We investigate ground state and finite temperature properties of the
half-filled Hubbard model on a honeycomb lattice using quantum monte carlo and
series expansion techniques. Unlike the square lattice, for which magnetic
order exists at T=0 for any non-zero U, the honeycomb lattice is known to
have a semi-metal phase at small U and an antiferromagnetic one at large U.
We investigate the phase transition at T=0 by studying the magnetic
structureandcompressibilityusingquantummontecarlosimulationsandbycalculatingthesublatticemagnetization,uniformsusceptibility,spinβwaveandsingleholeorderedphase.OurresultsareconsistentwithasinglecontinuoustransitionatU_c/tintherange4β5.Finitetemperaturesignaturesofthisphasetransitionareseeninthebehaviorofthespecificheat,C(T),whichchangesfromatwoβpeakedstructureforU>U_ctoaoneβpeakedstructureforU <
U_c.Furthermore,theUdependenceofthelowtemperaturecoefficientofC(T)exhibitsananomalyatU \approx U_c$.Comment: 11 pages, 19 figure