4 papers
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…
Revisiting the Charge Transport in Quantum Hall Systems
Tohru Koma
We reexamine the charge transport induced by a weak electric field in two-dimensional quantum Hall systems in a finite, periodic box at very low temperatures. The resulting linear…
The spectral gap for the ferromagnetic spin-J XXZ chain
Tohru Koma, Bruno Nachtergaele, Shannon Starr
We investigate the spectrum above the kink ground states of the spin J ferromagnetic XXZ chain. Our main theorem is that there is a non-vanishing gap above all ground states of thi…
Detecting Gapless Excitations above Ferromagnetic Domain Walls
Tohru Koma, Masanori Yamanaka
In a two or three dimensional ferromagnetic XXZ model, a low energy excitation mode above a magnetic domain wall is gapless, whereas all of the usual spin wave excitations moving a…