I05-ARPES
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Paolo
Sessi
,
Feng-ren
Fan
,
Felix
Küster
,
Kaustuv
Manna
,
Niels B. M.
Schroeter
,
Jing-rong
Ji
,
Samuel
Stolz
,
Jonas A.
Krieger
,
Ding
Pei
,
Timur K.
Kim
,
Pavel
Dudin
,
Cephise
Cacho
,
Remo N.
Widmer
,
Horst
Borrmann
,
Wujun
Shi
,
Kai
Chang
,
Yan
Sun
,
Claudia
Felser
,
Stuart S. P.
Parkin
Diamond Proposal Number(s):
[2470, 20617]
Open Access
Abstract: It has recently been proposed that combining chirality with topological band theory results in a totally new class of fermions. Understanding how these unconventional quasiparticles propagate and interact remains largely unexplored so far. Here, we use scanning tunneling microscopy to visualize the electronic properties of the prototypical chiral topological semimetal PdGa. We reveal chiral quantum interference patterns of opposite spiraling directions for the two PdGa enantiomers, a direct manifestation of the change of sign of their Chern number. Additionally, we demonstrate that PdGa remains topologically non-trivial over a large energy range, experimentally detecting Fermi arcs in an energy window of more than 1.6 eV that is symmetrically centered around the Fermi level. These results are a consequence of the deep connection between chirality in real and reciprocal space in this class of materials, and, thereby, establish PdGa as an ideal topological chiral semimetal.
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Jul 2020
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I05-ARPES
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Shuo-ying
Yang
,
Yaojia
Wang
,
Brenden R.
Ortiz
,
Defa
Liu
,
Jacob
Gayles
,
Elena
Derunova
,
Rafael
Gonzalez-hernandez
,
Libor
Šmejkal
,
Yulin
Chen
,
Stuart S. P.
Parkin
,
Stephen D.
Wilson
,
Eric S.
Toberer
,
Tyrel
Mcqueen
,
Mazhar N.
Ali
Diamond Proposal Number(s):
[22367]
Open Access
Abstract: The anomalous Hall effect (AHE) is one of the most fundamental phenomena in physics. In the highly conductive regime, ferromagnetic metals have been the focus of past research. Here, we report a giant extrinsic AHE in KV3Sb5, an exfoliable, highly conductive semimetal with Dirac quasiparticles and a vanadium Kagome net. Even without report of long range magnetic order, the anomalous Hall conductivity reaches 15,507 Ω−1 cm−1 with an anomalous Hall ratio of ≈ 1.8%; an order of magnitude larger than Fe. Defying theoretical expectations, KV3Sb5 shows enhanced skew scattering that scales quadratically, not linearly, with the longitudinal conductivity, possibly arising from the combination of highly conductive Dirac quasiparticles with a frustrated magnetic sublattice. This allows the possibility of reaching an anomalous Hall angle of 90° in metals. This observation raises fundamental questions about AHEs and opens new frontiers for AHE and spin Hall effect exploration, particularly in metallic frustrated magnets.
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Jul 2020
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I05-ARPES
|
D. F.
Liu
,
A. J.
Liang
,
E. K.
Liu
,
Q. N.
Xu
,
Y. W.
Li
,
C.
Chen
,
D.
Pei
,
W. J.
Shi
,
S. K.
Mo
,
P.
Dudin
,
T.
Kim
,
C.
Cacho
,
G.
Li
,
Y.
Sun
,
L. X.
Yang
,
Z. K.
Liu
,
S. S. P.
Parkin
,
C.
Felser
,
Y. L.
Chen
Diamond Proposal Number(s):
[22367, 20683]
Abstract: Weyl semimetals are crystalline solids that host emergent relativistic Weyl fermions and have characteristic surface Fermi-arcs in their electronic structure. Weyl semimetals with broken time reversal symmetry are difficult to identify unambiguously. In this work, using angle-resolved photoemission spectroscopy, we visualized the electronic structure of the ferromagnetic crystal Co3Sn2S2 and discovered its characteristic surface Fermi-arcs and linear bulk band dispersions across the Weyl points. These results establish Co3Sn2S2 as a magnetic Weyl semimetal that may serve as a platform for realizing phenomena such as chiral magnetic effects, unusually large anomalous Hall effect and quantum anomalous Hall effect.
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Sep 2019
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I05-ARPES
|
J.
Jiang
,
Z. K.
Liu
,
Y.
Sun
,
H. F.
Yang
,
C. R.
Rajamathi
,
Y. P.
Qi
,
L. X.
Yang
,
C.
Chen
,
H.
Peng
,
C.-c.
Hwang
,
S. Z.
Sun
,
S.-k.
Mo
,
I.
Vobornik
,
J.
Fujii
,
S. S. P.
Parkin
,
C.
Felser
,
B. H.
Yan
,
Y.l.
Chen
Diamond Proposal Number(s):
[14132]
Open Access
Abstract: Topological Weyl semimetal (TWS), a new state of quantum matter, has sparked enormous research interest recently. Possessing unique Weyl fermions in the bulk and Fermi arcs on the surface, TWSs offer a rare platform for realizing many exotic physical phenomena. TWSs can be classified into type-I that respect Lorentz symmetry and type-II that do not. Here, we directly visualize the electronic structure of MoTe2, a recently proposed type-II TWS. Using angle-resolved photoemission spectroscopy (ARPES), we unravel the unique surface Fermi arcs, in good agreement with our ab initio calculations that have nontrivial topological nature. Our work not only leads to new understandings of the unusual properties discovered in this family of compounds, but also allows for the further exploration of exotic properties and practical applications of type-II TWSs, as well as the interplay between superconductivity (MoTe2 was discovered to be superconducting recently) and their topological order.
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Jan 2017
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Magnets
Theoretical Physics
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L. J.
Collins-mcintyre
,
L. B.
Duffy
,
A.
Singh
,
N-j
Steinke
,
C. J.
Kinane
,
T. R.
Charlton
,
A.
Pushp
,
A. J.
Kellock
,
S. S. P.
Parkin
,
S. N.
Holmes
,
C. H. W.
Barnes
,
G.
Van Der Laan
,
S.
Langridge
,
T.
Hesjedal
Open Access
Abstract: We report the structural, electronic, and magnetic study of Cr-doped Sb2Te3 thin films grown by a two-step deposition process using molecular-beam epitaxy (MBE). The samples were investigated using a variety of complementary techniques, namely, x-ray diffraction (XRD), atomic force microscopy, SQUID magnetometry, magneto-transport, and polarized neutron reflectometry (PNR). It is found that the samples retain good crystalline order up to a doping level of x = 0.42 (in CrxSb2−xTe3), above which degradation of the crystal structure is observed by XRD. Fits to the recorded XRD spectra indicate a general reduction in the c-axis lattice parameter as a function of doping, consistent with substitutional doping with an ion of smaller ionic radius. The samples show soft ferromagnetic behavior with the easy axis of magnetization being out-of-plane. The saturation magnetization is dependent on the doping level, and reaches from 2 μB to almost 3 μB per Cr ion. The transition temperature (Tc) depends strongly on the Cr concentration and is found to increase with doping concentration. For the highest achievable doping level for phase pure films of x = 0.42, a Tc of 125K was determined. Electric transport measurements find surface-dominated transport below 10K. The magnetic properties extracted from anomalous Hall effect data are in excellent agreement with the magnetometry data. PNR studies indicate a uniform magnetization profile throughout the film, with no indication of enhanced magnetic order towards the sample surface.
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Sep 2016
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I10-Beamline for Advanced Dichroism
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S. E.
Harrison
,
L.
Collins-mcintyre
,
S. L.
Zhang
,
A. A.
Baker
,
A. I.
Figueroa
,
A. J.
Kellock
,
A.
Pushp
,
Y. L.
Chen
,
S. S. P.
Parkin
,
J. S.
Harris
,
G.
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[10207]
Open Access
Abstract: Breaking time-reversal symmetry through magnetic doping of topological insulators has been identified as a key strategy for unlocking exotic physical states. Here, we report the growth of Bi2Te3 thin films doped with the highest magnetic moment element Ho. Diffraction studies demonstrate high quality films for up to 21% Ho incorporation. Superconducting quantum interference device magnetometry reveals paramagnetism down to 2K with an effective magnetic moment of 5 muB/Ho. Angle-resolved photoemission spectroscopy shows that the topological surface state remains intact with Ho doping, consistent with the material’s paramagnetic state. The large saturation moment achieved makes these films useful for incorporation into heterostructures, whereby magnetic order can be introduced via interfacial coupling.
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Nov 2015
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I10-Beamline for Advanced Dichroism
Theoretical Physics
|
S. E.
Harrison
,
L. J.
Collins-mcintyre
,
S.-l.
Zhang
,
A. A.
Baker
,
A. I.
Figueroa
,
A. J.
Kellock
,
A.
Pushp
,
S. S. P.
Parkin
,
J. S.
Harris
,
G.
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[9234]
Abstract: Breaking the time-reversal symmetry (TRS) in topological insulators (TIs) through ferromagnetic doping is an essential prerequisite for unlocking novel physical phenomena and exploring potential device applications. Here, we report the successful growth of high-quality (DyxBi1−x)2Te3 thin films with Dy concentrations up to x = 0.355 by molecular beam epitaxy. Bulk-sensitive magnetisation studies using superconducting quantum interference device magnetometry find paramagnetic behaviour down to 2 K for the entire doping series. The effective magnetic moment, μeff, is strongly doping concentration-dependent and reduces from ~12.6 μB Dy−1 for x = 0.023 to ~4.3 μB Dy−1 for x = 0.355. X-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Dy M4,5 edge are employed to provide a deeper insight into the magnetic nature of the Dy3+-doped films. XMCD, measured in surface-sensitive total-electron-yield detection, gives μeff = 4.2 μB Dy−1. The large measured moments make Dy-doped films interesting TI systems in which the TRS may be broken via the proximity effect due to an adjacent ferromagnetic insulator.
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Jun 2015
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I10-Beamline for Advanced Dichroism
|
W. Q.
Liu
,
M. Y.
Song
,
N. J.
Maltby
,
S. P.
Li
,
J. G.
Lin
,
M. G.
Samant
,
S. S. P.
Parkin
,
P.
Bencok
,
P.
Steadman
,
A
Dobrynin
,
Y. B.
Xu
,
R.
Zhang
Abstract: The spin and orbital magnetic moments of the Fe3O4 epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μ B/f.u., which is ∼70% of that for the bulk-like Fe3O4. A significant unquenched orbital moment up to 0.54 ± 0.05 μ B/f.u. was observed, which could come from the symmetry breaking at the Fe3O4/MgO interface. Such sizable orbital moment will add capacities to the Fe3O4-based spintronics devices in the magnetization reversal by the electric field.
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May 2015
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I10-Beamline for Advanced Dichroism
|
Liam
Collins-mcintyre
,
M. D.
Watson
,
A. A.
Baker
,
S. L.
Zhang
,
A. I.
Coldea
,
S. E.
Harrison
,
A.
Pushp
,
A. J.
Kellock
,
S. S. P.
Parkin
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
Diamond Proposal Number(s):
[8529]
Open Access
Abstract: We report the growth of Mn-doped Bi2Se3 thin films by molecular beam epitaxy
(MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to ¡7.5 atomic-% Mn, determined by Rutherford backscattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mn is observed with increasing doping concentration. A magnetic moment of 5.1 ¥ìB/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 ¥ìB/Mn from surface-sensitive XMCD. At ¡2.5 K, XMCD at the Mn L2,3 edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K.
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Dec 2014
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I10-Beamline for Advanced Dichroism
|
Liam
Collins-mcintyre
,
S. E.
Harrison
,
P.
Schönherr
,
N.-j.
Steinke
,
Christy
Kinane
,
Timothy
Charlton
,
D.
Alba-veneroa
,
A.
Pushp
,
A. J.
Kellock
,
S. S. P.
Parkin
,
J. S.
Harris
,
Sean
Langridge
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
Abstract: We report the structural and magnetic study of Cr-doped Bi2Se3 thin films using x-ray diffraction (XRD), magnetometry and polarized neutron reflectometry (PNR). Epitaxial layers were grown on c-plane sapphire by molecular beam epitaxy in a two-step process. High-resolution XRD shows the exceptionally high crystalline quality of the doped films with no parasitic phases up to a Cr concentration of 12% (in % of the Bi sites occupied by substitutional Cr). The magnetic moment, measured by SQUID magnetometry, was found to be per Cr ion. The magnetic hysteresis curve shows an open loop with a coercive field of . The ferromagnetic transition temperature was determined to be analyzing the magnetization-temperature gradient. PNR shows the film to be homogeneously ferromagnetic with no enhanced magnetism near the surface or interface.
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Sep 2014
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