bar showing similar values to the ones of the VdP configuration (see Fig. 2 of the main text).

Extended Data Fig. 3 Ti 3+ and Ti 4+ spectra.

The possibility that the small changes of the Ti-L2,3 edge spectra near the interface indicate the presence of Ti3+ has been quantitatively studied by fitting them to a linear combination of reference spectra for pure Ti4+ and Ti3+. (a, b) Fitting weights of the Ti4+ and Ti3+ components near the NdNiO2//SrTiO3 interface, at room temperature and low temperature (ca. 115 K), along with the HAADF-STEM profile. (c) EELS reference spectra for Ti4+ and Ti3+ at room temperature. The Ti4+ spectrum was chosen as the signal measured far (typically 20 nm) from the interface in the same spectrum-imaging data. The Ti3+ spectrum was measured on a DyTiO3 thin film66. The relative intensity of the references was obtained by normalizing both spectra in the continuum range (ca. 480 eV). A very reduced weight of Ti3+ spectra is observed, not exceeding 0.05 electrons per unit cell (e/uc), even at the last planes (IF and IF-1). This is very weak in comparison with similar spectroscopic charge assessment by EELS for LAO-STO41,67,68 or GdOx-STO69 where more than 0.1 e/uc are measured next to the interface. In summary, the EELS indicates a largely predominant Ti4+ state at the interface, ruling out the formation of a 2DEG in the STO substrate, both at room and low temperature.

Extended Data Fig. 4 HAADF image of NNO/STO interface.

(a) HAADF image of NNO/STO interface at room temperature (b) HAADF image of the similar region at low temperature (115 K), (c) out-of-plane parameter of unit cells at the interface. Error bars correspond to the pixel size in the real space HAADF image, that is, the minimum resolved measurement possible, +−0.05 A. At room temperature, a small expansion of ca. 3% is observed for the last STO unit cell, confirming the experimental work by B. Goodge et al [18]. Interestingly, at 115 K, the expansion becomes more pronounced, reaching approximately 6% and resulting in a unit cell c-axis parameter around 4.10 Å at the last STO. This expansion at 115 K aligns remarkably with the ab initio derived value [18]. Moreover, Ti off-centering is evident in the last STO unit cell (uc -1) at both temperatures, with a cation moving toward the interface.

Extended Data Fig. 5 Temperature dependent evolution of Ti-L fine structure.

(a) Comparison of bulk STO Ti-L3 fine structure at 300 K (RT) and around 115 K (LT). (b) Bulk STO Ti-L3 fine structure at intermediate temperatures from 300 K to around 115 K. (c) HAADF image at RT of the interface showing the interface unit cells. (d) Evolution of Ti-L3 t2g-eg splitting at the last STO unit cell (−1) on going from RT to LT. Error bars correspond to the pixel size in the EELS spectrum, that is, the minimum resolved measurement possible, +−0.025 eV. (e) Low temperature unit-cell resolved STEM-EELS Fine structure at the Ti-L3 edge on unit cells near the interface compared with a bulk unit cell. In summary, the temperature-dependent HR-STEM and EELS studies indicate a temperature-dependent electronic reconstruction at the very interfacial titanium site, that has a stronger out-of-plane parameter when compared from RT to ca. 115 K. However, charge quantification by EELS at low temperatures is similar to at RT, with an almost absence of Ti3+. A transition toward an AFD STO is structurally confirmed starting at a temperature below ca. 100 K.

Extended Data Fig. 6 Visualization of the 2DEG electron density for higher charge.

Visualization of the 2DEG electron density in the STO substrate for ∆q = 1.5 e− (integrated from −0.7 eV to EF; yellow orbitals) and accumulated 2DEG charge for varying ∆q (modeling different light intensities). From this plot, one can extract the fraction of the additional charge that is accommodated in the two-dimensional electron gas (2DEG), which in this case amounts to approximately 0.95 e− (63%). For comparison, the corresponding values are ~0.19 e− (76%) and 0.36 e− (72%) for ∆q = 0.25 and 0.5 e−, respectively. Additionally, in our calculations, holes are treated as a homogeneous background distributed throughout the entire simulation cell. It should be noted that for such a large ∆q, finite-size effects become significant, that is, the actual 2DEG is expected to be more spatially extended than our simulation cell allows.

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Supplementary Figs. 1–10.

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Sanchez-Manzano, D., Krieger, G., Raji, A. et al. Giant photoconductance at infinite-layer nickelate/SrTiO3 interfaces via an optically induced high-mobility electron gas. Nat. Mater. (2025). https://doi.org/10.1038/s41563-025-02363-y

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