[
{
"id": "authors:k96m5-hfp79",
"collection": "authors",
"collection_id": "k96m5-hfp79",
"cite_using_url": "https://authors.library.caltech.edu/records/k96m5-hfp79",
"type": "article",
"title": "Turning excitons to the dark side",
"author": [
{
"family_name": "Han",
"given_name": "Yuchen",
"orcid": "0000-0002-9636-7127",
"clpid": "Han-Yuchen"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "Hubbard excitons capture the many-body correlations of Mott insulators. Using ultrafast light, their quantum wavefunction can be coherently rotated, opening a path towards optical quantum control and sensing in strongly correlated materials.",
"doi": "10.1038/s41563-026-02577-8",
"issn": "1476-1122",
"publisher": "Nature Publishing Group",
"publication": "Nature Materials",
"publication_date": "2026-06",
"volume": "25",
"pages": "887-888"
},
{
"id": "authors:8s0zb-96h09",
"collection": "authors",
"collection_id": "8s0zb-96h09",
"cite_using_url": "https://authors.library.caltech.edu/records/8s0zb-96h09",
"type": "article",
"title": "2D van der Waals magnets: From fundamental physics to\u00a0applications",
"author": [
{
"family_name": "Park",
"given_name": "Je-Geun",
"orcid": "0000-0002-3930-4226"
},
{
"family_name": "Zhang",
"given_name": "Kai-Xuan",
"orcid": "0000-0002-9958-6018"
},
{
"family_name": "Cheong",
"given_name": "Hyeonsik",
"orcid": "0000-0002-2347-4044"
},
{
"family_name": "Kim",
"given_name": "Jae Hoon",
"orcid": "0000-0002-7840-3630"
},
{
"family_name": "Belvin",
"given_name": "Carina A.",
"orcid": "0000-0002-6540-1185",
"clpid": "Belvin-Carina-A"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
},
{
"family_name": "Ning",
"given_name": "Honglie"
},
{
"family_name": "Gedik",
"given_name": "Nuh",
"orcid": "0000-0002-6394-4987"
}
],
"abstract": "Magnetism has played a central role in the long and rich history of modern condensed matter physics, with many foundational insights originating from theoretical studies of two-dimensional (2D) spin systems. The discovery of 2D van der Waals (vdW) magnets has revolutionized this area by providing real, atomically thin magnetic systems for experimental investigation. Since the first experimental reports of antiferromagnetic vdW insulators in 2016—followed by studies on ferromagnetic vdW systems in 2017—the field has witnessed rapid and expansive growth, with more than two dozen vdW magnetic materials now identified, including both ferromagnets and antiferromagnets. This review presents a comprehensive overview of the major scientific and technological developments in this rapidly evolving field. These developments include experimental realizations of various 2D spin Hamiltonians, as well as unexpected phenomena such as magnetic excitons, Floquet-engineered states, and light-induced metastable magnetic phases. In parallel, 2D vdW magnets have shown significant promise in spintronics and related applications, offering a new platform for engineering quantum functionalities. This review traces the historical development of the field, synthesizes key milestones, and highlights its broader impact across condensed matter physics and materials science. The review concludes by outlining several promising directions for future research, charting a path forward in this vibrant and still rapidly growing area.
",
"doi": "10.1103/2pff-xy6n",
"issn": "0034-6861",
"publisher": "American Physical Society",
"publication": "Reviews of Modern Physics",
"publication_date": "2026-05-27",
"series_number": "2",
"volume": "98",
"issue": "2",
"pages": "025003"
},
{
"id": "authors:q07d1-z4w79",
"collection": "authors",
"collection_id": "q07d1-z4w79",
"cite_using_url": "https://authors.library.caltech.edu/records/q07d1-z4w79",
"type": "article",
"title": "High-speed antiferromagnetic domain walls driven by coherent spin waves",
"author": [
{
"family_name": "Seyler",
"given_name": "Kyle L.",
"orcid": "0000-0003-1553-4518",
"clpid": "Seyler-Kyle-L"
},
{
"family_name": "Zhang",
"given_name": "Hantao",
"orcid": "0000-0001-6281-6708"
},
{
"family_name": "Van Beveren",
"given_name": "Daniel"
},
{
"family_name": "Rotundu",
"given_name": "Costel R.",
"orcid": "0000-0002-1571-8352"
},
{
"family_name": "Lee",
"given_name": "Young S.",
"orcid": "0000-0002-7022-8313"
},
{
"family_name": "Cheng",
"given_name": "Ran",
"orcid": "0000-0003-0166-2172"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "The ability to rapidly manipulate domain walls in magnetic materials is key to developing novel high-speed spintronic memory and computing devices. Antiferromagnetic materials present a particularly promising platform due to their robustness against stray fields and their potential for exceptional domain wall velocities. Among various proposed driving mechanisms, coherent spin waves could potentially propel antiferromagnetic domain walls to the magnon group velocity while minimizing dissipation from Joule heating. However, experimental realization has remained elusive due to the dual challenges of generating coherent antiferromagnetic spin waves near isolated mobile antiferromagnetic domain walls and simultaneously measuring high-speed domain wall dynamics. Here we experimentally realize an approach where ultrafast laser pulses generate coherent spin waves that drive antiferromagnetic domain walls and develop a technique to directly map the spatiotemporal domain wall dynamics. Using the room-temperature antiferromagnetic insulator Sr2Cu3O4Cl2, we observe antiferromagnetic domain wall motion with record-high velocities up to ~50 km s−1. Remarkably, the direction of domain wall propagation is controllable through both the pump laser helicity and the sign of the domain wall winding number. This bidirectional control can be theoretically explained, and numerically reproduced, by the domain wall dynamics induced by coherent spin waves of the in-plane magnon mode—a phenomenon unique to magnets with an easy-plane anisotropy. Our work uncovers a novel domain wall propulsion mechanism that is generalizable to a wide range of antiferromagnetic materials, unlocking new opportunities for ultrafast coherent antiferromagnetic spintronics.
",
"doi": "10.1038/s41467-025-64803-2",
"issn": "2041-1723",
"publisher": "Nature Publishing Group",
"publication": "Nature Communications",
"publication_date": "2025-11-07",
"series_number": "1",
"volume": "16",
"issue": "1",
"pages": "9836"
},
{
"id": "authors:9st9q-tx308",
"collection": "authors",
"collection_id": "9st9q-tx308",
"cite_using_url": "https://authors.library.caltech.edu/records/9st9q-tx308",
"type": "article",
"title": "Twist-programmable superconductivity in spin\u2013orbit-coupled bilayer graphene",
"author": [
{
"family_name": "Zhang",
"given_name": "Yiran",
"orcid": "0000-0002-8477-0074",
"clpid": "Zhang-Yiran"
},
{
"family_name": "Shavit",
"given_name": "Gal",
"orcid": "0000-0003-1792-9249",
"clpid": "Shavit-Gal"
},
{
"family_name": "Ma",
"given_name": "Huiyang",
"orcid": "0009-0000-3028-2668"
},
{
"family_name": "Han",
"given_name": "Youngjoon",
"clpid": "Han-Youngjoon"
},
{
"family_name": "Siu",
"given_name": "Chi Wang",
"clpid": "Siu-Chi-Wang"
},
{
"family_name": "Mukherjee",
"given_name": "Ankan",
"clpid": "Mukherjee-Ankan"
},
{
"family_name": "Watanabe",
"given_name": "Kenji",
"orcid": "0000-0003-3701-8119"
},
{
"family_name": "Taniguchi",
"given_name": "Takashi",
"orcid": "0000-0002-1467-3105"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
},
{
"family_name": "Lewandowski",
"given_name": "Cyprian",
"orcid": "0000-0002-6944-9805"
},
{
"family_name": "von Oppen",
"given_name": "Felix",
"orcid": "0000-0002-2537-7256"
},
{
"family_name": "Oreg",
"given_name": "Yuval",
"orcid": "0000-0001-8753-8468"
},
{
"family_name": "Nadj-Perge",
"given_name": "Stevan",
"orcid": "0000-0002-2394-9070",
"clpid": "Nadj-Perge-S"
}
],
"abstract": "The relative twist angle between layers of near-lattice-matched van der Waals materials is critical for the emergent phenomena associated with moiré flat bands. However, the concept of angle rotation control is not exclusive to moiré superlattices in which electrons directly experience a twist-angle-dependent periodic potential. Instead, it can also be used to induce programmable symmetry-breaking perturbations with the goal of stabilizing desired correlated states. Here we experimentally demonstrate 'moiréless' twist-tuning of superconductivity together with other correlated orders in Bernal bilayer graphene proximitized by tungsten diselenide. The precise alignment between the two materials systematically controls the strength of induced Ising spin–orbit coupling (SOC), profoundly altering the phase diagram. As Ising SOC is increased, superconductivity onsets at a higher displacement field and features a higher critical temperature, reaching up to 0.5 K. Within the main superconducting dome and in the strong Ising SOC limit, we find an unusual phase transition characterized by a nematic redistribution of holes among trigonally warped Fermi pockets and enhanced resilience to in-plane magnetic fields. The superconducting behaviour is theoretically compatible with the prominent role of interband interactions between symmetry-breaking Fermi pockets. Moreover, we identify two additional superconducting regions, one of which descends from an inter-valley coherent normal state and shows a Pauli-limit violation ratio exceeding 40, among the highest for all known superconductors. Our results provide insights into ultraclean graphene superconductors and underscore the potential of utilizing moiréless-twist engineering across a wide range of van der Waals heterostructures.
",
"doi": "10.1038/s41586-025-08959-3",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "2025-05-15",
"series_number": "8063",
"volume": "641",
"issue": "8063",
"pages": "625-631"
},
{
"id": "authors:vej7z-7w929",
"collection": "authors",
"collection_id": "vej7z-7w929",
"cite_using_url": "https://authors.library.caltech.edu/records/vej7z-7w929",
"type": "article",
"title": "Time-hidden magnetic order in a multi-orbital Mott insulator",
"author": [
{
"family_name": "Li",
"given_name": "Xinwei",
"orcid": "0000-0003-0555-2624",
"clpid": "Li-Xinwei"
},
{
"family_name": "Esin",
"given_name": "Iliya",
"orcid": "0000-0003-2959-0617",
"clpid": "Esin-Iliya"
},
{
"family_name": "Han",
"given_name": "Youngjoon",
"clpid": "Han-Youngjoon"
},
{
"family_name": "Liu",
"given_name": "Yincheng",
"orcid": "0000-0002-0283-5111",
"clpid": "Liu-Yincheng"
},
{
"family_name": "Zhao",
"given_name": "Hengdi",
"orcid": "0000-0003-4606-6323"
},
{
"family_name": "Ning",
"given_name": "Honglie",
"orcid": "0000-0003-4867-0751",
"clpid": "Ning-Honglie"
},
{
"family_name": "Barrett",
"given_name": "Cora"
},
{
"family_name": "Shan",
"given_name": "Jun-Yi",
"orcid": "0000-0001-7665-2169",
"clpid": "Shan-Jun-Yi"
},
{
"family_name": "Seyler",
"given_name": "Kyle",
"orcid": "0000-0003-1553-4518",
"clpid": "Seyler-Kyle"
},
{
"family_name": "Cao",
"given_name": "Gang",
"orcid": "0000-0001-9779-430X"
},
{
"family_name": "Refael",
"given_name": "Gil",
"orcid": "0009-0007-4566-8441",
"clpid": "Refael-G"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "Photo-excited quantum materials can be driven into thermally inaccessible metastable states that exhibit structural, charge, spin, topological and superconducting orders. Metastable states typically emerge on timescales set by the intrinsic electronic and phononic energy scales, ranging from femtoseconds to picoseconds, and can persist for weeks. Therefore, studies have primarily focused on ultrafast or quasi-static limits, leaving the intermediate time window less explored. Here we reveal a metastable state with broken glide-plane symmetry in photo-doped Ca2RuO4 using time-resolved optical second-harmonic generation and birefringence measurements. We find that the metastable state appears long after intralayer antiferromagnetic order has melted and photo-carriers have recombined. Its properties are distinct from all known states in the equilibrium phase diagram and are consistent with intralayer ferromagnetic order. Furthermore, model Hamiltonian calculations reveal that a non-thermal trajectory to this state can be accessed via photo-doping. Our results expand the search space for out-of-equilibrium electronic matter to metastable states emerging at intermediate timescales.",
"doi": "10.1038/s41567-024-02752-1",
"issn": "1745-2473",
"publisher": "Nature Publishing Group",
"publication": "Nature Physics",
"publication_date": "2025-03",
"volume": "21",
"pages": "451\u2013457"
},
{
"id": "authors:swxwr-smz38",
"collection": "authors",
"collection_id": "swxwr-smz38",
"cite_using_url": "https://authors.library.caltech.edu/records/swxwr-smz38",
"type": "article",
"title": "Observation of excitons bound by antiferromagnetic correlations",
"author": [
{
"family_name": "Mehio",
"given_name": "Omar",
"orcid": "0000-0001-7923-2178",
"clpid": "Mehio-Omar"
},
{
"family_name": "Han",
"given_name": "Yuchen",
"orcid": "0000-0002-9636-7127",
"clpid": "Han-Yuchen"
},
{
"family_name": "Li",
"given_name": "Xinwei",
"orcid": "0000-0003-0555-2624",
"clpid": "Li-Xinwei"
},
{
"family_name": "Ning",
"given_name": "Honglie",
"orcid": "0000-0003-4867-0751",
"clpid": "Ning-Honglie"
},
{
"family_name": "Porter",
"given_name": "Zach",
"orcid": "0000-0002-2945-9558"
},
{
"family_name": "Wilson",
"given_name": "Stephen D.",
"orcid": "0000-0003-3733-930X"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "Two-dimensional Mott insulators host antiferromagnetic (AFM) correlations that are predicted to enhance the attractive interaction between empty (holons) and doubly occupied (doublons) sites, creating a novel pathway for exciton formation. However, experimental confirmation of this spin-mediated binding mechanism remains elusive. Leveraging the distinct magnetic critical properties of the Mott antiferromagnets Sr\u2082\u2062IrO\u2084 and Sr\u2083Ir\u2082\u2062O\u2087, we show using time-resolved THz spectroscopy that excitons exist only at temperatures below where short-range AFM correlation develops. The excitons remain stable up to photodoping densities approaching the predicted excitonic Mott insulator-to-metal transition, revealing a unique robustness against screening. Our results establish the viability of spin-bound excitons and introduce opportunities for excitonic control through magnetic degrees of freedom.
",
"doi": "10.1103/physrevresearch.7.013114",
"issn": "2643-1564",
"publisher": "American Physical Society",
"publication": "Physical Review Research",
"publication_date": "2025-01-30",
"series_number": "1",
"volume": "7",
"issue": "1",
"pages": "013114"
},
{
"id": "authors:p9xn7-cdb83",
"collection": "authors",
"collection_id": "p9xn7-cdb83",
"cite_using_url": "https://authors.library.caltech.edu/records/p9xn7-cdb83",
"type": "article",
"title": "Dynamic magnetic phase transition induced by parametric magnon pumping",
"author": [
{
"family_name": "Shan",
"given_name": "Jun-Yi",
"orcid": "0000-0001-7665-2169",
"clpid": "Shan-Jun-Yi"
},
{
"family_name": "Curtis",
"given_name": "Jonathan B.",
"orcid": "0000-0001-8544-0555",
"clpid": "Curtis-Jonathan-B"
},
{
"family_name": "Guo",
"given_name": "Mingyao",
"orcid": "0000-0003-1109-2548",
"clpid": "Guo-Mingyao"
},
{
"family_name": "Roh",
"given_name": "Chang Jae",
"orcid": "0009-0009-0369-0311",
"clpid": "Roh-Chang-Jae"
},
{
"family_name": "Rotundu",
"given_name": "C. R.",
"orcid": "0000-0002-1571-8352",
"clpid": "Rotundu-Costel-R"
},
{
"family_name": "Lee",
"given_name": "Young S.",
"clpid": "Lee-Young-S"
},
{
"family_name": "Narang",
"given_name": "Prineha",
"orcid": "0000-0003-3956-4594",
"clpid": "Narang-Prineha"
},
{
"family_name": "Noh",
"given_name": "Tae Won",
"orcid": "0000-0003-1905-2321",
"clpid": "Noh-Tae-Won"
},
{
"family_name": "Demler",
"given_name": "Eugene",
"orcid": "0000-0002-2499-632X",
"clpid": "Demler-Eugene"
},
{
"family_name": "Hsieh",
"given_name": "D.",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "Uncovering pathways to optically drive magnetic order-disorder transitions on ultrashort timescales can lead to the realization of novel out-of-equilibrium quantum phenomena. A long-sought pathway is to directly excite a highly nonthermal energy-momentum distribution of magnons, bypassing both charge and lattice degrees of freedom. However, this remains elusive owing to the weak coupling and large momentum mismatch between photons and magnons. Here we demonstrate strong parametric excitation of magnons across the entire Brillouin zone of the antiferromagnetic insulator Sr\u2082Cu\u2083O\u2084Cl\u2082 by periodically modulating the superexchange interaction with the electric field of light. The excitation efficiency is greatly enhanced by tuning to the van Hove singularity in the magnon spectrum, sufficient to transiently collapse the antiferromagnetic state using a pulsed laser field of 10\u2079 V/m. The order parameter recovery timescale increases by over 1000 times as a function of excitation density, reflecting a crossover from high- to low-energy magnon dominated decay dynamics. This electric-field induced parametric magnon pumping mechanism is applicable to a broad range of magnetic insulators and opens up the possibility of dynamically engineering magnon distributions by design.
",
"doi": "10.1103/physrevb.109.054302",
"issn": "2469-9950",
"publisher": "American Physical Society",
"publication": "Physical Review B",
"publication_date": "2024-02-01",
"series_number": "5",
"volume": "109",
"issue": "5",
"pages": "054302"
},
{
"id": "authors:xzrcg-q7w19",
"collection": "authors",
"collection_id": "xzrcg-q7w19",
"cite_using_url": "https://authors.library.caltech.edu/records/xzrcg-q7w19",
"type": "article",
"title": "Nonlinear and Nonreciprocal Transport Effects in Untwinned Thin Films of Ferromagnetic Weyl Metal SrRuO\u2083",
"author": [
{
"family_name": "Kar",
"given_name": "Uddipta",
"clpid": "Kar-Uddipta"
},
{
"family_name": "Lu",
"given_name": "Elisha Cho-Hao",
"clpid": "Lu-Elisha-Cho-Hao"
},
{
"family_name": "Singh",
"given_name": "Akhilesh Kr.",
"clpid": "Singh-Akhilesh-Kr"
},
{
"family_name": "Reddy",
"given_name": "P.\u2009V. Sreenivasa",
"orcid": "0000-0003-1460-342X",
"clpid": "Peram-Venkata-Sreenivasa-Reddy"
},
{
"family_name": "Han",
"given_name": "Youngjoon",
"orcid": "0000-0003-1256-9328",
"clpid": "Han-Youngjoon"
},
{
"family_name": "Li",
"given_name": "Xinwei",
"clpid": "Li-Xinwei"
},
{
"family_name": "Cheng",
"given_name": "Cheng-Tung",
"orcid": "0000-0002-9117-5783",
"clpid": "Cheng-Cheng-Tung"
},
{
"family_name": "Yang",
"given_name": "Song",
"orcid": "0000-0003-4296-8856",
"clpid": "Yang-Song"
},
{
"family_name": "Lin",
"given_name": "Chun-Yen",
"orcid": "0000-0002-5083-9256",
"clpid": "Lin-Chun-Yen"
},
{
"family_name": "Cheng",
"given_name": "I-Chun",
"orcid": "0000-0003-2209-3298",
"clpid": "Cheng-I-Chun"
},
{
"family_name": "Hsu",
"given_name": "Chia-Hung",
"orcid": "0009-0002-7087-4718",
"clpid": "Hsu-Chia-Hung"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
},
{
"family_name": "Lee",
"given_name": "Wei-Cheng",
"orcid": "0000-0002-6140-6448",
"clpid": "Lee-Wei-Cheng"
},
{
"family_name": "Guo",
"given_name": "Guang-Yu",
"orcid": "0000-0003-3097-0916",
"clpid": "Guo-Guang-Yu"
},
{
"family_name": "Lee",
"given_name": "Wei-Li",
"orcid": "0000-0001-7207-1607",
"clpid": "Lee-Wei-Li"
}
],
"abstract": "The identification of distinct charge transport features, deriving from nontrivial bulk band and surface states, has been a challenging subject in the field of topological systems. In topological Dirac and Weyl semimetals, nontrivial conical bands with Fermi-arc surface states give rise to negative longitudinal magnetoresistance due to chiral anomaly effect and unusual thickness dependent quantum oscillation from Weyl-orbit effect, which were demonstrated recently in experiments. In this work, we report the experimental observations of large nonlinear and nonreciprocal transport effects for both longitudinal and transverse channels in an untwinned Weyl metal of SrRuO\u2083 thin film grown on a SrTiO\u2083 substrate. From rigorous measurements with bias current applied along various directions with respect to the crystalline principal axes, the magnitude of nonlinear Hall signals from the transverse channel exhibits a simple sinα dependence at low temperatures, where α is the angle between bias current direction and orthorhombic [001]\u2092, reaching a maximum when current is along orthorhombic [1¯10]\u2092. On the contrary, the magnitude of nonlinear and nonreciprocal signals in the longitudinal channel attains a maximum for bias current along [001]o, and it vanishes for bias current along [1¯10]\u2092. The observed α-dependent nonlinear and nonreciprocal signals in longitudinal and transverse channels reveal a magnetic Weyl phase with an effective Berry curvature dipole along [1¯10]\u2092 from surface states, accompanied by 1D chiral edge modes along [001]\u2092.
",
"doi": "10.1103/physrevx.14.011022",
"issn": "2160-3308",
"publisher": "American Physical Society",
"publication": "Physical Review X",
"publication_date": "2024-01",
"series_number": "1",
"volume": "14",
"issue": "1",
"pages": "011022"
},
{
"id": "authors:b8j5v-rrk37",
"collection": "authors",
"collection_id": "b8j5v-rrk37",
"cite_using_url": "https://authors.library.caltech.edu/records/b8j5v-rrk37",
"type": "article",
"title": "A coherent phonon-induced hidden quadrupolar ordered state in Ca\u2082RuO\u2084",
"author": [
{
"family_name": "Ning",
"given_name": "Honglie",
"orcid": "0000-0003-4867-0751",
"clpid": "Ning-Honglie"
},
{
"family_name": "Mehio",
"given_name": "Omar",
"orcid": "0000-0001-7923-2178",
"clpid": "Mehio-Omar"
},
{
"family_name": "Li",
"given_name": "Xinwei",
"orcid": "0000-0003-0555-2624",
"clpid": "Li-Xinwei"
},
{
"family_name": "Buchhold",
"given_name": "Michael",
"orcid": "0000-0001-5194-9388",
"clpid": "Buchhold-Michael"
},
{
"family_name": "Driesse",
"given_name": "Mathias",
"orcid": "0000-0002-3983-5852",
"clpid": "Driesse-Mathias"
},
{
"family_name": "Zhao",
"given_name": "Hengdi",
"orcid": "0000-0003-4606-6323",
"clpid": "Zhao-Hengdi"
},
{
"family_name": "Cao",
"given_name": "Gang",
"orcid": "0000-0001-9779-430X",
"clpid": "Cao-Gang"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "AbstractUltrafast laser excitation provides a means to transiently realize long-range ordered electronic states of matter that are hidden in thermal equilibrium. Recently, this approach has unveiled a variety of thermally inaccessible ordered states in strongly correlated materials, including charge density wave, ferroelectric, magnetic, and intertwined charge-orbital ordered states. However, more exotic hidden states exhibiting higher multipolar ordering remain elusive owing to the challenge of directly manipulating and detecting them with light. Here we demonstrate a method to induce a dynamical transition from a thermally allowed to a thermally forbidden spin-orbit entangled quadrupolar ordered state in Ca\u2082RuO\u2084 by coherently exciting a phonon that is strongly coupled to the order parameter. Combining probe photon energy-resolved coherent phonon spectroscopy measurements with model Hamiltonian calculations, we show that the dynamical transition is manifested through anomalies in the temperature, pump excitation fluence, and probe photon energy dependence of the strongly coupled phonon. With this procedure, we introduce a general pathway to uncover hidden multipolar ordered states and to control their re-orientation on ultrashort timescales.
",
"doi": "10.1038/s41467-023-44021-4",
"issn": "2041-1723",
"publisher": "Nature Publishing Group",
"publication": "Nature Communications",
"publication_date": "2023-12-13",
"volume": "14",
"pages": "8258"
},
{
"id": "authors:8v2db-dxg10",
"collection": "authors",
"collection_id": "8v2db-dxg10",
"cite_using_url": "https://authors.library.caltech.edu/records/8v2db-dxg10",
"type": "article",
"title": "Transforming a strain-stabilized ferroelectric into an intrinsic polar metal with light",
"author": [
{
"family_name": "Ron",
"given_name": "Alon",
"orcid": "0000-0002-1840-7824",
"clpid": "Ron-Alon"
},
{
"family_name": "Ahadi",
"given_name": "Kaveh",
"orcid": "0000-0003-2280-4037",
"clpid": "Ahadi-Kaveh"
},
{
"family_name": "Hickox-Young",
"given_name": "Daniel",
"orcid": "0000-0002-5411-0497",
"clpid": "Hickox-Young-Daniel"
},
{
"family_name": "Puggioni",
"given_name": "Danilo",
"orcid": "0000-0002-2128-4191",
"clpid": "Puggioni-Danilo"
},
{
"family_name": "Mehio",
"given_name": "Omar",
"orcid": "0000-0001-7923-2178",
"clpid": "Mehio-Omar"
},
{
"family_name": "Rondinelli",
"given_name": "James M.",
"orcid": "0000-0003-0508-2175",
"clpid": "Rondinelli-James-M"
},
{
"family_name": "Stemmer",
"given_name": "Susanne",
"orcid": "0000-0002-3142-4696",
"clpid": "Stemmer-Susanne"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "We explore the effects of chemical doping and photodoping in the strain-induced multiferroic EuTiO\u2083 grown on DyScO\u2083 substrates. The polar order is probed experimentally using second harmonic generation (SHG) and modeled using ab initio calculations. At low photodoping concentrations, we observe a reduction in SHG signal, indicating a destructive coupling between charge carriers and polar order in accordance with our simulations and expectations for a second-order Jahn-Teller driven ferroelectric. However, under increased photodoping the reduction in SHG plateaus at 84% of its original magnitude, indicating resilience of the polar order in the presence of a high concentration of delocalized electrons. This behavior stands in contrast with our first-principles simulations, indicating that EuTiO\u2083 undergoes a transition from ferroelectric to polar metallic character under photodoping. We suggest several hypotheses for the mechanism behind this change in distortion character.
",
"doi": "10.1103/physrevb.108.224308",
"issn": "2469-9950",
"publisher": "American Physical Society",
"publication": "Physical Review B",
"publication_date": "2023-12-01",
"series_number": "22",
"volume": "108",
"issue": "22",
"pages": "224308"
},
{
"id": "authors:f2wj0-p4753",
"collection": "authors",
"collection_id": "f2wj0-p4753",
"cite_using_url": "https://authors.library.caltech.edu/records/f2wj0-p4753",
"type": "article",
"title": "A Hubbard exciton fluid in a photo-doped antiferromagnetic Mott insulator",
"author": [
{
"family_name": "Mehio",
"given_name": "Omar",
"orcid": "0000-0001-7923-2178",
"clpid": "Mehio-Omar"
},
{
"family_name": "Li",
"given_name": "Xinwei",
"orcid": "0000-0003-0555-2624",
"clpid": "Li-Xinwei"
},
{
"family_name": "Ning",
"given_name": "Honglie",
"orcid": "0000-0003-4867-0751",
"clpid": "Ning-Honglie"
},
{
"family_name": "Lenar\u010di\u010d",
"given_name": "Zala",
"orcid": "0000-0001-8374-8011",
"clpid": "Lenar\u010di\u010d-Zala"
},
{
"family_name": "Han",
"given_name": "Yuchen",
"orcid": "0000-0002-9636-7127",
"clpid": "Han-Yuchen"
},
{
"family_name": "Buchhold",
"given_name": "Michael",
"orcid": "0000-0001-5194-9388",
"clpid": "Buchhold-Michael"
},
{
"family_name": "Porter",
"given_name": "Zach",
"orcid": "0000-0002-2945-9558",
"clpid": "Porter-Zach"
},
{
"family_name": "Laurita",
"given_name": "Nicholas J.",
"orcid": "0000-0002-7794-7951",
"clpid": "Laurita-Nicholas-J"
},
{
"family_name": "Wilson",
"given_name": "Stephen D.",
"orcid": "0000-0003-3733-930X",
"clpid": "Wilson-Stephen-D"
},
{
"family_name": "Hsieh",
"given_name": "David",
"orcid": "0000-0002-0812-955X",
"clpid": "Hsieh-David"
}
],
"abstract": "\n
\n
The undoped antiferromagnetic Mott insulator naturally has one charge carrier per lattice site. When it is doped with additional carriers, they are unstable to spin-fluctuation-mediated Cooper pairing as well as other unconventional types of charge, spin and orbital current ordering. Photo-excitation can produce charge carriers in the form of empty (holons) and doubly occupied (doublons) sites that may also exhibit charge instabilities. There is evidence that antiferromagnetic correlations enhance attractive interactions between holons and doublons, which can then form bound pairs known as Hubbard excitons, and that these might self-organize into an insulating Hubbard exciton fluid. However, this out-of-equilibrium phenomenon has not been experimentally detected. Here we report the transient formation of a Hubbard exciton fluid in the antiferromagnetic Mott insulator Sr2IrO4 using ultrafast terahertz conductivity. Following photo-excitation, we observe rapid spectral-weight transfer from a Drude metallic response to an insulating response. The latter is characterized by a finite-energy peak originating from intraexcitonic transitions, whose assignment is corroborated by our numerical simulations of an extended Hubbard model. The lifetime of the peak is short (approximately one picosecond) and scales exponentially with the Mott gap size, implying extremely strong coupling to magnon modes.
\n
\n