Tsutomu Momoi
Harvard University
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Featured researches published by Tsutomu Momoi.
Physical Review B | 2000
Tsutomu Momoi; Keisuke Totsuka
We study the magnetization process in two-dimensional S=1/2 spin systems, to discuss the appearance of a plateau structure. The following three cases are considered: (1) the Heisenberg antiferromagnet and multiple-spin exchange model on the triangular lattice, (2) Shastry-Sutherland type lattice, [which is a possible model for SrCu2(BO3)2,] (3) 1/5-depleted lattice (for CaV4O9). We find in these systems that magnetization plateaus can appear owing to a transition from superfluid to a Mott insulator of magnetic excitations. The plateau states have CDW order of the excitations. The magnetizations of the plateaus depend on components of the magnetic excitations, range of the repulsive interaction, and the geometry of the lattice.
Physical Review B | 2000
Tsutomu Momoi; Keisuke Totsuka
We study the Heisenberg antiferromagnet on the Shastry-Sutherland lattice under magnetic fields, to clarify the magnetic properties of SrCu_2(BO_3)_2. Treating magnetic excitations promoted by the field as Bose particles and using strong coupling expansion, we derive an effective Hamiltonian for the effective magnetic particles. Anisotropic repulsive interactions between effective particles induce `insulating states with a stripe SDW structure at magnetization m/m_{sat}=1/3 and a checkerboard structure at 1/2, and thereby form magnetization plateaus. Supersolid phases appear around insulating SDW phases by changing the magnetic field. Nature of these supersolid phases is discussed in detail. We also demonstrate how the geometry of the Shastry-Sutherland lattice affects dynamical properties of magnetic excitations significantly and makes a novel type of quintuplet (S=2) boundstates condense for very small magnetization.
Physical Review B | 2000
Tsutomu Momoi; Keisuke Totsuka
We study the Heisenberg antiferromagnet on the Shastry-Sutherland lattice under magnetic fields, to clarify the magnetic properties of SrCu_2(BO_3)_2. Treating magnetic excitations promoted by the field as Bose particles and using strong coupling expansion, we derive an effective Hamiltonian for the effective magnetic particles. Anisotropic repulsive interactions between effective particles induce `insulating states with a stripe SDW structure at magnetization m/m_{sat}=1/3 and a checkerboard structure at 1/2, and thereby form magnetization plateaus. Supersolid phases appear around insulating SDW phases by changing the magnetic field. Nature of these supersolid phases is discussed in detail. We also demonstrate how the geometry of the Shastry-Sutherland lattice affects dynamical properties of magnetic excitations significantly and makes a novel type of quintuplet (S=2) boundstates condense for very small magnetization.
Journal of the Physical Society of Japan | 2000
Kentaro Nagai; Tsutomu Momoi; Kenn Kubo
We studied magnetic properties of the double exchange (DE) model with S =1/2 localized spins at T =0, using exact diagonalization in the framework of the dynamical mean field theory. Obtained phase diagram contains ferromagnetic, antiferromagnetic and paramagnetic phases. Comparing the phase diagram with that of the DE model with classical localized spins, we found that the quantum fluctuations of localized spins partly destabilize the ferromagnetism and expand the paramagnetic phase region. We found that phase separations occur between the antiferromagnetic and paramagnetic phases as well as the paramagnetic and ferromagnetic ones.
Physical Review Letters | 2012
Tsutomu Momoi; Philippe Sindzingre; Kenn Kubo
We figure out that the ground state of a multiple-spin exchange model applicable to thin films of solid {3}He possesses an octahedral spin nematic order. In the presence of a magnetic field, it is deformed into an antiferroquadrupolar order in the perpendicular spin plane, in which lattice Z{3} rotational symmetry is also broken. Furthermore, this system shows a narrow magnetization plateau at half, m/m{sat}=1/2, which resembles recent magnetization measurements [H. Nema et al., Phys. Rev. Lett. 102, 075301 (2009)].
Physical Review B | 2016
Luis Filipe Oleiro Seabra; Philippe Sindzingre; Tsutomu Momoi; Nic Shannon
A large part of the interest in magnets with frustrated antiferromagnetic interactions comes from the many new phases found in applied magnetic field. In this Article, we explore some of the new phases which arise in a model with frustrated ferromagnetic interactions, the
Physical Review B | 2011
Ryuichi Shindou; Seiji Yunoki; Tsutomu Momoi
J_1-J_2-J_3
Physical Review B | 2011
Luis Filipe Oleiro Seabra; Tsutomu Momoi; Philippe Sindzingre; Nic Shannon
Heisenberg model on a square lattice. Using a combination of classical Monte-Carlo simulation and spin-wave theory, we uncover behaviour reminiscent of some widely-studied frustrated antiferromagnets, but with a number of new twists. We first demonstrate that, for a suitable choice of parameters, the phase diagram as a function of magnetic field and temperature is nearly identical to that of the Heisenberg antiferromagnet on a triangular lattice, including the celebrated 1/3-magnetisation plateau. We then examine how this phase diagram changes when the model is tuned to a point where the classical ground--state is highly degenerate. In this case, two new phases emerge; a classical, finite-temperature spin-liquid, characterised by a ring in the spin structure--factor
Bulletin of the American Physical Society | 2013
Hiroaki Ueda; Tsutomu Momoi
mathcal{S}({mathbf q})
Physical Review B | 2013
Ryuichi Shindou; Seiji Yunoki; Tsutomu Momoi
; and a vortex crystal, a multiple-Q state with finite magnetisation, which can be viewed as an ordered lattice of magnetic vortices. All of these new phases persist for a wide range of magnetic field. We discuss the relationship between these results and published studies of frustrated antiferromagnets, together with some of the materials where these new phases might be observed in experiment.