Finite Temperature Effects in One-dimensional Mott-Hubbard Insulator: Angle-Resolved Photoemission Study of Na$_{0.96}$V$_{2}$O$_{5}$

We have made an angle-resolved photoemission study of a one-dimensional (1D) Mott-Hubbard insulator Na$_{0.96}$V$_{2}$O$_{5}$ and found that the spectra of the V $3d$ lower Hubbard band are strongly dependent on the temperature. We have calculated the one-particle spectral function of the one-dimensional t-J model at finite temperatures by exact diagonalization and compared them with the experimental results. Good overall agreement is obtained between experiment and theory. The strong finite temperature effects are discussed in terms of the existence of the ``Fermi surface'' of the spinon band.