Author(s)Madhab Neupane, Chang Liu, Su-Yang Xu, Yung-Jui Wang, Ni Ni, J. M. Allred, N. Alidoust, Hsin Lin, R. S.Markiewicz, A. Bansil, R. J. Cava, and M. Z. Hasan

This article is available at IRis: http://iris.lib.neu.edu/physics_fac_pubs/521

PHYSICAL REVIEW B 85, 094510 (2012)

Fermi-surface topology and low-lying electronic structure of the iron-based superconductorCa10(Pt3As8)(Fe2As2)5

Madhab Neupane,1 Chang Liu,1 Su-Yang Xu,1 Yung-Jui Wang,2 Ni Ni,3 J. M. Allred,3 L. A. Wray,1,4 N. Alidoust,1 Hsin Lin,2

R. S. Markiewicz,2 A. Bansil,2 R. J. Cava,3 and M. Z. Hasan1

1Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA2Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA3Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA

4Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94305, USA(Received 25 October 2011; revised manuscript received 3 February 2012; published 20 March 2012)

We report a study of low-energy electronic structure and Fermi surface topology for the recently discoverediron-based superconductor Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase, with Tc ∼ 8 K), via angle-resolvedphotoemission spectroscopy (ARPES). Despite its triclinic crystal structure, ARPES results reveal a fourfoldsymmetric band structure with the absence of Dirac-cone-like Fermi dots (related to magnetism) found aroundthe Brillouin zone corners in other iron-based superconductors. Considering that the triclinic lattice and structuralsupercell arise from the Pt3As8 intermediary layers, these results indicate that those layers couple only weakly tothe FeAs layers in this new superconductor at least near the surface, which has implications for the determinationof its pairing mechanism.

DOI: 10.1103/PhysRevB.85.094510 PACS number(s): 74.70.Xa, 74.25.Jb, 74.10.+v, 74.70.Dd

I. INTRODUCTION

The recent discovery and characterization of superconduct-ing phases in the Ca-Fe-Pt-As system Ca10(PtnAs8)(Fe2As2)5

(Refs. 1–4) has potentially significant impact on the fieldof iron-based high-Tc superconductors.5–12 Most importantly,these phases serve as ideal platforms for systematic studiesof the physics of the intermediary layers and their impacton the superconducting properties, which is an important yetopen question in the field of arsenide superconductivity. Inhigh-Tc cuprates,13–17 such a study is made possible by theavailability of materials such as the Bi2Sr2Can−1CunO2n+4+x

(n = 1–3) series,16,17 within which one finds a drasticcorrelation between the number of intermediary layers andthe superconducting transition temperature (Tc). In the ironpnictides, a similar type of survey has previously beenunavailable due to the lack of appropriate systems: One needsto search for a series of stoichiometric materials with differentbut systematically adjusted chemical compositions in either theiron-containing layers or the intermediary layers. The uniquecrystal structures in the Ca-Fe-Pt-As systems, on the otherhand, yield drastically different symmetries and periodicitiesfor the layers of FeAs tetrahedra and the intermediary layers.Therefore, the intralayer (hopping within the FeAs layers) andinterlayer (hopping between the FeAs and Ca-Pt-As layers)contribution to the density of states at the Fermi level (EF ) canbe uniquely distinguished. Studies of the electronic structure ofthe Ca-Fe-Pt-As system are thus of crucial importance towardthe understanding of the interlayer physics and the microscopicmechanism of high-Tc superconductivity in the iron pnictides.

In this paper we report a study of the electronic structureof the Ca-Fe-Pt-As system for n = 3 [the 10-3-8 phase withTc ∼ 8 K] using angle-resolved photoemission spectroscopy(ARPES) as well as first-principles calculations. ARPESmeasurements reveal the three-dimensional Fermi surfacetopology and the band structure close to EF . We observewell-defined Fermi surfaces with tetragonal symmetry thatare similar to those of other iron-based superconductors,

even though arising from an unambiguously triclinic crystalstructure with a larger in-plane unit cell. First-principles bandcalculations find very small contribution of the platinumdensity of states at EF for the 10-3-8 phase. These resultsare indicative of a weak interlayer hopping between the FeAsand the PtAs intermediary layers in this Ca-Fe-Pt-As system.

II. METHODS

High-quality single crystals of the 10-3-8 phase used in thisstudy were grown by a conventional flux method.2 ARPESmeasurements were performed in the Synchrotron RadiationCenter (SRC), Wisconsin, using a VG-Scienta R4000 electronanalyzer. Energy resolution was set to 10–30 meV. Sampleswere cleaved in situ and measured at 10–30 K under a vacuumcondition better than 4 × 10−11 Torr. The samples were foundto be very stable and without degradation for the typicalmeasurement period of 20 h. First-principles calculations arebased on the density functional theory (DFT) framework plusthe local density approximation (LDA), the Ceperley-Alderexchange-correlation functional,18 and projector augmentedwave method,19 all implemented in the VASP package.20 Thecrystal structure of the 10-3-8 phase is taken from Ref. 2, andthe off-(Pt3As8) Pt atom is assigned to a position above the(Pt3As8) plane.2 The self-consistency of bulk calculation isdone with 8 × 8 × 8 k-point mesh. For in-plane Fermi surfacecalculation, the k mesh is increased to 201 × 201 in the kx-ky

plane. The total energy convergence with respect to the k pointis 0.3 meV per atom. The kinetic energy cutoff is 280 eV.

III. RESULTS AND DISCUSSION

We begin our discussion with a detailed examination ofthe crystallographic properties of the 10-3-8 single crystal, assummarized in Fig. 1. This crystal has a triclinic unit cell withprimitive vectors of length a = b = 8.759 A, c = 10.641 A,α = 94.744◦, β = 104.335◦, and γ = 90.044◦ � 90◦ (Ref. 2)

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FIG. 1. (Color online) Crystallographic and superconductingproperties of Ca10(Pt3As8)(Fe2As2)5 (10-3-8). (a) Crystal structureof the 10-3-8 phase. (b)–(c) Schematic crystal structure in (b) thea-b plane and (c) three dimensions. (d) Low-temperature resistivity(right axis) and magnetic susceptibility (left axis) for the 10-3-8 phase.(e) Laue picture of a 10-3-8 single crystal. Reflection peaks for boththe triclinic (yellow circles) and tetragonal (orange squares) latticesare clearly observed.

[see Fig. 1(a)–1(c) for definitions]. Markedly, such a triclinicatomic arrangement is experienced only by the platinum atomsin the crystal; the calcium atoms and the FeAs4 tetrahedraarrange in a tetragonal fashion with lattice parameters a0 =b0 = 3.917 A, c0 = 20.548 A. From Fig. 1(b) one notices thatthe in-plane triclinic unit cell is essentially a

√5 superlattice

that forms along the (210) direction of the tetragonal cell,making an in-plane inclusion angle of θ = arctan(1/2) =26.56◦ and a length relation a = √

5a0 between the twolattices. Figure 1(c) reveals that the top and bottom surfacecenters of the triclinic unit cell displace horizontally via anin-plane vector (a0/2, a0/2). Therefore, the height of the

tetragonal cell measures c0 = 2√

c2 − a20/2 = 20.548 A. If the

interlayer hopping between the PtAs and FeAs layers is weak,the ARPES Fermi surface should reflect a similar topology tothe other prototype pnictides, with possibly weak FeAs shadowbands associated with superlattice folding and additionalfeatures associated with the PtAs layer. Figure 1(d) presents thesuperconducting properties of the 10-3-8 single crystals usedfor ARPES measurements. Both the resistivity and magneticsusceptibility data show clear signature of superconductivityat Tc ∼ 8 K. The transition width in temperature is less than3 K, indicating high quality and spatial homogeneity for theas-grown crystals.

Figure 1(e) shows the x-ray Laue picture of a 10-3-8 crystal.Reflection peaks are clearly resolved, and correspondinghigh-symmetry directions are marked and labeled. It is veryimportant to point out here that crystal twinning effectis unlikely to hinder the ARPES observation of the PtAssuperlattice. It is true that a sufficiently large crystal mustcontain structural domains in which the triclinic superlattice isrotated by either θ or −θ with respect to the tetragonal lattice.Thus, the ARPES signal for the triclinic PtAs lattice containsingredients from both domains, and the intensity for signalfrom each domain is weakened. We argue here, based on thex-ray Laue picture, that this effect should not be the mainreason for the invisibility of the ARPES superlattice signal. InFig. 1(e) reflection peaks for the triclinic lattice (yellow circles)are clearly observed at a clockwise angle of θ (±0.1◦ accuracy)with respect to the tetragonal lattice (orange squares). In thecounterclockwise angle of θ , however, reflection peaks are notpresent (or the intensity is very weak). This observation pointsout that the domains may have a preferred orientation, whichlimits the possible influence on the ARPES visibility. Wefurther state here that, even if there is no preferred orientationfor the structural domains, the ARPES signal for both domainswill still be visible given a large enough interlayer hopping,since these domains are well defined by bright peaks in x-raydiffraction. Therefore, the corresponding ARPES intensity willbe comparable to that of the tetragonal lattice.

We now present the ARPES data for the Fermi surfacetopology of the 10-3-8 phase. Figure 2(a) shows the Fermisurface plots for four different photon energies. The circular-or diamond-shaped α1 and α2 Fermi pockets around the zonecenter as well as the elliptical β1 Fermi pocket around the zonecorners are clearly observed. Raw ARPES intensity maps inFig. 2(b) and the corresponding energy distribution curves(EDCs) in Fig. 2(c) (cuts nos. 1 and 2) verify the holelikenature of the α1 and α2 bands and the electronlike nature ofthe β1 band. There is a less dispersive but clearly visible bandat a binding energy of ∼0.2 eV [tracked by brown markersin Fig. 2(c)]. First-principles calculation shows a considerablecontribution of the Pt d orbitals to the total density of states(DOS) at about 0.2–0.3 eV below EF . Thus, this band maybe influenced to some extent by the Pt 5d orbitals. Figure2(a) also reveals that the shape and sizes of the X electronpockets at the Brillouin zone corners are different than thoseof the observed holelike Fermi surfaces at the zone center. Asa result, the nesting condition among these Fermi surfaces isnot perfect. Based on the ARPES k-E maps [Fig. 2(b)], wealso calculate the Fermi velocities for the three Fermi crossingbands α1, α2, and β1. The values are vF (α1) ∼ 0.494 eV A,

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FIG. 2. (Color online) ARPES Fermi surface maps and k-E cuts for selected incident photon energies. (a) Fermi surface maps for fourdifferent photon energies (lower right corner in each panel). Inset of the 31 eV panel shows definition of high symmetry points and a schematicin-plane electronic structure. Brillouin zone sizes are determined based on the tetragonal cell [see Fig. 3(c) for relations between momenta inthe triclinic and tetragonal cells]. (b) Raw k-E maps and (c) corresponding energy distribution curves along directions marked by cut nos. 1–3in Fig. 2(a). The two hole pockets around �/Z0 and the electron pocket around X0 are labeled as α1, α2, and β1, respectively and are trackedwith blue (dark gray), green (medium gray), and pink (light gray) in Fig. 2(b)–2(c).

vF (α2) ∼ 0.182 eV A, and vF (β1) ∼ 0.587 eV A, which arevery similar to the ones obtained for BaFe2As2 (Ref. 30).

In Fig. 3 we present the variation of the electron and holepockets with photon energy, i.e., dispersion along the kz axisof the Brillouin zone. Figure 3(a) shows the kz dispersiondata (Fermi surface map in the �-X-Z plane). In Fig. 3(b)we plot the momentum distribution curves (MDCs) at EF foreach photon energy. The variation of α1 and α2 Fermi pocketsis tracked by blue and green markers. In Fig. 3(d) we plotthe raw ARPES k-E maps across the zone center at selectedphoton energies (kz values). The presence of multiple Fermicrossings is further verified by the MDCs (yellow curves atthe top of each intensity plot) at EF . The inner holelike Fermisurface (α1) shows considerable kz dispersion. In particular,the α1 pocket is essentially closed at kz values 19.4 and20.6π/c0, while the two MDC peaks at other kz values signifyits opening. This dispersive pattern results in ellipsoidal Fermipockets with a periodicity of 4π/c0. These observations arecaptured in the schematic three-dimensional Fermi surface[Fig. 3(c)]. It is worthwhile to point out that the presence ofkz dispersion proves the bulk sensitivity for the ARPES datain this compound. For other Fermi crossing bands, a weakintensity variation is observed for the α2 pocket, and almostno kz dispersion is observed for the β1 pockets, indicating thequasi-two-dimensional nature of these bands.

The most important observation from Figs. 2 and 3 is thatthe ARPES electronic structure has a tetragonal symmetry,and the experimental Brillouin zone size is proportional toπ/a0 rather than π/a in the kx-ky plane [Fig. 2(a)]. In otherwords, the ARPES signal reveals that the electronic system istetragonal, with the periodicity of the FeAs layer sublattice.This observation is noteworthy for two reasons. First, it points

out directly that the triclinic arrangement and larger supercellperiodicity of the platinum atoms have very little influence onthe electronic structure. If the platinum orbitals had a strongcontribution at EF , then the observation of Fermi pocketsarranged according to the triclinic Brillouin zone is expected.From this we deduce that the hybridization between bandsfrom the PtAs intermediary layers and those from the FeAslayers has to be weak. Although this is only a qualitativestatement, the unique crystal structure of the 10-3-8 phasedoes provide an important estimation of the interlayer hoppingstrength that is otherwise hard to obtain from experiment inthe FeAs superconductors: Interlayer hopping must be so weakthat it renders the triclinic lattice invisible by photoemission.Second, the ARPES electronic structure mimics the electronicstructures of other prototype pnictides like AEFe2As2 (“122”,AE = Ca, Sr, Ba, etc.). Not only the in-plane lattice parametera0 but also the shapes, sizes, and Fermi velocities of the �

and X0 Fermi pockets show very little difference with those ofthe 122 parent compounds.21–30 This indicates that a universalelectronic structure capturing the underlying superconductingmechanism may exist for different subfamilies of the Fe-basedsuperconductors (except for the KαFe2−βSe2 series, whereelectron pockets instead of hole pockets are observed aroundthe � point31,32).

Despite the overall similarity, there are observable dif-ferences between the Fermi surface of the 10-3-8 phaseand that of the prototype pnictides. In Fig. 4 we compareexplicitly the in-plane ARPES Fermi surfaces for the 10-3-8phase, BaFe2As2 (Ref. 33), and LaFeAsO (Ref. 34). First, theDirac-cone-like Fermi dots around the X points in BaFe2As2

are absent in the 10-3-8 phase [seen most clearly in the 42 eVpanel of Fig. 2(a)]. Since these dots are direct consequences

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FIG. 3. (Color online) Analysis of kz dispersion data. (a) kz dispersion data for the 10-3-8 phase, taken along the �-X0 direction withphoton energies 15 to 64 eV. Inner potential is set to 9.5 eV. (b) Momentum distribution curves (MDCs) for different kz values. Fermi crossingbands are marked with the same colors as in Fig. 2. (c) Schematics of an experiment-derived Fermi surface construction in three dimensions.(d) Raw ARPES k-E maps across the zone center (k = 0) for selected photon energies. Yellow (light gray) curves are MDCs at EF . The α1

band evolves below EF around 19.4 and 20.6 π/c0 and crosses EF for other photon energies, forming a bigger ellipsoidal hole pocket centeringat Z0/� and a smaller hole pocket centering at �/Z0.

of the long range antiferromagnetic order present in the 122compound,33,35 their absence is consistent with the absenceof an antiferromagnetic signature in transport measurementsup to room temperature.2 It is important to point out thatthe 10-3-8 phase is a superconductor, whereas no sign ofsuperconductivity is found in BaFe2As2. Related to theabsence or presence of the Fermi dots near the X point, ourfinding is consistent with the idea that superconductivity canbe found in the iron pnictide compounds only if the in-planeelectronic structure reduces to its paramagnetic appearance33

(except for the case of KαFe2−βSe2). Second, extended ARPESintensity along one of the �-X0 directions is seen only for the10-3-8 phase. A close look into the k-E maps (data of cut no. 3

in Fig. 2) reveals that there is a Fermi crossing in these locationsand that the band is holelike. We point out that this bandalso originates from the Fe orbitals, since it shows reflectivesymmetry along the high-symmetry directions of the iron unitcell rather than the triclinic platinum cell. Third, from the kz

dispersion data [Fig. 3(a)–3(b)], one notices that ellipsoidalhole pockets are observed around both the � and Z0 pointsfor the 10-3-8 phase, while in the 122 parent compounds onlyZ ellipsoids are observed.28,29 According to band calculation(Fig. 5), this signifies the weak but existent Pt influence on theFermi surface topology.

We now examine the electronic structure of the Ca-Fe-Pt-Assystem from the results of first-principles calculations.18–20 In

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FIG. 4. Comparison of in-plane ARPES Fermi surfaces of the 10-3-8 phase, BaFe2As2 (Ref. 33), and LaFeAsO (Ref. 34). Incident photonenergies are 22, 105, and 45 eV, respectively. The “Fermi dots” seen around the X pockets of BaFe2As2 come from antiferromagneticreconstructions of the electronic structure,33 and the large � hole pocket in LaFeAsO originates from surface effects.34

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orbitals (Pt1 and Pt2, respectively). Right column: Total DOS forall elements. Inset shows the integrated DOS (IDOS) near EF . (b)Calculated band structure of 10-3-8 in the triclinic Brillouin zone. Red(gray) dots indicate the contribution of platinum orbitals. (c) Fermisurfaces sketched in the triclinic zone. (d) Fermi surfaces unfoldedinto the tetragonal zone.

these calculations, spin-orbit coupling effects are not includedand EF is fixed assuming zero electron doping. The crystalstructure of the 10-3-8 phase is taken from Ref. 2 with theoff-plane Pt (Pt2) atom in the Pt3As8 layer assigned to oneof its two possible positions: slightly above the plane.2 Weshow in Fig. 5(a) the calculated curves for the total densityof states (DOS) as well as the partial DOS (PDOS) forthe two different kinds of platinum atoms [Pt1 and Pt2, seeFig. 1(a)]. Similar to the prototype pnictides, the DOS in thevicinity of EF for the 10-3-8 phase is dominated by Fe 3d

orbitals. In Fig. 5(b)–5(c), the calculated LDA band structureand Fermi surface are shown in the triclinic Brillouin zone.From Fig. 5(b) we see that the innermost � band has strongerkz dispersion than the other two holelike iron bands, whichis consistent with the ARPES observations [Fig. 3(a)–3(c)].This band is hybridized with the Pt dxz orbitals. Since theexperimental data reveal no sign of the triclinic Fermi surfaces,we assume that the potential from the

√5 superlattice arising

from the Pt3As8 layers is very weak, in which case we canapproximately “unfold” the LDA superlattice band structureinto the tetragonal BZ, as shown in Fig. 5(d). The tetragonal �,

X0, and M0 points form a subset of the supercell �, X, and M

points. Therefore, we systematically “erase” all superlattice FSmaps not associated with the tetragonal symmetry points. FromFig. 5(d), we see that this process works well for the Fe Fermisurfaces, reproducing the familiar 122 structure. The fate ofthe electronlike Pt bands (the four pedal-like small pocketsnear �) under this unfolding process is less clear, but it shouldbe noted that these pockets are not clearly distinguished byARPES.

Interlayer hopping plays an important role in the presenceof high-Tc superconductivity in both the cuprates and theFe-based superconductors. It is believed that the hoppingstrength in the prototype pnictides is somewhat strongerthan that in the cuprates (although still on the weak side)and that this may lead to the differences between Tc andpairing symmetry in these two families. Zhai et al. proposethat the superconducting gap symmetry changes from d-waveto s-wave with increasing hopping strength.36 Although themodel in Ref. 36 may not apply directly to the Ca-Fe-Pt-Assystems, where spin density wave signatures have not yetbeen detected at low temperatures, it is likely that the uniquemomentum-space separation of the inter- and intralayer signalsin the 10-3-8 system helps to determine the hopping strengthwith considerably higher accuracy, thus shedding light on theultimate determination of the superconducting mechanism inboth classes of high-Tc superconductors.

IV. CONCLUSION

In conclusion, we have presented a systematic study ofthe band structure and Fermi surfaces of one of the Ca-Fe-Pt-As superconductors in the vicinity of EF . Our ARPESobservations, reduced tetragonal electronic structure and littlekz dispersion, point to a weak interlayer hopping strengthin this system. The Dirac-cone-like Fermi dots around X

are absent in the 10-3-8 phase, consistent with the absenceof long-range antiferromagnetism in this compound. First-principles calculations agree well with experimental data ifthe potential from the

√5 superlattice arising from the PtAs

layers is considered to be very weak, and the triclinic bandstructure can be unfolded onto the tetragonal Brillouin zone.The Ca-Fe-Pt-As superconductors are ideal systems for thestudy of interlayer hopping in the iron-based superconductors.The present detailed study of the electronic structure of the10-3-8 phase serves as an important step in that direction.

ACKNOWLEDGMENTS

M.N. and C.L. contributed equally in this work. C.L.acknowledges T. Kondo and A. Kaminski for provision ofdata analysis software. Work at Princeton is supported byNSF-DMR-1006492 and the AFOSR MURI on supercon-ductivity. The Synchrotron Radiation Center is supportedby NSF-DMR-0537588. Work at Northeastern is supportedby the Basic Energy Sciences, US Department of Energy(DE-FG02-07ER46352 and AC03-76SF00098), and benefitedfrom the allocation of supercomputer time at NERSC andNortheastern University’s Advanced Scientific ComputationCenter. M.Z.H. acknowledges Visiting Scientist support fromLBNL and additional support from the A. P. Sloan Foundation.

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1K. Kudo et al., International Workshop on Novel Superconductorsand Super Materials, 6–8 March, Tokyo, Japan (2011).

2N. Ni, J. M. Allred, B. C. Chan, and R. J. Cava, Proc. Natl. Acad.Sci. USA 108, E1019 (2011).

3C. Lohnert, T. Sturzer, M. Tegel, R. Frankovsky, G. Friederichs,and D. Johrendt, Angew. Chem. Int. Ed. 50, 9195 (2011).

4S. Kakiya, K. Kudo, Y. Nishikubo, K. Oku, E. Nishibori, H. Sawa,T. Yamamoto, T. Nozaka, and M. Nohara, J. Phys. Soc. Jpn. 80,093704 (2011).

5Y. Kamihara, T. Watanabe, M. Hirano, and H. Hosono, J. Am.Chem. Soc. 130, 3296 (2008).

6M. Rotter, M. Tegel, and D. Johrendt, Phys. Rev. Lett. 101, 107006(2008).

7X. C. Wang, Q. Q. Liu, Y. X. Lv, W. B. Gao, L. X. Yang, R. C. Yu,F. Y. Li, and C. Q. Jin, Solid State Commun. 148, 538 (2008).

8F.-C. Hsu, J.-Y. Luo, K.-W. Yeh, T.-K. Chen, T.-W. Huang, P. M.Wu, Y.-C. Lee, Y.-L. Huang, Y.-Y. Chu, D.-C. Yan, and M.-K. Wu,Proc. Natl. Acad. Sci. USA 105, 14262 (2008).

9J. Guo, S. Jin, G. Wang, S. Wang, K. Zhu, T. Zhou, M. He, andX. Chen, Phys. Rev. B 82, 180520(R) (2010).

10D. C. Johnston, Adv. Phys. 59, 803 (2010).11P. C. Canfield, S. L. Bud’ko, N. Ni, J. Q. Yan, and A. Kracher, Phys.

Rev. B 80, 060501(R) (2009).12N. Ni and S. L. Bud’ko, MRS Bull. 36, 620 (2011).13J. G. Bednorz and K. A. Muller, Z. Phys. B 64, 189 (1986).14D. M. Ginsberg, Physical Properties of High Temperature Super-

conductors, Vol. 5 (World Scientific, Singapore, 1996).15A. Mourachkine, High-Temperature Superconductivity in Cuprates:

The Nonlinear Mechanism and Tunneling Measurements (Springer,New York, 2002).

16A. Damascelli, Z. Hussain, and Z.-X. Shen, Rev. Mod. Phys. 75,473 (2003).

17J. C. Campuzano, M. Norman, and M. Randeria, in Superconductiv-ity: Physics of Conventional and Unconventional Superconductors,Vol. 1, edited by K. H. Bennemann and J. B. Ketterson (Springer,Berlin, 2008).

18G. Kresse and D. Joubert, Phys. Rev. B 59, 1758 (1999).19P. E. Blochl, Phys. Rev. B 50, 17953 (1994).20G. Kresse and J. Furthmuller, Comput. Mater. Sci. 6, 15 (1996).21H. Ding, P. Richard, K. Nakayama, K. Sugawara, T. Arakane,

Y. Sekiba, A. Takayama, S. Souma, T. Sato, T. Takahashi, Z. Wang,X. Dai, Z. Fang, G. F. Chen, J. L. Luo, and N. L. Wang, Europhys.Lett. 83, 47001 (2008).

22L. Zhao, H.-Y. Liu, W.-T. Zhang, J.-Q. Meng, X.-W. Jia, G.-D. Liu,X.-L. Dong, G.-F. Chen, J.-L. Luo, N.-L. Wang, W. Lu, G.-L. Wang,Y. Zhou, Y. Zhu, X.-Y. Wang, Z.-Y. Xu, C.-T. Chen, and X.-J. Zhou,Chin. Phys. Lett. 25, 4402 (2008).

23L. Wray, D. Qian, D. Hsieh, Y. Xia, L. Li, J. G. Checkelsky,A. Pasupathy, K. K. Gomes, C. V. Parker, A. V. Fedorov, G. F.

Chen, J. L. Luo, A. Yazdani, N. P. Ong, N. L. Wang, and M. Z.Hasan, Phys. Rev. B 78, 184508 (2008).

24Y. Xia, L. Wray, D. Qian, D. Hsieh, H. Lin, A. Bansil, D. Grauer,Y. Hor, R. J. Cava, and M. Z. Hasan, Nature Phys. 5, 398 (2009).

25V. B. Zabolotnyy, D. S. Inosov, D. V. Evtushinsky, A. Koitzsch,A. A. Kordyuk, G. L. Sun, J. T. Park, D. Haug, V. Hinkov,A. V. Boris, C. T. Lin, M. Knupfer, A. N. Yaresko, B. Buchner,A. Varykhalov, R. Follath, and S. V. Borisenko, Nature (London)457, 569 (2009).

26P. Richard, T. Sato, K. Nakayama, S. Souma, T. Takahashi, Y.-M.Xu, G. F. Chen, J. L. Luo, N. L. Wang, and H. Ding, Phys. Rev.Lett. 102, 047003 (2009).

27A. Koitzsch, D. S. Inosov, D. V. Evtushinsky, V. B. Zabolotnyy,A. A. Kordyuk, A. Kondrat, C. Hess, M. Knupfer, B. Buchner,G. L. Sun, V. Hinkov, C. T. Lin, A. Varykhalov, and S. V. Borisenko,Phys. Rev. Lett. 102, 167001 (2009).

28C. Liu, T. Kondo, N. Ni, A. D. Palczewski, A. Bostwick, G. D.Samolyuk, R. Khasanov, M. Shi, E. Rotenberg, S. L. Bud’ko,P. C. Canfield, and A. Kaminski, Phys. Rev. Lett. 102, 167004(2009).

29T. Kondo, R. M. Fernandes, R. Khasanov, C. Liu, A. D. Palczewski,N. Ni, M. Shi, A. Bostwick, E. Rotenberg, J. Schmalian, S. L.Bud’ko, P. C. Canfield, and A. Kaminski, Phys. Rev. B 81,060507(R) (2010).

30H. Ding, K. Nakayama, P. Richard, S. Souma, T. Sato, T. Takahashi,M. Neupane, Y.-M. Xu, Z.-H. Pan, A. V. Federov, Z. Wang, X. Dai,Z. Fang, G. F. Chen, J. L. Luo, and N. L. Wang, J. Phys. Condens.Matter 13, 135701 (2011).

31Y. Zhang, L. X. Yang, M. Xu, Z. R. Ye, F. Chen, C. He, H. C. Xu,J. Jiang, B. P. Xie, J. J. Ying, X. F. Wang, X. H. Chen, J. P. Hu,M. Matsunami, S. Kimura, and D. L. Feng, Nat. Mater. 10, 273(2011).

32T. Qian, X.-P. Wang, W.-C. Jin, P. Zhang, P. Richard, G. Xu, X. Dai,Z. Fang, J.-G. Guo, X.-L. Chen, and H. Ding, Phys. Rev. Lett. 106,187001 (2011).

33C. Liu, T. Kondo, R. M. Fernandes, A. D. Palczewski, E.-D. Mun,N. Ni, A. N. Thaler, A. Bostwick, E. Rotenberg, J. Schmalian,S. L. Bud’ko, P. C. Canfield, and A. Kaminski, Nature Phys. 6, 419(2010).

34C. Liu, Y. Lee, A. D. Palczewski, J.-Q. Yan, T. Kondo, B. N.Harmon, R. W. McCallum, T. A. Lograsso, and A. Kaminski, Phys.Rev. B 82, 075135 (2010).

35Y. Xia, L. Wray, D. Qian, D. Hsieh, H. Lin, A. Bansil, D. Grauer,Y. Hor, R. J. Cava, and M. Z. Hasan, Nature Phys. 5, 398 (2009);D. Hsieh, D. Qian, L. Wray, Y. Xia, Y. Hor, R. J. Cava, and M. Z.Hasan, Nature (London) 452, 970 (2008); M. Z. Hasan and B. A.Bernevig, Physics 3, 27 (2010).

36H. Zhai, F. Wang, and D.-H. Lee, Phys. Rev. B 80, 064517 (2009)and references therein.

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