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1. Elucidations of Chain-Level Structure of Semicrystalline Polymer Freeze-Dried from a Dilute Solution by Solid-State NMR spectroscopy

   Hosseini, Leilasadat; Sun, Chenxuan; Miyoshi, Toshikazu (March 2025, APS)

   Chain entanglements play a crucial role in polymer crystallization, yet their effects on crystallization remain not fully understood. Freeze-drying is one way to potentially preserve disentangled states of long polymer chains. In fact, it is known that freeze-drying (FD) significantly accelerates the crystallization kinetics of semicrystalline polymers. However, the chain-level structure of the FD polymer chains without a long-range order (glass) has been a debatable matter. In this study, we investigate the effect of freeze-drying on single chain-level structures of 13CH3 enriched poly(L-lactic Acid) and 13CH enriched poly(D-lactic acid) racemate by using 1H-1H spin diffusion via 13C detection solid-state NMR spectroscopy. Spatial distributions of PLLA and PDLA glassy chains in the range of a few Å – 30 nm are evaluated via 1H-1H spin diffusion. This analysis provides core-shell morphology of single chains where the outer shell layers include both PDLA and PLLA mixture and the inner core possess a single component. 

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2. Rapid mixing of path integral Monte Carlo for 1D stoquastic Hamiltonians

   https://doi.org/10.22331/q-2021-02-11-395  

   Crosson, Elizabeth; Harrow, Aram W. (February 2021, Quantum)

   null (Ed.)

   Path integral quantum Monte Carlo (PIMC) is a method for estimating thermal equilibrium properties of stoquastic quantum spin systems by sampling from a classical Gibbs distribution using Markov chain Monte Carlo. The PIMC method has been widely used to study the physics of materials and for simulated quantum annealing, but these successful applications are rarely accompanied by formal proofs that the Markov chains underlying PIMC rapidly converge to the desired equilibrium distribution.In this work we analyze the mixing time of PIMC for 1D stoquastic Hamiltonians, including disordered transverse Ising models (TIM) with long-range algebraically decaying interactions as well as disordered XY spin chains with nearest-neighbor interactions. By bounding the convergence time to the equilibrium distribution we rigorously justify the use of PIMC to approximate partition functions and expectations of observables for these models at inverse temperatures that scale at most logarithmically with the number of qubits.The mixing time analysis is based on the canonical paths method applied to the single-site Metropolis Markov chain for the Gibbs distribution of 2D classical spin models with couplings related to the interactions in the quantum Hamiltonian. Since the system has strongly nonisotropic couplings that grow with system size, it does not fall into the known cases where 2D classical spin models are known to mix rapidly. 

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3. Spinning and corkscrewing of oceanic macroplankton revealed through in situ imaging

   https://doi.org/10.1126/sciadv.adm9511  

   Sutherland, Kelly R; Damian-Serrano, Alejandro; Du_Clos, Kevin T; Gemmell, Brad J; Colin, Sean P; Costello, John H (May 2024, Science Advances)

   Helical motion is prevalent in nature and has been shown to confer stability and efficiency in microorganisms. However, the mechanics of helical locomotion in larger organisms (>1 centimeter) remain unknown. In the open ocean, we observed the chain forming salp,Iasis cylindrica, swimming in helices. Three-dimensional imaging showed that helicity derives from torque production by zooids oriented at an oblique orientation relative to the chain axis. Colonies can spin both clockwise and counterclockwise and longer chains (>10 zooids) transition from spinning around a linear axis to a helical swimming path. Propulsive jets are non-interacting and directed at a small angle relative to the axis of motion, thus maximizing thrust while minimizing destructive interactions. Our integrated approach reveals the biomechanical advantages of distributed propulsion and macroscale helical movement. 

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4. Quasispins of vacancy defects in Ising chains with nearest- and next-to-nearest-neighbor interactions

   https://doi.org/10.1103/PhysRevB.108.174436  

   Sun, Shijun; Ramirez, Arthur P; Syzranov, Sergey (November 2023, Physical Review B)

   Motivated by frustrated magnets and quasi-one-dimensional magnetic materials, we study the magnetic properties of one-dimensional (1D) Ising chains with nearest-neighbor (NN) and weaker next-to-nearest-neighbor (NNN) interactions in the presence of vacancy defects. The effect of a vacancy on the magnetic susceptibility of a spin chain is twofold: it reduces the length of the chain by an effective “vacancy size” and may also act as a free spin, a “quasispin,” with a Curie-type 𝜒_{quasi}=⟨𝑆^2⟩/𝑇 contribution to the susceptibility. In chains with antiferromagnetic short-range order, the susceptibility of vacancy-free chains is exponentially suppressed at low temperatures, and quasispins dominate the effect of impurities on the chains' magnetic properties. For chains with antiferromagnetic NN interactions, the quasispin matches the value ⟨𝑆^2⟩=1 of the Ising spins in the chain for ferromagnetic NNN interactions and vanishes for antiferromagnetic NNN interactions. For chains with ferromagnetic short-range order, quasispin effects are insignificant due to exponentially large low-temperature susceptibilities, and the dominant effect of a vacancy is effectively changing the length of the chain. 

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5. Isolation of Diamond Spin Chains in a Layered Halide Perovskite Heterostructure

   https://doi.org/10.1021/jacs.5c08981  

   Caniglia, Caravaggio D; Li, Yuntian; Wen, Jiajia; Brueggemeyer, Magdalene T; Lee, Young S; Solomon, Edward I; Fisher, Ian R; Karunadasa, Hemamala I (August 2025, Journal of the American Chemical Society)

   The halide perovskite heterostructure (CuCl4)2(MTPA)4Cu3Cl6 (Cu_Cu; MTPA = 3-(methylthio)-propylammonium) forms from solution as single crystals consisting of alternating layers of 2D CuII–Cl perovskite and 1D CuII–Cl diamond–chain intergrowth. Using magnetometry, heat capacity, and electron paramagnetic resonance measurements, we interrogate the magnetic ordering of the 2D perovskite and 1D intergrowth layers at temperatures down to 0.055 K. As with other Cu‒Cl perovskites, the perovskite-layer spins order ferromagnetically at 10 K. Magnetization data of Cu_Cu feature a multi–component curve, consistent with magnetization of the perovskite layers and one of the three additional CuII sites in the intergrowth layer, suggesting antiferromagnetic coupling of the remaining two intergrowth-layer spins. A broad feature in AC susceptibility measurements at 6 K and an anomalous heat capacity feature at 0.3 K suggest that local ordering events occur at dramatically different energy scales with decreasing temperature. EPR spectra indicate that these local orderings occur within the 1D chains. Notably, no long–range magnetic ordering event in the intergrowth is evident down to 0.055 K, suggesting that the geometric constraints imposed by the perovskite framework and the steric bulk of the MTPA ligands physically separate and magnetically isolate the diamond chains. In contrast, well–studied diamond-spin-chain materials such as azurite show long-range magnetic order at low-temperatures due to interchain interactions. Thus, Cu_Cu provides an ideal platform for studying isolated, anisotropic spin chains. More generally, this study illustrates the capability of halide perovskite heterostructures to serve as vehicles for the scalable synthesis of complex magnetic materials. 

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