Next seminar
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)
4:00 AM Wednesday (Tokyo)
3:00 AM Wednesday (Beijing)
Link:
https://riceuniversity.zoom.
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
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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)
4:00 AM Wednesday (Tokyo)
3:00 AM Wednesday (Beijing)Link:
https://riceuniversity.zoom.us/j/93872419348?pwd=A8ytB7lddenltpVmyTOLZl0XZUIcZ8.1Abstract: 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)
4:00 AM Wednesday (Tokyo)
3:00 AM Wednesday (Beijing)
Link:
https://riceuniversity.zoom.us/j/93872419348?pwd= A8ytB7lddenltpVmyTOLZl0XZUIcZ8 .1
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);
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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)
4:00 AM Wednesday (Tokyo)
3:00 AM Wednesday (Beijing)
Link:
https://riceuniversity.zoom.us/j/93872419348?pwd=A8ytB7lddenltpVmyTOLZl0XZUIcZ8.1
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.
References:
Previous Records:
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2> Click 'VIEW FULL PLAYLIST' on the 1st video.
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Meeting ID: 938 7241 9348
Passcode: 111111