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W. S. Lee,
A. P. Sorini,
M. Yi,
Y. D. Chuang,
B. Moritz, W. L. Yang,
J. -H. Chu,
H. H. Kuo,
A. G. Cruz Gonzalez,
I. R. Fisher,
Z. Hussain,
T. P. Devereaux,
Z. X. Shen
[show abstract]
[hide abstract]
ABSTRACT: We performed resonant soft X-ray diffraction on known charge density wave
(CDW) compounds, rare earth tri-tellurides. Near the $M_5$ (3d - 4f) absorption
edge of rare earth ions, an intense diffraction peak is detected at a
wavevector identical to that of CDW state hosted on Te$_2$ planes, indicating a
CDW-induced modulation on the rare earth ions. Surprisingly, the temperature
dependence of the diffraction peak intensity demonstrates an exponential
increase at low temperatures, vastly different than that of the CDW order
parameter. Assuming 4f multiplet splitting due to the CDW states,we present a
model to calculate X-ray absorption spectrum and resonant profile of the
diffraction peak, agreeing well with experimental observations. Our results
demonstrate a situation where the temperature dependence of resonant X-ray
diffraction peak intensity is not directly related to the intrinsic behavior of
the order parameter associated with the electronic order, but is dominated by
the thermal occupancy of the valence states.
04/2012;
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S Y Zhou,
Y Zhu,
M C Langner,
Y-D Chuang,
P Yu, W L Yang,
A G Cruz Gonzalez,
N Tahir,
M Rini,
Y-H Chu,
R Ramesh,
D-H Lee,
Y Tomioka,
Y Tokura,
Z Hussain,
R W Schoenlein
[show abstract]
[hide abstract]
ABSTRACT: We present resonant soft x-ray scattering results from small bandwidth manganites (Pr,Ca)MnO(3), which show that the CE-type spin ordering (SO) at the phase boundary is stabilized only below the canted antiferromagnetic transition temperature and enhanced by ferromagnetism in the macroscopically insulating state (FM-I). Our results reveal the fragility of the CE-type ordering that underpins the colossal magnetoresistance effect in this system, as well as an unexpected cooperative interplay between FM-I and CE-type SO which is in contrast to the competitive interplay between the ferromagnetic metallic state and CE-type ordering.
Physical Review Letters 05/2011; 106(18):186404. · 7.37 Impact Factor
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S. Y. Zhou,
Y. Zhu,
M. C. Langner,
Y. -D. Chuang,
P Yu, W. L. Yang,
A. G. Cruz Gonzalez,
N. Tahir,
M Rini,
Y H Chu,
R. Ramesh,
D H Lee,
Y Tomioka,
Z. Hussain,
R W Schoenlein
[show abstract]
[hide abstract]
ABSTRACT: We present resonant soft X-ray scattering (RSXS) results from small band
width manganites (Pr,Ca)MnO$_3$, which show that the CE-type spin ordering (SO)
at the phase boundary is stabilized only below the canted antiferromagnetic
transition temperature and enhanced by ferromagnetism in the macroscopically
insulating state (FM-I). Our results reveal the fragility of the CE-type
ordering that underpins the colossal magnetoresistance (CMR) effect in this
system, as well as an unexpected cooperative interplay between FM-I and CE-type
SO which is in contrast to the competitive interplay between the ferromagnetic
metallic (FM-M) state and CE-type ordering.
04/2011;
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H Yagi,
T Yoshida,
A. Fujimori,
K Tanaka,
N. Mannella, W. L. Yang,
X. J. Zhou,
D. H. Lu,
Z. -X. Shen,
Z. Hussain,
M Kubota,
K Ono,
K Segawa,
Y Ando,
D. Iijima,
M Goto,
K. M. Kojima,
S Uchida
[show abstract]
[hide abstract]
ABSTRACT: We have performed an angle resolved photoemission spectroscopy (ARPES) study of lightly-doped to underdoped YBa2Cu3Oy (YBCO) untwinned single crystals and a core-level x-ray photoemission spectroscopy (XPS) study of YBCO single and polycrystals. In the zone diagonal (nodal) direction, dispersive quasi-particle (QP) features crossing the Fermi level were observed down to the hole concentration of ~ 4%, which explains the metallic transport of the lightly-doped YBCO. The chemical potential shift estimated from XPS was more rapid than in the Bi2212 cuprates. Upon hole doping, very rapid spectral weight transfer from high binding energies to the QP feature, even faster than La2-xSrxCuO4, was observed. Comment: 7 pages, 7 figures
02/2010;
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W. L. Yang,
P. O. Velasco,
J. D. Denlinger,
A. P. Sorini,
C C Chen,
B. Moritz,
W. S. Lee,
F. Vernay,
B. Delley,
J. -H. Chu,
J. G. Analytis,
I. R. Fisher,
Z. A. Ren,
J Yang,
W Lu,
Z. X. Zhao,
J. van den Brink,
Z. Hussain,
Z. -X. Shen,
T. P. Devereaux
[show abstract]
[hide abstract]
ABSTRACT: Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe $L$ edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. Best agreement with experiment is obtained using Hubbard parameters $U\lesssim 2$eV and $J\approx 0.8$eV. Comment: 11 pages, 12 figures
05/2009;
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S. Sahrakorpi,
R. S. Markiewicz,
Hsin Lin,
M. Lindroos,
X. J. Zhou,
T Yoshida, W. L. Yang,
T. Kakeshita,
H. Eisaki,
S Uchida,
Seiki Komiya,
Yoichi Ando,
F Zhou,
Z. X. Zhao,
T Sasagawa,
A. Fujimori,
Z. Hussain,
Z. -X. Shen,
A. Bansil
[show abstract]
[hide abstract]
ABSTRACT: We have investigated the dispersion renormalization $Z_{disp}$ in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over the wide doping range of $x=0.03-0.30$, for binding energies extending to several hundred meV's. Strong correlation effects conspire in such a way that the system exhibits an LDA-like dispersion which essentially `undresses' ($Z_{disp}\to 1$) as the Mott insulator is approached. Our finding that the Mott insulator contains `nascent' or `preformed' metallic states with a vanishing spectral weight offers a challenge to existing theoretical scenarios for cuprates. Comment: 7 pages, 4 figures. PRB 2008 in press
09/2008;
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V. Brouet, W. L. Yang,
X. J. Zhou,
Z. Hussain,
R. G. Moore,
R. He,
D. H. Lu,
Z. X. Shen,
J. Laverock,
S. B. Dugdale,
N. Ru,
I. R. Fisher
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe3 family, which sets this system as an ideal “textbook” example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe3 is that the band structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tin orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(EF), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.
Phys. Rev. B. 06/2008; 77(23).
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V. Brouet, W. L. Yang,
X. J. Zhou,
Z. Hussain,
R. G. Moore,
R. He,
D. H. Lu,
Z. -X. Shen,
J. Laverock,
S. Dugdale,
N. Ru,
I. R. Fisher
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed ARPES investigation of the RTe3 family, which sets this system as an ideal "textbook" example for the formation of a nesting driven Charge Density Wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi Surface (FS) (up to 0.4eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k-space. An additional advantage of RTe3 is that the band structure can be very accurately described by a simple 2D tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure, by comparing our ARPES measurements with Linear Muffin-Tin Orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and, for the first time, of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k-space, the evolution of the CDW wave vector with R and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(Ef), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties. Comment: 18 pages, 25 figures
01/2008;
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N. Mannella, W. L. Yang,
K Tanaka,
X. J. Zhou,
H Zheng,
J. F. Mitchell,
J. Zaanen,
T. P. Devereaux,
N. Nagaosa,
Z. Hussain,
Z. -X. Shen
[show abstract]
[hide abstract]
ABSTRACT: Angle-resolved photoemission spectroscopy data for the bilayer manganite La1.2Sr1.8Mn2O7 show that, upon lowering the temperature below the Curie point, a coherent polaronic metallic groundstate emerges very rapidly with well defined quasiparticles which track remarkably well the electrical conductivity, consistent with macroscopic transport properties. Our data suggest that the mechanism leading to the insulator-to-metal transition in La1.2Sr1.8Mn2O7 can be regarded as a polaron coherence condensation process acting in concert with the Double Exchange interaction. Comment: 4 pages, 3 figures, in press
11/2007;
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S.L. Molodtsov,
S. Danzenbacher,
Y. Kucherenko,
C. Laubschat,
D.V. Vyalikh,
Z. Hossain,
C. Geibel,
X.J. Zhou, W.L. Yang,
N. Mannella,
Z. Hussain,
Z.X. Shen,
M. Shi,
L. Patthey
J.Magn.Magn.Mater.310:443-445,2007. 09/2007;
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W L Yang,
J D Fabbri,
T M Willey,
J R I Lee,
J E Dahl,
R M K Carlson,
P R Schreiner,
A A Fokin,
B A Tkachenko,
N A Fokina,
W Meevasana,
N Mannella,
K Tanaka,
X J Zhou,
T van Buuren,
M A Kelly,
Z Hussain,
N A Melosh,
Z-X Shen
[show abstract]
[hide abstract]
ABSTRACT: We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68% of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flat-panel displays.
Science 07/2007; 316(5830):1460-2. · 31.20 Impact Factor
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W. S. Lee,
T. Cuk,
W. Meevasane,
D. H. Lu,
K. M. Shen,
Z.-X. Shen, W. L. Yang,
X. J. Zhou,
Z. Hussain,
C. T. Lin,
J.-I. Shimoyama,
T. P. Devereaux
[show abstract]
[hide abstract]
ABSTRACT: The band renormalizations of optimally-doped Bi2223 system were studied by angle-resolved photoemission
spectroscopy. In the superconducting state, we found that the band renormalizations are dominated by one
bosonic mode. In the normal state, the band renormalizations are weak, but still observable. To better
visualize the renormalization features in the normal state, we extracted the real part of the self-energy,
ReΣ, in which we found ashoulder at about 35 meV in
addition to the maximum at about 70 meV. This result suggests that multiple bosonic modes contribute
to the band renormalizations, instead of just one single mode. These modes are likely oxygen related optical
phonon mode. Compared to the extracted ReΣ in the superconducting
state, we show that the renormalization effect exhibits an interesting and subtle temperature dependence
at the nodal region.
03/2007: pages 227-236;
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S. Danzenbächer,
Yu. Kucherenko,
D. V. Vyalikh,
M. Holder,
C. Laubschat,
A. N. Yaresko,
C. Krellner,
Z. Hossain,
C. Geibel,
X. J. Zhou, W. L. Yang,
N. Mannella,
Z. Hussain,
Z.-X. Shen,
M. Shi,
L. Patthey,
S. L. Molodtsov
[show abstract]
[hide abstract]
ABSTRACT: Heavy-fermion compounds YbIr2Si2 and YbRh2Si2 were studied by means of angle-resolved photoemission (PE). The splittings and dispersions of the 4f13 bulk and surface PE signals in the region of the expected energy crossings of the 4f final states and the valence bands in the Brillouin zone are observed. The experimental results are explained in terms of a simplified periodic Anderson model by a momentum dependence of the electron hopping matrix element between the 4f and valence-band states.
Phys. Rev. B. 01/2007; 75(4).
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W. Meevasana,
X. J. Zhou,
S. Sahrakorpi,
W. S. Lee, W. L. Yang,
K Tanaka,
N. Mannella,
T Yoshida,
D. H. Lu,
Y L Chen, [......],
S Uchida,
H. Eisaki,
A. Fujimori,
Z. Hussain,
R. S. Markiewicz,
A. Bansil,
N. Nagaosa,
J. Zaanen,
T. P. Devereaux,
Z. -X. Shen
[show abstract]
[hide abstract]
ABSTRACT: To date, angle-resolved photoemission spectroscopy has been successful in identifying energy scales of the many-body interactions in correlated materials, focused on binding energies of up to a few hundred meV below the Fermi energy. Here, at higher energy scale, we present improved experimental data from four families of high-Tc superconductors over a wide doping range that reveal a hierarchy of many-body interaction scales focused on: the low energy anomaly ("kink") of 0.03-0.09eV, a high energy anomaly of 0.3-0.5eV, and an anomalous enhancement of the width of the LDA-based CuO2 band extending to energies of ~ 2 eV. Besides their universal behavior over the families, we find that all of these three dispersion anomalies also show clear doping dependence over the doping range presented. Comment: 7 pages, 6 figures
12/2006;
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W. S. Lee,
T Yoshida,
W. Meevasana,
K. M. Shen,
D. H. Lu, W. L. Yang,
X. J. Zhou,
X Zhao,
G Yu,
Y. Cho,
M. Greven,
Z. Hussain,
Z. -X. Shen
[show abstract]
[hide abstract]
ABSTRACT: We present the first angle-resolved photoemission measurement on the single-layer Hg-based cuprate, HgBa$_2$CuO$_{4+\delta}$ (Hg1201). A quasi-particle peak in the spectrum and a kink in the band dispersion around the diagonal of the Brillouin zone are observed, whereas no structure is detected near the Brillouin zone boundary. To search for a material-dependent trend among hole-doped cuprates, including Hg1201, we use a tight-binding model to fit their Fermi surfaces. We find a positive correlation between the $T_{c,\mathrm{max}}$ and $t'/t$, consistent with theoretical predictions.
07/2006;
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S Danzenbächer,
Yu Kucherenko,
C Laubschat,
D V Vyalikh,
Z Hossain,
C Geibel,
X J Zhou, W L Yang,
N Mannella,
Z Hussain,
Z-X Shen,
S L Molodtsov
[show abstract]
[hide abstract]
ABSTRACT: Angle-resolved photoemission spectra of the heavy-fermion system YbIr(2)Si(2) are reported that reveal strong momentum (k) dependent splittings of the 4f(13) bulk and surface emissions around the expected intersection points of the 4f final states with valence bands in the Brillouin zone. The obtained dispersion is explained in terms of a simplified periodic Anderson model by a k dependence of the electron hopping matrix element disregarding clearly interpretation in terms of a single-impurity model.
Physical Review Letters 04/2006; 96(10):106402. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the 'd-wave' symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite 'Fermi arcs'. This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La1.2Sr1.8Mn2O7. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.
Nature 12/2005; 438(7067):474-8. · 36.28 Impact Factor
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T Yoshida,
X. J. Zhou,
K Tanaka, W. L. Yang,
Z. Hussain,
Z. -X. Shen,
A. Fujimori,
Seiki Komiya,
Yoichi Ando,
H. Eisaki,
T. Kakeshita,
S Uchida
[show abstract]
[hide abstract]
ABSTRACT: We have performed a systematic doping dependent study of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) (0.03$\leq x \leq$0.3) by angle-resolved photoemission spectroscopy. In the entire doping range, the underlying ``Fermi surface" determined from the low energy spectral weight approximately satisfies Luttinger's theorem, even down to the lightly-doped region. This is in strong contrast to the result on Ca$_{2-x}$Na$_x$CuO$_2$Cl$_2$ (Na-CCOC), which shows a strong deviation from Luttinger's theorem. The differences between LSCO and Na-CCOC are correlated with the different behaviors of the chemical potential shift and spectral weight transfer induced by hole doping. Comment: 4 pages, 4 figures
10/2005;
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X J Zhou,
Junren Shi,
T Yoshida,
T Cuk, W L Yang,
V Brouet,
J Nakamura,
N Mannella,
Seiki Komiya,
Yoichi Ando, [......],
T Sasagawa,
T Kakeshita,
H Eisaki,
S Uchida,
A Fujimori,
Zhenyu Zhang,
E W Plummer,
R B Laughlin,
Z Hussain,
Z-X Shen
[show abstract]
[hide abstract]
ABSTRACT: High resolution angle-resolved photoemission spectroscopy data along the (0,0)-(pi,pi) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La2-xSrx)CuO4 samples in the normal state. Fine structure at energies of (40-46) meV and (58-63) meV, and possible fine structure at energies of (23-29) meV and (75-85) meV, have been identified. These observations indicate that, in (La2-xSrx)CuO4, more than one bosonic modes are involved in the coupling with electrons.
Physical Review Letters 10/2005; 95(11):117001. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: From consistency among different measurements, new measurements with better energy resolution, as well as simulations, we show that the fine structure we have identified in the electron self-enery of LSCO is intrinsic, not due to random noise as Valla speculated.
03/2005;
