Doping effect on spin-Peierls instability.
Doping effect on spin-Peierls instability.
复制标题
掺杂对自旋 Peierls 不稳定性的影响。
DOI：
10.1103/physrevlett.72.1276
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发表时间：
1994
影响因子：
8.6
通讯作者：
Yu.
中科院分区：
文献类型：
--
作者：
Lu;Su;Yu.
我们使用单模平均场理论研究掺杂对自旋 Peierls (SP) 系统的影响。杂质自旋影响单线态价键场并使磁激发重新正常化。 SP 转变温度和磁激发能隙分别减小 ~ n« 和 ~ nf 因子，其中 rii 作为杂质密度。在一定的 rij 值下，出现无间隙 SP 相，并且杂质之间的相互作用变得类似 RKKY。最近观察到的 SP 转变温度在掺杂和自旋玻璃相出现时的降低可以使用所提出的理论进行解释。 MIRAMARE TRIESTE 1994 年 1 月 '现地址：国际高级研究学院 (SISSA), Via Beirut No.24, 34013 Trieste, Italy。迄今为止，仅在少数具有反铁磁（AF）相互作用的准一维（ID）有机化合物中观察到了理论上预测的具有交替键长的自旋佩尔斯（SP）态[1]。最近，在无机化合物 CuGeO: 中发现了它[2]。此外，在 Zn 掺杂后观察到 SP 转变温度 Tr 急剧降低，并且在掺杂范围 0.02 < n、< 0.08 中出现自旋玻璃 (SG) 色调 [3]。在这封信中，我们提出了掺杂系统中的 SP 跃迁理论，解释了这些发现，并对间隙 SP 态做出了进一步的预测，以通过实验进行检查。 SP跃迁是由（1-D）自旋1/2链和三维（3-D）晶格之间的相互作用驱动的，这使得平均场（MF）方法由于其抑制涨落而可用。在 SP 跃迁以下，均匀的 AF 链变形为具有单重基态和磁隙的交替 AF 链 [4]。迄今为止，有两种成功的SP转变理论，即Pytte [S]和Cross and Fisher [6]的理论。在这些理论中，通过 Jordan-Wigner 变换 (JWT) 的费米子表示用于描述自旋 1/2 链，并且在随机相位近似中考虑费米子-声子相互作用。然而，由于 JWT 的非局部特征，在这种方法中很难研究杂质掺杂对 SP 系统的影响。 P.W. Anderson [7] 提出了共振价键模型来描述二维自旋 1/2 AF 系统。后来，Arovas和Girvin [8]提出了unimodulr作为杂质密度，而能隙的减小与nf成正比，并且在n的某个值时崩溃，但系统仍处于SP相，即自旋晶格二聚仍然存在。因此，我们预测 gnpiess SP 状态的存在，并通过直接实验来检查。这与掺杂顺磁杂质的超导体非常相似，顺磁杂质会减小能隙并最终产生无间隙超导性[13]。描述杂质掺杂 SP 系统的哈密顿量为 [12,14] H = #„ #1 = Zi H"" = E An, = ff(a + 1)5, • S,+, + AnI • Si, 5TM J(a,l)Sn, Ei 2A-u, (1)
We study the effects of doping on spin-Peierls (SP) systems using the unimodular mean-field theory. The impurity spins affect the singlet valence bond field and renormalize the magnetic excitations. The SP transition temperature and the energy gap of magnetic excitations are reduced by factors ~ n« and ~ nf, respectively, with rii as the impurity density. At certain value of rij, a gapless SP phase occurs, and the interaction between impurities becomes RKKY-like. The recently observed reduction of SP transition temperature upon doping and occurrence of a spin glass phase is interpreted using the proposed theory. MIRAMARE TRIESTE January 1994 'Present address: International School for Advanced Studies (SISSA), Via Beirut No.24, 34013 Trieste, Italy. The theoretically predicted spin-Peierls (SP) state with alternating bond length has been observed, so far only in a few quasi-one-dimensional (ID) organic compounds with antiferromagnetic (AF) interactions [1]. Very recently, it was found in an inorganic compound CuGeO:, [2]. Moreover, a drastic reduction of SP transition temperature Tr was observed upon Zn-doping and a spin glass (SG) phue appeared in the doping range 0.02 < n, < 0.08 [3]. In this Letter we propose a theory of SP transition in doped systems explaining these findings and making further predictions on a gapleat SP state to be checked by experiments. The SP transition is driven by the interaction between the (1-D) spin-1/2 chains and the three-dimensional (3-D) lattice,which makes a mean-field (MF) approach available due to its suppression of fluctuations. Below the SP transition an uniform AF chain is deformed into an alternating AF chain with a singlet ground state and a magnetic gap [4]. Up to now there are two successful theories of SP transition, i.e. that of Pytte [S] and of Cross and Fisher [6]. In these theories, a fermion representation via the Jordan-Wigner transformation (JWT) is used to describe the spin-1/2 chain, and the fermion-phonon interactions are taken into account in the random phase approximation. However, it is difficult to investigate effects of impurity doping upon the SP system) within this approach due to nonlocal features of JWT. P.W. Anderson [7] has proposed the Resonant-Valence-Bond model to describe twodimensional spin-1/2 AF systems. Later, Arovas and Girvin [8] put forward an unimodulr as the impurity density, whereas the decrease of the energy gap is proportional to nf and it collapses at some value of n,, but the system is still in the SP phase, i.e. the spin-lattice dimeriz&tion remains. Thus we predict the existence of a gnpiess SP state to be checked by direct experiments. This is rather similar to superconductors doped with paramagnetic impurities which reduce the energy gap and eventually give rise to gapless superconductivity [13]. The Hamiltonian describing an impurity-doped SP system is [12,14] H = #„ #1 = Zi H"" = E An, = ff(a + 1)5, • S,+, + AnI • Si, 5TM J(a,l)Sn, Ei 2A-u, (1)