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Altermagnets: Two Talks

Symposia

Computational Quantum Physics

Speakers

When

  • – ET

Where

Virtual

160 Fifth Avenue

New York, NY 10010

Talk 1

Title: Electronic Correlations in Altermagnets: NiS2 and RuO2

Speaker: Ina Park, Flatiron Institute

Altermagnetic (AM) order has recently emerged as a new class of collinear magnetism that is distinct, on symmetry grounds, from both ferromagnetic (FM) and antiferromagnetic (AFM) orders. While AM phase can be realized in a broad range of materials, spanning electronic ground state from metals to Mott insulators and different dimensionalities, the effect of electronic correlation in material’s altermagnetic phase and electronic structure has remain little explored.

In this talk, I’ll introduce two material examples, pyrite NiS2 and rutile RuO2. The former hosts both altermagnetism and Mott metal-insulator transition providing an unique material platform to study wide range of correlation strength within altermagnetic order, where DFT+DMFT calculation shows that spin-dependent lifetime of quasiparticles can be significantly asymmetric, aided by Hund’s correlation. The latter is a moderately correlated 4d metal, for which comparison with ARPES and optical conductivity experiments shows that the dynamic correlation effect is still important. Moreover, correlation effects makes the PM-AM phase transition highly susceptible to external perturbations such as strain. This sensitivity may help clarify the ongoing debate over the magnetic ground state of RuO2.

Talk 2

Title: X-ray Circular Dichroism in Altermagnets

Speaker: Jan Kunes, Masaryk University

Altermagnets are compensated collinear magnets in which time-reversed states are macroscopically distinguishable. This property arises from the combined symmetry of the crystal and magnetic structure and can lead to characteristic spin-dependent features in the electronic structure as well appearance of linear magneto-optical effects. I will discuss the x-ray magnetic circular dichroism (XMCD) as a probe of altermagnetism. After a brief introduction to the relevant symmetry aspects of altermagnets and to the basic principles of XMCD spectroscopy, I will present calculations of XMCD spectra for selected materials, including MnTe, Fe2O3, NiF2, MnF2, and BiFeO3. The theoretical analysis combines DFT+DMFT calculations, which account for electronic structure and local correlation effects, with Anderson impurity model calculations that provide insight into multiplet effects and local symmetry contributions to the XMCD response. I will discuss how the magnetic and crystallographic symmetries constrain the presence or absence of XMCD signals, and which material parameters affect the XMCD spectra in altermagnets. By comparing the spectra across different materials, the talk will illustrate both the opportunities and the limitations of XMCD as a probe of altermagnetism.

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