585 citations · 1.1k across the 46 of their papers we have counts for
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Superconductivity and Low Energy Excitations in an Attractive Hubbard Model
Yukimi Goto, Tohru Koma, Hironobu Yoshida
We study an attractive Hubbard model on bipartite lattices. In the grand canonical formalism,we prove the existence of superconducting long-range order in the ground state on Lieb…
Antiferromagnetic Long-Range Order in a Lattice Fermion Model
Yukimi Goto, Tohru Koma
We study a lattice fermion model with antiferromagnetic interactions on the three-dimensional cubic lattice. The hopping term of the Hamiltonian has a Weyl-type dispersion. We prov…
Nambu-Goldstone modes in a lattice Nambu-Jona-Lasinio model with multi flavor symmetries
Yukimi Goto, Tohru Koma
We study a lattice Nambu-Jona-Lasinio model with SU(2) and SU(3) flavor symmetries of staggered fermions in the Kogut-Susskind Hamiltonian formalism. This type of four-fermion inte…
A Concrete Example of Fractional Chern Insulator
Tohru Koma
We present a concrete example of fractional Chern insulator whose fermion Hamiltonian consists of hopping and Coulomb repulsive interaction terms. Both of them are of finite range…
Spontaneous mass generation and chiral symmetry breaking in a lattice Nambu-Jona-Lasinio model
Yukimi Goto, Tohru Koma
We study a lattice Nambu-Jona-Lasinio model with interacting staggered fermions in the Kogut-Susskind Hamiltonian formalism. The model has a discrete chiral symmetry but not the us…
Stability of Majorana Edge Zero Modes against Interactions
Tohru Koma
We study an interacting Majorana chain with an open boundary condition. In the case without interactions, the system shows a prototypical Majorana edge zero mode in the sector of t…
Flux Phase and Superconductivity for Lattice Fermions Coupled to Classical Gauge Fields
Tohru Koma
We study superconducting lattice fermions coupled to classical gauge fields. Namely, without the gauge fields, the lattice fermions show superconducting long-range order. In the pr…
Nambu-Goldstone Modes for Superconducting Lattice Fermions
Tohru Koma
We present a lattice model for superconducting fermions whose nearest-neighbour two-body interactions are a Bardeen-Cooper-Schrieffer-type pairing on the hypercubic lattice $\mathb…
Bose-Einstein Condensation for Lattice Bosons
Tohru Koma
We present a class of models of interacting lattice bosons which show complete Bose-Einstein condensation for the ground state.
Dispersion Relations of Nambu-Goldstone Modes
Tohru Koma
We study the energy-momentum relations of the Nambu-Goldstone modes in quantum antiferromagnetic Heisenberg models on a hypercubic lattice. This work is a sequel to the previous se…
Power-Law Decay Exponents of Nambu-Goldstone Transverse Correlations
Tohru Koma
We study a quantum antiferromagnetic Heisenberg model on a hypercubic lattice in three or higher dimensions . When a phase transition occurs with the continuous symmetry br…
Stability of the Spectral Gap for Lattice Fermions
Tohru Koma
It is widely believed that the spectral gap above the Fermi sea ground state of lattice free fermions is stable against generic weak interactions. Quite recently, Hastings presente…
Maximum Spontaneous Magnetization and Nambu-Goldstone Mode
Tohru Koma
We study quantum antiferromagnetic Heisenberg models on a hypercubic lattice. We prove the following three theorems without any assumption: (i) The spontaneous magnetization which…
Decay of Superconducting Correlations for Gauged Electrons in Dimensions
Yasuhiro Tada, Tohru Koma
We study lattice superconductors coupled to gauge fields, such as an attractive Hubbard model in electromagnetic fields, with a standard gauge fixing. We prove upper bounds for a t…
The Noncommutative Index Theorem and the Periodic Table for Disordered Topological Insulators and Superconductors
Hosho Katsura, Tohru Koma
We study a wide class of topological free-fermion systems on a hypercubic lattice in spatial dimensions . When the Fermi level lies in a spectral gap or a mobility gap, the…
Two No-Go Theorems on Superconductivity
Yasuhiro Tada, Tohru Koma
We study lattice superconductors such as attractive Hubbard models. As is well known, Bloch's theorem asserts absence of persistent current in ground states and equilibrium states…
Improving the Lieb-Robinson bound for long-range interactions
T. Matsuta, T. Koma, S. Nakamura
We improve the Lieb-Robinson bound for a wide class of quantum many-body systems with long-range interactions decaying by power law. As an application, we show that the group veloc…
The Index of Disordered Topological Insulators with Time Reversal Symmetry
Hosho Katsura, Tohru Koma
We study disordered topological insulators with time reversal symmetry. Relying on the noncommutative index theorem which relates the Chern number to the projection onto the Fermi…
Topological Current in Fractional Chern Insulators
Tohru Koma
We consider interacting fermions in a magnetic field on a two-dimensional lattice with the periodic boundary conditions. In order to measure the Hall current, we apply an electric…
The Spectral Shift Function and The Friedel Sum Rule
Mahito Kohmoto, Tohru Koma, Shu Nakamura
We study the relationship between the spectral shift function and the excess charge in potential scattering theory. Although these quantities are closely related to each other, the…
Algebraic Topology of Spin Glasses
Tohru Koma
We study topology of frustration in -dimensional Ising spin glasses with with nearest-neighbor interactions. We prove the following: For any given spin configuration, t…
Widths of the Hall Conductance Plateaus
Tohru Koma
We study the charge transport of the noninteracting electron gas in a two-dimensional quantum Hall system with Anderson-type impurities at zero temperature. We prove that there exi…
Friedel Sum Rule as a Trace Formula
Mahito Kohmoto, Tohru Koma
We examine the Friedel sum rule which states that the "excess charge" due to a single impurity potential in a metal is equal to a sum of phase shifts for scatterings of electrons b…
Spectral Gap and Exponential Decay of Correlations
Matthew B. Hastings, Tohru Koma
We study the relation between the spectral gap above the ground state and the decay of the correlations in the ground state in quantum spin and fermion systems with short-range int…