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A publication with Libor Šmejkal about the spontaneous formation of altermagnetism from orbital ordering has been published in Physical Review Letters.

Altermagnetism has emerged as a third type of collinear magnetism. In contrast to standard ferromagnets and antiferromagnets, altermagnets exhibit extra even-parity wave spin order parameters resulting in a spin splitting of electronic bands in momentum space. In real space, sublattices of opposite spin polarization are anisotropic and related by rotational symmetry. In the hitherto identified altermagnetic candidate materials, the anisotropies arise from the local crystallographic symmetry. Here, they show that altermagnetism can also form as an interaction-induced electronic instability in a lattice without the crystallographic sublattice anisotropy. They provide a microscopic example of a two-orbital model showing that the coexistence of staggered antiferromagnetic and orbital order can realize robust altermagnetism. They quantify the spin-splitter conductivity as a key experimental observable and discuss material candidates for the interaction-induced realization of altermagnetism.

A publication with Jairo Sinova, Libor Šmejkal, Atasi Chakraborty and Rafael González Hernández about strain-induced phase transitions from antiferromagnets to altermagnets has been published in Physical Review B.

A key challenge for future applications and functionalization of altermagnets is to demonstrate controlled transitioning to the altermagnetic phase from other conventional phases in a single material. Here they prove a viable path toward overcoming this challenge through a strain-induced transition from an antiferromagnetic to an altermagnetic phase in ReO2. Combining spin group symmetry analysis and ab initio calculations, they demonstrate that under compressive strain ReO2 undergoes such transition, lifting the Kramers degeneracy of the band structure of the antiferromagnetic phase in the nonrelativistic regime. In addition, they show that this magnetic transition is accompanied by a metal-insulator transition, and calculate the distinct spin-polarized spectral functions of the two phases, which can be detected in angle-resolved photoemission spectroscopy experiments.

A publication with Libor Šmejkal about x-ray magnetic circular dichroism in altermagnetic -MnTe has been published in Physical Review Letters.

In this work they use symmetry, ab initio theory, and experiments to explore x-ray magnetic circular dichroism (XMCD) in the altermagnetic class. As a representative material for our XMCD study they choose -MnTe with compensated antiparallel magnetic order in which an anomalous Hall effect has been already demonstrated. They predict and experimentally confirm a characteristic XMCD line shape for compensated moments lying in a plane perpendicular to the light propagation vector. Their results highlight the distinct phenomenology in altermagnets of this time-reversal symmetry breaking response, and its potential utility for element-specific spectroscopy and microscopy.

A publication with Olena Gomonay about current-controlled chirality dynamics in a mesoscopic magnetic domain wall has been published in Physical Review B.

Chirality as internal degree of freedom of a mesoscopic domain wall inside a quasi-one-dimensional fixture can be controlled by spin-polarized current for ferro- as well as antiferromagnetic domain walls. They show that the current density required for the chirality manipulation can be significantly reduced in the low-temperature regime where the chirality dynamics exhibits quantum effects. In this quantum regime, weak currents can excite Bloch oscillations of the domain wall angular rotation velocity, with the oscillation frequency proportional to the current, modulated by a much higher magnon-range frequency. In addition to that, the Wannier-Stark localization effects enable controlled switching between different chiral states, suppressing inertial effects characteristic for the classical regime. They also show that for recently discovered novel class of magnetic materials — altermagnets — chirality switching can be driven by the usual charge current (not spin polarized).

A publication with Jairo Sinova, Libor Šmejkal, Nayra Alvarez and Venkata K. Bharadwaj about Strain control of band topology and surface states in antiferromagnetic EuCd2As2 has been published in Physical Review B.

They investigate via ab initio density functional theory calculations, the effects of shear strain on the bulk and surface states in two antiferromagnetic EuCd2⁢As2 phases with out-of-plane and in-plane spin configurations. When magnetic moments are along the axis, a 3% longitudinal or diagonal shear strain can tune the Dirac semimetal phase to an axion insulator phase, characterized by the parity-based invariant 4⁢=2. For an in-plane magnetic order, the axion insulator phase remains robust under all shear strains. They further find that for both magnetic orders, the bulk gap increases, and a surface gap opens on the (001) surface up to 16 meV. Because of a nonzero 4⁢ index and gapped states on the (001) surface, hinge modes are expected to happen on the side surface states between those gapped surface states. This result can provide valuable insight into the realization of the long-sought axion states.

A publication with Jairo Sinova, Libor Šmejkal, Anna B. Hellenes, Rodrigo Jaeschke Ubiergo and Venkata K. Bharadwaj about supercell altermagnets has been published in Physical Review B.

They substantially broaden the family of altermagnetic candidates by predicting supercell altermagnets. Their magnetic unit cell is constructed by enlarging the nonmagnetic primitive unit cell, resulting in a nonzero propagation vector for the magnetic structure. This connection of the magnetic configuration to the ordering of sublattices gives an extra degree of freedom to supercell altermagnets, which can allow for the control over the order parameter spatial orientation. They identify realistic candidates ${\mathrm{MnSe}}_2$ with a $d$-wave order, and ${\mathrm{RbCoBr}}_3,{\mathrm{CsCoCr}}_3$, and ${\mathrm{BaMnO}}_3$ with $g$-wave order. They demonstrate the reorientation of the order parameter in ${\mathrm{MnSe}}_2$, which has two different magnetic configurations, whose energy difference is only 5 meV, opening the possibility of controlling the orientation of the altermagnetic order parameter by external perturbations.

A joint publication with Jairo Sinova, Libor Šmejkal, Anna B. Hellenes, Rodrigo Jaeschke Ubiergo, Warlley H. Campos, Venkata K. Bharadwaj and Atasi Chakraborty about the direct observation of altermagnetic band splitting in CrSb thin films has been published in Nature Communications.

They investigate directly this unconventional band splitting near the Fermi energy through spin-integrated soft X-ray angular resolved photoemission spectroscopy. The experimentally obtained angle-dependent photoemission intensity, acquired from epitaxial thin films of the predicted altermagnet CrSb, demonstrates robust agreement with the corresponding band structure calculations. In particular, they observe the distinctive splitting of an electronic band on a low-symmetry path in the Brilliouin zone that connects two points featuring symmetry-induced degeneracy. The measured large magnitude of the spin splitting of approximately 0.6 eV and the position of the band just below the Fermi energy underscores the significance of altermagnets for spintronics based on robust broken time reversal symmetry responses arising from exchange energy scales, akin to ferromagnets, while remaining insensitive to external magnetic fields and possessing THz dynamics, akin to antiferromagnets.