Directional Andreev-Reflection Signatures of Inter-Orbital Pairing in Sr$_2$RuO$_4$
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| Main Authors: | , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866908947350290432 |
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| author | Csire, G. Fukaya, Y. Cuoco, M. Tanaka, Y. Kremer, R. K. Gibbs, A. S. Ummarino, G. A. Daghero, D. Gonnelli, R. S. |
| author_facet | Csire, G. Fukaya, Y. Cuoco, M. Tanaka, Y. Kremer, R. K. Gibbs, A. S. Ummarino, G. A. Daghero, D. Gonnelli, R. S. |
| contents | Unconventional superconductivity in quasi--two-dimensional systems is commonly identified through the emergence of Andreev bound states (ABS) at in-plane edges, while surfaces perpendicular to out-of-plane direction remain fully gapped due to weak interlayer coherence. This directional anisotropy has long served as a key paradigm for constraining pairing symmetries. Here, we show that Sr$_2$RuO$_4$ exhibits a striking reversal of this behavior. Using edge- and surface-sensitive spectroscopy, we observe pronounced in-gap ABS at surfaces perpendicular to the out-of-plane direction, whereas in-plane edges exhibit a reduced intensity of the in-gap spectral features. We show that this anomalous anisotropy can arise from the inter-orbital character of the superconducting pairing. Both even- and odd-parity inter-orbital pairing channels naturally generate robust surface ABS while suppressing planar edge modes and can also provide a mechanism for the appearance of a horizontal line node. Supported by \textit{ab initio} and model calculations, including Sr$_2$RuO$_4$/Ag interface reconstructions, our results highlight the possible role of inter-orbital correlations in shaping the spectroscopic response and provide constraints on the structure of the superconducting order parameter in Sr$_2$RuO$_4$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_06706 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Directional Andreev-Reflection Signatures of Inter-Orbital Pairing in Sr$_2$RuO$_4$ Csire, G. Fukaya, Y. Cuoco, M. Tanaka, Y. Kremer, R. K. Gibbs, A. S. Ummarino, G. A. Daghero, D. Gonnelli, R. S. Superconductivity Mesoscale and Nanoscale Physics Materials Science Strongly Correlated Electrons Unconventional superconductivity in quasi--two-dimensional systems is commonly identified through the emergence of Andreev bound states (ABS) at in-plane edges, while surfaces perpendicular to out-of-plane direction remain fully gapped due to weak interlayer coherence. This directional anisotropy has long served as a key paradigm for constraining pairing symmetries. Here, we show that Sr$_2$RuO$_4$ exhibits a striking reversal of this behavior. Using edge- and surface-sensitive spectroscopy, we observe pronounced in-gap ABS at surfaces perpendicular to the out-of-plane direction, whereas in-plane edges exhibit a reduced intensity of the in-gap spectral features. We show that this anomalous anisotropy can arise from the inter-orbital character of the superconducting pairing. Both even- and odd-parity inter-orbital pairing channels naturally generate robust surface ABS while suppressing planar edge modes and can also provide a mechanism for the appearance of a horizontal line node. Supported by \textit{ab initio} and model calculations, including Sr$_2$RuO$_4$/Ag interface reconstructions, our results highlight the possible role of inter-orbital correlations in shaping the spectroscopic response and provide constraints on the structure of the superconducting order parameter in Sr$_2$RuO$_4$. |
| title | Directional Andreev-Reflection Signatures of Inter-Orbital Pairing in Sr$_2$RuO$_4$ |
| topic | Superconductivity Mesoscale and Nanoscale Physics Materials Science Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2604.06706 |