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Coalescence of multiple topological orders in quasi-one-dimensional bismuth halide chains
Authors:
Jingyuan Zhong,
Ming Yang,
Wenxuan Zhao,
Kaiyi Zhai,
Xuan Zhen,
Lifu Zhang,
Dan Mu,
Yundan Liu,
Zhijian Shi,
Ningyan Cheng,
Wei Zhou,
Jianfeng Wang,
Weichang Hao,
Zhenpeng Hu,
Jincheng Zhuang,
Jinhu Lü,
Yi Du
Abstract:
Topology is being widely adopted to understand and to categorize quantum matter in modern physics. The nexus of topology orders, which engenders distinct quantum phases with benefits to both fundamental research and practical applications for future quantum devices, can be driven by topological phase transition through modulating intrinsic or extrinsic ordering parameters. The conjoined topology,…
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Topology is being widely adopted to understand and to categorize quantum matter in modern physics. The nexus of topology orders, which engenders distinct quantum phases with benefits to both fundamental research and practical applications for future quantum devices, can be driven by topological phase transition through modulating intrinsic or extrinsic ordering parameters. The conjoined topology, however, is still elusive in experiments due to the lack of suitable material platforms. Here we use scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and theoretical calculations to investigate the doping-driven band structure evolution of a quasi-one-dimensional material system, bismuth halide, which contains rare multiple band inversions in two time-reversal-invariant momenta. According to the unique bulk-boundary correspondence in topological matter, we unveil a composite topological phase, the coexistence of a strong topological phase and a high-order topological phase, evoked by the band inversion associated with topological phase transition in this system. Moreover, we reveal multiple-stage topological phase transitions by varying the halide element ratio: from high-order topology to weak topology, the unusual dual topology, and trivial/weak topology subsequently. Our results not only realize an ideal material platform with composite topology, but also provide an insightful pathway to establish abundant topological phases in the framework of band inversion theory.
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Submitted 8 December, 2025;
originally announced December 2025.
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Observation of Orbital-Selective Dual Modulations in an Anisotropic Antiferromagnetic Kagome Metal TbTi3Bi4
Authors:
Renjie Zhang,
Bocheng Yu,
Hengxin Tan,
Yiwei Cheng,
Feiran Shen,
Junye Yang,
Dan Mu,
Xinru Han,
Alfred Zong,
Quanxin Hu,
Xuezhi Chen,
Yudong Hu,
Chengnuo Meng,
Junchao Ren,
Junqin Li,
Zhenhua Chen,
Zhengtai Liu,
Mao Ye,
Makoto Hashimoto,
Donghui Lu,
Shifeng Jin,
Binghai Yan,
Lunhua He,
Ziqiang Wang,
Tian Shang
, et al. (3 additional authors not shown)
Abstract:
Orbital selectivity is pivotal in dictating the phase diagrams of multiorbital systems, with prominent examples including the orbital-selective Mott phase and superconductivity, etc. The intercalation of anisotropic layers represents an effective method for enhancing orbital selectivity and, thereby shaping the low-energy physics of multiorbital systems. Despite its potential, related experimental…
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Orbital selectivity is pivotal in dictating the phase diagrams of multiorbital systems, with prominent examples including the orbital-selective Mott phase and superconductivity, etc. The intercalation of anisotropic layers represents an effective method for enhancing orbital selectivity and, thereby shaping the low-energy physics of multiorbital systems. Despite its potential, related experimental studies remain limited. In this work, we systematically examine the interplay between orbital selectivity and magnetism in the newly discovered anisotropic kagome TbTi3Bi4 single crystal, and report a unidirectional, orbital-selective band reconstruction within the antiferromagnetic (AFM) state. By combining soft X-ray and vacuum ultraviolet angle-resolved photoemission spectroscopy (ARPES) measurements with orbital-resolved density functional theory (DFT) calculations, we identify that the band reconstruction is a manifestation of the AFM order, driven by a 1/3 nesting instability of the intercalated Tb 5dxz orbitals. Such an orbital-selective modulation leads the unusual momentum-dependent band folding and the emergence of symmetry-protected Dirac cones only at the M1 point. More importantly, the discovery of orbital-selective 3 x 1 AFM order offers crucial insights into the underlying mechanism of the fractional magnetization plateau in this Kagome AFM metal. Our findings not only underscore the essential role of both conducting and localized electrons in determining the magnetic orders of LnTi3Bi4 (Ln = Lanthanide) kagome metals but also offer a pathway for manipulating magnetism through selective control of anisotropic electronic structures.
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Submitted 19 June, 2025; v1 submitted 21 December, 2024;
originally announced December 2024.
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Mass Acquisition of Dirac Fermions in Bi4I4 by Spontaneous Symmetry Breaking
Authors:
Ming Yang,
Wenxuan Zhao,
Dan Mu,
Zhijian Shi,
Jingyuan Zhong,
Yaqi Li,
Yundan Liu,
Jianxin Zhong,
Ningyan Cheng,
Wei Zhou,
Jianfeng Wang,
Yan Shi,
Ying Sun,
Weichang Hao,
Lexian Yang,
Jincheng Zhuang,
Yi Du
Abstract:
Massive Dirac fermions, which are essential for realizing novel topological phenomena, are expected to be generated from massless Dirac fermions by breaking the related symmetry, such as time-reversal symmetry (TRS) in topological insulators or crystal symmetry in topological crystalline insulators. Here, we report scanning tunneling microscopy and angle-resolved photoemission spectroscopy studies…
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Massive Dirac fermions, which are essential for realizing novel topological phenomena, are expected to be generated from massless Dirac fermions by breaking the related symmetry, such as time-reversal symmetry (TRS) in topological insulators or crystal symmetry in topological crystalline insulators. Here, we report scanning tunneling microscopy and angle-resolved photoemission spectroscopy studies of α-Bi4I4, which reveals the realization of massive Dirac fermions in the (100) surface states without breaking the TRS. Combined with first-principle calculations, our experimental results indicate that the spontaneous symmetry breaking engenders two nondegenerate edges states at the opposite sides of monolayer Bi4I4 after the structural phase transition, imparting mass to the Dirac fermions after taking the interlayer coupling into account. Our results not only demonstrate the formation of the massive Dirac fermions by spontaneous symmetry breaking, but also imply the potential for the engineering of Dirac fermions for device applications.
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Submitted 17 December, 2024;
originally announced December 2024.
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Towards Layer-Selective Quantum Spin Hall Channels in Weak Topological Insulator Bi4Br2I2
Authors:
Jingyuan Zhong,
Ming Yang,
Zhijian Shi,
Yaqi Li,
Dan Mu,
Yundan Liu,
Ningyan Cheng,
Wenxuan Zhao,
Weichang Hao,
Jianfeng Wang,
Lexian Yang,
Jincheng Zhuang,
Yi Du
Abstract:
Weak topological insulators, constructed by stacking quantum spin Hall insulators with weak interlayer coupling, offer promising quantum electronic applications through topologically nontrivial edge channels. However, the currently available weak topological insulators are stacks of the same quantum spin Hall layer with translational symmetry in the out-of-plane direction, leading to the absence o…
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Weak topological insulators, constructed by stacking quantum spin Hall insulators with weak interlayer coupling, offer promising quantum electronic applications through topologically nontrivial edge channels. However, the currently available weak topological insulators are stacks of the same quantum spin Hall layer with translational symmetry in the out-of-plane direction, leading to the absence of the channel degree of freedom for edge states. Here, we study a candidate weak topological insulator, Bi4Br2I2, which is alternately stacked by three different quantum spin Hall insulators, each with tunable topologically non-trivial edge states. Our angle-resolved photoemission spectroscopy and first-principles calculations show that an energy gap opens at the crossing points of different Dirac cones correlated with different layers due to the interlayer interaction. This is essential to achieve the tunability of topological edge states as controlled by varying the chemical potential. Our work offers a perspective for the construction of tunable quantized conductance devices for future spintronic applications.
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Submitted 16 August, 2023;
originally announced August 2023.
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Large-Gap Quantum Spin Hall State and Temperature-Induced Lifshitz Transition in Bi4Br4
Authors:
Ming Yang,
Yundan Liu,
Wei Zhou,
Chen Liu,
Dan Mu,
Yani Liu,
Jiaou Wang,
Weichang Hao,
Jin Li,
Jianxin Zhong,
Yi Du,
Jincheng Zhuang
Abstract:
Searching for new quantum spin Hall insulators with large fully opened energy gap to overcome the thermal disturbance at room temperature has attracted tremendous attention due to the one-dimensional (1D) spin-momentum locked topological edge states serving as dissipationless channels for the practical applications in low consumption electronics and high performance spintronics. Here, we report th…
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Searching for new quantum spin Hall insulators with large fully opened energy gap to overcome the thermal disturbance at room temperature has attracted tremendous attention due to the one-dimensional (1D) spin-momentum locked topological edge states serving as dissipationless channels for the practical applications in low consumption electronics and high performance spintronics. Here, we report the investigation of topological nature of monolayer Bi4Br4 by the techniques of scanning tunneling microscopy and angle-resolved photoemission spectroscopy (ARPES). The topological non-triviality of 1D edge state integrals within the large bulk energy gap (~ 0.2 eV) is revealed by the first-principle calculations. The ARPES measurements at different temperature show a temperature-induced Lifshitz transition, corresponding to the resistivity anomaly caused by the shift of chemical potential. The connection between the emergency of superconductivity and the Lifshitz transition is discussed.
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Submitted 13 October, 2021;
originally announced October 2021.
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Resolving the Intrinsic Bandgap and Edge Effect of BiI3 Film Epitaxially Grown on Graphene
Authors:
Dan Mu,
Wei Zhou,
Yundan Liu,
Jin Li,
Ming Yang,
Jincheng Zhuang,
Yi Du,
Jianxin Zhong
Abstract:
Two-dimensional materials with layered structures, appropriate bandgap, and high carrier mobilities have gathered tremendous interests due to their potential applications in optoelectronic and photovoltaic devices. Here, we report the growth of BiI3 thin film with controllable atomic thickness on graphene-terminated 6H-SiC(0001) substrate by molecular beam epitaxy (MBE) method. The growth kinetic…
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Two-dimensional materials with layered structures, appropriate bandgap, and high carrier mobilities have gathered tremendous interests due to their potential applications in optoelectronic and photovoltaic devices. Here, we report the growth of BiI3 thin film with controllable atomic thickness on graphene-terminated 6H-SiC(0001) substrate by molecular beam epitaxy (MBE) method. The growth kinetic processes and crystalline properties of the BiI3 film are studied by scanning tunneling microscopy (STM). The scanning tunneling spectroscopy (STS) reveals a bandgap of 2.8 eV for monolayer BiI3 with a weak dependence on film thickness for few-layer BiI3, which greatly exceeds the previous reported values identified by macroscopic optical measurements. This discrepancy originates from the edge effect of BiI3 that renders the bandgap downshift to 1.5 - 1.6 eV, as identified by the STS curves and the further confirmed by density functional theory (DFT) calculations. Our work provides a method to fabricate high-quality monolayer BiI3 film and resolves its intrinsic bandgap as well as the edge effect on reduction of bandgap, benefitting not only to fundamental researches but also to nanoelectronic and optoelectronic applications.
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Submitted 12 March, 2021;
originally announced March 2021.
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Epitaxial Growth of Quasi-One-Dimensional Bismuth-Halide Chains with Topological Non-Trivial Edge States
Authors:
Jincheng Zhuang,
Jin Li,
Yundan Liu,
Dan Mu,
Ming Yang,
Yani Liu,
Wei Zhou,
Weichang Hao,
Jianxin Zhong,
Yi Du
Abstract:
Quantum spin Hall insulators have one-dimensional (1D) spin-momentum locked topological edge states (ES) inside the bulk band gap, which can serve as dissipationless channels for the practical applications in low consumption electronics and high performance spintronics. However, the clean and atomically sharp ES serving as ideal 1D conducting channels are still lack. Here, we report the formation…
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Quantum spin Hall insulators have one-dimensional (1D) spin-momentum locked topological edge states (ES) inside the bulk band gap, which can serve as dissipationless channels for the practical applications in low consumption electronics and high performance spintronics. However, the clean and atomically sharp ES serving as ideal 1D conducting channels are still lack. Here, we report the formation of the quasi-1D Bi4I4 nanoribbons on the surface of Bi(111) with the support of the graphene-terminated 6H-SiC(0001) and the direct observations of the topological ES at the step edge by scanning tunneling microscopy and spectroscopic-imaging results. The ES reside surround the edge of Bi4I4 nanoribbons and exhibits remarkable robustness against non time reversal symmetry perturbations. The theoretical simulations verify the topological non-trivial character of 1D ES, which is retained after considering the presence of the underlying Bi(111). Our study supports the existence of topological ES in Bi4I4 nanoribbons, paving the way to engineer the novel topological features by using the nanoribbons as the 1D building block.
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Submitted 12 March, 2021;
originally announced March 2021.
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Unusual Electronic Structure and Observation of Dispersion Kink in CeFeAsO Parent Compound of FeAs-Based Superconductors
Authors:
Haiyun Liu,
G. F. Chen,
Wentao Zhang,
Lin Zhao,
Guodong Liu,
T. -L. Xia,
Xiaowen Jia,
Daixiang Mu,
Shanyu Liu,
Shaolong He,
Yingying Peng,
Junfeng He,
Zhaoyu Chen,
Xiaoli Dong,
Jun Zhang,
Guiling Wang,
Yong Zhu,
Zuyan Xu,
Chuangtian Chen,
X. J. Zhou
Abstract:
We report the first comprehensive high-resolution angle-resolved photoemission measurements on CeFeAsO, a parent compound of FeAs-based high temperature superconductors with a mangetic/structural transition at $\sim$150 K. In the magnetic ordering state, four hole-like Fermi surface sheets are observed near $Γ$(0,0) and the Fermi surface near M(+/-$π$,+/-$π$) shows a tiny electron-like pocket at M…
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We report the first comprehensive high-resolution angle-resolved photoemission measurements on CeFeAsO, a parent compound of FeAs-based high temperature superconductors with a mangetic/structural transition at $\sim$150 K. In the magnetic ordering state, four hole-like Fermi surface sheets are observed near $Γ$(0,0) and the Fermi surface near M(+/-$π$,+/-$π$) shows a tiny electron-like pocket at M surrounded by four Dirac cone-like strong spots. The unusual Fermi surface topology deviates strongly from the band structure calculations. The electronic signature of the magnetic/structural transition shows up in the dramatic change of the quasiparticle scattering rate. A dispersion kink at $\sim$ 25meV is for the first time observed in the parent compound of Fe-based superconductors.
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Submitted 8 June, 2010; v1 submitted 15 December, 2009;
originally announced December 2009.
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Coexistence of Fermi arcs and Fermi pockets in a high Tc copper oxide superconductor
Authors:
Jianqiao Meng,
Guodong Liu,
Wentao Zhang,
Lin Zhao,
Haiyun Liu,
Xiaowen Jia,
Daixiang Mu,
Shanyu Liu,
Xiaoli Dong,
Wei Lu,
Guiling Wang,
Yong Zhou,
Yong Zhu,
Xiaoyang Wang,
Zuyan Xu,
Chuangtian Chen,
X. J. Zhou
Abstract:
In the pseudogap state of the high-Tc copper-oxide (cuprate) superconductors, angle-resolved photoemission (ARPES) measurements have seen an Fermi arc, i.e., an open-ended gapless section in the large Fermi surface, rather than a closed loop expected of an ordinary metal. This is all the more puzzling because Fermi pockets (small closed Fermi surface features) have been suggested from recent qua…
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In the pseudogap state of the high-Tc copper-oxide (cuprate) superconductors, angle-resolved photoemission (ARPES) measurements have seen an Fermi arc, i.e., an open-ended gapless section in the large Fermi surface, rather than a closed loop expected of an ordinary metal. This is all the more puzzling because Fermi pockets (small closed Fermi surface features) have been suggested from recent quantum oscillation measurements. The Fermi arcs have worried the high-Tc community for many years because they cannot be understood in terms of existing theories. Theorists came up with a way out in the form of conventional Fermi surface pockets associated with competing order, with a back side that is for detailed reasons invisible by photoemission. Here we report ARPES measurements of La-Bi2201 that give direct evidence of the Fermi pocket. The charge carriers in the pocket are holes and the pockets show an unusual dependence upon doping, namely, they exist in underdoped but not overdoped samples. A big surprise is that these Fermi pockets appear to coexist with the Fermi arcs. This coexistence has not been expected theoretically and the understanding of the mysterious pseudogap state in the high-Tc cuprate superconductors will rely critically on understanding such a new finding.
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Submitted 23 November, 2009; v1 submitted 15 June, 2009;
originally announced June 2009.