I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[18398]
Abstract: Using the normal incidence x-ray standing-wave technique as well as low-energy electron microscopy we have investigated the structure of quasifreestanding monolayer graphene (QFMLG) obtained by intercalation of antimony under the
(
6
√
3
×
6
√
3
)
R
30
∘
reconstructed graphitized
6
H
-SiC(0001) surface, also known as zeroth-layer graphene. We found that Sb intercalation decouples the QFMLG well from the substrate. The distance from the QFMLG to the Sb layer almost equals the expected van der Waals bonding distance of C and Sb. The Sb intercalation layer itself is monoatomic, flat, and located much closer to the substrate, at almost the distance of a covalent Sb-Si bond length. All data is consistent with Sb located on top of the uppermost Si atoms of the SiC bulk.
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Oct 2022
|
|
I05-ARPES
|
J.
Küspert
,
R.
Cohn Wagner
,
C.
Lin
,
K.
Von Arx
,
Q.
Wang
,
K.
Kramer
,
W. R.
Pudelko
,
N. C.
Plumb
,
C. E.
Matt
,
C. G.
Fatuzzo
,
D.
Sutter
,
Y.
Sassa
,
J.-Q.
Yan
,
J.-S.
Zhou
,
J. B.
Goodenough
,
S.
Pyon
,
T.
Takayama
,
H.
Takagi
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
M.
Hoesch
,
C.
Cacho
,
T. K.
Kim
,
M.
Horio
,
J.
Chang
Diamond Proposal Number(s):
[27768, 10550]
Open Access
Abstract: We carried out a comprehensive high-resolution angle-resolved photoemission spectroscopy (ARPES) study of the pseudogap interplay with superconductivity in La-based cuprates. The three systems
La
2
−
x
Sr
x
CuO
4
,
La
1.6
−
x
Nd
0.4
Sr
x
CuO
4
, and
La
1.8
−
x
Eu
0.2
Sr
x
CuO
4
display slightly different pseudogap critical points in the temperature versus doping phase diagram. We studied the pseudogap evolution into the superconducting state for doping concentrations just below the critical point. In this setting, near optimal doping for superconductivity and in the presence of the weakest possible pseudogap, we uncover how the pseudogap is partially suppressed inside the superconducting state. This conclusion is based on the direct observation of a reduced pseudogap energy scale and re-emergence of spectral weight suppressed by the pseudogap. Altogether these observations suggest that the pseudogap phenomenon in La-based cuprates is in competition with superconductivity for antinodal spectral weight.
|
Oct 2022
|
|
I04-Macromolecular Crystallography
|
Céline
Mariette
,
Philippe
Rabiller
,
Laurent
Guérin
,
Claude
Ecolivet
,
Ilya
Frantsuzov
,
Bo
Wang
,
Shane M.
Nichols
,
Philippe
Bourges
,
Alexei
Bosak
,
Yu-Sheng
Chen
,
Mark D.
Hollingsworth
,
Bertrand
Toudic
Diamond Proposal Number(s):
[5019]
Abstract: Aperiodic crystals possess long-range order without translational symmetry. They constitute a state of matter that has forced a profound paradigm shift in solid-state physics. A common feature of aperiodic crystals is that they recover periodicity in higher dimensional spaces, the so-called crystallographic superspaces. Much work has been dedicated to the structural order within these superspaces and also to their specific dynamics. This paper focuses on the phase transitions within crystallographic superspaces. Aperiodic crystals are divided into three families: incommensurately modulated crystals, composite crystals, and quasicrystals. Incommensurately modulated crystals have been studied heavily and appear now to be relatively well understood, since they possess a periodic high-symmetry phase. The other two members of the family are aperiodic by construction. In this paper, we present a comprehensive and systematic study of a prototype composite host-guest family of
n
-alkane/urea inclusion compounds
[
n
−
C
n
H
2
n
+
2
/
CO
(
NH
2
)
2
]
. For these materials, which exhibit a rich sequence of phases, the phase transitions are described in terms of group/subgroup symmetry breaking within crystallographic superspaces. Such phase transitions may decrease, increase, or maintain the dimension of the crystallographic superspace. These results highlight the multiplicity of specific structural solutions that aperiodicity offers.
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Oct 2022
|
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I10-Beamline for Advanced Dichroism - scattering
|
Open Access
Abstract: Resonant soft-x-ray reflectivity and vibrating sample magnetometry have been used to characterize field driven and spin orbit torque driven magnetization reversal in a CoFeTaB/Pt bilayer. Reversal of the magnetization occurs either along the applied field direction or perpendicular to the current flow direction. Magnetometry results show that field driven (current driven) coercivities are reduced by application of a current (field) highlighting the roles played by the two external parameters. In the current switching case, it is demonstrated with soft-x-ray hysteresis loops that only the layers near the interface with Pt switch, possibly highlighting the role of proximity effects of the magnetized Pt. We show how magnetization reversal perpendicular to the beam results in hysteresis behavior in the reflected intensity that is dependent on the magnetization but independent of the helicity of the circular polarization of the incident beam
|
Sep 2022
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[25201]
Abstract: Misfit compounds are thermodynamically stable stacks of two-dimensional materials, forming a three-dimensional structure that remains incommensurate in one direction parallel to the layers. As a consequence, no true bonding is expected between the layers, with their interaction being dominated by charge transfer. In contrast to this well-established picture, we show that interlayer coupling can strongly influence the electronic properties of one type of layer in a misfit structure, in a similar way to the creation of modified band structures in an artificial moiré structure between two-dimensional materials. Using angle-resolved photoemission spectroscopy with a micron-scale light focus, we selectively probe the electronic properties of hexagonal
NbSe
2
and square BiSe layers that terminate the surface of the
(
BiSe
)
1
+
δ
NbSe
2
misfit compound. We show that the band structure in the BiSe layers is strongly affected by the presence of the hexagonal
NbSe
2
layers, leading to quasi-one-dimensional electronic features. The electronic structure of the
NbSe
2
layers, on the other hand, is hardly influenced by the presence of the BiSe. Using density functional theory calculations of the unfolded band structures, we argue that the preferred modification of one type of band is mainly due to the atomic and orbital character of the states involved, opening a promising way to design electronic states that exploit the partially incommensurate character of the misfit compounds.
|
Sep 2022
|
|
I10-Beamline for Advanced Dichroism - scattering
|
Diamond Proposal Number(s):
[27196]
Abstract: Isotropic helimagnets are known to host a diverse range of chiral magnetic states. In 2016, Rybakov et al., theorized the presence of a surface-pinned stacked spin spiral phase [F. N. Rybakov et al., New J. Phys. 18, 045002 (2016)], which has yet to be observed experimentally. The phase is characterized by surface spiral periods exceeding the host material's fundamental winding period
L
D
. Here, we present experimental evidence for the observation of this state in lamellae of FeGe using resonant x-ray holographic imaging data and micromagnetic simulations. We find images of FeGe lamellae, exceeding a critical thickness of 300 nm (
4.3
L
D
), exhibit contrast modulations with a field-dependent periodicity of
λ
≥
1.4
L
D
, consistent with theoretical predictions of the stacked spiral state. The identification of this spiral state has significant implications for the stability of other coexisting spin textures, and will help complete our understanding of helimagnetic systems.
|
Aug 2022
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
U.
Kumar
,
A.
Nag
,
J.
Li
,
H. C.
Robarts
,
A. C.
Walters
,
M.
Garcia-Fernandez
,
R.
Saint-Martin
,
A.
Revcolevschi
,
J.
Schlappa
,
T.
Schmitt
,
Steven
Johnston
,
K.-J.
Zhou
Diamond Proposal Number(s):
[21184]
Abstract: Resonant inelastic x-ray scattering (RIXS) is an evolving tool for investigating the spin dynamics of strongly correlated materials, which complements inelastic neutron scattering. In isotropic spin-
1
2
Heisenberg antiferromagnetic (HAFM) spin chains, both techniques have observed non-spin-conserving (NSC) excitations confined to the two-spinon phase space. However, a recent O
K
-edge RIXS study of the one-dimensional HAFM
Sr
2
CuO
3
observed spin-conserving (SC) four-spinon excitations outside the two-spinon phase space. Here, we demonstrate that analogous four-spinon excitations can also be accessed at the Cu
L
3
edge in the related material
SrCuO
2
. Through detailed modeling, we establish that these excitations appear in both the SC and NSC channels of the Cu
L
3
edge, and are only captured by higher-order terms in the ultrashort core-hole lifetime expansion. Since these terms encode information about spin-spin correlations extending beyond nearest neighbors, our results offer different possibilities for studying nonlocal spin correlations in quantum magnets.
|
Aug 2022
|
|
I05-ARPES
|
Z. X.
Yin
,
X.
Du
,
S.
Zhang
,
C.
Chen
,
D.
Pei
,
J. S.
Zhou
,
X.
Gu
,
R. Z.
Xu
,
Q. Q.
Zhang
,
W. X.
Zhao
,
Y. D.
Li
,
Y. F.
Xu
,
A.
Bernevig
,
Z. K.
Liu
,
E. K.
Liu
,
Y. L.
Chen
,
L. X.
Yang
Diamond Proposal Number(s):
[24167]
Abstract: Recently, magnetic topological quantum materials have attracted substantial research attention due to their great application potential. Here, using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structure of antiferromagnet Dirac semimetal candidate
Gd
In
3
. According to our ab initio calculation, there exist two and one pair(s) of Dirac fermions in the paramagnetic and antiferromagnetic state, respectively. In the antiferromagnetic state, the magnetic Dirac semimetal phase is protected by
C
4
z
rotation symmetry in the type-IV magnetic space group. Our experiment above the Néel temperature is well reproduced by the calculated band structure in the paramagnetic state, from which we identify a pair of Dirac fermions at 1.5 eV below the Fermi level. However, we do not observe the signature of electronic reconstruction in the antiferromagnetic state, suggesting a weak interaction between the localized Gd
4
f
states of spin configuration
S
=
7
/
2
μ
B
and the itinerant conduction electrons. Our results confirm the Dirac semimetal nature of the paramagnetic
Gd
In
3
and provide important insights into its antiferromagnetic Dirac semimetal phase.
|
Aug 2022
|
|
Theoretical Physics
|
Abstract: Circular dichroism in resonant elastic x-ray scattering (CD-REXS) has recently been observed in chiral
structures composed of multiferroic materials as well as magnetic moments or electric polarization vectors. In order to comprehensively understand the experimental results of these previous studies, we present here in detail the analytical formulation of CD-REXS for one-dimensional helices composed of magnetic moments and electric polarization vectors, respectively. In particular, by comparing CD-REXS for a proper-screw-shaped Bloch-type helix and cycloid-shaped Néel-type helix, we found that CD-REXS for both magnetic and polar helices can discriminate between both types of helices.We also found that the x-ray polarization factor depending on the scattering geometry is a significant factor in determining the characteristics of CD-REXS for chiral structures. The results obtained from the detailed formulas can be intuitively understood using the concept of mirror reflection. In particular, in this way it can be understood that Bloch- and Néel-type helices correspond to truly chiral and achiral structures, respectively, and why CD-REXS is able to distinguish between these two types of helices.
|
Jul 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Hepting
,
M.
Bejas
,
A.
Nag
,
H.
Yamase
,
N.
Coppola
,
D.
Betto
,
C.
Falter
,
Mirian
Garcia-Fernandez
,
S.
Agrestini
,
K.-J.
Zhou
,
M.
Minola
,
C.
Sacco
,
L.
Maritato
,
P.
Orgiani
,
H. I.
Wei
,
K. M.
Shen
,
D. G.
Schlom
,
A.
Galdi
,
A.
Greco
,
B.
Keimer
Diamond Proposal Number(s):
[23933]
Open Access
Abstract: We use resonant inelastic x-ray scattering to probe the propagation of plasmons in the electron-doped cuprate superconductor
Sr
0.9
La
0.1
CuO
2
. We detect a plasmon gap of
∼
120
meV
at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in
Sr
0.9
La
0.1
CuO
2
are not strictly acoustic. The plasmon dispersion, including the gap, is accurately captured by layered
t
−
J
−
V
model calculations. A similar analysis performed on recent resonant inelastic x-ray scattering data from other cuprates suggests that the plasmon gap is generic and its size is related to the magnitude of the interlayer hopping
t
z
. Our work signifies the three dimensionality of the charge dynamics in layered cuprates and provides a new method to determine
t
z
.
|
Jul 2022
|
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