Masaki Oshikawa

Bose-Einstein condensation of dilute magnons in TlCuCl3.

The recent observation [A. Oosawa et al., J. Phys. Condens. Matter 11, 265 (1999)] of the field-induced Neel ordering in the spin-gap magnetic compound TlCuCl3 is interpreted as a Bose-Einstein condensation of magnons. A Hartree-Fock-type calculation based on this picture is shown to describe the temperature dependence of the magnetization well.

FIELD-INDUCED GAP IN S = 1/2 ANTIFERROMAGNETIC CHAINS

In a recent neutron-scattering experiment on the quasi-one-dimensional

Boundary conformal field theory approach to the critical two-dimensional Ising model with a defect line

S=1/2

Symmetry protection of topological phases in one-dimensional quantum spin systems

antiferromagnet Cu Benzoate, a gap was induced by an applied magnetic field. We argue that the primary mechanism of the gap formation is an effective staggered field due to both the alternating

FIELD-INDUCED GAP IN CU BENZOATE AND OTHER S=1/2 ANTIFERROMAGNETIC CHAINS

g

Topological Approach to Luttinger's Theorem and the Fermi Surface of a Kondo Lattice

-tensor and the Dzyaloshinskii-Moriya interaction. We explain the dependence of the gap on the applied field, as well as identify several peaks in the structure factor

Commensurability, excitation gap, and topology in quantum many-particle systems on a periodic lattice

S(q,\omega)

Characterization of a quasi-one-dimensional spin-1/2 magnet which is gapless and paramagnetic for g μ B H ≲ J and k B T ≪ J

.

Quasiparticle statistics and braiding from ground state entanglement

We study the critical two-dimensional Ising model with a defect line (altered bond strength along a line) in the continuum limit. By folding the system at the defect line, the problem is mapped to a special case of the critical Ashkin-Teller model, the continuum limit of which is the Z2 orbifold of the free boson, with a boundary. Possible boundary states on the Z2 orbifold theory are explored, and a special case is applied to the Ising defect problem. We find the complete spectrum of boundary operators, exact two-point correlation functions and the universal term in the free energy of the defect line for arbitrary strength of the defect. We also find a new universality class of defect lines. It is conjectured that we have found all the possible universality classes of defect lines in the Ising model. Relative stabilities among the defect universality classes are discussed.

Field-Induced Gap Formation in Yb4As3.

We discuss the characterization and stability of the Haldane phase in integer spin chains on the basis of simple, physical arguments. We find that an odd-S Haldane phase is a topologically nontrivial phase which is protected by any one of the following three global symmetries: (i) the dihedral group of π rotations about the x, y, and z axes, (ii) time-reversal symmetry Sx,y,z→−Sx,y,z, and (iii) link inversion symmetry (reflection about a bond center), consistent with previous results [ Phys. Rev. B 81 064439 (2010)]. On the other hand, an even-S Haldane phase is not topologically protected (i.e., it is indistinct from a trivial, site-factorizable phase). We show some numerical evidence that supports these claims, using concrete examples.