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Title: Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca{sub 0.9}La{sub 0.1}FeAs{sub 2}

Abstract

CaFeAs{sub 2} is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal system for the realization of Majorana modes. We performed a systematical angle-resolved photoemission spectroscopy and first-principles calculation study of the slightly electron-doped CaFeAs{sub 2}. We found that the zigzag As chain of 112-type iron-based superconductors play a considerable role in the low-energy electronic structure, resulting in the characteristic Dirac-cone like band dispersion as the prediction. Our experimental results further confirm that these Dirac cones only exist around the X but not Y points in the Brillouin zone, breaking the S{sub 4} symmetry at iron sites. Our findings present the compelling support to the theoretical prediction that the 112-type iron-based superconductors might host the topological nontrivial edge states. The slightly electron doped CaFeAs{sub 2} would provide us a unique opportunity to realize and explore Majorana fermion physics.

Authors:
; ; ; ; ;  [1]; ; ; ;  [2];  [1];  [3];  [1];  [3];  [3];  [1];  [3];  [4]
  1. State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, Shanghai 200050 (China)
  2. Department of Physics and Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing 211189 (China)
  3. (China)
  4. (CENSE), Shanghai 200050 (China)
Publication Date:
OSTI Identifier:
22594378
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 109; Journal Issue: 4; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; BRILLOUIN ZONES; CONES; DISPERSIONS; DOPED MATERIALS; ELECTRONIC STRUCTURE; ELECTRONS; IRON; LAYERS; MAJORANA FERMIONS; MAJORANA SPINORS; PHOTOELECTRON SPECTROSCOPY; PHOTOEMISSION; SPIN; SUPERCONDUCTORS; SYMMETRY; TOPOLOGY

Citation Formats

Liu, Z. T., Li, M. Y., Fan, C. C., Yang, H. F., Liu, J. S., Wang, Z., Xing, X. Z., Zhou, W., Sun, Y., Shi, Z. X., Yao, Q., State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, Li, W., State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, CAS-Shanghai Science Research Center, Shanghai 201203, Shen, D. W., E-mail: dwshen@mail.sim.ac.cn, CAS-Shanghai Science Research Center, Shanghai 201203, and CAS Center for Excellence in Superconducting Electronics. Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca{sub 0.9}La{sub 0.1}FeAs{sub 2}. United States: N. p., 2016. Web. doi:10.1063/1.4960164.
Liu, Z. T., Li, M. Y., Fan, C. C., Yang, H. F., Liu, J. S., Wang, Z., Xing, X. Z., Zhou, W., Sun, Y., Shi, Z. X., Yao, Q., State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, Li, W., State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, CAS-Shanghai Science Research Center, Shanghai 201203, Shen, D. W., E-mail: dwshen@mail.sim.ac.cn, CAS-Shanghai Science Research Center, Shanghai 201203, & CAS Center for Excellence in Superconducting Electronics. Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca{sub 0.9}La{sub 0.1}FeAs{sub 2}. United States. doi:10.1063/1.4960164.
Liu, Z. T., Li, M. Y., Fan, C. C., Yang, H. F., Liu, J. S., Wang, Z., Xing, X. Z., Zhou, W., Sun, Y., Shi, Z. X., Yao, Q., State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, Li, W., State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, CAS-Shanghai Science Research Center, Shanghai 201203, Shen, D. W., E-mail: dwshen@mail.sim.ac.cn, CAS-Shanghai Science Research Center, Shanghai 201203, and CAS Center for Excellence in Superconducting Electronics. Mon . "Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca{sub 0.9}La{sub 0.1}FeAs{sub 2}". United States. doi:10.1063/1.4960164.
@article{osti_22594378,
title = {Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca{sub 0.9}La{sub 0.1}FeAs{sub 2}},
author = {Liu, Z. T. and Li, M. Y. and Fan, C. C. and Yang, H. F. and Liu, J. S. and Wang, Z. and Xing, X. Z. and Zhou, W. and Sun, Y. and Shi, Z. X. and Yao, Q. and State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433 and Li, W. and State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433 and CAS-Shanghai Science Research Center, Shanghai 201203 and Shen, D. W., E-mail: dwshen@mail.sim.ac.cn and CAS-Shanghai Science Research Center, Shanghai 201203 and CAS Center for Excellence in Superconducting Electronics},
abstractNote = {CaFeAs{sub 2} is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal system for the realization of Majorana modes. We performed a systematical angle-resolved photoemission spectroscopy and first-principles calculation study of the slightly electron-doped CaFeAs{sub 2}. We found that the zigzag As chain of 112-type iron-based superconductors play a considerable role in the low-energy electronic structure, resulting in the characteristic Dirac-cone like band dispersion as the prediction. Our experimental results further confirm that these Dirac cones only exist around the X but not Y points in the Brillouin zone, breaking the S{sub 4} symmetry at iron sites. Our findings present the compelling support to the theoretical prediction that the 112-type iron-based superconductors might host the topological nontrivial edge states. The slightly electron doped CaFeAs{sub 2} would provide us a unique opportunity to realize and explore Majorana fermion physics.},
doi = {10.1063/1.4960164},
journal = {Applied Physics Letters},
number = 4,
volume = 109,
place = {United States},
year = {Mon Jul 25 00:00:00 EDT 2016},
month = {Mon Jul 25 00:00:00 EDT 2016}
}
  • The recently discovered high-T c superconductor Ca 1-xLa xFeAs 2 is a unique compound not just because of its low-symmetry crystal structure but also because of its electronic structure, which hosts Dirac-like metallic bands resulting from (spacer) zigzag As chains. We present a comprehensive first-principles theoretical study of the electronic and crystal structures of Ca 1-xLa xFeAs 2. After discussing the connection between the crystal structure of the 112 family, which Ca 1-xLa xFeAs 2 is a member of, with the other known structures of Fe pnictide superconductors, we check the thermodynamic phase stability of CaFeAs 2, and similar hyphotheticalmore » compounds SrFeAs 2 and BaFeAs 2 which, we find, are slightly higher in energy. We calculate the optical conductivity of Ca 1-xLa xFeAs 2 using the DFT+DMFT method and predict a large in-plane resistivity anisotropy in the normal phase, which does not originate from electronic nematicity, but is enhanced by the electronic correlations. In particular, we predict a 0.34 eV peak in the yy component of the optical conductivity of the 30% La-doped compound, which corresponds to coherent interband transitions within a fast-dispersing band arising from the zigzag As chains, which are unique to this compound. We also study the Landau free energy for Ca 1-xLa xFeAs 2 including the order parameter relevant for the nematic transition and find that the free energy does not have any extra terms that could induce ferro-orbital order. This explains why the presence of As chains does not broaden the nematic transition in Ca 1-xLa xFeAs 2.« less
  • The superconducting penetration depth {lambda}(T) has been measured in RFeAsO{sub 0.9}F{sub 0.1} (R=La, Nd) single crystals (R-1111). In Nd-1111, we find an upturn in {lambda}(T) upon cooling and attribute it to the paramagnetism of the Nd ions, similar to the case of the electron-doped cuprate Nd-Ce-Cu-O. After the correction for paramagnetism, the London penetration depth variation is found to follow a power-law behavior, {Delta}{lambda}L(T) {proportional_to} T{sup 2} at low temperatures. The same T{sup 2} variation of {lambda}(T) was found in nonmagnetic La-1111 crystals. Analysis of the superfluid density and of penetration depth anisotropy over the full temperature range is consistentmore » with two-gap superconductivity. Based on this and on our previous work, we conclude that both the RFeAsO (1111) and BaFe{sub 2}As{sub 2} (122) families of pnictide superconductors exhibit unconventional two-gap superconductivity.« less
  • Here we report a study of the Ca 0.73La 0.27FeAs 2 single crystals. We unravel a monoclinic to triclinic phase transition at 58 K, and a paramagnetic to stripe antiferromagnetic (AFM) phase transition at 54 K, below which spins order 45° away from the stripe direction. Furthermore, we demonstrate this material is substantially structurally untwinned at ambient pressure with the formation of spin rotation walls (S-walls). Finally, in addition to the central-hole and corner-electron Fermi pockets usually appearing in FPS, angle-resolved photoemission (ARPES) measurements resolve a Fermiology where an extra electron pocket of mainly As chain character exists at themore » Brillouin zone edge.« less
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