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Anomalous Spin‐Optical Helical Effect in Ti‐Based Kagome Metal

Mazzola, Federico [University of Padova (Italy); Consiglio Nazionale delle Ricerche (CNR), Napoli (Italy). Istituto Superconduttori, Materiali Innovativi e Dispositivi (CNR-SPIN); Istituto Nazionale di Fisica Nucleare (INFN), Napoli (Italy). Complesso Universitario di Monte S. Angelo] (ORCID:0000000253804374)·Brzezicki, Wojciech [Jagiellonian University, Krakow (Poland); Polish Academy of Sciences (PAS), Krakow (Poland)]·Bigi, Chiara [Synchrotron SOLEIL, Saint-Aubin (France)]·Consiglio, Armando [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)]·D'Onofrio, Luciano Jacopo [Consiglio Nazionale delle Ricerche (CNR), Fisciano (Italy). Istituto Superconduttori, Materiali Innovativi e Dispositivi (CNR-SPIN); Universitá di Salerno Fisciano (SA) (Italy)]·Mercaldo, Maria Teresa [Universitá di Salerno Fisciano (SA) (Italy)]·Kłosiński, Adam [University of Warsaw (Poland)]·Bertran, François [Synchrotron SOLEIL, Saint-Aubin (France)]·Le Fèvre, Patrick [Université de Rennes (France). Institut de Physique de Rennes (IPR)]·Clark, Oliver J. [Monash University, Clayton, VIC (Australia)]·Edmonds, Mark T. [Monash University, Clayton, VIC (Australia)]·Tuniz, Manuel [Universita degli Studi di Trieste (Italy)]·De Vita, Alessandro [Fritz Haber Institute of the Max Planck Society, Berlin (Germany)]·Polewczyk, Vincent [Université Paris‐Saclay, Versailles (France); Université de Versailles Saint-Quentin-en-Yvelines (UVSQ) (France); Centre National de la Recherche Scientifique (CNRS), Versailles (France). Groupe d'Étude de la Matière Condensée (GEMaC)]·Jacobsen, Jeppe B. [University of Copenhagen (Denmark). The Niels Bohr Institute]·Jacobsen, Henrik [European Research Infrastructure Consortium (ERIC), Lyngby (Denmark). European Spallation Source (ESS)]·Miwa, Jill A. [Aarhus University (Denmark)]·Wells, Justin W. [University of Oslo (UiO) (Norway)]·Jana, Anupam [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)]·Vobornik, Ivana [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)]·Fujii, Jun [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)]·Mignani, Niccolo [Politecnico di Milano (Italy)]·Samani, Narges Tarakameh [Politecnico di Milano (Italy)]·Crepaldi, Alberto [Politecnico di Milano (Italy)]·Sangiovanni, Giorgio [University of Würzburg (Germany)]·Kataria, Anshu [Universitá di Parma (Italy)]·Morresi, Tommaso [Fondazione Bruno Kessler, Trento (Italy). European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*)]·Sanna, Samuele [University of Bologna (Italy)]·Bonfá, Pietro [Universitá di Parma (Italy)]·Ortiz, Brenden R. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000213337003)·Pokharel, Ganesh [University of California, Santa Barbara, CA (United States); University of West Georgia, Carrollton, GA (United States)]·Wilson, Stephen D. [University of California, Santa Barbara, CA (United States)]·Sante, Domenico Di [University of Bologna (Italy)]·Ortix, Carmine [Università di Salerno Fisciano (SA) (Italy)]·Cuoco, Mario [Consiglio Nazionale delle Ricerche (CNR), Fisciano (Italy). Istituto Superconduttori, Materiali Innovativi e Dispositivi (CNR-SPIN); Universitá di Salerno Fisciano (SA) (Italy)]
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Abstract

The kagome lattice stands as a rich platform for hosting a wide array of correlated quantum phenomena, ranging from charge density waves and superconductivity to electron nematicity and loop current states. Direct detection of loop currents in kagome systems has remained a formidable challenge due to their intricate spatial arrangements and the weak magnetic field signatures they produce, and this has made their identification experimentally subtle. This has left their existence and underlying mechanisms a topic of intense debate. In this work, we uncover signatures compatible with loop currents: spin handedness-selective signals that surpass conventional dichroic, spin, and spin-dichroic responses. We observe this phenomenon in the kagome metal CsTi 3 ⁢Bi 5 and we call it the anomalous spin-optical helical effect. This effect arises from the coupling of light's helicity with spin-orbital electron correlations, thereby providing an indirect yet sensitive approach to probe loop-current–related electronic correlations in quantum materials. Our discovery not only enriches the debate surrounding loop currents but also offers new experimental strategies to exploit the electronic phases of quantum materials via light–matter interaction.

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Mazzola, Federico [University of Padova (Italy); Consiglio Nazionale delle Ricerche (CNR), Napoli (Italy). Istituto Superconduttori, Materiali Innovativi e Dispositivi (CNR-SPIN); Istituto Nazionale di Fisica Nucleare (INFN), Napoli (Italy). Complesso Universitario di Monte S. Angelo] (ORCID:0000000253804374), Brzezicki, Wojciech [Jagiellonian University, Krakow (Poland); Polish Academy of Sciences (PAS), Krakow (Poland)], Bigi, Chiara [Synchrotron SOLEIL, Saint-Aubin (France)], Consiglio, Armando [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)], D'Onofrio, Luciano Jacopo [Consiglio Nazionale delle Ricerche (CNR), Fisciano (Italy). Istituto Superconduttori, Materiali Innovativi e Dispositivi (CNR-SPIN); Universitá di Salerno Fisciano (SA) (Italy)], Mercaldo, Maria Teresa [Universitá di Salerno Fisciano (SA) (Italy)], Kłosiński, Adam [University of Warsaw (Poland)], Bertran, François [Synchrotron SOLEIL, Saint-Aubin (France)], Le Fèvre, Patrick [Université de Rennes (France). Institut de Physique de Rennes (IPR)], Clark, Oliver J. [Monash University, Clayton, VIC (Australia)], Edmonds, Mark T. [Monash University, Clayton, VIC (Australia)], Tuniz, Manuel [Universita degli Studi di Trieste (Italy)], De Vita, Alessandro [Fritz Haber Institute of the Max Planck Society, Berlin (Germany)], Polewczyk, Vincent [Université Paris‐Saclay, Versailles (France); Université de Versailles Saint-Quentin-en-Yvelines (UVSQ) (France); Centre National de la Recherche Scientifique (CNRS), Versailles (France). Groupe d'Étude de la Matière Condensée (GEMaC)], Jacobsen, Jeppe B. [University of Copenhagen (Denmark). The Niels Bohr Institute], Jacobsen, Henrik [European Research Infrastructure Consortium (ERIC), Lyngby (Denmark). European Spallation Source (ESS)], Miwa, Jill A. [Aarhus University (Denmark)], Wells, Justin W. [University of Oslo (UiO) (Norway)], Jana, Anupam [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)], Vobornik, Ivana [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)], Fujii, Jun [Consiglio Nazionale delle Ricerche (CNR), Trieste (Italy). Istituto Officina dei Materiali (CNR-IOM)], Mignani, Niccolo [Politecnico di Milano (Italy)], Samani, Narges Tarakameh [Politecnico di Milano (Italy)], Crepaldi, Alberto [Politecnico di Milano (Italy)], Sangiovanni, Giorgio [University of Würzburg (Germany)], Kataria, Anshu [Universitá di Parma (Italy)], Morresi, Tommaso [Fondazione Bruno Kessler, Trento (Italy). European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*)], Sanna, Samuele [University of Bologna (Italy)], Bonfá, Pietro [Universitá di Parma (Italy)], Ortiz, Brenden R. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000213337003), Pokharel, Ganesh [University of California, Santa Barbara, CA (United States); University of West Georgia, Carrollton, GA (United States)], Wilson, Stephen D. [University of California, Santa Barbara, CA (United States)], Sante, Domenico Di [University of Bologna (Italy)], Ortix, Carmine [Università di Salerno Fisciano (SA) (Italy)], Cuoco, Mario [Consiglio Nazionale delle Ricerche (CNR), Fisciano (Italy). Istituto Superconduttori, Materiali Innovativi e Dispositivi (CNR-SPIN); Universitá di Salerno Fisciano (SA) (Italy)]. 2026-03-18. Anomalous Spin‐Optical Helical Effect in Ti‐Based Kagome Metal. https://doi.org/10.1002/adma.202522533

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