Rikako Yamamoto

Altermagnetism represents a magnetic phase in which the combination of compensated antiferromagnetic order with an anisotropic crystal field leads to time-reversal symmetry breaking. The resulting combination of properties typically associated with ferromagnets, but with net-zero magnetization, has generated significant interest for both fundamental research and technological applications. With many candidate altermagnetic materials, Mn Te has emerged as one of the most promising systems, with growing experimental evidence for altermagnetic phenomena. So far, the majority of measurements have been performed on thin films, or have involved surface measurements. However, the question of altermagnetic order in the bulk system—in the absence of substrate or surface effects—remains. Here we show evidence for bulk altermagnetism in single-crystal Mn Te through spectroscopic x-ray microscopy. By performing nanoscale x-ray magnetic circular dichroic (XMCD) imaging in transmission on a 200 -nm-thick lamella, we observe domains and magnetic textures with a spectroscopic signature characteristic of altermagnetic order, thereby confirming the intrinsic nature of altermagnetism in Mn Te . Quantitative analysis of the XMCD signal reveals excellent agreement with predicted signals, establishing that the altermagnetic order exists throughout the thickness of the lamella and confirming the intrinsic, bulk nature of the state. With these results, we demonstrate that transmission XMCD spectroscopic imaging is a robust, quantitative technique to probe altermagnetic order, providing a means to probe individual altermagnetic domains within complex configurations. This ability to investigate and characterize altermagnetic order in bulk crystals represents an important tool for the exploration of altermagnetism across a wide range of candidate materials, of key importance for the development of future technologies.

Spin splitting in electronic band structures via antiferromagnetic orders is a new route to control spin-polarized carriers that is available for spintronics applications. Here, we investigated the spin degrees of freedom in the electronic band structures of the antiferromagnet NdBi using laser-based spin- and angle-resolved photoemission spectroscopy (laser-SARPES). Our laser-SARPES experiments revealed that the two surface bands that appear in the antiferromagnetic state are spin polarized in opposite directions as a counterpart of the spin splitting. Moreover, we observed that the spin polarization is antisymmetric to the time-reversal invariant momentum, indicating that spin degeneracy is lifted due to the breaking of inversion symmetry at the surface. These results are well reproduced by our density functional theory calculations with the single- q magnetic structure, implying that the spin-split surface state is determined by the breaking of inversion symmetry in concert with the antiferromagnetic order.

The emergence of charge-neutral fermionic excitations in magnetic systems is one of the unresolved issues in recent condensed matter physics. This type of excitations has been observed in various systems, such as low-dimensional quantum spin liquids, Kondo insulators, and antiferromagnetic insulators. Here, we report the presence of a pronounced gapless spin excitation in the low-temperature antiferromagnetic state of YbCuS₂ semiconductor, where trivalent ytterbium atoms form a zigzag chain structure. We confirm the presence of this gapless excitations by a combination of experimental probes, namely ^63/65Cu-nuclear magnetic resonance and nuclear quadrupole resonance, as well as specific heat measurements, revealing a linear low-temperature behavior of both the nuclear spin-lattice relaxation rate 1/T₁ and the specific heat. This system provides a platform to investigate the origin of gapless excitations in spin chains and the relationship between emergent fermionic excitations and frustration.

We report the electrical resistivity, specific heat, and magnetization measurements of Y _{1-x} 1 − x Nd _{x} x Co _{2} 2 Zn _{20} 20 for 0.017 \leq x \leq 0.95 0.017 ≤ x ≤ 0.95 . The Schottky-type specific heat peak at around 13 K for all the samples is reproduced by the crystalline electric field model with the \Gamma_{6} Γ 6 doublet ground state of a Nd ^{3+} 3 + ion. The magnetization and magnetic susceptibility data of the samples for x \leq 0.06 x ≤ 0.06 are well reproduced by the calculation without intersite magnetic interactions among Nd moments. Therefore, the dilute Nd system Y _{1-x} 1 − x Nd _{x} x Co _{2} 2 Zn _{20} 20 for x \leq 0.06 x ≤ 0.06 is a good candidate to study on-site interaction of the \Gamma_{6} Γ 6 doublet ground state of 4 f f electrons with conduction electrons.