I09-Surface and Interface Structural Analysis
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Z. H.
Lim
,
N. F.
Quackenbush
,
A. N.
Penn
,
M.
Chrysler
,
M.
Bowden
,
Z.
Zhu
,
J. M.
Ablett
,
T.-l.
Lee
,
J. M.
Lebeau
,
J. C.
Woicik
,
P. V.
Sushko
,
S. A.
Chambers
,
J. H.
Ngai
Diamond Proposal Number(s):
[17449]
Abstract: We report charge transfer and built-in electric fields across the epitaxial
SrNb
x
Ti
1
−
x
O
3
−
δ
/
Si
(
001
)
interface. Electrical transport measurements indicate the formation of a hole gas in the Si and the presence of built-in fields. Hard x-ray photoelectron measurements reveal pronounced asymmetries in core-level spectra that arise from these built-in fields. Theoretical analysis of core-level spectra enables built-in fields and the resulting band bending to be spatially mapped across the heterojunction. The demonstration of tunable charge transfer, built-in fields, and the spatial mapping of the latter, lays the groundwork for the development of electrically coupled, functional heterojunctions.
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Jul 2019
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H.
Wo
,
Q.
Wang
,
Y.
Shen
,
X.
Zhang
,
Y.
Hao
,
Y.
Feng
,
S.
Shen
,
Z.
He
,
B.
Pan
,
W.
Wang
,
K.
Nakajima
,
S.
Ohira-kawamura
,
P.
Steffens
,
M.
Boehm
,
K.
Schmalzl
,
T. R.
Forrest
,
M.
Matsuda
,
Y.
Zhao
,
J. W.
Lynn
,
Z.
Yin
,
J.
Zhao
Abstract: We report neutron scattering measurements of single-crystalline
YFe
2
Ge
2
in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors.
YFe
2
Ge
2
does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides,
YFe
2
Ge
2
displays anisotropic stripe-type antiferromagnetic spin fluctuations at (
π
, 0,
π
). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector (0, 0,
π
). These ferromagnetic spin fluctuations are isotropic in the (
H
,
K
) plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in
YFe
2
Ge
2
and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.
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May 2019
|
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I05-ARPES
|
Diamond Proposal Number(s):
[19771, 18555, 16262]
Abstract: We revisit the enduring problem of the 2 × 2 × 2 charge density wave (CDW) order in TiSe2, utilizing photon energy-dependent angle-resolved photoemission spectroscopy to probe the full three-dimensional high- and low-temperature electronic structure. Our measurements demonstrate how a mismatch of dimensionality between the 3D conduction bands and the quasi-2D valence bands in this system leads to a hybridization that is strongly kz dependent. While such a momentum-selective coupling can provide the energy gain required to form the CDW, we show how additional “passenger” states remain, which couple only weakly to the CDW and thus dominate the low-energy physics in the ordered phase of TiSe2.
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Feb 2019
|
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Theoretical Physics
|
Open Access
Abstract: The scope of magnetic neutron scattering has been expanded by the observation of electronic Dirac
dipoles (anapoles) that are polar (parity odd) and magnetic (time odd). A zero-magnetization ferromagnet Sm0.976Gd0.024Al2 with a diamond-type structure presents Dirac multipoles at basis-forbidden reflections that include the standard (2, 2, 2) reflection. Magnetic amplitudes measured at four such reflections are in full accord with a structure factor calculated from the appropriate magnetic space group.
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Feb 2019
|
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I05-ARPES
|
Daichi
Takane
,
Zhiwei
Wang
,
Seigo
Souma
,
Kosuke
Nakayama
,
Takechika
Nakamura
,
Hikaru
Oinuma
,
Yuki
Nakata
,
Hideaki
Iwasawa
,
Cephise
Cacho
,
Timur
Kim
,
Koji
Horiba
,
Hiroshi
Kumigashira
,
Takashi
Takahashi
,
Yoichi
Ando
,
Takafumi
Sato
Diamond Proposal Number(s):
[18839]
Abstract: Topological semimetals materialize a new state of quantum matter where massless fermions protected by a specific crystal symmetry host exotic quantum phenomena. Distinct from well-known Dirac and Weyl fermions, structurally chiral topological semimetals are predicted to host new types of massless fermions characterized by a large topological charge, whereas such exotic fermions are yet to be experimentally established. Here, by using angle-resolved photoemission spectroscopy, we experimentally demonstrate that a transition-metal silicide CoSi hosts two types of chiral topological fermions, a spin-1 chiral fermion and a double Weyl fermion, in the center and corner of the bulk Brillouin zone, respectively. Intriguingly, we found that the bulk Fermi surfaces are purely composed of the energy bands related to these fermions. We also find the surface states connecting the Fermi surfaces associated with these fermions, suggesting the existence of the predicted Fermi-arc surface states. Our result provides the first experimental evidence for the chiral topological fermions beyond Dirac and Weyl fermions in condensed-matter systems, and paves the pathway toward realizing exotic electronic properties associated with unconventional chiral fermions.
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Feb 2019
|
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I05-ARPES
I19-Small Molecule Single Crystal Diffraction
|
Diamond Proposal Number(s):
[8776, 11039, 13797, 17065]
Abstract: The charge density wave (CDW) in ZrTe3 is quenched in samples with a small amount of Te isoelectronically substituted by Se. Using angle-resolved photoemission spectroscopy we observe subtle changes in the electronic band dispersions and Fermi surfaces upon Se substitution. The scattering rates are substantially increased, in particular for the large three-dimensional Fermi surface sheet. The quasi-one-dimensional band is unaffected by the substitution and still shows a gap at low temperature, which starts to open from room temperature. Long-range order is, however, absent in the electronic states as in the periodic lattice distortion. The competition between superconductivity and the CDW is thus linked to the suppression of long-range order of the CDW.
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Jan 2019
|
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I15-Extreme Conditions
|
Diamond Proposal Number(s):
[15949]
Abstract: Two-dimensional materials have proven to be a prolific breeding ground of new and unstudied forms of magnetism and unusual metallic states, particularly when tuned between their insulating and metallic phases. Here we present work on a new metal-to-insulator transition system FePS3. This compound is a two-dimensional van der Waals antiferromagnetic Mott insulator. We report the discovery of an insulator-metal transition in FePS3, as evidenced by x-ray diffraction and electrical transport measurements, using high pressure as a tuning parameter. Two structural phase transitions are observed in the x-ray diffraction data as a function of pressure, and resistivity measurements show evidence of the onset of a metallic state at high pressures. We propose models for the two new structures that can successfully explain the x-ray diffraction patterns.
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Dec 2018
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E02-JEM ARM 300CF
|
Diamond Proposal Number(s):
[17918]
Abstract: We report a method for quantitative phase recovery and simultaneous electron energy loss spectroscopy analysis using ptychographic reconstruction of a data set of “hollow” diffraction patterns. This has the potential for recovering both structural and chemical information at atomic resolution with a new generation of detectors.
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Oct 2018
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I05-ARPES
|
C. H. P.
Wen
,
H. C.
Xu
,
Q.
Yao
,
R.
Peng
,
X. H.
Niu
,
Q. Y.
Chen
,
Z. T.
Liu
,
D. W.
Shen
,
Q.
Song
,
X.
Lou
,
Y. F.
Fang
,
X. S.
Liu
,
Y. H.
Song
,
Y. J.
Jiao
,
T. F.
Duan
,
H. H.
Wen
,
P.
Dudin
,
G.
Kotliar
,
Z. P.
Yin
,
D. L.
Feng
Diamond Proposal Number(s):
[14737, 16345, 20697]
Abstract: The mechanism of high superconducting transition temperatures (Tc) in bismuthates remains under debate despite more than 30 years of extensive research. Our angle-resolved photoemission spectroscopy studies on Ba0.51K0.49BiO3 reveal an unexpectedly 34% larger bandwidth than in conventional density functional theory calculations. This can be reproduced by calculations that fully account for long-range Coulomb interactions—the first direct demonstration of bandwidth expansion due to the Fock exchange term, a long-accepted and yet uncorroborated fundamental effect in many body physics.Furthermore, we observe an isotropic superconducting gap with 2Δ0/kBTc=3.51±0.05, and strong electron-phonon interactions with a coupling constant λ∼1.3±0.2. These findings solve a long-standing mystery—Ba0.51K0.49BiO3 is an extraordinary Bardeen-Cooper-Schrieffer superconductor, where long-range Coulomb interactions expand the bandwidth, enhance electron-phonon coupling, and generate the high Tc. Such effects will also be critical for finding new superconductors.
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Sep 2018
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Diagnostics
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R.
Kieffer
,
L.
Bartnik
,
M.
Bergamaschi
,
V. V.
Bleko
,
M.
Billing
,
L.
Bobb
,
J.
Conway
,
M.
Forster
,
P.
Karataev
,
A. S.
Konkov
,
R. O.
Jones
,
T.
Lefevre
,
J. S.
Markova
,
S.
Mazzoni
,
Y.
Padilla Fuentes
,
A. P.
Potylitsyn
,
J.
Shanks
,
S.
Wang
Open Access
Abstract: We report on the observation of incoherent Cherenkov radiation emitted by a 5.3 GeV positron beam circulating in the Cornell electron-positron storage ring as the beam passes in the close vicinity of the surface of a fused silica radiator (i.e., at a distance larger than 0.8 mm). The shape of the radiator was designed in order to send the Cherenkov photons towards the detector, consisting of a compact optical system equipped with an intensified camera. The optical system allows both the measurements of 2D images and angular distribution including polarization study. The corresponding light intensity has been measured as a function of the distance between the beam and the surface of the radiator and has shown a good agreement with theoretical predictions. For highly relativistic particles, a large amount of incoherent radiation is produced in a wide spectral range. A light yield of 0.8×10−3 photon per particle per turn has been measured at a wavelength of 600±10 nm in a 2 cm long radiator and for an impact parameter of 1 mm. This will find applications in accelerators as noninvasive beam diagnostics for both leptons and hadrons.
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Aug 2018
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