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1. Weyl nodal ring states and Landau quantization with very large magnetoresistance in square-net magnet EuGa4

   https://doi.org/10.1038/s41467-023-40767-z  

   Lei, Shiming; Allen, Kevin; Huang, Jianwei; Moya, Jaime M.; Wu, Tsz Chun; Casas, Brian; Zhang, Yichen; Oh, Ji Seop; Hashimoto, Makoto; Lu, Donghui; et al (December 2023, Nature Communications)

   Magnetic topological semimetals allow for an effective control of the topological electronic states by tuning the spin configuration. Among them, Weyl nodal line semimetals are thought to have the greatest tunability, yet they are the least studied experimentally due to the scarcity of material candidates. Here, using a combination of angle-resolved photoemission spectroscopy and quantum oscillation measurements, together with density functional theory calculations, we identify the square-net compound EuGa₄as a magnetic Weyl nodal ring semimetal, in which the line nodes form closed rings near the Fermi level. The Weyl nodal ring states show distinct Landau quantization with clear spin splitting upon application of a magnetic field. At 2 K in a field of 14 T, the transverse magnetoresistance of EuGa₄exceeds 200,000%, which is more than two orders of magnitude larger than that of other known magnetic topological semimetals. Our theoretical model suggests that the non-saturating magnetoresistance up to 40 T arises as a consequence of the nodal ring state. 

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2. Orphan high field superconductivity in non-superconducting uranium ditelluride

   https://doi.org/10.1038/s41467-024-47090-1  

   Frank, Corey E.; Lewin, Sylvia K.; Saucedo Salas, Gicela; Czajka, Peter; Hayes, Ian M.; Yoon, Hyeok; Metz, Tristin; Paglione, Johnpierre; Singleton, John; Butch, Nicholas P. (April 2024, Nature Communications)

   Abstract Reentrant superconductivity is an uncommon phenomenon in which the destructive effects of magnetic field on superconductivity are mitigated, allowing a zero-resistance state to survive under conditions that would otherwise destroy it. Typically, the reentrant superconducting region derives from a zero-field parent superconducting phase. Here, we show that in UTe₂crystals extreme applied magnetic fields give rise to an unprecedented high-field superconductor that lacks a zero-field antecedent. This high-field orphan superconductivity exists at angles offset between 29^oand 42^ofrom the crystallographicbtocaxes with applied fields between 37 T and 52 T. The stability of field-induced orphan superconductivity presented in this work defies both empirical precedent and theoretical explanation and demonstrates that high-field superconductivity can exist in an otherwise non-superconducting material. 

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3. Proton-fluence dependent magnetic properties of exfoliable quasi-2D van der Waals Cr ₂ Si ₂ Te ₆ magnet

   https://doi.org/10.1088/1361-648X/ad27ff  

   Iturriaga, Hector; Chen, Ju; Yang, Jing; Martinez, Luis M; Shao, Lin; Liu, Yu; Petrovic, Cedomir; Kirk, Martin; Singamaneni, Srinivasa R (March 2024, Journal of Physics: Condensed Matter)

   Abstract The discovery of long-range magnetic ordering in atomically thin materials catapulted the van der Waals (vdW) family of compounds into an unprecedented popularity, leading to potentially important technological applications in magnetic storage and magneto-transport devices, as well as photoelectric sensors. With the potential for the use of vdW materials in space exploration technologies it is critical to understand how the properties of such materials are affected by ionizing proton irradiation. Owing to their robust intra-layer stability and sensitivity to external perturbations, these materials also provide excellent opportunities for studying proton irradiation as a non-destructive tool for controlling their magnetic properties. Specifically, the exfoliable Cr₂Si₂Te₆(CST) is a ferromagnetic semiconductor with the Curie temperature (T_C) of ∼32 K. Here, we have investigated the magnetic properties of CST upon proton irradiation as a function of fluence (1 × 10¹⁵, 5 × 10¹⁵, 1 × 10¹⁶, 5 × 10¹⁶, and 1 × 10¹⁸H⁺/cm⁻²) by employing variable-temperature, variable-field magnetization measurements, and detail how the magnetization, magnetic anisotropy vary as a function of proton fluence across the magnetic phase transition. While theT_Cremains constant as a function of proton fluence, we observed that the saturation magnetization and magnetic anisotropy diverge at the proton fluence of 5 × 10¹⁶H⁺/cm⁻², which is prominent in the ferromagnetic phase, in particular.This work demonstrates that proton irradiation is a feasible method for modifying the magnetic properties and local magnetic interactions of vdWs crystals, which represents a significant step forward in the design of future spintronic and magneto-electronic applications. 

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4. Observation of unidirectional spin Hall magnetoresistance in amorphous PtSn ₄ /CoFeB bilayers

   https://doi.org/10.1063/5.0097355  

   Fan, Yihong; Cresswell, Zach; Guo, Silu; Zhang, Delin; Peterson, Thomas J.; Liu, Jinming; Lv, Yang; Andre Mkhoyan, K.; Wang, Jian-Ping (August 2022, Applied Physics Letters)

   Unidirectional spin Hall magnetoresistance (USMR) is a magnetoresistance effect with potential applications to read two-terminal spin–orbit-torque (SOT) devices directly. In this work, we observed a large USMR value (up to 0.7 × 10 −11 per A/cm 2 , 50% larger than reported values from heavy metals) in sputtered amorphous PtSn 4 /CoFeB bilayers. Ta/CoFeB bilayers with interfacial MgO insertion layers are deposited as control samples. The control experiments show that increasing the interfacial resistance can increase the USMR value, which is the case in PtSn 4 /CoFeB bilayers. The observation of a large USMR value in an amorphous spin–orbit-torque material has provided an alternative pathway for USMR application in two-terminal SOT devices. 

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5. Electronic structure of YV6Sn6 probed by de Haas–van Alphen oscillations and density functional theory

   https://doi.org/10.1063/5.0252563  

   Shtefiienko, Kyryl; Phillips, Cole; Mozaffari, Shirin; Madhogaria, Richa P; Meier, William R; Mandrus, David G; Graf, David E; Shrestha, Keshav (March 2025, APL Quantum)

   This study investigates the electronic structure of the vanadium-based kagome metal YV6Sn6 using magnetoresistance (MR) and torque magnetometry. The MR exhibits a nearly linear, non-saturating behavior, increasing by up to 55% at 35 T but shows no evidence of Shubnikov–de Haas oscillations. In contrast, the torque signal, measured up to 41.5 T, reveals clear de Haas–van Alphen (dHvA) oscillations over a wide frequency range, from a low frequency of Fα ∼20 T to high frequencies between 8 and 10 kT. Angular and temperature-dependent dHvA measurements were performed to probe the Fermi surface parameters of YV6Sn6. The dHvA frequencies display weak angular dependence, and the effective mass, determined by fitting the temperature-dependent data to the Lifshitz–Kosevich formula, is 0.097 mo, where mo represents the free electron mass. To complement the experimental findings, we computed the electronic band structure and Fermi surface using density functional theory. The calculations reveal several notable features, including multiple Dirac points near the Fermi level, flatbands, and Van Hove singularities. Two bands cross the Fermi level, contributing to the Fermi surface, with theoretical frequencies matching well with the observed dHvA frequencies. These combined experimental and theoretical insights enhance our understanding of the electronic structure of YV6Sn6 and provide a valuable framework for studying other vanadium- and titanium-based kagome materials. 

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