Two distinct superconducting states controlled by orientations of local wrinkles in LiFeAs

Cao, Lu; Liu, Wenyao; Li, Geng; Dai, Guangyang; Zheng, Qi; Wang, Yuxin; Jiang, Kun; Zhu, Shiyu; Li, Huang; Kong, Ling-Yuan; Yang, Fuhan; Wang, Xiancheng; Zhou, Wu; Lin, Xiao; Hu, Jiangping; Chen, Jin; Ding, Hong; Gao, Hongjun

doi:10.1038/s41467-021-26708-8

Cited by 20 publications

(28 citation statements)

References 48 publications

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“…Besides FeTe 1−x Se x , evidences of Dirac surface states and vortex Majorana modes have also been found in other tFeSCs such as LiFeAs [25][26][27] and (Li,Fe)OHFeSe [24]. We first note that the topological band physics in (Li,Fe)OHFeSe is mainly attributed to the band inversion at Γ, thus leaving the system with zero weak indices.…”

Section: B Other Fe-based Superconductorsmentioning

confidence: 67%

“…Meanwhile, 1D ET of vortex-line defects has been possibly established in the state-of-the-art experiments of topological iron-based superconductors (tFeSCs) such as FeTe 1−x Se x [21][22][23], (Li,Fe)OHFeSe [24], LiFeAs [25][26][27], etc. Notably, the topology of bulk tFeSCs only lies in their normal states, that a band inversion at Z point generates both a nontrivial Z 2 electronic band topology and an accompanied helical Dirac surface [28].…”

Section: Introductionmentioning

confidence: 99%

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Dislocation Majorana Bound States in Iron-based Superconductors

Hu¹,

Zhang²

2022

Preprint

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We show that lattice dislocations of topological iron-based superconductors such as FeTe1−xSex will intrinsically trap non-Abelian Majorana quasiparticles, in the absence of any external magnetic field. Our theory is motivated by the recent experimental observations of normal-state topology and surface magnetism that coexist with superconductivity in FeTe1−xSex, the combination of which naturally evokes an emergent second-order topological superconductivity in a two-dimensional subsystem spanned by screw or edge dislocations. This exemplifies a new embedded higher-order topological phase in class D, where Majorana zero modes appear around the "corners" of a lowdimensional embedded subsystem, instead of those of the full crystal. A nested domain wall theory is developed to understand the origin of these defect Majorana zero modes. When the surface magnetism is absent, we further find that s± pairing symmetry itself is capable of inducing a different type of class-DIII embedded higher-order topology with defect-bound Majorana Kramers pairs. We also provide detailed discussions on the real-world material candidates for our proposals, including FeTe1−xSex, LiFeAs, β-PdBi2, and heterostructures of bismuth, etc. Our work establishes lattice defects as a new venue to achieve high-temperature topological quantum information processing.

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Section: B Other Fe-based Superconductorsmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Dislocation Majorana Bound States in Iron-based Superconductors

Hu¹,

Zhang²

2022

Preprint

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“…3(a) shows a topographic image of sample 1 where atomic [26,34] (see FIG. 9) and line-type defects [44] are visible. The unfortunate lack of atomically resolved images of these line defects complicates the identification of such structures.…”

Section: B Vortex Lattice Analysismentioning

confidence: 99%

“…In addition, it should be noted that these structure were only observed after sample 1 was cleaved again to clean the surface. It is therefore highly likely that the sample surface was subjected to an unusual amount of force during cleaving, causing the surface to buckle and thereby creating the observed line defects in the form of wrinkles [44]. FIG.…”

Section: B Vortex Lattice Analysismentioning

confidence: 99%

Absence of hexagonal to square structural transition in LiFeAs vortex matter

Hoffmann¹,

Schlegel²,

Salazar³

et al. 2022

Preprint

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We investigated magnetic vortices in two stoichiometric LiFeAs samples by means of scanning tunneling microscopy and spectroscopy. The vortices were revealed by measuring the local electronic density of states (LDOS) at zero bias conductance of samples in magnetic fields between 0.5 and 12 T. From single vortex spectroscopy we extract the Ginzburg-Landau coherence length of both samples as 4.4 ± 0.5 nm and 4.1 ± 0.5 nm, in accordance with previous findings. However, in contrast to previous reports, our study reveals that the reported hexagonal to square-like vortex lattice transition is absent up to 12 T both in field-cooling and zero-field-cooling processes. Remarkably, a highly ordered zero field cooled hexagonal vortex lattice is observed up to 8 T. We argue that several factors are likely to determine the structure of the vortex lattice in LiFeAs such as (i) details of the cooling procedure (ii) sample stoichiometry that alters the formation of nematic fluctuations, (iii) details of the order parameter and (iv) magnetoelastic coupling.

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“…1). The existence of strain in the LiFeAs lattice leads to the formation of wrinkles 30 or electronic ordering such as CDWs 31 . We identified such strained regions with a biaxial CDW phase (Fig.…”

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confidence: 99%

Ordered and tunable Majorana-zero-mode lattice in naturally strained LiFeAs

Cao

et al. 2022

Nature

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Majorana zero modes (MZMs) obey non-Abelian statistics and are considered building blocks for constructing topological qubits 1,2 . Iron-based superconductors with topological band structures have emerged as promising hosting materials, since isolated candidate MZMs in the quantum limit have been observed inside the topological vortex cores 3-9 . However, these materials suffer from issues related to alloying-induced disorder, uncontrolled vortex lattices 10-13 and a low yield of topological vortices 5-8 . Here, we report the formation of an ordered and tunable MZM lattice in naturally-strained stoichiometric LiFeAs by scanning tunneling microscopy/spectroscopy (STM/S). We observe biaxial charge density wave (CDW) stripes along the Fe-Fe and As-As directions in the strained regions. The vortices are pinned on the CDW stripes in the As-As direction and form an ordered lattice. We detect more than 90 percent of the vortices to be topological and possess the characteristics of isolated MZMs at the vortex center, forming an ordered MZM lattice with the density and the geometry tunable by an external magnetic field. Remarkably, with decreasing the spacing of neighboring vortices, the MZMs start to couple with each other. Our findings provide a new pathway towards tunable and ordered MZM lattices as a platform for future topological quantum computation.The long quest for Majorana excitations [14][15][16][17][18][19] has been fueled by recent experimental progress in material platforms where the localized MZM has been observed 16,[20][21][22][23] . Among these platforms, ironbased superconductors are considered promising for the observation of clean and robust MZMs 3-5 . FeTe0.55Se0.45 was the first iron-based superconductor found to possess topological surface states (TSS) 24,25 . The largeratio, where Δ is the superconducting (SC) energy gap and 𝐸 𝐹 is the Fermi energy, allows the observation of an isolated MZM in the center of a topological vortex 4 , which exhibits nearly quantized plateaus in differential conductance 9 . Later on, stoichiometric iron pnictides were investigated and the existence of MZMs has been verified in CaKFe4As4 (ref. 8 ) and LiFeAs (ref. 6 ). Very recently, 1D dispersing Majorana modes and MZMs have been observed in the layered 2D superconductors with topological band structures [26][27][28] . However, these platforms suffer from alloyinginduced disorder, uncontrolled vortex lattice and a low yield of topological vortices, hindering their potential applications.We start with LiFeAs crystal due to its homogeneous bulk electronic structure, well-defined cleaving surface and rich topological band structures 29 . LiFeAs belongs to the tetragonal crystal system, with lattice constants a=b=3.8 Å and c=6.3 Å (Fig. 1a). The As-As atomic direction defines the high-

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Two distinct superconducting states controlled by orientations of local wrinkles in LiFeAs

Cited by 20 publications

References 48 publications

Dislocation Majorana Bound States in Iron-based Superconductors

Dislocation Majorana Bound States in Iron-based Superconductors

Absence of hexagonal to square structural transition in LiFeAs vortex matter

Ordered and tunable Majorana-zero-mode lattice in naturally strained LiFeAs

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