Photoemission spectra of a two-dimensional S=1/2 quantum antiferromagnet in magnetic fields: a theoretical study

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We calculate the angular resolved photoemission spectra (ARPES) of a spin-1/2 Heisenberg antiferromagnet as a function of magnetic fields using both the exact diagonalization method and self-consistent Born approximation. Below the saturation field BC, strong scattering between spin waves and a hole, created by photoemission of an electron, significantly narrows the quasiparticle band that is characterized by the lowering of the quasiparticle energy at (π,π) with increasing field. Accordingly, in ARPES the quasiparticle peak gets shaper near (π,π) and broader elsewhere. Furthermore, we observe that an anomalous extended van Hove region (EVHR) around (π,π) appears in a half saturation field, while EVHRs around (π,0) and (0,π) in zero field gradually disappear with increasing field.