I05-ARPES
|
Mihir
Date
,
Francesco
Petocchi
,
Yun
Yen
,
Jonas A.
Krieger
,
Banabir
Pal
,
Vicky
Hasse
,
Emily C.
Mcfarlane
,
Chris
Körner
,
Jiho
Yoon
,
Matthew D.
Watson
,
Vladimir N.
Strocov
,
Yuanfeng
Xu
,
Ilya
Kostanovski
,
Mazhar N.
Ali
,
Sailong
Ju
,
Nicholas C.
Plumb
,
Michael A.
Sentef
,
Georg
Woltersdorf
,
Michael
Schüler
,
Philipp
Werner
,
Claudia
Felser
,
Stuart S. P.
Parkin
,
Niels B. M.
Schröter
Diamond Proposal Number(s):
[29240]
Open Access
Abstract: Crystalline solids can become band insulators due to fully filled bands, or Mott insulators due to strong electronic correlations. While Mott insulators can theoretically occur in systems with an even number of electrons per unit cell, distinguishing them from band insulators experimentally has remained a longstanding challenge. In this work, we present a unique momentum-resolved signature of a dimerized Mott-insulating phase in the experimental spectral function of Nb3Br8: the top of the highest occupied band along the out-of-plane direction kz has a momentum-space separation Δkz = 2π/d, whereas that of a band insulator is less than π/d, where d is the average interlayer spacing. Identifying Nb3Br8 as a Mott insulator is crucial to understand its role in the field-free Josephson diode effect. Moreover, our method could be extended to other van der Waals systems where tuning interlayer coupling and Coulomb interactions can drive a band- to Mott-insulating transition.
|
Apr 2025
|
|
I05-ARPES
|
Jonas A.
Krieger
,
Samuel
Stolz
,
Iñigo
Robredo
,
Kaustuv
Manna
,
Emily C.
Mcfarlane
,
Mihir
Date
,
Banabir
Pal
,
Jiabao
Yang
,
Eduardo
B. Guedes
,
J. Hugo
Dil
,
Craig M.
Polley
,
Mats
Leandersson
,
Chandra
Shekhar
,
Horst
Borrmann
,
Qun
Yang
,
Mao
Lin
,
Vladimir N.
Strocov
,
Marco
Caputo
,
Matthew D.
Watson
,
Timur K.
Kim
,
Cephise
Cacho
,
Federico
Mazzola
,
Jun
Fujii
,
Ivana
Vobornik
,
Stuart S. P.
Parkin
,
Barry
Bradlyn
,
Claudia
Felser
,
Maia G.
Vergniory
,
Niels B. M.
Schröter
Diamond Proposal Number(s):
[20617, 26098, 24703]
Open Access
Abstract: Spin-orbit coupling in noncentrosymmetric crystals leads to spin-momentum locking – a directional relationship between an electron’s spin angular momentum and its linear momentum. Isotropic orthogonal Rashba spin-momentum locking has been studied for decades, while its counterpart, isotropic parallel Weyl spin-momentum locking has remained elusive in experiments. Theory predicts that Weyl spin-momentum locking can only be realized in structurally chiral cubic crystals in the vicinity of Kramers-Weyl or multifold fermions. Here, we use spin- and angle-resolved photoemission spectroscopy to evidence Weyl spin-momentum locking of multifold fermions in the chiral topological semimetal PtGa. We find that the electron spin of the Fermi arc surface states is orthogonal to their Fermi surface contour for momenta close to the projection of the bulk multifold fermion at the Γ point, which is consistent with Weyl spin-momentum locking of the latter. The direct measurement of the bulk spin texture of the multifold fermion at the R point also displays Weyl spin-momentum locking. The discovery of Weyl spin-momentum locking may lead to energy-efficient memory devices and Josephson diodes based on chiral topological semimetals.
|
May 2024
|
|
I05-ARPES
|
D. F.
Liu
,
E. K.
Liu
,
Q. N.
Xu
,
J. L.
Shen
,
Y. W.
Li
,
D.
Pei
,
A. J.
Liang
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
Y. F.
Xu
,
Y.
Sun
,
L. X.
Yang
,
Z. K.
Liu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Open Access
Abstract: The spin–orbit coupling (SOC) lifts the band degeneracy that plays a vital role in the search for different topological states, such as topological insulators (TIs) and topological semimetals (TSMs). In TSMs, the SOC can partially gap a degenerate nodal line, leading to the formation of Dirac/Weyl semimetals (DSMs/WSMs). However, such SOC-induced gap structure along the nodal line in TSMs has not yet been systematically investigated experimentally. Here, we report a direct observation of such gap structure in a magnetic WSM Co3Sn2S2 using high-resolution angle-resolved photoemission spectroscopy. Our results not only reveal the existence and importance of the strong SOC effect in the formation of the WSM phase in Co3Sn2S2, but also provide insights for the understanding of its exotic physical properties.
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Jan 2022
|
|
|
|
D. F.
Liu
,
Q. N.
Xu
,
E. K.
Liu
,
J. L.
Shen
,
C. C.
Le
,
Y. W.
Li
,
D.
Pei
,
A. J.
Liang
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
Y. F.
Xu
,
Y.
Sun
,
L. X.
Yang
,
Z. K.
Liu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Abstract: Topological Weyl semimetals (TWSs) are exotic crystals possessing emergent relativistic Weyl fermions connected by unique surface Fermi arcs (SFAs) in their electronic structures. To realize the TWS state, certain symmetries (such as the inversion or time reversal symmetry) must be broken, leading to a topological phase transition (TPT). Despite the great importance in understanding the formation of TWSs and their unusual properties, direct observation of such a TPT has been challenging. Here, using a recently discovered magnetic TWS
Co
3
Sn
2
S
2
, we were able to systematically study its TPT with detailed temperature dependence of the electronic structures by angle-resolved photoemission spectroscopy. The TPT with drastic band structure evolution was clearly observed across the Curie temperature
(
T
C
=
177
K
)
, including the disappearance of the characteristic SFAs and the recombination of the spin-split bands that leads to the annihilation of Weyl points with opposite chirality. These results not only reveal important insights on the interplay between the magnetism and band topology in TWSs, but also provide a method to control their exotic physical properties.
|
Nov 2021
|
|
I05-ARPES
|
D. F.
Liu
,
L. Y.
Wei
,
C. C.
Le
,
H. Y.
Wang
,
X.
Zhang
,
N.
Kumar
,
C.
Shekhar
,
N. B. M.
Schröter
,
Y. W.
Li
,
D.
Pei
,
L. X.
Xu
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
J.
Fujii
,
I.
Vobornik
,
M. X.
Wang
,
L. X.
Yang
,
Z. K.
Liu
,
Y. F.
Guo
,
J. P.
Hu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Diamond Proposal Number(s):
[18005]
Open Access
Abstract: Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system.
|
Jun 2021
|
|
I05-ARPES
|
Wujun
Shi
,
Benjamin J.
Wieder
,
Holger L.
Meyerheim
,
Yan
Sun
,
Yang
Zhang
,
Yiwei
Li
,
Lei
Shen
,
Yanpeng
Qi
,
Lexian
Yang
,
Jagannath
Jena
,
Peter
Werner
,
Klaus
Koepernik
,
Stuart
Parkin
,
Yulin
Chen
,
Claudia
Felser
,
B. Andrei
Bernevig
,
Zhijun
Wang
Abstract: Topological physics and strong electron–electron correlations in quantum materials are typically studied independently. However, there have been rapid recent developments in quantum materials in which topological phase transitions emerge when the single-particle band structure is modified by strong interactions. Here we demonstrate that the room-temperature phase of (TaSe4)2I is a Weyl semimetal with 24 pairs of Weyl nodes. Owing to its quasi-one-dimensional structure, (TaSe4)2I also hosts an established charge-density wave instability just below room temperature. We show that the charge-density wave in (TaSe4)2I couples the bulk Weyl points and opens a bandgap. The correlation-driven topological phase transition in (TaSe4)2I provides a route towards observing condensed-matter realizations of axion electrodynamics in the gapped regime, topological chiral response effects in the semimetallic phase, and represents an avenue for exploring the interplay of correlations and topology in a solid-state material.
|
Jan 2021
|
|
|
|
Yangkun
He
,
Gerhard H.
Fecher
,
Chenguang
Fu
,
Yu
Pan
,
Kaustuv
Manna
,
Johannes
Kroder
,
Ajay
Jha
,
Xiao
Wang
,
Zhiwei
Hu
,
Stefano
Agrestini
,
Javier
Herrero-Martin
,
Manuel
Valvidares
,
Yurii
Skourski
,
Walter
Schnelle
,
Plamen
Stamenov
,
Horst
Borrmann
,
Liu Hao
Tjeng
,
Rudolf
Schaefer
,
Stuart S. P.
Parkin
,
John Michael D.
Coey
,
Claudia
Felser
Open Access
Abstract: The development of high‐density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat‐assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin‐film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m−3 is combined with a saturation magnetization of μ0Ms = 0.52 T at 2 K (2.2 MJ m−3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare‐earth‐free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m−1 K−1, make Rh2CoSb a candidate for the development of heat‐assisted writing with a recording density in excess of 10 Tb in.−2.
|
Oct 2020
|
|
I05-ARPES
|
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.
|
Jul 2020
|
|
I05-ARPES
|
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.
|
Jul 2020
|
|
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.
|
Sep 2019
|
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