Using a novel time-resolved neutron scattering technique and a new class of ultra-pure crystals, two distinct magnetic relaxation processes were discovered in the spin-ice compound Ho2Ti2O7. The cross-over in the relaxation dynamics is associated with spin fractionalization into monopoles.

Monopolar and dipolar relaxation in spin ice Ho2Ti2O7

Using a novel time-resolved neutron scattering technique and a new class of ultra-pure crystals, two distinct magnetic relaxation processes were discovered in the spin-ice compound Ho2Ti2O7. The cross-over in the relaxation dynamics is associated with spin fractionalization into monopoles.

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kitaevchain

Duality and domain wall dynamics in a twisted Kitaev chain

By combining synthesis, THz spectroscopy, and theory, we show CoNb2O6 is a “twisted Kitaev chain” with bond dependent anisotropic interactions similar to those of the honeycomb Kitaev spin liquid.

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A previously unreported family of materials has been discovered with unconventional magnetic properties that are consistent the realization of the quantum spin liquid. The materials consist of triangular lattices of magnetic trimer molecules of the form Rh3O12 and Ir3O12 with 4d and 5d electron based magnetism.

New trimer-based spin liquid candidates

A previously unreported family of materials has been discovered with unconventional magnetic properties that are consistent the realization of the quantum spin liquid. The materials consist of triangular lattices of magnetic trimer molecules of the form Rh3O12 and Ir3O12 with 4d and 5d electron based magnetism.

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SQUID

Interfacing a Dirac semimetal with magnetism

We have measured Fermi-energy-dependent quantum transport in electrostatically-gated thin films of the Dirac semimetal Cd3As2 interfaced with a ferromagnet.

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Room-temperature THz anomalous Hall effect

Room-temperature THz anomalous Hall effect in Weyl antiferromagnet Mn3Sn films

Using time-domain THz spectroscopy and polarimetry, we have measured the magneto-optical response of the Weyl AF Mn3Sn. A large anomalous Hall conductivity |σxy|~20 Ω- 1cm-1 at THz frequencies is clearly observed as polarization rotation. Gapping of the Fermi surfaces is apparent due to translation symmetry breaking in the helical phase.

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magnons

Magnons from molecular spins in chiral Cu20Se03

The asymmetric magnetic interactions that control the low energy excitations and the skyrmionic spin texture of Cu2OSeO3 were determined using inelastic neutron scattering and a coarse-grained description of this chiral breathing pyrochlore ferrimagnet.

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Axion Magnetoelectric Coupling

Axion Magnetoelectric Coupling in the Hybrid Wannier Representation

A large class of topological insulators (TIs) is characterized by the presence of a quantized magneto-electric (ME) “axion” coupling. We have developed a detailed theory connecting this axion coupling to features of the hybrid Wannier (HW) representation, which has emerged as one of the most important theoretical tools for understanding TIs.

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Anti-chiral spin

Anti-chiral spin order its Goldstone modes and their hybridization with phonons in the topological semimetal Mn3Ge

The anti-chiral spin structure of Mn3Ge and its low energy excitations were determined using neutron scattering techniques. We developed a field theory of long-wavelength spin waves for Mn3Ge and establish a spin-Hamiltonian model, which accounts for the spin order and low energy excitations.

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metals

Dirac Fermions and Possible Weak Antilocalizationin LaCuSb2

We predicted and then experimentally showed that LaCuSb2, previously reported to be superconducting, hosts Dirac fermions with an effective mass of 0.06 me.

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chain graph

Probing magnon dynamics and interactions in a ferromagnetic spin-1 chain

Using time-domain THz spectroscopy, we measure the low-energy EM response of the spin-1 ferromagnetic spin chain NiNb2O6 as a function of temperature and external magnetic field.

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image for slider

Antiferromagnetic domain walls in ferromagnetic Yb2Ti2O7

We show that ferromagnetic and antiferromagnetic states are nearly degenerate in the frustrated quantum magnet Yb2Ti2O7. The long range nature of dipole interactions consequently induce a mixed FM/AFM state at low fields where AFM slabs serve as domain walls.

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Yi Li and two graduate students, Eric Bobrow and Keaton Stubis, studied itinerant ferro magnetism arising from the coherent motion of a single hole in the strong interaction regime. Using the mathematics of the 15-puzzle, they extended a well-known theorem that describes this itinerant ferromagnetism to almost every non-separable graph.

Puzzling Itinerant Magnetism

Yi Li and two graduate students, Eric Bobrow and Keaton Stubis, studied itinerant ferro magnetism arising from the coherent motion of a single hole in the strong interaction regime. Using the mathematics of the 15-puzzle, they extended a well-known theorem that describes this itinerant ferromagnetism to almost every non-separable graph.

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A team led by Satoru Nakatsuji discovered large anomalous Hall, anomalous Nernst, and magneto-optical Kerr effects at room temperature in the antiferromagnetic metal Mn3Sn – a first example of a magnetic Weyl metal.  In collaboration with Chia-Ling Chien’s group at JHU, they also succeeded in making high-quality Mn3Sn thin films through sputtering.

Topological Magnetic Metal for Spintronics

A team led by Satoru Nakatsuji discovered large anomalous Hall, anomalous Nernst, and magneto-optical Kerr effects at room temperature in the antiferromagnetic metal Mn3Sn – a first example of a magnetic Weyl metal.  In collaboration with Chia-Ling Chien’s group at JHU, they also succeeded in making high-quality Mn3Sn thin films through sputtering.

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The Institute for Quantum Matter is an Energy Frontier Research Center that is realizing revolutionary quantum materials and structures where quantum effects such as entanglement and coherence find collective macroscopic manifestations. We expose, understand, and control the corresponding physical properties and explore their potential for energy-related applications.

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Job Opening: Condensed Matter Physics Postdoctoral Positions

The Institute for Quantum Matter at Johns Hopkins University explores the anomalous magnetic, electronic, and superconducting properties of quantum materials in bulk and thin film forms. Applications are invited for two postdoc positions specializing in the use of neutron scattering to probe quantum materials in the group of Prof. Collin Broholm. The successful candidates will […]

Liang Wu Receives Macronix Prize from International Organization of Chinese Physicists and Astronomers

IQM alumni, Liang Wu who is now an Assistant Professor at University of Pennsylvania, was awarded the Outstanding Young Researcher Award (Macronix Prize) by the International Organization of Chinese Physicists and Astronomers for “his pioneering experiments exploring topological materials with terahertz and nonlinear spectroscopy.” Congratulations to Liang and his former JHU mentor Peter Armitage!