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Tomohiro Soejima

Bio: Tomohiro Soejima is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Physics & Superlattice. The author has an hindex of 6, co-authored 14 publications receiving 226 citations. Previous affiliations of Tomohiro Soejima include Florida State University College of Arts and Sciences & Massachusetts Institute of Technology.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the ground state of twisted bilayer graphene (tBLG) has been determined using matrix product operator (MPO) compression with mixed-$x\phantom{\rule{0}{0ex}}k$ space density matrix renormalization group (DMRG) with matrix product operators compression.
Abstract: Despite considerable interest, it has been difficult to conclusively determine the ground state of twisted bilayer graphene (tBLG), due to the long-range nature of the Coulomb interaction and the fragile topology of the tBLG flat bands. This paper puts forward a method for studying tBLG more efficiently: mixed-$x\phantom{\rule{0}{0ex}}k$ space density-matrix renormalization group (DMRG) with matrix product operator (MPO) compression. The method enables the authors to calculate accurately the ground state of single-valley single-spin tBLG, and it puts DMRG with more degrees of freedom, such as valley, within reach.

91 citations

Journal ArticleDOI
TL;DR: This approach establishes a method for understanding critical aspects of cation exchange in different MOFs and other materials by studying the effect of various solvents on the insertion of Ni(2+) into MOF-5 and Co( 2+) into MFU-4l.
Abstract: We investigated which factors govern the critical steps of cation exchange in metal-organic frameworks by studying the effect of various solvents on the insertion of Ni(2+) into MOF-5 and Co(2+) into MFU-4l. After plotting the extent of cation insertion versus different solvent parameters, trends emerge that offer insight into the exchange processes for both systems. This approach establishes a method for understanding critical aspects of cation exchange in different MOFs and other materials.

69 citations

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional metal-organic framework (MOF) using phenalenyl-based ligands was designed from first principles to exhibit a half-filled flat band of the kagome lattice.
Abstract: We design from first principles a type of two-dimensional metal-organic framework (MOF) using phenalenyl-based ligands to exhibit a half-filled flat band of the kagome lattice, which is one of a family of lattices that show Lieb-Mielke-Tasaki's flat-band ferromagnetism. Among various MOFs, we find that trans-Au-THTAP (THTAP=trihydroxytriaminophenalenyl) has such an ideal band structure, where the Fermi energy is adjusted right at the flat band due to unpaired electrons of radical phenalenyl. The spin-orbit coupling opens a band gap giving a nonzero Chern number to the nearly flat band, as confirmed by the presence of the edge states in first-principles calculations and by fitting to the tight-binding model. This is a novel and realistic example of a system in which a nearly flat band is both ferromagnetic and topologically nontrivial.

68 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of uniaxial heterostrain on the interacting phase diagram of magic-angle twisted bilayer graphene was investigated, and it was shown that small strain values (e∼0.1%-0.2%) drive a zero-temperature phase transition between the symmetry-broken "Kramer intervalley-coherent" insulator and a nematic semimetal.
Abstract: We investigate the effect of uniaxial heterostrain on the interacting phase diagram of magic-angle twisted bilayer graphene. Using both self-consistent Hartree-Fock and density-matrix renormalization group calculations, we find that small strain values (e∼0.1%-0.2%) drive a zero-temperature phase transition between the symmetry-broken "Kramers intervalley-coherent" insulator and a nematic semimetal. The critical strain lies within the range of experimentally observed strain values, and we therefore predict that strain is at least partly responsible for the sample-dependent experimental observations.

58 citations

Journal ArticleDOI
TL;DR: This work introduces two related non-negative measures of tripartite entanglement g and h and proves structure theorems which show that states with nonzero g or h have nontrivial tripartites entangled with each other.
Abstract: Motivated by conjectures in holography relating the entanglement of purification and reflected entropy to the entanglement wedge cross section, we introduce two related non-negative measures of tripartite entanglement g and h. We prove structure theorems which show that states with nonzero g or h have nontrivial tripartite entanglement. We then establish that in one dimension these tripartite entanglement measures are universal quantities that depend only on the emergent low-energy theory. For a gapped system, we argue that either g≠0 and h=0 or g=h=0, depending on whether the ground state has long-range order. For a critical system, we develop a numerical algorithm for computing g and h from a lattice model. We compute g and h for various CFTs and show that h depends only on the central charge whereas g depends on the whole operator content.

28 citations


Cited by
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01 May 2005

2,648 citations

Journal ArticleDOI
TL;DR: This Review discusses the efforts undertaken so far to achieve efficient charge transport in MOFs and focuses on four common strategies that have been harnessed toward high conductivities.
Abstract: Metal–organic frameworks (MOFs) are intrinsically porous extended solids formed by coordination bonding between organic ligands and metal ions or clusters. High electrical conductivity is rare in M...

751 citations

Journal ArticleDOI
TL;DR: This work addresses which SBUs undergo exchange, why certain ions replace others, how the framework influences the process, the role of the solvent, and current applications, and provides a conceptual framework for approaching this task.
Abstract: Cation exchange is an emerging synthetic route for modifying the secondary building units (SBUs) of metal–organic frameworks (MOFs). This technique has been used extensively to enhance the properties of nanocrystals and molecules, but the extent of its applications for MOFs is still expanding. To harness cation exchange as a rational tool, we need to elucidate its governing factors. Not nearly enough experimental observations exist for drawing these conclusions, so we provide a conceptual framework for approaching this task. We address which SBUs undergo exchange, why certain ions replace others, how the framework influences the process, the role of the solvent, and current applications. Using these guidelines, certain trends emerge from the available data and missing experiments become obvious. If future studies follow this framework, then a more comprehensive body of observations will furnish a deeper understanding of cation exchange and inspire future applications.

398 citations

Journal ArticleDOI
TL;DR: An overview of the extensive strategies which have been developed to improve the functionality of Zifs is provided, including linker modifications, functional hybridization of ZIFs via the encapsulation of guest species, and hybridization with polymeric matrices to form mixed matrix membranes for industrial gas and liquid separations.
Abstract: Zeolitic imidazolate frameworks (ZIFs), a subclass of metal-organic frameworks (MOFs) built with tetrahedral metal ions and imidazolates, offer permanent porosity and high thermal and chemical stabilities. While ZIFs possess some attractive physical and chemical properties, it remains important to enhance their functionality for practical application. Here, an overview of the extensive strategies which have been developed to improve the functionality of ZIFs is provided, including linker modifications, functional hybridization of ZIFs via the encapsulation of guest species (such as metal and metal oxide nanoparticles and biomolecules) into ZIFs, and hybridization with polymeric matrices to form mixed matrix membranes for industrial gas and liquid separations. Furthermore, the developed strategies for achieving size and shape control of ZIF nanocrystals are considered, which are important for optimizing the textural characteristics as well as the functional performance of ZIFs and their derived materials/hybrids. Moreover, the recent trends of using ZIFs as templates for the derivation of nanoporous hybrid materials, including carbon/metal, carbon/oxide, carbon/sulfide, and carbon/phosphide hybrids, are discussed. Finally, some perspectives on the potential future research directions and applications for ZIFs and ZIF-derived materials are offered.

339 citations

01 May 2014
TL;DR: In this article, the authors provide a conceptual framework for approaching this task, addressing which SBUs undergo exchange, why certain ions replace others, how the framework influences the process, the role of the solvent, and current applications.
Abstract: Cation exchange is an emerging synthetic route for modifying the secondary building units (SBUs) of metal–organic frameworks (MOFs). This technique has been used extensively to enhance the properties of nanocrystals and molecules, but the extent of its applications for MOFs is still expanding. To harness cation exchange as a rational tool, we need to elucidate its governing factors. Not nearly enough experimental observations exist for drawing these conclusions, so we provide a conceptual framework for approaching this task. We address which SBUs undergo exchange, why certain ions replace others, how the framework influences the process, the role of the solvent, and current applications. Using these guidelines, certain trends emerge from the available data and missing experiments become obvious. If future studies follow this framework, then a more comprehensive body of observations will furnish a deeper understanding of cation exchange and inspire future applications.

301 citations