Marzieh Baradaran, Pavel Exner, Jiri Lipovsky
Magnetic square lattice with vertex coupling of a preferred orientation
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ABSTRACT.  We analyze a square lattice graph in a magnetic field assuming that the vertex coupling is of a particular type violating the time reversal invariance. Calculating the spectrum numerically for rational values of the flux per plaquette we show how the two effects compete; at the high energies it is the magnetic field which dominates restoring asymptotically the familiar Hofstadter's butterfly pattern.