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1. Imprinting a Three-Dimensional Skyrmion in a Bose–Einstein Condensate Via a Raman Process

   https://doi.org/10.1007/s10909-022-02724-w  

   Chen, Zekai; Hu, S. X.; Bigelow, Nicholas P. (July 2022, Journal of Low Temperature Physics)

   We describe an experimental protocol for the creation of a three- dimensional topological defect, a skyrmion, in a pseudo-spin-1/2 Bose-Einstein condensate (BEC) confined in a spin-independent har- monic trap. We show that one can imprint the skyrmion on the BEC within a few tens of microseconds using a Raman process with the structured laser fields. We numerically solved the mean- field Gross-Pitaevskii equation to examine our imprinting scheme, and found that all parameters we use are experimentally feasible. 

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2. Conservation of imprinted expression across genotypes is correlated with consistency of imprinting across endosperm development in maize

   https://doi.org/10.1093/g3journal/jkaf028  

   Higgins, Kaitlin; Nyabashi, Vital; Anderson, Sarah; Birchler, ed., J. (February 2025, G3: Genes, Genomes, Genetics)

   Abstract Imprinted expression is an essential process for seed viability affecting hundreds of genes in Zea mays endosperm; however, most studies have examined just one time point for analysis. The focus on single time points can limit our ability to identify imprinted genes and our ability to draw conclusions for the role of imprinting in endosperm. In this study, we examine imprinted expression across 4 time points ranging from the transition to endoreduplication from mitotic division through the beginning of programmed cell death. Additionally, we assessed imprinting variation across 8 diverse maize lines, 6 of which have never before been assessed for imprinting. Through this analysis, we identify over 700 imprinted genes with varying consistency across time points including 255 genes imprinted at every time point and 105 genes displaying transient imprinting. We find a correlation between high consistency of imprinting across time and high conservation of parental bias across 8 diverse maize lines reciprocally crossed with B73. Additionally, we identify evidence of imprinting for 3 zein genes that are critical for nutrient accumulation in the endosperm, suggesting that imprinting may play a more important role in seed composition than previously thought. Taken together, this study provides a more holistic view of imprinting variation across time and across genotypes in maize and enables us to more thoroughly investigate the complex imprinting landscape. 

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3. Semi-Dirac Fermions in a Topological Metal

   https://doi.org/10.1103/PhysRevX.14.041057  

   Shao, Yinming; Moon, Seongphill; Rudenko, A N; Wang, Jie; Herzog-Arbeitman, Jonah; Ozerov, Mykhaylo; Graf, David; Sun, Zhiyuan; Queiroz, Raquel; Lee, Seng Huat; et al (December 2024, Physical Review X)

   Topological semimetals with massless Dirac and Weyl fermions represent the forefront of quantum materials research. In two dimensions, a peculiar class of fermions that are massless in one direction and massive in the perpendicular direction was predicted 16 years ago. These highly exotic quasiparticles—the semi-Dirac fermions—ignited intense theoretical and experimental interest but remain undetected. Using magneto-optical spectroscopy, we demonstrate the defining feature of semi-Dirac fermions— $B^{2/3}$scaling of Landau levels—in a prototypical nodal-line metal ZrSiS. In topological metals, including ZrSiS, nodal lines extend the band degeneracies from isolated points to lines, loops, or even chains in the momentum space. With calculations and theoretical modeling, we pinpoint the observed semi-Dirac spectrum to the crossing points of nodal lines in ZrSiS. Crossing nodal lines exhibit a continuum absorption spectrum but with singularities that scale as $B^{2/3}$at the crossing. Our work sheds light on the hidden quasiparticles emerging from the intricate topology of crossing nodal lines and highlights the potential to explore quantum geometry with linear optical responses. Published by the American Physical Society2024 

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4. Nodal band-off-diagonal superconductivity in twisted graphene superlattices

   https://doi.org/10.1038/s41467-023-42471-4  

   Christos, Maine; Sachdev, Subir; Scheurer, Mathias S. (December 2023, Nature Communications)

   Abstract The superconducting state and mechanism are among the least understood phenomena in twisted graphene systems. Recent tunneling experiments indicate a transition between nodal and gapped pairing with electron filling, which is not naturally understood within current theory. We demonstrate that the coexistence of superconductivity and flavor polarization leads to pairing channels that are guaranteed by symmetry to be entirely band-off-diagonal, with a variety of consequences: most notably, the pairing invariant under all symmetries can have Bogoliubov Fermi surfaces in the superconducting state with protected nodal lines, or may be fully gapped, depending on parameters, and the band-off-diagonal chiralp-wave state exhibits transitions between gapped and nodal regions upon varying the doping. We demonstrate that band-off-diagonal pairing can be the leading state when only phonons are considered, and is also uniquely favored by fluctuations of a time-reversal-symmetric intervalley coherent order motivated by recent experiments. Consequently, band-off-diagonal superconductivity allows for the reconciliation of several key experimental observations in graphene moiré systems. 

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5. Nonsymmorphic symmetry-protected band crossings in a square-net metal PtPb4

   https://doi.org/10.1038/s41535-022-00441-x  

   Wu, Han; Hallas, Alannah M.; Cai, Xiaochan; Huang, Jianwei; Oh, Ji Seop; Loganathan, Vaideesh; Weiland, Ashley; McCandless, Gregory T.; Chan, Julia Y.; Mo, Sung-Kwan; et al (December 2022, npj Quantum Materials)

   Abstract Topological semimetals with symmetry-protected band crossings have emerged as a rich landscape to explore intriguing electronic phenomena. Nonsymmorphic symmetries in particular have been shown to play an important role in protecting the crossings along a line (rather than a point) in momentum space. Here we report experimental and theoretical evidence for Dirac nodal line crossings along the Brillouin zone boundaries in PtPb 4 , arising from the nonsymmorphic symmetry of its crystal structure. Interestingly, while the nodal lines would remain gapless in the absence of spin–orbit coupling (SOC), the SOC, in this case, plays a detrimental role to topology by lifting the band degeneracy everywhere except at a set of isolated points. Nevertheless, the nodal line is observed to have a bandwidth much smaller than that found in density functional theory (DFT). Our findings reveal PtPb 4 to be a material system with narrow crossings approximately protected by nonsymmorphic crystalline symmetries. 

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