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[show abstract]
[hide abstract]
ABSTRACT: Systematic high resolution angle-resolved photoemission spectroscopic studies have been performed on the optimally electron-doped
BaFe1.82Co0.18As2 (T
c
=24K) and hole-doped Ba0.6K0.4Fe2As2 (T
c
=37K) superconductors. The superconducting gap is nearly isotropic in momentum space. Utilizing different experimental geometries,
the detailed electronic band structures were determined experimentally and compared with first principle LDA calculations.
The overall bandwidth is reduced by a factor of2. However, the low energy quasiparticle dispersions near zone corner exhibit
stronger renormalization by a factor of 4–5. k
z
dependence was observed on the electron pockets at zone corner.
Electronic structures-Pnictide
Journal of Superconductivity and Novel Magnetism 04/2012; 23(5):617-619. · 0.65 Impact Factor
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D. Hsieh,
Y Xia, L. Wray,
D. Qian,
J. H. Dil,
F. Meier,
L. Patthey,
J. Osterwalder,
G. Bihlmayer,
Y. S. Hor,
R. J. Cava,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: We report high-resolution spin-resolved photoemission spectroscopy
(Spin-ARPES) measurements on the parent compound Sb of the first discovered 3D
topological insulator Bi{1-x}Sb{x} [D. Hsieh et al., Nature 452, 970 (2008)
Submitted 2007]. By modulating the incident photon energy, we are able to map
both the bulk and (111) surface band structure, from which we directly
demonstrate that the surface bands are spin polarized by the spin-orbit
interaction and connect the bulk valence and conduction bands in a
topologically non-trivial way. A unique asymmetric Dirac surface state gives
rise to a $k$-splitting of its spin polarized electronic channels. These
results complement our previously published works on this materials class and
re-confirm our discovery of first bulk (3D) topological insulator - topological
order in bulk solids. [Invited article for NJP-IOP Focus issue on "Topological
Insulators"]
03/2011;
-
D Hsieh, L Wray,
D Qian,
Y Xia,
J H Dil,
F Meier,
L Patthey,
J Osterwalder,
G Bihlmayer,
Y S Hor,
R J Cava,
M Z Hasan
[show abstract]
[hide abstract]
ABSTRACT: We report high-resolution spin-resolved photoemission spectroscopy (spin-ARPES) measurements on the parent compound Sb of the recently discovered three-dimensional topological insulator Bi1−xSbx (Hsieh et al 2008 Nature 452 970, Hsieh et al 2009 Science 323 919). By modulating the incident photon energy, we are able to map both the bulk and the (111) surface band structure, from which we directly demonstrate that the surface bands are spin polarized by the spin–orbit interaction and connect the bulk valence and conduction bands in a topologically non-trivial way. A unique asymmetric Dirac surface state gives rise to a k-splitting of its spin-polarized electronic channels. These results complement our previously published works on this class of materials and re-confirm our discovery of topological insulator states in the Bi1−xSbx series.
New Journal of Physics 11/2010; 12(12):125001. · 4.18 Impact Factor
-
D. Hsieh,
Y Xia,
D. Qian, L. Wray,
J. H. Dil,
F. Meier,
J. Osterwalder,
L. Patthey,
J. G. Checkelsky,
N. P. Ong,
A. V. Fedorov,
H Lin,
A. Bansil,
D. Grauer,
Y. S. Hor,
R. J. Cava,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: Both the theoretical and experimental discovery of single-Dirac-cone topological-insulator-class was reported at arXiv:0812.2078 (2008) [Y. Xia et.al., Nature Physics 5, 398-402 (2009) http://www.nature.com/nphys/journal/v5/n6/full/nphys1294.html]. Here we report the first observation of Spin-Momentum Helical Locking and Spin-Vortex structures in Bi2Se3 and Bi2Te3, demonstrate the existence of Topological-Order at 300K and report a material realization of topological-transport-regime for helical Dirac fermions. Our results reveal a one-to-one spin-momentum locked Dirac structure in Bi2Se3 and Bi2Te3 that is nearly 100% spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers' point and can be driven to the long-sought topological-transport-regime. The observed topological nodal Dirac ground state is found to be protected even up to room temperature (300 K). Our results pave the way for future transport based studies of topological insulators, and possible room temperature applications of protected spin-polarized edge channels we observe with spin-ARPES in spintronic technology. All of these new results are made possible due to the Spin-resolved-ARPES (Mott polarimetric) technique [http://www.nature.com/nature/journal/v460/n7259/full/nature08234.html ] . Comment: 17 pages, 4 Figures, Published nature-Online in July-2009, Submitted to NATURE in April-2009
01/2010;
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[show abstract]
[hide abstract]
ABSTRACT: The Cu-doped topological insulator Bi$_2$Se$_3$ has recently been found to undergo a superconducting transition upon cooling, raising the possibilities that it is the first known "topological superconductor" or realizes a novel non-Abelian superconducting state. Its true nature depends critically on the bulk and surface state band topology. We present the first photoemission spectroscopy results where by examining the band topology at many different copper doping values we discover that the topologically protected spin-helical surface states remain well protected and separate from bulk Dirac bands at the Fermi level where Copper pairing occurs in the optimally doped topological insulator. The addition of copper is found to result in nonlinear electron doping and strong renormalization of the topological surface states. These highly unusual observations strongly suggest that superconductivity on the topological surface of Cu$_x$Bi$_2$Se$_3$ cannot be of any conventional type in account of the general topological theory. Characteristics of the three dimensional bulk Dirac band structure are reported for the first time with respect to the superconducting doping state and topological invariant properties which should help formulate a specific theory for this novel superconductor. Comment: 4 Figures, 5 pages, Submitted December 2009
12/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the extreme quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi{1-x}Sbx single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic spin-textured surface states that are higher dimensional analogues of the edge states that characterize a quantum spin Hall insulator. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy, we report the direct observation of massive Dirac particles in the bulk of Bi0.9Sb0.1, locate the Kramers' points at the sample's boundary and provide a comprehensive mapping of the topological Dirac insulator's gapless surface modes. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the much sought exotic "topological metal". They also suggest that this material has potential application in developing next-generation quantum computing devices that may incorporate "light-like" bulk carriers and topologically protected spin-textured edge-surface currents. This work is a detailed version of [Hsieh et.al., NATURE 452, 970 (2008), {Submitted in November 2007}]. Comment: 12 pages, 7 figures, This is a detailed version of the work presented at NATURE 452, 970 (2008), {Submitted in November 2007}
10/2009;
-
D Hsieh,
Y Xia,
D Qian, L Wray,
F Meier,
J H Dil,
J Osterwalder,
L Patthey,
A V Fedorov,
H Lin,
A Bansil,
D Grauer,
Y S Hor,
R J Cava,
M Z Hasan
[show abstract]
[hide abstract]
ABSTRACT: We show that the strongly spin-orbit coupled materials Bi2Te3 and Sb2Te3 and their derivatives belong to the Z2 topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that Bi2Te3 is a large spin-orbit-induced indirect bulk band gap (delta approximately 150 meV) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped Sb2Te3 exhibits similar Z2 topological properties. We demonstrate that the dynamics of spin-Dirac fermions can be controlled through systematic Mn doping, making these materials classes potentially suitable for topological device applications.
Physical Review Letters 10/2009; 103(14):146401. · 7.37 Impact Factor
-
D. Hsieh,
Y Xia, L. Wray,
D. Qian,
A. Pal,
J. H. Dil,
F. Meier,
J. Osterwalder,
G. Bihlmayer,
C. L. Kane,
Y. S. Hor,
R. J. Cava,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry based classification of condensed matter. Exotic spin transport phenomena such as the dissipationless quantum spin Hall effect have been speculated to originate from a novel topological order whose identification requires a spin sensitive measurement. Using Spin-resolved-ARPES, we probe the spin degrees of freedom and demonstrate that topological quantum numbers are uniquely determined from spin-texture Berry Phase imaging measurements. Applying this method to pure antimony (Sb) and Bi-Sb, we identify the origin of its novel Topological Order and the negative value of the mirror Chern number. These results taken together constitute the first observation of surface electrons collectively carrying a topological Berry's phase and definite mirror Chern chirality in pure Antimony (Sb) which are the key electronic properties for realizing topological quantum computing via the interface Majorana fermion framework. This paper contains the details of the above mentioned previously reported (Science \textbf{323}, 919 (2009)) results. Comment: 6 Figures, 10 Pages, RevTex Format, Detailed version of Hsieh et.al., SCIENCE 323, 919 (2009)
09/2009;
-
D. Hsieh,
Y Xia,
D. Qian, L. Wray,
J. H. Dil,
F. Meier,
J. Osterwalder,
L. Patthey,
A. V. Fedorov,
H Lin,
A. Bansil,
D. Grauer,
Y. S. Hor,
R. J. Cava,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: We show that the strongly spin-orbit coupled materials Bi2Te3 and Sb2Te3 (first non-Bi topological insulator) and their derivatives belong to the Z2 (Time-Reversal-Protected, elastic backscattering suppressed) topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that Bi2Te3 is a large spin-orbit-induced indirect bulk band gap (about 150 meV) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped Sb2Te3 exhibits similar Z2 topological properties. We demonstrate that the dynamics of surface spin-only Dirac fermions can be controlled through systematic Mn doping, making these materials classes potentially suitable for exploring novel topological physics. We emphasize (theoretically and experimentally) that the Dirac node is well within the bulk-gap and not degenerate with the bulk valence band. Comment: 5 Pages, 4 Figures, Accepted for publication in Physical Review Letters (submitted, June 2009)
09/2009;
-
Y Xia,
D. Qian,
D. Hsieh, L. Wray,
A. Pal,
H Lin,
A. Bansil,
D. Grauer,
Y. S. Hor,
R. J. Cava,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: Recent theories and experiments have suggested that strong spin-orbit coupling effects in certain band insulators can give rise to a new phase of quantum matter, the so-called topological insulator, which can show macroscopic entanglement effects. Such systems feature two-dimensional surface states whose electrodynamic properties are described not by the conventional Maxwell equations but rather by an attached axion field, originally proposed to describe strongly interacting particles. It has been proposed that a topological insulator with a single spin-textured Dirac cone interfaced with a superconductor can form the most elementary unit for performing fault-tolerant quantum computation. Here we present an angle-resolved photoemission spectroscopy study and first-principle theoretical calculation-predictions that reveal the first observation of such a topological state of matter featuring a single-surface-Dirac-cone realized in the naturally occurring Bi$_2$Se$_3$ class of materials. Our results, supported by our theoretical predictions and calculations, demonstrate that undoped compound of this class of materials can serve as the parent matrix compound for the long-sought topological device where in-plane surface carrier transport would have a purely quantum topological origin. Our study further suggests that the undoped compound reached via n-to-p doping should show topological transport phenomena even at room temperature. Comment: 3 Figures, 18 pages, Submitted to NATURE PHYSICS in December 2008
08/2009;
-
D Hsieh,
Y Xia,
D Qian, L Wray,
J H Dil,
F Meier,
J Osterwalder,
L Patthey,
J G Checkelsky,
N P Ong,
A V Fedorov,
H Lin,
A Bansil,
D Grauer,
Y S Hor,
R J Cava,
M Z Hasan
[show abstract]
[hide abstract]
ABSTRACT: Helical Dirac fermions-charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum-are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose-Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene or bismuth. It has recently been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators-materials with a bulk insulating gap of spin-orbit origin and surface states protected against scattering by time-reversal symmetry-and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime. However, helical Dirac fermions have not been observed in existing topological insulators. Here we report the realization and characterization of a tunable topological insulator in a bismuth-based class of material by combining spin-imaging and momentum-resolved spectroscopies, bulk charge compensation, Hall transport measurements and surface quantum control. Our results reveal a spin-momentum locked Dirac cone carrying a non-trivial Berry's phase that is nearly 100 per cent spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers point and can be driven to the long-sought topological spin transport regime. The observed topological nodal state is shown to be protected even up to 300 K. Our demonstration of room-temperature topological order and non-trivial spin-texture in stoichiometric Bi(2)Se(3).M(x) (M(x) indicates surface doping or gating control) paves the way for future graphene-like studies of topological insulators, and applications of the observed spin-polarized edge channels in spintronic and computing technologies possibly at room temperature.
Nature 08/2009; 460(7259):1101-5. · 36.28 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report the first photoemission study of Fe1+xTe-the host compound of the newly discovered iron-chalcogenide superconductors (maximum Tc approximately 27 K). Our results reveal a pair of nearly electron-hole compensated Fermi pockets, strong Fermi velocity renormalization, and an absence of a spin-density-wave gap. A shadow hole pocket is observed at the "X" point of the Brillouin zone which is consistent with a long-range ordered magnetostructural ground state. No signature of Fermi surface nesting instability associated with Q=(pi/2,pi/2) is observed. Our results collectively reveal that the Fe1+xTe series is different from the undoped phases of the high Tc pnictides and likely harbor an unusual mechanism for superconductivity and magnetic order.
Physical Review Letters 08/2009; 103(3):037002. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report the first photoemission study of Fe$_{1+x}$Te - the host compound of the newly discovered iron-chalcogenide superconductors (maximum T$_c$ $\sim$ 27K). Our results reveal a pair of nearly electron-hole compensated Fermi pockets, strong Fermi velocity renormalization and an absence of a spin-density-wave gap. A shadow hole pocket is observed at the X-point of the Brillouin zone which is consistent with a long-range ordered magneto-structural groundstate. No signature of Fermi surface nesting instability associated with Q=($\pi$/2, $\pi$/2) is observed. Our results collectively reveal that the Fe$_{1+x}$Te series is dramatically different from the high T$_{c}$ pnictides and likely harbor unusual mechanism for superconductivity and magnetic order. Comment: 10 pages, 4 Figures, Accepted for publications in Physical Review Letters (2009)
06/2009;
-
D. Hsieh,
Y Xia,
D. Qian, L. Wray,
J. H. Dil,
F. Meier,
L. Patthey,
J. Osterwalder,
A. V. Fedorov,
H Lin,
A. Bansil,
D. Grauer,
Y. S. Hor,
R. J. Cava,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: Electron systems that possess light-like dispersion relations or the conical Dirac spectrum, such as graphene and bismuth, have recently been shown to harbor unusual collective states in high magnetic fields. Such states are possible because their light-like electrons come in spin pairs that are chiral,which means that their direction of propagation is tied to a quantity called pseudospin that describes their location in the crystal lattice. An emerging direction in quantum materials research is the manipulation of atomic spin-orbit coupling to simulate the effect of a spin dependent magnetic field,in attempt to realize novel spin phases of matter. This effect has been proposed to realize systems consisting of unpaired Dirac cones that are helical, meaning their direction of propagation is tied to the electron spin itself, which are forbidden to exist in graphene or bismuth. The experimental existence of topological order can not be determined without spin-resolved measurements. Here we report a spin-and angle-resolved photoemission study of the hexagonal surface of the Bi2Te3 and Bi{2-x}MnxTe3 series, which is found to exhibit a single helical Dirac cone that is fully spin-polarized. Our observations of a gap in the bulk spin-degenerate band and a spin-resolved surface Dirac node close to the chemical potential show that the low energy dynamics of Bi2Te3 is dominated by the unpaired spin-helical Dirac modes. Our spin-texture measurements prove the existence of a rare topological phase in this materials class for the first time, and suggest its suitability for novel 2D Dirac spin device applications beyond the chiral variety or traditional graphene. Comment: 13 pages, 4 figures
04/2009;
-
D Hsieh,
Y Xia, L Wray,
D Qian,
A Pal,
J H Dil,
J Osterwalder,
F Meier,
G Bihlmayer,
C L Kane,
Y S Hor,
R J Cava,
M Z Hasan
[show abstract]
[hide abstract]
ABSTRACT: A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry-based classification of condensed matter. Exotic spin-transport phenomena, such as the dissipationless quantum spin Hall effect, have been speculated to originate from a topological order whose identification requires a spin-sensitive measurement, which does not exist to this date in any system. Using Mott polarimetry, we probed the spin degrees of freedom and demonstrated that topological quantum numbers are completely determined from spin texture-imaging measurements. Applying this method to Sb and Bi(1-x)Sb(x), we identified the origin of its topological order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a topological quantum Berry's phase and definite spin chirality, which are the key electronic properties component for realizing topological quantum computing bits with intrinsic spin Hall-like topological phenomena.
Science 03/2009; 323(5916):919-22. · 31.20 Impact Factor
-
D. Hsieh,
Y Xia, L. Wray,
D. Qian,
A. Pal,
J. H. Dil,
F. Meier,
J. Osterwalder,
G. Bihlmayer,
C. L. Kane,
Y. S. Hor,
R. J. Cava,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry based classification of condensed matter. Exotic spin transport phenomena such as the dissipationless quantum spin Hall effect have been speculated to originate from a novel topological order whose identification requires a spin sensitive measurement, which does not exist to this date in any system (neither in Hg(Cd)Te quantum wells nor in the topological insulator BiSb). Using Mott polarimetry, we probe the spin degrees of freedom of these quantum spin Hall states and demonstrate that topological quantum numbers are uniquely determined from spin texture imaging measurements. Applying this method to the Bi{1-x}Sb{x} series, we identify the origin of its novel order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a geometrical quantum (Berry's) phase and definite chirality (mirror Chern number, n_M =-1), which are the key electronic properties for realizing topological computing bits with intrinsic spin Hall-like topological phenomena. Our spin-resolved results not only provides the first clear proof of a topological insulating state in nature but also demonstrate the utility of spin-resolved ARPES technique in measuring the quantum spin Hall phases of matter. Comment: 15 pages, 3 figures, first Submitted to SCIENCE on July-22, 2008
02/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the extreme quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic field. Bulk Bi$_{1-x}$Sb$_x$ single crystals are expected to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher dimensional analogues of the edge states that characterize a spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi$_{1-x}$Sb$_x$ is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest. Here, using incident-photon-energy-modulated (IPEM-ARPES), we report the first direct observation of massive Dirac particles in the bulk of Bi$_{0.9}$Sb$_{0.1}$, locate the Kramers' points at the sample's boundary and provide a comprehensive mapping of the topological Dirac insulator's gapless surface modes. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the much sought exotic "topological metal". They also suggest that this material has potential application in developing next-generation quantum computing devices. Comment: 16 pages, 3 Figures. Submitted to NATURE on 25th November(2007)
02/2009;
-
L. 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,
M. Z. Hasan
[show abstract]
[hide abstract]
ABSTRACT: We present a systematic angle-resolved photoemission spectroscopic study of the high-Tc superconductor class (Sr/Ba){1-x}(K/Na)xFe2As2. By utilizing a photon-energy-modulation contrast and scattering geometry we report the Fermi surface and the momentum dependence of the superconducting gap, Delta(k). A prominent quasiparticle dispersion kink reflecting strong scattering processes is observed in a binding-energy range of 25-55 meV in the superconducting state, and the coherence length or the extent of the Cooper pair wave function is found to be about 20-angstrom, which is uncharacteristic of a superconducting phase realized by the BCS-phonon-retardation mechanism. The observed 40 meV kink likely reflects contributions from the frustrated spin excitations and scattering from the soft phonons. Results taken collectively provide direct clues to the nature of the pairing potential including an internal phase-shift factor in the superconducting order parameter which leads to a Brillouin zone node in a strong-coupling setting.
01/2009;
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[show abstract]
[hide abstract]
ABSTRACT: Like high Tc cuprates, the newly discovered iron based superconductors lie in close proximity to a magnetically ordered parent phase. However, while the magnetic order in parent cuprates is known to derive from a spin-spin local superexchange interaction, a plethora of experiments including neutron scattering have so far been unable to conclusively resolve whether a local moment Heisenberg description applies in parent iron based compounds, or whether magnetism arises from a collective SDW order instability. These two alternatives can in principle be distinguished by measuring the low energy momentum-resolved bulk-representative electronic structure of the magnetically ordered phase. Using a combination of polarization dependent ARPES and STM, we have isolated the complete low-lying bulk representative electronic structure of magnetic SrFe2As2 with d-orbital symmetry specificity for the first time. Our results show that while multiple bands with different iron d-orbital character indeed contribute to charge transport, only one pair of bands with opposite mirror symmetries microscopically exhibit an itinerant SDW instability with energy scales on the order of 50 meV. The orbital resolved band topology below T_SDW point uniquely to a nesting driven band hybridization mechanism of the observed antiferromagnetism in the iron pnictides, and is consistent with an unusual anisotropic nodal-density-wave state. In addition, these results place strong constraints on many theories of pnictide superconductivity that require a strict local moment magnetism starting point.
01/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: We report the first photoemission study of Fe1+xTe - the host compound of the
newly discovered iron-chalcogenide superconductors. Our results reveal a pair
of nearly electron- hole compensated Fermi pockets, strong Fermi velocity
renormalization and an absence of a spin-density-wave gap. A shadow hole pocket
is observed at the "X"-point of the Brillouin zone which is consistent with a
long-range ordered magneto-structural groundstate. No signature of Fermi
surface nesting instability associated with Q= pi(1/2, 1/2) is observed. Our
results collectively reveal that the Fe1+xTe series is dramatically different
from the undoped phases of the high Tc pnictides and likely harbor unusual
mechanism for superconductivity and quantum magnetic order.
01/2009;
