Next Seminar
Detecting magnon spin current by Resonant Inelastic X-ray Scattering in Yittrium Iron Garnet
Valentina Bisogni
Brookhaven National Laboratory
Time:
Tuesday, Nov./25/2025, 2:00 PM to 3:30 PM (Houston)
5:00 AM Wednesday (Tokyo, Seoul)
4:00 AM Wednesday (Beijing)
Link:
https://riceuniversity.zoom.us/j/93872419348?pwd=A8ytB7lddenltpVmyTOLZl0XZUIcZ8.1
Abstract: Magnon-based transport in insulators is fostering the next generation of ultra-fast, low-power, miniaturized electronics [1]. The understanding of the magnon current is, however, hampered by the difficulty in detecting the flowing electron angular momenta, requiring, for example, a conversion to charge current (through inverse spin Hall effect) for determining its transport properties [2]. This process may hinder the extraction of fundamental, microscopic transport parameters due to the involvement of complex mechanisms happening during the magnon/charge conversion.
In this talk, I will present a new method for directly visualizing the magnon current in yttrium iron garnet (YIG), with energy- and momentum-resolution [3, 4]. Using the Spin Seebeck effect as a magnon current source, we demonstrated that resonant inelastic x-ray scattering (RIXS) is sensitive to the non-equilibrium magnons conveying the current. Our results reveal that acoustic magnons with non-negligible momentum, e.g., q=0.2 r.l.u., contribute to the transport phenomena. This approach enables the extraction of key transport parameters, like the momentum-resolved magnon lifetime, as well as their relation to material properties, essential for developing faster electronics. More broadly, we demonstrate that RIXS can access both equilibrium and non-equilibrium magnons, becoming a potential tool for exotic forms of transport based on collective excitations.
References:
[1] Bauer, G. E., et al., Spin caloritronics. Nat. Mater. 11, 391 (2012).
[2] Saitoh, E., et al. Conversion of spin current into charge current at room temperature: inverse spin-Hall effect. Appl. Phys. Lett. 88, 182509 (2006).
[3] Gu, Y. et al. Observing differential spin currents by resonant inelastic X-ray scattering. Nature 645, 900 (2025)
[4] McNally, D. Spectroscopic probe of spin current. Nat. Mater. 24, 1685 (2025)
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Spring Semester Schedule
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High temperature superconductivity in bilayer nickelates and beyond
Qimiao Si
Rice University
Time:
Tuesday, Nov./18/2025, 2:00 PM to 3:30 PM (Houston)
Abstract: The discovery of superconductivity under pressure with a transition temperature of 80 K in the bilayer nickelate compound La3Ni2O7 [9] has generated considerable excitement. The recent extension of the phenomena to ambient conditions has further amplified the interest in the field. Some of the central questions concern the roles of electron correlations and multiple active orbitals. In this talk, I will introduce these systems in the broader context of correlated superconductors that develop out of bad metals, including the infinite layer nickelates and the even more extensively studied iron-based superconductors. I will then address the role of electron correlations, with a particular emphasis on orbital-selective behavior, for both the normal and superconducting states. I will show how such effects influence the low-energy electronic structure [1,2] and electronic dynamics [2], and how they drive the superconducting pairing through both interlayer and intralayer exchange pathways [3]. Our theoretical findings, especially on the orbital-selective effects, compare well with experimental results, including spectroscopic measurements that shed light on the underlying correlation effects in the normal state [4,5] as well as the measurements on the pairing gap structure in thin films of the bilayer system at ambient conditions [6,7]. Finally, I will touch upon related systems within the broader family of multilayer Ruddlesden-Popper nickelates [8].
References:
[1] Z. Liao et al, Phys. Rev. B 108, 214522 (2023);
[2] Z. Liao et al, arXiv:2412.21019;
[3] G. Duan et al., arXiv:2502.09195
[4] J. Yang et al., Nat. Comm. 15, 4373 (2024);
[5] Z. Liu et al, Nat. Comm. 15, 7570 (2024)
[6] J. Shen et al., arXiv:2502.17831
[7] S. Fan et al., arXiv:2506.01788
[8] K-S Lin, Y. Wang, Z. G. Liao, R. Yu, QS, to be published (2025).
[9] H. Sun et al, Nature 621, 493 (2023)
Triangular van der Waals topological magnet Co1/3 -TaS2
Je-Geun Park
Physics & Astronomy, Seoul National University, Republic of Korea
Time:
Tuesday, Nov./11/2025, 3:00 PM to 4:30 PM (Houston) (1h later than usual)
Abstract: Since monolayer magnetism was first conceptualised and demonstrated for several antiferromagnets experimentally in 2016 [1,2], two-dimensional van der Waals (vdW) magnets have opened a new frontier where reduced dimensionality and topology intertwine. In recent years, efforts have focused on discovering new vdW materials that host unconventional magnetic ground states, particularly topological magnets. Antiferromagnetic metallic Co 1/3 -TaS 2 represents the latest addition to this family [3]. It exhibits a pronounced anomalous Hall effect with extreme sensitivity to composition, recently attributed to a unique 3Q tetrahedral magnetic structure, the densest possible Skyrmion lattice [4,5]. Our inelastic neutron scattering results provide clear evidence distinguishing 1Q and 3Q states through their contrasting low-energy spin-wave dispersions [6]. I will also discuss recent electrostatic-gating [7] and optical-spectroscopy [8] studies that demonstrate external control and dynamical signatures of the 3Q phase.
References:
[1] Je-Geun Park, et al., J. Phys. Condens. Matter 28, 301001 (2016).
[2] Je-Geun Park, et al., Review of Modern Physics (submitted): arXiv:2505.02355
[3] Pyeongjae Park, et al., npj Quantum Materials 7, 42 (2022).
[4] Pyeongjae Park, et al., Nature Communications 14, 8346 (2023).
[5] Pyeongjae Park, et al., Phys. Rev. B Letter 109, L060403 (2024).
[6] Pyeongjae Park, et al., Phys. Rev. X 15, 031032 (2025)
[7] Junghyu Kim, et al., Nat. Comm. 16, 8943 (2025)
[8] Erik Kirstein*, Pyeongjae Park*, et al., (under review): arXiv:2507.08148
Electronic structure and lattice dynamics in kagome metals
S. Blanco-Canosa
Donostia International Physics Center (DIPC), Spain
IKERBASQUE, Basque Foundation for Science, Spainürich
Time:
Tuesday, Nov./04/2025, 2:00 PM to 3:30 PM (Houston)
Abstract: The long-range electronic modulations recently discovered in the geometrically frustrated kagome lattice have opened new avenues to explore the effect of correlations in materials with topological electron flat bands. Here, I will present ARPES, diffuse scattering, and inelastic X-ray scattering data to comprehensively study the electronic structure and lattice dynamics of kagome metals hosting charge order. We will navigate through different examples of kagome systems whose charge density wave origin is controversial, implying a phonon collapse at a different propagation vector as the periodic lattice distortion [1], and order-disorder transformations [2], akin to the canonical spin glasses.
References:
[1] A. Korshunov et al., Nature Comm (2023)
[2] D. Subires et al., Nature Comm (2025)
FCMP: Nonperturbative Semiclassical Spin Dynamics for Ordered Quantum Magnets
Cristian D. Batista
Lincoln Professor of Physics, University of TennesseeTime:
Tuesday, Sep./30/2025, 2:00 PM to 3:30 PM (Houston)Abstract: I will present a nonperturbative semiclassical framework for computing spin dynamics in ordered quantum magnets when interactions dominate over kinetic energy. The talk opens with an overview of the SU(N) coherent-state dynamics, which is a generalization of the Landau–Lifshitz dynamics, and clarify how classical trajectories encode quantum spectra. I will then use FeI2 as a case study in which strong interactions reshape the excitation landscape—producing hybridized dipolar–quadrupolar modes, spontaneous magnon decay, and multi-magnon bound states that hybridize with single magnons and redistribute spectral weight observed by inelastic neutron scattering and terahertz time-domain spectroscopy. The focus is our recent work introducing a genuinely nonperturbative strategy based on exact diagonalization in a carefully truncated Hilbert space, quantitatively benchmarked against matrix-product-state simulations. Applied to the triangular-lattice antiferromagnet at the one-third magnetization plateau, this approach captures two-magnon bound states, resonance-enhanced continua from bound-state/continuum hybridization, and overlapping bound states embedded within the continuum—phenomena inaccessible to standard loop expansions yet quantitatively comparable with experiment. I will conclude by outlining how this toolbox, together with SU(N) semiclassics, provides an end-to-end route—from microscopic model inference to predictive calculations of dynamical response—that we are implementing in the Sunny platform to enable reproducible, high-performance simulations.
FCMP: Spin-charge separation and resonant valence bond spin liquid in a kinetically-frustrated lightly-doped Mott insulator
Claudio Castelnovo
Theory of Condensed Matter Group, Physics, University of Cambridge
Time:
Tuesday, Sep./23/2025, 2:00 PM to 3:30 PM (Houston)
Abstract: Ideas about resonant valence bond liquid and spin-charge separation have led to key concepts in physics such as quantum spin liquids, emergent gauge symmetries, topological order, and fractionalisation. Despite extensive efforts to demonstrate the existence of a resonant valence bond phase in the Hubbard model that originally motivated the concept, a definitive realisation has yet to be achieved. Here, we present a solution to this long-standing problem by uncovering a resonant valence bond phase exhibiting spin-charge separation in realistic Hamiltonians. We show analytically that this ground state emerges in the dilute-doping and infinite-onsite-repulsion limit of a half-filled Mott insulator on corner-sharing tetrahedral lattices with frustrated hopping. We confirm numerically that the results extend to finite exchange interactions, finite-sized systems and finite dopant density. We further conducted a preliminary study on the nature of the excitations and spin-liquid correlations, suggestive of bosonic holon behaviour. Although much attention has been devoted to the emergence of unconventional states from geometrically frustrated interactions, our work demonstrates that kinetic energy frustration in doped Mott insulators may be essential for stabilising robust, topologically ordered states in real materials.
References:
[1] Glittum, C., et al. A resonant valence bond spin liquid in the dilute limit of doped frustrated Mott insulators. Nat. Phys. 21, 1211–1216 (2025).
FCMP: Electronic Nematic Order in a Layered Antiferromagnet
Linda Ye
Division of Physics, Mathematics & Astronomy, Caltech
Time:
Tuesday, Sep./16/2025, 2:00 PM to 3:30 PM (Houston)
Abstract: The operation mechanism of nematic liquid crystals lies in the control of their optical properties by the orientation of underlying nematic directors. In analogy, electronic nematicity refers to a state whose electronic properties spontaneously break rotation symmetries of the host crystalline lattice, leading to anisotropic electronic properties. In this work, we demonstrate that the layered antiferromagnet CoTa3S6 exhibits a switchable nematic order, evidenced by the emergence of both resistivity anisotropy and optical birefringence. This nematic state sets in at a temperature T* distinct from that of the antiferromagnetic transitions in the system, indicating a separate symmetry-breaking mechanism. The nematic order can be manipulated either by an in-plane rotation symmetry-breaking strain or in-plane magnetic field, with the latter exhibiting a pronounced non-volatile memory effect. Remarkably, we find that the broken three-fold rotation symmetry in electronic transport is restored with a moderate out-of-plane field. We hypothesize that the nematicity is of electronic origin and emerges from instabilities associated with van Hove singularities. The resulting phase diagram points to an intertwined interplay between the electronic nematicity and the proposed underlying collinear and non-coplanar spin orders. Our findings establish CoTa3S6 as a versatile antiferromagnetic platform with highly tunable functionalities arising from the breaking of rotational, time-reversal, and inversion symmetries. We will also discuss elastoresistance results that may help shed light on the nature of the nematic order.
References:
[1] Zili Feng, et al., Nonvolatile Nematic Order Manipulated by Strain and Magnetic Field in a Layered Antiferromagnet
FCMP: Altermagnetic Anomalous Hall Effect Emerging from Electronic Correlations
Jeroen van den Brink
Institute for Theoretical Solid State Physics, IFW Dresden, Germany
Time:
Tuesday, Sep./09/2025, 2:00 PM to 3:30 PM (Houston)Abstract: Altermagnetic materials are characterized by collinear magnetic order with a vanishing net magnetic moment, but nevertheless have a spin-splitting in their non-relativistic electronic band structure. From ab initio calculations, we have identified around 60 altermagnetic materials. From a theoretical point of view, several physical properties that render altermagnets different from canonical antiferro-, ferro- and ferri-magnets will be discussed. These include certain spin and heat transport features and piezomagnetic responses. By symmetry in principle also an anomalous Hall effect (AHE) is allowed in certain altermagnets. In particular we introduce an altermagnetic model in which the emergence of an AHE is driven by interactions. Quantum Monte Carlo simulations show that the system undergoes a finite temperature phase transition governed by a primary antiferromagnetic order parameter accompanied by a secondary altermagnetic one. The emergence of both orders turns the metallic state of the system, away from half-filling, into an altermagnet with zero net moment but a finite AHE.
References:
[1] Y. Guo, et al., Spin-split collinear antiferromagnets: A large-scale ab-initio study, Materials Today Physics, 32, 100991 (2023)
[2] T. Sato, et al., Altermagnetic anomalous Hall effect emerging from electronic correlations, Phys. Rev. Lett. 133, 086503 (2024)
[3] O. Gomonay, et al., Structure, control, and dynamics of altermagnetic textures, npj Spintronics 2, 35 (2024)
[4] C. Li, et al., Topological Weyl Altermagnetism in CrSb, Communications Physics 8, 311 (2025)
FCMP: High-temperature quantum coherence in a rare-earth spin chain
Igor A. Zaliznyak
CMPMSD, Brookhaven National Laboratory, Upton
Time:
Tuesday, Sep./02/2025, 2:00 PM to 3:30 PM (Houston)
Abstract: At high temperatures, quantum effects are generally considered unimportant, giving way to classical behavior. In magnetic systems, when thermal energies exceed the interaction strength between atomic magnetic moments, the spins typically become uncorrelated, resulting in classical paramagnetism. This thermal decoherence of quantum spins is a major hindrance to quantum information applications of spin systems. Remarkably, our neutron scattering experiments on Yb chains in an insulating perovskite crystal defy these conventional expectations [1]. Specific origin of effective quantum spins describing the ground crystal field doublet of Yb J=7/2 spin-orbital multiplet affords an opportunity to study excitations at temperatures much greater than spin interactions. It also provides remarkable sensitivity to specific entangled quantum spin states. We observe a sharply defined spinon continuum, a hallmark of fractionalized excitations in one-dimensional quantum magnets, persisting to temperatures well above the energy scale of Yb-Yb interactions. The observed sharpness of the spinon continuum’s dispersive upper boundary indicates a spinon mean free path exceeding ≈ 35 inter-atomic spacings at temperatures more than an order of magnitude above the interaction energy scale. By Fourier transforming the measured dynamical spin susceptibility we obtain a real space-time linear response function which allows direct measurement of the spinon propagation velocity both at low and high temperature. We thus discover an important and highly unique quantum behavior, which expands the realm of quantumness to high temperatures where entropy-governed classical behaviors were previously believed to dominate. These results have profound implications for spin systems in quantum information applications operating at finite temperatures and inspire new developments in quantum metrology.
References:
[1] L. L. Kish, et al. Nature Communications 16, 6594 (2025);
FCMP: Phase Diagram and Spectroscopic Signatures of a Supersolid in the Quantum Ising Magnet K2Co(SeO3)2
Tong Chen
Johns Hopkins University
Time:
Tuesday, Aug./26/2025, 2:00 PM to 3:30 PM (Houston)
Abstract: A supersolid is a quantum-entangled state of matter exhibiting the dual characteristics of superfluidity and solidity. Theory predicts that hard-core bosons with repulsive interactions on a triangular lattice can form supersolid phases at half filling and near complete filling. Leveraging an exact mapping between bosons and spin-1/2 degrees of freedom, we investigate these phases in the spin-1/2 triangular-lattice antiferromagnet K2Co(SeO3)2 with exchange constants = 2.96(2) meV and meV. At zero field, neutron diffraction reveals the gradual development for K of quasi-two-dimensional magnetic order with Z3 translational symmetry breaking (solidity) albeit with 44(5)% reduced amplitude at K indicating strong quantum fluctuations. These are apparent in equidistant bands of continuum neutron scattering for, where the quasi-elastic Q-dependent continuum has a lower resonant edge and is gapless to within 0.7% at K, consistent with broken U(1) spin rotational symmetry (boson superfluidity). Competing instabilities are apparent in soft albeit finite-energy modes at M and at K. For c-axis-oriented magnetic fields that almost saturate the magnetization, corresponding to nearly filling the lattice with bosons, we find a new phase consistent with a second supersolid. These phases are separated by a pronounced 1/3 magnetization plateau that supports coherent spin waves, from which we determine the spin Hamiltonian. - 2024 Seminars
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FCMP: Recent progress on emergent quantum electrodynamics in dipolar-octupolar quantum spin ice
Yong Baek Kim
University of Toronto
Time:
Tuesday, Sep/10/2024, 2:00 PM to 3:30 PM (CST)
Abstract: The unambiguous experimental confirmation of a quantum spin liquid remains a longstanding issue in modern condensed matter physics. In particular, significant efforts have been made to realize quantum spin ice, a three-dimensional quantum spin liquid that provides a lattice realization of quantum electrodynamics and hosts emergent photons as well as gapped spinon excitations. Recent experiments on Ce-based dipolar-octupolar pyrochlore systems, Ce2Zr2O7 and Ce2Sn2O7, suggest that these materials may host the so-called π-flux quantum spin ice. We will first discuss the theoretical background for quantum spin ice and present our recent theoretical results on the dipolar-octupolar quantum spin ice states. Then we will compare our theoretical predictions on dynamical properties of spinons and emergent photons with recent experimental results.
FCMP: Bulk high-temperature superconductivity in the pressurized bilayer nickelate La2PrNi2O7
Jinguang Cheng
Institute of Physics, Chinese Academy of Sciences
Time:
Tuesday, Sep/03/2024, 2:00 PM to 3:30 PM (CDT)
Abstract: Recently, much attention has been paid to the nickelates that emerge as a new family of unconventional high-Tc superconductors. Superconductivity has been observed in the infinite-layer Nd(1-x)SrxNiO2 thin films at ambient pressure [1], and in the bilayer La3Ni2O7 [2] and trilayer La4Ni3O10 [3] under high pressures. Despite of these exciting achievements, there remain many unsolved issues and open questions in these nickelate superconductors, especially for the case of La3Ni2O7 that shows the highest onset of Tc ~80 K at pressures above 14 GPa [2]. Although zero resistivity has been achieved in the single- and poly-crystalline samples of La3Ni2O7 under hydrostatic pressure conditions [4, 5], obvious diamagnetic signals, the other hallmark of superconductors, are still lacking owing to the filamentary nature with low superconducting volume fraction [6]. In this talk, I will first give an overview on recent experimental progress, the current status, and open issues about the nickelates superconductors. Then, I will present our recent high-pressure results on the rare-earth-substituted La(3-x)RxNi2O7 (R = Pr, Nd, Tb) polycrystalline samples. For La2PrNi2O7, in addition to achieving zero resistivity below Tc^zero = 60 K at 18-20 GPa, we confirmed the bulk nature of high-T c superconductivity by detecting clear diamagnetic signals below ~75 K in the ac magnetic susceptibility [7]. In addition, we have revealed distinct effects of chemical versus physical pressures on the structural transition of bilayer nickelates [8]. Our results not only resolve some existing controversies but also illuminate directions for exploring bulk high-Tc superconductivity in the bilayer nickelates.
References:
[1] Nature 572, 624 (2019);
[2] Nature 621, 493 (2023);
[3] Nature 631, 531 (2024);
[4] Nature Phys. 20, 1269 (2024);
[5] Phys. Rev. X 14, 011040 (2024);
[6] ArXiv: 2311.12361 (2023);
[7] ArXiv: 2407.05681 (2024);
[8] ArXiv: 2408.09421 (2024)
FCMP: Electronic orders in correlated kagome metal systems
Ming Yi
Rice University
Time:
Tuesday, Aug/27/2024, 2:00 PM to 3:30 PM (CDT)
Abstract: Kagome metals are a class of quantum materials where the geometry of the lattice leads to key signatures in the electronic structure including topological flat bands, Dirac cones, and Van Hove singularities. As the chemical potential is tuned across each of these electronic singularities, emergent orders are theoretically expected, including magnetic orders and charge density wave orders. In recent years, a number of bulk materials have been discovered to exhibit the kagome lattice motif, where electronic orders have also been found to emerge. In this talk, I will discuss progress in understanding the Fe-based magnetic kagome systems FeSn and FeGe. I will also present experimental results on the recently discovered Cr-based kagome material CsCr3Sb5, where superconductivity has been found to emerge under hydrostatic pressure when density-wave orders are suppressed. Specifically, I will show angle-resolved photoemission spectroscopy and resonant inelastic x-ray scattering results that reveal the presence of the kagome flat band in close proximity to the Fermi level and the role of the flat band in the density wave orders at ambient pressure.