Charge-density waves and surface Mott insulators for adlayer structures on semiconductors: Extended Hubbard modeling
Charge-density waves and surface Mott insulators for adlayer structures on semiconductors: Extended Hubbard modeling
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半导体吸附层结构的电荷密度波和表面莫特绝缘体：扩展哈伯德模型
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发表时间：
1998
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通讯作者：
Ictp
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作者：
G. Santoro;S. Sorella;F. Becca;S. Scandolo;E. Sissa;Infm;Ictp
基于最近在Pb/Ge（111）和Sn/Ge（111）sqrt{3}-吸附层结构中发现的相称表面电荷密度波（CDW）的实验证据，以及在K/Si（111）：B和SiC（0001）上发现的绝缘态，我们研究了电子-电子相互作用以及电子-声子耦合对源自表面外悬挂键轨道的窄表面态带的作用.我们用扩展的二维Hubbard模型在三角形晶格上半填充时模拟了sqrt{3}悬挂键晶格。我们包括一个现场哈伯德排斥U和最近邻库仑相互作用V，加上长程库仑尾。电子-声子相互作用在形变势近似下处理。我们已经探索了这个模型的相图，包括相称的3x 3相位的可能性，主要使用Hartree-Fock近似。对于大于带宽的U，我们发现一个非共线的反铁磁SDW绝缘体，可能对应于SiC和K/Si表面上的情况。对于U相当或更小，丰富的相图出现，有几个阶段涉及电荷和自旋密度波（SDW）的组合，有或没有净磁化。我们发现，绝缘，或部分金属3x 3 CDW相可以通过两种不同的物理机制稳定。一个是位间排斥V，其与电子-声子耦合一起可以降低电荷调制的能量。另一个是一种新的磁感应费米面嵌套，稳定的净细胞磁化1/3，加上共线SDW，加上相关的弱CDW。比较现有的实验证据，并与第一原理计算。
Motivated by the recent experimental evidence of commensurate surface charge density waves (CDW) in Pb/Ge(111) and Sn/Ge(111) sqrt{3}-adlayer structures, as well as by the insulating states found on K/Si(111):B and SiC(0001), we have investigated the role of electron-electron interactions, and also of electron-phonon coupling, on the narrow surface state band originating from the outer dangling bond orbitals of the surface. We model the sqrt{3} dangling bond lattice by an extended two-dimensional Hubbard model at half-filling on a triangular lattice. We include an on-site Hubbard repulsion U and a nearest-neighbor Coulomb interaction V, plus a long-ranged Coulomb tail. The electron-phonon interaction is treated in the deformation potential approximation. We have explored the phase diagram of this model including the possibility of commensurate 3x3 phases, using mainly the Hartree-Fock approximation. For U larger than the bandwidth we find a non-collinear antiferromagnetic SDW insulator, possibly corresponding to the situation on the SiC and K/Si surfaces. For U comparable or smaller, a rich phase diagram arises, with several phases involving combinations of charge and spin-density-waves (SDW), with or without a net magnetization. We find that insulating, or partly metallic 3x3 CDW phases can be stabilized by two different physical mechanisms. One is the inter-site repulsion V, that together with electron-phonon coupling can lower the energy of a charge modulation. The other is a novel magnetically-induced Fermi surface nesting, stabilizing a net cell magnetization of 1/3, plus a collinear SDW, plus an associated weak CDW. Comparison with available experimental evidence, and also with first-principle calculations is made.