Persistent current distributions along a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>p</mml:mi><mml:mo>−</mml:mo><mml:mi>n</mml:mi></mml:math> junction in graphene in a magnetic field

A $p\ensuremath{-}n$ junction, induced in graphene by gating, works to contrast the edge states of electrons and holes on each side of it. In a magnetic field those edge states carry two species of persistent current, which are intimately tied to the edge-mode spectra. We study how those persistent currents change along each side of the junction as the Fermi level is varied, with special emphasis on the electron-hole conjugation property of the Dirac electrons. A close look is made into the electromagnetic response of the valence band filled with negative-energy electrons, or the Dirac sea, which as a whole turns out to be electrically inactive while showing intrinsic orbital diamagnetism. Recently, in experiment, it became possible to observe local currents in planar samples by use of a nanoscale magnetometer. The $p\ensuremath{-}n$ junctions in graphene and related atomic layers, via detection of associated microscopic currents, will be a useful platform for exploring many-body quantum phenomena.