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1. Instabilities of heavy magnons in an anisotropic magnet

   https://doi.org/10.1038/s41467-023-39940-1  

   Bai, Xiaojian; Zhang, Shang-Shun; Zhang, Hao; Dun, Zhiling; Phelan, W. Adam; Garlea, V. Ovidiu; Mourigal, Martin; Batista, Cristian D. (December 2023, Nature Communications)

   Abstract The search for new elementary particles is one of the most basic pursuits in physics, spanning from subatomic physics to quantum materials. Magnons are the ubiquitous elementary quasiparticle to describe the excitations of fully-ordered magnetic systems. But other possibilities exist, including fractional and multipolar excitations. Here, we demonstrate that strong quantum interactions exist between three flavors of elementary quasiparticles in the uniaxial spin-one magnet FeI₂. Using neutron scattering in an applied magnetic field, we observe spontaneous decay between conventional and heavy magnons and the recombination of these quasiparticles into a super-heavy bound-state. Akin to other contemporary problems in quantum materials, the microscopic origin for unusual physics in FeI₂is the quasi-flat nature of excitation bands and the presence of Kitaev anisotropic magnetic exchange interactions. 

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2. Tuning the Fermi liquid crossover in Sr2RuO4 with uniaxial stress

   https://doi.org/10.1038/s41535-022-00519-6  

   Chronister, A; Zingl, M; Pustogow, A; Luo, Yongkang; Sokolov, D A; Jerzembeck, F; Kikugawa, N; Hicks, C W; Mravlje, J; Bauer, E D; et al (December 2022, npj Quantum Materials)

   Abstract We perform nuclear magnetic resonance (NMR) measurements of the oxygen-17 Knight shifts for Sr₂RuO₄, while subjected to uniaxial stress applied along [100] direction. The resulting strain is associated with a strong variation of the temperature and magnetic field dependence of the inferred magnetic response. A quasiparticle description based on density-functional theory calculations, supplemented by many-body renormalizations, is found to reproduce our experimental results, and highlights the key role of a van-Hove singularity. The Fermi-liquid coherence scale is shown to be tunable by strain, and driven to low values as the associated Lifshitz transition is approached. 

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3. Quest for quantum states via field-altering technology

   https://doi.org/10.1038/s41535-020-00286-2  

   Cao, Gang; Zhao, Hengdi; Hu, Bing; Pellatz, Nicholas; Reznik, Dmitry; Schlottmann, Pedro; Kimchi, Itamar (November 2020, npj Quantum Materials)

   Abstract We report quantum phenomena in spin-orbit-coupled single crystals that are synthesized using an innovative technology that “field-alters” crystal structures via application of magnetic field during crystal growth. This study addresses a major challenge facing the research community today: A great deal of theoretical work predicting exotic states for strongly spin-orbit-coupled, correlated materials has thus far met very limited experimental confirmation. These conspicuous discrepancies are due in part to the extreme sensitivity of these materials to structural distortions. The results presented here demonstrate that the field-altered materials not only are much less distorted but also exhibit phenomena absent in their non-altered counterparts. The field-altered materials include an array of4dand5dtransition metal oxides, and three representative materials presented here are Ba₄Ir₃O₁₀, Ca₂RuO₄, and Sr₂IrO₄. This study provides an approach for discovery of quantum states and materials otherwise unavailable. 

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4. Identifying Internal Stresses during Mechanophore Activation

   https://doi.org/10.1002/adem.202101080  

   Rencheck, Mitchell_L; Mackey, Brandon_T; Hu, Yu-Yang; Chang, Chia-Chih; Sangid, Michael_D; Davis, Chelsea_S (October 2021, Advanced Engineering Materials)

   Mechanophores (MPs) undergo chemical reactions to become fluorescent in response to a mechanical stimulus that reflects the magnitude and distribution of applied stress. MPs are an emerging technology for self‐reporting damage sensing applications in polymeric materials in the aeronautical, energy generation, and automotive industries. However, quantitative calibration of the MP response to local stresses remains an outstanding challenge. Herein, a method to calibrate the intensity of the MP fluorescent activation (I) with local hydrostatic stresses (σ_h) is presented. Uniaxial tension is applied to a simple composite comprised of a rigid sphere (silica) embedded in a MP‐functionalized elastomeric matrix (spiropyran (SPN) functionalized polydimethylsiloxane (PDMS)). By monitoring the fluorescence intensity with a confocal microscope while a quasi‐static deformation is applied, in situ observations of MP activation as a function of applied uniaxial strain are obtained. To calculate the associated stress fields, a finite element analysis (FEA) with cohesive zone elements is employed. By comparingσ_h, calculated through FEA with theIof the PDMS/SPN system, a linear relationship betweenIandσ_his directly determined. The technique presented can be employed for many MP‐containing materials systems to calibrateItoσ_h. 

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5. Strain-tuned topological phase transition and unconventional Zeeman effect in ZrTe5 microcrystals

   https://doi.org/10.1038/s43246-022-00316-5  

   Gaikwad, Apurva; Sun, Song; Wang, Peipei; Zhang, Liyuan; Cano, Jennifer; Dai, Xi; Du, Xu (November 2022, Communications Materials)

   Abstract The geometric phase of an electronic wave function, also known as Berry phase, is the fundamental basis of the topological properties in solids. This phase can be tuned by modulating the band structure of a material, providing a way to drive a topological phase transition. However, despite significant efforts in designing and understanding topological materials, it remains still challenging to tune a given material across different topological phases while tracing the impact of the Berry phase on its quantum transport properties. Here, we report these two effects in a magnetotransport study of ZrTe₅. By tuning the band structure with uniaxial strain, we use quantum oscillations to directly map a weak-to-strong topological insulator phase transition through a gapless Dirac semimetal phase. Moreover, we demonstrate the impact of the strain-tunable spin-dependent Berry phase on the Zeeman effect through the amplitude of the quantum oscillations. We show that such a spin-dependent Berry phase, largely neglected in solid-state systems, is critical in modeling quantum oscillations in Dirac bands of topological materials. 

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