铁磁转变附近条纹和板片的形成
Formation of stripes and slabs near the ferromagnetic transition
摘要:
我们考虑d=2和d=3维的伊辛模型,其中最近邻的铁磁相互作用和长程反铁磁相互作用,后者在大的距离上随距离^(-p)衰减,p>2d.如果铁磁相互作用强度J大于临界值J_c,则基态是均匀的。当J小于J_c但接近J_c时,基态是周期性的条纹,条纹宽度为h=h(J),当J从下往上趋向J_c时,h趋向无穷大。(In d=3条纹表示板,而不是柱。)这里我们严格证明了,如果我们以均匀态的能量为零的方式归一化能量,那么当J从下往上趋向于J_c时,比值e_0(J)/e_S(J)趋向于1,其中e_S(J)是最佳周期条/板态的每格点能量,e_0(J)是系统的实际每格点基态能量。我们的证明给出了在小但有限的J_c-J处的差异e_0(J)-e_S(J)的明确界限,并且还表明在此参数范围内,基态在某种意义上是条纹状/板状的:即,如果观察一个随机选择的窗口,其大小为适当的l(与最佳条纹大小h(J)相比非常大),则以高概率找到条纹状/板状态。
英文摘要:
We consider Ising models in d=2 and d=3 dimensions with nearest neighbor ferromagnetic and long-range antiferromagnetic interactions, the latter decaying as (distance)^(-p), p>2d, at large distances. If the strength J of the ferromagnetic interaction is larger than a critical value J_c, then the ground state is homogeneous. It has been conjectured that when J is smaller than but close to J_c the ground state is periodic and striped, with stripes of constant width h=h(J), and h tends to infinity as J tends to J_c from below. (In d=3 stripes mean slabs, not columns.) Here we rigorously prove that, if we normalize the energy in such a way that the energy of the homogeneous state is zero, then the ratio e_0(J)/e_S(J) tends to 1 as J tends to J_c from below, with e_S(J) being the energy per site of the optimal periodic striped/slabbed state and e_0(J) the actual ground state energy per site of the system. Our proof comes with explicit bounds on the difference e_0(J)-e_S(J) at small but finite J_c-J, and also shows that in this parameter range the ground state is striped/slabbed in a certain sense: namely, if one looks at a randomly chosen window, of suitable size l (very large compared to the optimal stripe size h(J)), one finds a striped/slabbed state with high probability.
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