掺杂维度和浓度调控的δ掺杂的La:SrTiO<sub>3</sub>超晶格结构金属-绝缘体转变

李云; 鲁文建

doi:10.7498/aps.70.20210830

摘要

利用密度泛函理论计算, 本文系统研究了δ掺杂的La:SrTiO₃超晶格结构的电子性质随掺杂维度和掺杂浓度改变而变化的规律性. 该结构通过在SrTiO₃等间距的单元层中掺入一定浓度的La来实现. 在25% La掺杂浓度下, 随着相邻掺杂层间距从1个单层增加到5个单层, 掺杂维度从三维过渡到二维, 超晶格从金属性变到绝缘体性, 并在带隙中产生局域态, 且该局域态呈现出电荷序、自旋序和轨道序. 这种金属-绝缘体转变是由于二维电子体系呈现出更强的关联性造成的. 而随着二维掺杂浓度提高到50%, 关联性降低, 体系变成金属性.

关键词:

Abstract

Electronic properties in δ-doped La:SrTiO₃ superlattices varying with the doping dimensionality and concentration are systematically studied through using first-principles calculation. The superlattices consist of periodically repeated La-doped single SrTiO₃ layers in SrTiO₃ film, and the doping dimensionality can be tuned by varying the space of the neighboring doped layers. At 25% doping concentration, the spacing between SrTiO₃ layers increases from 1 unit-cell layer to 5 unit-cell layers, i.e. the doping dimensionality changes three dimensions to two dimensions, the superlattice charater changes from metallic character into insulating character, and the charge sequence, spin sequence and orbital sequence are present in a localized state. This metal-insulator transition is ascribed to the stronger correlation effect in the two-dimensional electron system. With the two-dimensional doping concentration increasing to 50%, the correlation effect becomes weak and the system becomes metallic.

Keywords:

作者及机构信息

李云¹,
鲁文建²

1.
韩山师范学院物理与电子工程学院, 潮州　521041

2.
中国科学院合肥物质科学研究院固体物理研究所, 合肥　230031

通信作者: 李云, liyunphy@foxmail.com

基金项目: 教育部留学回国人员科研启动基金(批准号: [2015]-1098)资助的课题.

Authors and contacts

Li Yun¹,
Lu Wen-Jian²

1.
School of Physics and Electronic Engineering, Hanshan Normal University, Chaozhou 521041, China

2.
Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China

Corresponding author: Li Yun, liyunphy@foxmail.com

Funds: Project supported by the Scientific Research Staring Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China (Grant No. [2015]-1098).

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参考文献

[1]	Imada M, Fujimori A, Tokura Y 1998 Rev. Mod. Phys. 70 1039 Google Scholar
[2]	Dagotto E 2005 Science 309 257 Google Scholar
[3]	Tokura Y, Nagaosa N 2000 Science 288 462 Google Scholar
[4]	Ahn C H, Triscone J M, Mannhart J 2003 Nature 424 1015 Google Scholar
[5]	Mannhart J, Schlom D G 2010 Science 327 1607 Google Scholar
[6]	Camjayi A, Haule K, Dobrosavljević V, Kotliar G 2008 Nat. Phys. 4 932 Google Scholar
[7]	Boris A V, Matiks Y, Benckiser E, et al. 2011 Science 332 937 Google Scholar
[8]	Ohtomo A, Muller D A, Grazul J L, et al. 2002 Nature 419 378 Google Scholar
[9]	Ohtomo A, Hwang H Y 2004 Nature 427 423 Google Scholar
[10]	Reyren N, Thiel S, Caviglia A D, et al. 2007 Science 317 1196 Google Scholar
[11]	Caviglia A D, Gariglio S, Reyren N, et al. 2008 Nature 456 624 Google Scholar
[12]	Li L, Richter C, Mannhart J, Ashoori R C 2011 Nat. Phys. 7 762 Google Scholar
[13]	Brinkman A, Huijben M, Van Zalk M, et al. 2007 Nat. Mater. 6 493 Google Scholar
[14]	Ariando, Wang X, Baskaran G, et al. 2011 Nat. Commun. 2 188 Google Scholar
[15]	Wang Z, Okude M, Saito M, et al. 2010 Nat. Commum. 1 106 Google Scholar
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[20]	Song Q, Yu T L, Lou X, et al. 2019 Nat. Commum. 10 758 Google Scholar
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[29]	Bruus H, Flensberg K 2004 Many-body Quantum Theory in Condensed Matter Physics - An Introduction (New York: Oxford University Press) p41

施引文献

图 1 (a) 超晶格结构面内4 × 4周期俯视图; (b) [SLTO]1|[STO]1侧视图; (c) [SLTO]1|[STO]5侧视图. 绿色球代表Sr原子, 蓝色代表La原子, 红色代表O原子, Ti原子在八面体中心

Fig. 1. (a) Top view of the superlattices with in-plane 4 × 4 unit cells; (b) side view of [SLTO]1|[STO]1; (c) side view of [SLTO]1|[STO]5. Green balls represent Sr atom, blue balls La atom, red balls O atom, Ti atoms are at the centre of the octahedrons.

下载: 全尺寸图片幻灯片

图 2 分自旋总态密度图和能带图 (a1), (a2) U = 2 eV, [SLTO]1|[STO]1; (b1), (b2) U = 2 eV, [SLTO]1|[STO]5; (c1), (c2) U = 3.7 eV, [SLTO]1|[STO]1; (d1), (d2) U = 3.7 eV, [SLTO]1|[STO]5, 红色箭头所指为带隙内局域态. 图中红线为费米能级, 价带顶部设为能量零点. 态密度图中水平线上部为上自旋态密度, 下部为下自旋态密度

Fig. 2. Spin-polarized total densities of states and band structures: (a1), (a2) U = 2 eV, [SLTO]1|[STO]1; (b1), (b2) U = 2 eV, [SLTO]1|[STO]5; (c1), (c2) U = 3.7 eV, [SLTO]1|[STO]1; (d1), (d2) U = 3.7 eV, [SLTO]1|[STO]5, the in-gap localized states are pointed out by the red arrow. The red lines are Fermi level, the top of valence band is set to be zero.

下载: 全尺寸图片幻灯片

图 3 (a) [SLTO]1|[STO]5能带结构图, 其中带隙内局域态为Ti dxz和dyz轨道态. 水平红色虚线为费米能级; (b) [SLTO]1|[STO]5带隙内局域态电荷空间分布, 局域态为Ti dxz和dyz轨道态, 上下箭头代表自旋方向; (c)掺杂层局部结构和Ti³⁺O₆八面体键长, 沿着y和z方向Ti³⁺—O键较长

Fig. 3. (a) Band structure of [SLTO]1|[STO]5, in which the in-gap states mainly consist of Ti dxz and dyz orbitals; (b) charge distribution of the in-gap states, the charge is mainly localized at Ti dxz and dyz orbitals. The arrows represent spin directions; (c) local structure of the doped layer and bond lengths of Ti³⁺—O bonds of the Ti³⁺O₆ octehedron.

下载: 全尺寸图片幻灯片

图 4 掺杂离子层的电势V和掺杂电荷ρ分布示意图 (a) [SLTO]1|[STO]1, 虚线代表单个掺杂层阳离子产生的吸引势, 实线代表相邻掺杂层阳离子吸引势叠加后总的吸引; (b) [SLTO]1|[STO]5

Fig. 4. Diagrams of electric potential V and charge distribution: (a) [SLTO]1|[STO]1, dashed lines present the potential produced by a single impurity layer, the solid lines present the total potential of all impurity layers; (b) [SLTO]1|[STO]5.

下载: 全尺寸图片幻灯片

图 5 50% La掺杂的[SLTO]1|[STO]5总态密度图(a)和能带结构图(b), 红线为费米能级

Fig. 5. Total density of states (a) and band structure (b) of [SLTO]1|[STO]5 with 50% La doping in the doping layer.

下载: 全尺寸图片幻灯片

[1]	Imada M, Fujimori A, Tokura Y 1998 Rev. Mod. Phys. 70 1039 Google Scholar
[2]	Dagotto E 2005 Science 309 257 Google Scholar
[3]	Tokura Y, Nagaosa N 2000 Science 288 462 Google Scholar
[4]	Ahn C H, Triscone J M, Mannhart J 2003 Nature 424 1015 Google Scholar
[5]	Mannhart J, Schlom D G 2010 Science 327 1607 Google Scholar
[6]	Camjayi A, Haule K, Dobrosavljević V, Kotliar G 2008 Nat. Phys. 4 932 Google Scholar
[7]	Boris A V, Matiks Y, Benckiser E, et al. 2011 Science 332 937 Google Scholar
[8]	Ohtomo A, Muller D A, Grazul J L, et al. 2002 Nature 419 378 Google Scholar
[9]	Ohtomo A, Hwang H Y 2004 Nature 427 423 Google Scholar
[10]	Reyren N, Thiel S, Caviglia A D, et al. 2007 Science 317 1196 Google Scholar
[11]	Caviglia A D, Gariglio S, Reyren N, et al. 2008 Nature 456 624 Google Scholar
[12]	Li L, Richter C, Mannhart J, Ashoori R C 2011 Nat. Phys. 7 762 Google Scholar
[13]	Brinkman A, Huijben M, Van Zalk M, et al. 2007 Nat. Mater. 6 493 Google Scholar
[14]	Ariando, Wang X, Baskaran G, et al. 2011 Nat. Commun. 2 188 Google Scholar
[15]	Wang Z, Okude M, Saito M, et al. 2010 Nat. Commum. 1 106 Google Scholar
[16]	Choi W S, Lee S, Cooper V R, et al. 2012 Nano Lett. 12 4590 Google Scholar
[17]	Kornblum L 2019 Adv. Mater. Interfaces 6 1900480 Google Scholar
[18]	Niu W, Wang X F, Xu Y B, Zhang R 2021 ACS Appl. Electron. Mater. 3 128 Google Scholar
[19]	Mardegan J R L, Christensen D V, Chen Y Z, et al. 2019 Phys. Rev. B 99 134423 Google Scholar
[20]	Song Q, Yu T L, Lou X, et al. 2019 Nat. Commum. 10 758 Google Scholar
[21]	Chen J K, Mao W, Gao L, et al. 2019 Adv. Mater. 32 1905060 Google Scholar
[22]	Kresse G, Furthmüller J 1996 Phys. Rev. B 54 11169 Google Scholar
[23]	Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865 Google Scholar
[24]	Blöchl P E 1994 Phys. Rev. B 50 17953 Google Scholar
[25]	Kresse G, Joubert D 1999 Phys. Rev. B 59 1758 Google Scholar
[26]	Dudarev S L, Botton G A, Savrasov S Y, et al. 1998 Phys. Rev. B 57 1505 Google Scholar
[27]	Tokura Y, Taguchi Y, Okada Y, Fujishima Y, Iye Y 1993 Phys. Rev. Lett. 70 2126 Google Scholar
[28]	Okuda T, Nakanishi K, Miyasaka S, Tokura Y 2001 Phys. Rev. B 63 113104 Google Scholar
[29]	Bruus H, Flensberg K 2004 Many-body Quantum Theory in Condensed Matter Physics - An Introduction (New York: Oxford University Press) p41

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掺杂维度和浓度调控的δ掺杂的La:SrTiO₃超晶格结构金属-绝缘体转变