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In this work, we investigate the influence of quasi-periodic modulation on the localization properties of one-dimensional non-Hermitian cross-stitch lattices with flat bands. The crystalline Hamiltonian for this non-Hermitian cross-stitch lattice is given by: ˆH=∑n[t(a†nbn+b†nan)+Jeh(a†nbn+1+a†nan+1+Ab†nan+1+Ab†nbn+1)+Je−h(Aa†n+1bn+a†n+1an+b†n+1an+Ab†n+1bn)] withA=±1 . When A = 1, the clean lattice supports two bands with dispersion relationsE0=−t, E1=4cos(k−ih)+t . The compact localized states (CLSs) within the flat band E0 are localized in one unit cell, indicating that the system is characterized by the U = 1 class. Conversely, for A = –1, there are two flat bands in the system:E±=±√t2+4 . The CLSs within the flat bands are localized in two unit cells, indicating that the system is marked by the U = 2 class. After introducing quasi-periodic modulationsεβn=λβcos(2παn+ϕβ) (β={a,b} ), delocalization-localization transitions can be observed by numerically calculating the fractal dimension D2 and imaginary part of the energy spectrumln|Im(E)| . Our findings indicate that the symmetry of quasi-periodic modulations plays an important role in determining the localization properties of the system. For the case ofU=1 , the symmetric quasi-periodic modulation leads to two independent spectraσf andσp . Theσf retains its compact properties, while theσp owns an extended-localized transition atλc1=4M withM=max{eh,e−h} . However, in the case of antisymmetric modulation, the system exhibits an exact mobility edgeλc2=2√2|E−t|M . For the U = 2 class, all the eigenstates remain localized under any symmetric quasi-periodic modulation. In the case of antisymmetric modulation, all states transition from multifractal to localized states as the modulation strength increases, with a critical point atλc3=4M . This work expands the understanding of localization properties in non-Hermitian flat-band systems and provides a new perspective on delocalization-localization transitions.-
Keywords:
- flat-band systems /
- non-Hermitian systems /
- disorder /
- localization
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图 1 干净晶格情况 (a) 一维非厄米十字晶格示意图; (b) U=1类非厄米十字晶格的CLS占据; (c) U=2类非厄米十字晶格的CLS占据; (d)开边界条件下, U=1类十字晶格色散带中所有本征态的密度分布ρ(l)n. 这里的参数选取h=0.6, t=2, L=100
Fig. 1. Crystalline case: (a) Schematic diagram of the one-dimensional non-Hermitian cross-stitch lattice; (b) CLS occupations of the U=1 class non-Hermitian cross-stitch lattice with A=1; (c) CLS occupations of the U=2 class non-Hermitian cross-stitch lattice with A=−1; (d) density distributions ρ(l)n for all the eigenstates in dispersive bands of the cross-stitch lattice under open bonudary conditions. Here, h=0.6, t=2, L=100
图 2 对称情况时, U=1 类非厄米十字晶格的局域化性质 (a) σp谱的分型维度D(l)2随着能量实部Re(E)和无序强度λ的变化, 颜色表示分形维度D(l)2的大小. (b) σp谱的能量虚部ln|Im(E)|随着能量实部Re(E)和无序强度λ的变化, 颜色表示ln|Im(E)|的大小, 实线表示扩展-局域转变, σf被省略, 边界用虚线表示. (c)λ=5时, σp所对应的能谱. (d)λ=10时, σp所对应的能谱. 这里L=1000
Fig. 2. Symmetric case of the U=1 class non-Hermitian cross-stitch lattice: (a) Real part of the spectrum σp as a function of λ, where the color denotes the value of the fractal dimension D(l)2. (b) ln|Im(E)| of σp as a function of λ and Re(E), where the color denotes the value of ln|Im(E)|. Black solid lines represent the delocalization-localization transition. The spectrum σf is omitted, but its boundaries are indicated by black dashed lines. (c) Energy spectrum of σp with λ=5. (d) Energy spectrum of σp with λ=10. Here, L=1000.
图 3 反对称情况时, U=1 类非厄米十字型晶格的局域化 (a)分型维度D(l)2随着能量实部Re(E)和无序强度λ的变化; (b)能量虚部ln|Im(E)|随着能量实部Re(E)和无序强度λ的变化. 实线表示迁移率边. 这里L=1000
Fig. 3. Antisymmetric case of the U=1 class non-Hermitian cross-stitch lattice: (a) D(l)2 of the spectrum as a function of λ, where the color denotes the value of the fractal dimension D(l)2; (b) ln|Im(E)| of the spectrum as a function of λ and Re(E), where the color denotes the value of ln|Im(E)|. The black solid lines represent the mobility edges. Here, L=1000.
图 4 反对称情况时, U=2类非厄米十字晶格的局域化 (a)分型维度D(l)2随着能量实部Re(E)和无序强度λ的变化, 颜色表示分形维度D(l)2的大小. (b)能量虚部ln|Im(E)|随着能量实部Re(E)和无序强度λ的变化, 颜色表示ln|Im(E)|的大小, 实线表示多重分形-局域的转变, 这里L=1000. (c)多重分形区域的MIPR标度分析, 插图为局域区域的MIPR标度分析
Fig. 4. Antisymmetric case of U=2 non-Hermitian cross-stitch lattice: (a) D(l)2 of the spectrum as a function of λ and Re(E), where the color denotes the value of the fractal dimension D(l)2. (b) ln|Im(E)| of the spectrum as a function of λ and Re(E), where the color denotes the value of ln|Im(E)|. The black solid lines represent the multifractal-to-localized transition. Here, L=1000. (c) The MIPR scaling of multifractal regions for different λ. The inset shows the MIPR scaling of localized regions for λ=10.
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[1] Anderson P W 1958 Phys. Rev. 109 1492
Google Scholar
[2] Billy J, Josse V, Zuo Z, Bernard A, Hambrecht B, Lugan P, Clément D, Sanchez-Palencia L, Bouyer P, Aspect A 2008 Nature 453 891
Google Scholar
[3] Hu H, Strybulevych A, Page J H, Skipetrov S E, van Tiggelen B A 2008 Nat. Phys. 4 945
Google Scholar
[4] Pradhan P, Sridhar S 2000 Phys. Rev. Lett. 85 2360
Google Scholar
[5] Mott N 1987 J. Phys. C 20 3075
Google Scholar
[6] Wang Y, Zhang L, Sun W, Poon T F J, Liu X J 2022 Phys. Rev. B 106 L140203
Google Scholar
[7] Yamamoto K, Aharony A, Entin-Wohlman O, Hatano N 2017 Phys. Rev. B 96 155201
Google Scholar
[8] Aubry S, André G 1980 Ann. Isr. Phys. Soc. 3 133
[9] Longhi S 2019 Phys. Rev. Lett. 122 237601
Google Scholar
[10] Xu Z, Xia X, Chen S 2022 Sci. China: Phys. Mech. Astron. 65 227211
Google Scholar
[11] Biddle J, Das Sarma S 2010 Phys. Rev. Lett. 104 070601
Google Scholar
[12] Ganeshan S, Pixley J H, Sarma S D 2015 Phys. Rev. Lett. 114 146601
Google Scholar
[13] Leykam D, Flach S, Bahat-Treidel O, Desyatnikov A S 2013 Phys. Rev. B 88 224203
Google Scholar
[14] Zhang W, Addison Z, Trivedi N 2021 Phys. Rev. B 104 235202
Google Scholar
[15] Leykam D, Bodyfelt J D, Desyatnikov A S, Flach S 2017 Eur. Phy. J. B 90 1
Google Scholar
[16] Maimaiti W, Andreanov A 2021 Phys. Rev. B 104 035115
Google Scholar
[17] Bodyfelt D, Leykam D, Danieli C, Yu X, Flach S 2014 Phys. Rev. Lett. 113 236403
Google Scholar
[18] Danieli C, Bodyfelt J D, Flach S 2015 Phys. Rev. B 91 235134
Google Scholar
[19] Lee S, Andreanov A, Flach S 2023 Phys. Rev. B 107 014204
Google Scholar
[20] Lee S, Flach S, Andreanov A 2023 Chaos 33 073125
Google Scholar
[21] Ahmed A, Ramachandran A, Khaymovich I M, Sharma A 2022 Phys. Rev. B 106 205119
Google Scholar
[22] Liu C, Jiang H, Chen S 2019 Phys. Rev. B 99 125103
Google Scholar
[23] Liu C, Chen S 2019 Phys. Rev. B 100 144106
Google Scholar
[24] Bender C M, Boettcher S 1998 Phys. Rev. Lett. 80 5243
Google Scholar
[25] Zhao H, Miao P, Teimourpour M H, Malzard S, ElGanainy R, Schomerus H, Feng L 2018 Nat. Commun. 9 981
Google Scholar
[26] Jiang H, Lang L J, Yang C, Zhu S L, Chen S 2019 Phys. Rev. B 100 054301
Google Scholar
[27] Yao S, Song F, Wang Z 2018 Phys. Rev. Lett. 121 136802
Google Scholar
[28] Yao S, Wang Z 2018 Phys. Rev. Lett. 121 086803
Google Scholar
[29] Hatano N, Nelson D R 1996 Phys. Rev. Lett. 77 570
Google Scholar
[30] Hatano N, Nelson D R 1997 Phys. Rev. B 56 8651
Google Scholar
[31] Hatano N, Nelson D R 1998 Phys. Rev. B 58 8384
Google Scholar
[32] Flach S, Leykam D, Bodyfelt J D, Matthies P, Desyatnikov A S 2014 Europhys. Lett. 105 30001
Google Scholar
[33] Miroshnichenko A E, Flach S, Kivshar Y S 2010 Rev. Mod. Phys. 82 2257
Google Scholar
[34] Evers F, Mirlin A D 2008 Rev. Mod. Phys. 80 1355
Google Scholar
[35] Macé N, Alet F, Laflorencie N 2019 Phys. Rev. Lett. 123 180601
Google Scholar
[36] Liu H, Lu Z, Xia X, Xu Z 2024 arXiv: 2311.03166 [cond-mat.dis-nn]
[37] Zeng Q B, Chen S, Lü R 2017 Phys. Rev. A 95 062118
Google Scholar
[38] Tang L Z, Zhang G Q, Zhang L F, Zhang D W 2021 Phys. Rev. A 103 033325
Google Scholar
[39] Kawabata K, Shiozaki K, Ueda M, Sato M 2019 Phys. Rev. X 9 041015
Google Scholar
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