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### 9. Room-temperature THz anomalous Hall effect in Weyl antiferromagnet Mn_{3}Sn films

### May 2020

Using time-domain THz spectroscopy and polarimetry, we have measured the magneto-optical response of the Weyl AF Mn_{3}Sn. 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.

**“Terahertz conductivity of the magnetic Weyl semimetal Mn _{3}Sn films,” **B. Cheng, Y. Wang, D. Barbalas, T. Higo, S. Nakatsuji, and N. P. Armitage, Applied Physics Letters, 115, 012405 (2019).

**“Room-temperature terahertz anomalous Hall effect in Weyl antiferromagnet Mn _{3}Sn thin films,” **T. Matsuda, N. Kanda, T. Higo, N. P. Armitage, S. Nakatsuji, and R. Matsunaga, Nature Communications 11, 909 (2020).

### 8. Magnons from molecular spins in chiral Cu_{2}0Se0_{3}

### March 2020

The asymmetric magnetic interactions that control the low energy excitations and the skyrmionic spin texture of Cu_{2}OSeO_{3} were determined using inelastic neutron scattering and a coarse-grained description of this chiral breathing pyrochlore ferrimagnet.

**“Low energy magnons in the chiral ferrimagnet**** ****Cu**_{2}**OSeO**_{3}**: a coarse-grained approach,”**** **Yi Luo, G. G. Marcus, B. A. Trump, J. Kindervater, M. B. Stone, J. A. Rodriguez-Rivera, Yiming Qiu, T. M. McQueen, O. Tchernyshyov, and C. Broholm, Phys. Rev. B **101**, 144411 (2020).

### 7. **Anti-chiral spin order its Goldstone modes and their hybridization with phonons in the topological semimetal Mn**_{3}**Ge**

### January 2020

The anti-chiral spin structure of Mn_{3}Ge and its low energy excitations were determined using neutron scattering techniques. We developed a field theory of long-wavelength spin waves for Mn_{3}Ge and establish a spin-Hamiltonian model, which accounts for the spin order and low energy excitations. We identify two magneto-elastic modes that indicate an intimate relationship between strain, magnetism and transport in Mn_{3}Ge.

**“Antichiral spin order its Goldstone modes and their hybridization with phonons in the topological semimetal Mn3Ge,” **Y. Chen,J. Gaudet,S. Dasgupta,G. G. Marcus,J. Lin,T. Chen,T. Tomita,M. Ikhlas,Y. Zhao,W. C. Chen,M. B. Stone,O. Tchernyshyov,S. Nakatsuji,C. Broholm, arXiv:2001.09495, (2020).

### 6. Axion Magnetoelectric Coupling in the Hybrid Wannier Representation

January 2020

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.

**“Axion coupling in the hybrid Wannier representation,”** N. Varnava, I. Souza, D, Vanderbilt, Phys. Rev. B **101**, 155130 (2020).

### 5. Dirac Fermions and Possible Weak Antilocalization in LaCuSb_{2}

December 2019

We predicted and then experimentally showed that LaCuSb_{2}, previously reported to be superconducting, hosts Dirac fermions with an effective mass of 0.06 m_{e}.

**“Dirac fermions and possible weakantilocalization in LaCuSb _{2},” **J. R. Chamorro, A. Topp, Y. Fang, M. J. Winiarski, C. R. Ast, M. Krivenkov, A. Varykhalov, B. J.Ramshaw, L. M. Schoop, and T. M. McQueen, APL Mater. 7, 121108, (2019).

### 4. Probing Magnon Dynamics and Interactions in a Ferromagnetic Spin-1 Chain

December 2019

Using time-domain THz spectroscopy, we measure the low-energy EM response of the spin-1 ferromagnetic spin chain NiNb_{2}O_{6} as a function of temperature and external magnetic field. Prominent magnetic excitations are seen at low T. As we warm the system, we unexpectedly observe a T dependent renormalization of the lowest energy spin-excitation, which has a strong dependence on field direction. Using theoretical arguments, exact diagonalizations and finite temperature dynamical Lanczos calculations, we connect this renormalization to a picture of magnon-magnon interactions.

**“Tunable Magnon Interactions in a Ferromagnetic Spin-1 Chain,”** P. Chauhan, F. Mahmood, H. J. Changlani, S. M. Koohpayeh, and N. P. Armitage, Phys. Rev. Lett. **124**, 037203 (2020).

### 3. **Antiferromagnetic Domain Walls in Ferromagnetic Yb**_{2}Ti_{2}O_{7}

December 2019

_{2}Ti

_{2}O

_{7}

We show that ferromagnetic and antiferromagnetic states are nearly degenerate in the frustrated quantum magnet Yb_{2}Ti_{2}O_{7}. The long range nature of dipole interactions consequently induce a mixed FM/AFM state at low fields where AFM slabs serve as domain walls.

**“Multiphase Magnetism in Yb _{2}Ti_{2}O_{7},” **A. Scheie, J. Kindervater, S. Zhang, H.J. Changlani, G. Sala, G. Ehlers, A. Heinemann, G. S. Tucker, S.M. Koohpayeh, C. Broholm, arXiv:1912.04913, (2019).

### 2. Yi Li’s Work on Itinerant Ferromagnetism Featured in Quanta Magazine

January 2019

Yi Li’s group’s work (supported by IQM funding) about itinerant ferromagnetism is featured by *Quanta Magazine* in an article titled “A Child’s Puzzle Has Helped Unlock the Secrets of Magnetism.”

**“Exact results on itinerant ferromagnetism and the 15-puzzle problem,”** E. Bobrow, K. Stubis, Y. Li, Phys. Rev. B. **98**, 10.1103 (2018).

### 1. IQM study of Quantum Spin Fluctuations Highlighted by DOE

December 2017

A recent IQM study of quantum spin fluctuations in Pr_{2}Zr2O_{7} that was published in Physical Review Letter was highlighted by DOE. This was the thesis work of Jiajia Wen who is now at SLAC.

**“Disordered route to the Coulomb quantum spin liquid: Random transverse fields on spin ice in Pr _{2}Zr_{2}O_{7},”** J. J. Wen, S. M. Koohpayeh, K. A. Ross, B. A. Trump, T. M. McQueen, K. Kimura, S. Nakatsuji, Y. Qiu, D. M. Pajerowski, J. R. D. Copley, and C. L. Broholm, Phys. Rev. Lett.

**118**, 107206 (2017); arXiv:1609.08551.