Electronic structure of van der Waals magnetic semimetal GdGaI
Kohei Yamagami, Ryotaro Okuma, Yoshinari Okada
Okinawa Institute of Science and Technology Graduate University, Tancha, Onna-son, Kunigami-gun
Okinawa, 904-0495, Japan.

Recently, we have succeeded to grow relatively large size van der Waals (vdW) magnetic
semimetal GdGaI (GGI). The crystal structure and picture of GdGaI is shown in Fig. 1a. The
density functional theory (DFT) based band calculation for GGI suggests semi-metallic
electronic structure. The DFT band structure is analogous to that of TiSe2, which is know as a
2D material hosting charge density wave (CDW) and/or exciton formation [1]. Compared tonone-magnetic TiSe2, emergence of weak ferromagnetism at low temperature is interesting
unique characteristic in GGI. While rich deformation of band structure is naturally expected,
experimental report on electronic structure in GGI has been lacking so far.
Here, we report angle resolved photoemission spectroscopy (ARPES) on GGI. Fig. 1b shows
ARPES dispersion around  point, using 7eV laser with p-polarization [2]. For comparison,
ARPES dispersion using He discharge lamp is also shown in Fig. 1c. Bellow E-EF=-0.4 (eV),
two bands are clearly visualized in laser ARPED data (Fig. 1b). Above E-EF=-0.4 (eV), thehole bands around the Γ point were similarly observed in both cases. The band top of the holeband is around E-EF~-0.18 (eV), which reflects band gap opening by 2a x 2a ordering. The clear
difference between two ARPES dispersion (Fig. 1b and c) is near EF intensity distribution in
k space. This presumably suggest importance of understanding characteristic spin and orbital
nature in near EF hole band, together with prominent spin-orbital coupling effect in this system.

Figure 1. (a) The crystal structure and picture of GdGaI. (b)(c) The angle resolved photoemission
spectroscopy (ARPES) data around  point, using (b) He discharge lamp and (c) 7 eV laser. The measured
temperature for (b) and (c) are 10K and 14K, respectively. In (b), p-polarization is used.

References[1] H. Cercellier, et al. Phys. Rev. Lett. 99, 146403 (2007).
[2] K. Yaji et al., Rev. Sci. Instrum. 87, 053111 (2016).

ENHANCEMENT OF RASHBA SPLITTING IN SNPC/AU(111)
Kaname Kanai
Department of Physics, Faculty of Science and Technology, Tokyo University of Science
The growth of sub-monolayers of tin phthalocyanine (SnPc) molecules on Au(111) has been
confirmed by angle-resolved photoemission spectroscopy (ARPES) to enhance the energy band
splitting due to the Rashba spin-orbit interaction appearing in the Shockley state (SS). This result
provides knowledge for understanding the electronic structure of Rashba-type SS at the interface
between organic molecules and metal substrates.
The electronic structure of the interface between a metal surface and molecules adsorbed on that
surface has been a long-standing issue in surface science. Recently, this issue has attracted more
attention due to its importance in organic semiconductor devices. The electronic structure of aninterface at an electrode metal surface covered with organic semiconductor molecules (organic/metalinterface) is directly responsible for the electronic properties of the device because the relationshipbetween the molecular orbital energies and the Fermi level of the metal at the interface determines thecarrier injection barrier from the electrodes into the semiconducting layers. Thus, in order to realize adevice with high carrier injection efficiency, it is vital to understand the formation of the electronic
structure at the organic/metal interface.
SS is a characteristic electronic state peculiar to the crystal surface. By breaking the spatial inversion
symmetry of the crystal in the normal direction to the surface, a free electron-like parabolic dispersion
appears near the surface. In particular, it is known that in noble metal crystals such as copper, silver,
and gold, large spin-orbit coupling can cause Rashba effects of practically observable magnitude toappear. The Rashba effect lifts the spin degeneracy of the SS band dispersion and splits it into twoparabolas that are completely spin-polarized except at the G point. Recently, it has been reported that
this Rashba effect is enhanced at metal interfaces such as Bi/Ag(111) [1], TTC/Au(111) [2], and raregas atoms/Au(111) interfaces. Attempts have also been made to create devices that can convert spincurrents to spin currents by generating the Edelstein effect at the molecule/metal interface using the
giant Rashba effect [3,4]. Therefore, understanding the mechanism by which molecular adsorption
significantly affects the Rashba effect is not only of interest in surface science, but should provide
fundamental information for future spintronics. In this study, we aimed to directly observe in detail the
influence of tin-phthalocyanine (SnPc) molecules, a typical organic semiconductor molecule, on the
Rashba effect that appears in SS of Au(111).
The single crystal of Au(111) sample was used for the substrate. Before vapor deposition of SnPc on
it, the surface of this Au(111) substrate was cleaned in UHV by sputter-anneal cycles. Anneal
temperature was 773 K. This clean surface was evaluated by low energy electron diffraction (LEED)
measurement. After outgassing, SnPc was deposited on Au(111) at normal incidence from resistively
heated Knudsen cell. The deposition rate of 0.0005 ~ 0.002 nm/s was measured with a quartz crystal
microbalance oscillator. The deposition of SnPc on Au(111) was carried out in a stepwise manner: the
SnPc film thickness were 0.06, 0.13, 0.19, and 0.26 ML. The electronic structure of SnPc/Au(111) was
measured by ARPES at 28 K.
When SnPc thin film is grown on Au(111),
the SS rapidly disappears as the coverageincreases. This is probably due to the loss oftranslational symmetry in the direction
parallel to the surface, caused by the randomorientation of the molecules on the surface.
This hypothesis can be easily inferred fromthe three-dimensional molecular structure of
SnPc, which is called “shuttlecock” as shownin Fig. 1. However, when the coverage of thegrown SnPc thin film is very low, SnPc
appears to grow epitaxially on Au(111), andFig. 1. Molecular structure of SnPc (left).
Three-dimensional structure of SnPc (right).

the Au(111) SS does not disappear. Furthermore, it was observed that the Au(111) SS was greatly
affected by molecular adsorption.

Fig . 2. The thickness dependence of SnPc/Au(111) Rashba-type SS measured at 28 K using
ARPES. The results of (a) Au(111) clean surface, (b) SnPc 0.06ML/Au(111), (c) SnPc
0.13ML/Au(111), (d) SnPc 0.26ML/Au(111), and (e) SnPc 0.32ML/Au(111). The red or blue plotson the data are the results of peak fitting analysis at EDC (Energy Distribution Curve) and MDC(Momentum Distribution Curve) maps.

Fig. 2 shows the ARPES spectra (hn = 6.998 eV) of SnPc/Au(111). It can be seen that SS in
Au(111) is modified as the coverage of SnPc increases. Energy of SS in Au(111) was significantly
lowered with increasing the PbPc thickness. However, SS was observable only in the case of very low
coverage of SnPc, and SS disappeared before the coverage of one molecular layer was reached.
Fig. 3 shows thickness dependence of Rashba
parameter aR and Rashba splitting Dk|| calculated by
EDC and MDC analysis of the AEPES results in
Fig. 2. As the value of Dk|| increased, the value of aR
also tended to increase as the film thickness
increased.

In conclusion, we observed the enhancementof Rashba effect by adsorption SnPc thin film
on Au(111). One possible factor that enhances
the Rashba effect at the SnPc/Au (111) interface
is due to the potential gradient caused by theadsorption of molecules with evenly aligned
dipole directions, which is needed to be further
verified in the future. The results presented here
allowed us to discuss the interfacial electronic
states formed by adsorbed metallic
phthalocyanines, in relation to their effect on the
Rashba effect.

Fig. 3. Thickness dependence of Rashba
parameter 𝛼" and ∆𝑘∥ calculated from
SnPc/Au(111) Rashba-type SS observed by
ARPES.

REFERENCES[1] C. R. Ast, J. Henk, A. Ernst, L. Moreschini, M. C. Falub, D. Pacilé, P. Bruno, K. Kern andM Grioni, Phys. Rev. Lett. 98, 186807 (2007).
[2] H. Mizushima, H. Koike, K. Kuroda, Y. Ishida, M. Nakayama, K. Mase, T. Kondo, S. Shinand K. Kanai, Phys. Chem. Chem. Phys., 19, 18646 (2017).
[3] S. Takizawa, K. Kondou, H. Isshiki1, K. Shimose, T. Kawabe, S. Miwa and Y. Otani, IEEE
Trans. Magn., 54, 11 (2018).
[4] H. Isshiki, K.Kondou, S. Takizawa, K. Shimose, T. Kawabe, E. Minamitani, N. Yamaguchi,
F. Ishii, A. shiotari, Y. Sugimoto, S. Miwa and Y. Otani, Nano Lett., 19, 7119 (2019).

SARPES STUDY OF A NEW WEYL SEMIMETALOF THE CDW COMPONDS
Chun Lin1, Kenta Kuroda1, Ryo Noguchi1, Kaishu Kawaguchi1, Ayumi Harasawa1, Shik
Shin2, Masanobu Miyata3, Koyano Mikio3, and Takeshi Kondo1,4
1

The Institute for Solid State Physics, The University of Tokyo
Office of University Professor, The University of Tokyo

2

School of Materials Science, Japan Advanced Institute of Science and Technology

3

Trans-scale Quantum Science Institute, The University of Tokyo4

The emergent quantum phenomena in low dimensional materials have attracted increasingly
more attention in the realm of not only fundamental science but also practical applications.
These compounds typically host multiple broken symmetry orders such as charge density
wave (CDW), superconductivity, and other magnetism- and spin-related exotic quantum
phenomena [1], providing a multifunctional platform for investigations of basic physics andreal-world applications owing to their low dimensionality suitable for engineering. On theother hand, topological semimetal is a new class of quantum matters with characteristic
topological surface states originated from the topology of their bulk band structure [2]. In
particular, the Weyl semimetal is a condensed-matter realization of Weyl fermions manifested
as low-energy excitations, in which band dispersions exhibit linear crossings at pairs of Weyl
points, with either broken spatial inversion or time-reversal symmetry.
Ta2Se8I is well known as a prototypical quasi-one-dimension (quasi-1D) CDW system
stacked by TaSe4 chains along the c axis with body center tetragonal lattice (Figs. 1a,b). The
CDW sets in at a temperature around 260 K revealed by resistivity [3] as shown in Fig. 1d [4].
The CDW wave vector was confirmed by X-ray diffraction to be (±0.045 2π/a, ±0.045 2π/b,±0.085 2π/c) [5]. Nevertheless, a long-standing puzzle remains in that the energy gap is muchlarger than the mean-field value and it refrains from closing at temperatures far above the
CDW onset, as confirmed by, e.g., optical spectra [6] and angle-resolved photoemission
spectroscopy (ARPES) [7,8]. Such an anomalous behavior was attributed either to afluctuating CDW in an extreme 1D manifestation [6] or the formation of small polarons
dressing mobile electrons owing to strong electron-phonon coupling [7,8]. Recently, firstprinciple calculations indicate that the high-temperature phase of this compound is actually a
Weyl semimetal [9], from which the transport signals of chiral anomaly have beensuccessfully captured in the CDW state [4]. Ta2Se8I, therefore, offers a very rare realization ofstrong correlation driven topological phase transition [9].
Here, we present laser-based spin-resolved ARPES (at Institute for Solid State Physics, theUniversity of Tokyo) results in the distorted phase of this newly predicted Weyl semimetaland provide evidence of spin-polarized Weyl cone whose experimental observation remains
challenging in the literature.
Figure 1g shows the constant-energy contour map at a binding energy of 0.6 eV acquired at
100 K with 7 eV laser and on the (110) surface of conventional cell which is easily cleaved
due to the weak van der Waals interactions among quasi-1D chains. The bulk Brillouin zone
and its surface projection (reddish shaded) are shown in Fig. 1c. One can see that the band
structure features a wiggle perpendicular to the chain direction indicative of a finite interchaininteraction, which is consistent with synchrotron-ARPES [7,8]. In Figs. 1h,i, we present thedispersions along two momentum cuts crossing the Weyl points, as indicated in Fig. 1g withcorresponding colored arrows. A spectral suppression manifested as a 0.2 eV energy gap
agrees with the polaron scenario [7]. Below this polaron gap, the band disperses in a linear
Dirac-like manner as indicated by the red lines in Figs. 1h,i, consistent with the proposedelectronic structure of a Weyl semimetal (Fig. 1e [9]). Taking advantage of spin resolution,
we obtained the energy distribution curves of spin-up and spin-down states at a momentum
point of the (purple arrow in Fig. 1i), as shown in Fig. 1j. The resulting spin polarization(green curve in Fig. 1j) suggests a spin-polarized Weyl cone in the CDW state.

Fig. 1 a,b, Crystal structure of Ta2Se8I. c, Bulk Brillouin zone and its projection onto conventional (110) surface.
d, Characteristic resistivity showing a CDW transition around 260 K [4]. e, Band structure along high-symmetrylines calculated from density functional theory with spin-orbit coupling [9]. f, Schematic of a CDW gapped
Weyl semimetal [4]. g-i, Our preliminary data of constant-energy contour (EB = 0.6 eV) and band dispersions
along two momentum cuts indicated by the corresponding colors. Small polarons dress photoelectrons featured
by a polaron gap as indicated. Red lines in h,i are guides for the eyes. j, Our preliminary data of spin-resolved
energy distribution curves and spin polarization along the dashed purple arrow indicated in i.

REFERENCES[1] P. Monceau, Advances in Physics 61, 325 (2012)[2] N. P. Armitage et al., Rev. Mod. Phys. 90, 015001 (2018)[3] Z. Z. Wang et al., Solid State Commun. 46, 325–328 (1983)[4] J. Gooth et al., Nature 575, 315–319 (2019)[5] H. Fujishita et al., Solid State Commun. 49, 313–316 (1984)[6] H. P. Geserich et al., Physica B+C 143, 198–200 (1986)[7] L. Perfetti et al., Phys. Rev. Lett. 87, 216404 (2001)[8] C. Tournier-Colletta et al., Phys. Rev. Lett. 110, 236401 (2013)[9] W. Shi et al., Nature Physics 17, 381–387 (2021)

OBSERVATION AND CONTROL OF THE WEAK TOPOLOGICALINSULATOR STATE IN ZRTE5Peng Zhang1, Ryo Noguchi1, Kenta Kuroda1, Chun Lin1, Kaishu Kawaguchi1, Koichiro
Yaji2, Ayumi Harasawa1, Mikk Lippmaa1, Simin Nie3, Hongming Weng4, V. Kandyba5, A.
Giampietri5, A. Barinov5, Qiang Li6, G. D. Gu6, Shik Shin1, Takeshi Kondo1
1

Institute for Solid State Physics, University of Tokyo
Research Center for Advanced Measurement and Characterization, NIMS
3
Department of Materials Science and Engineering, Stanford University
4
Institute of Physics, Chinese Academy of Sciences
5
Elettra - Sincrotrone Trieste
6
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory
2

A quantum spin Hall insulator hosts topologically protected edge states, in whichbackscattering by nonmagnetic impurities is prohibited and dissipationless current is possible.
Its 3D analogue, a weak topological insulator (WTI), possesses surface states at the ‘side’
surface that are not weak, but as robust as the wide-studied strong topological insulators, andthere may be even less scattering channels due to the highly directional surface electrons [1].
However, since the topological states only appear on side surfaces, it is difficult to prepare sucha clean surface and to study the WTI states. Here, we report for the first time the visualizationof the topological surface states of the WTI candidate ZrTe5. A quasi-1D spin-momentum
locked band on the side surface was distinguished. Furthermore, control of the band gap byexternal strain was confirmed directly by ARPES: a WTI state with a larger gap and a
topological phase transition to an ideal Dirac semimetal state are realized.
Topological surface states observed on the side surface
ZrTe5 was predicted to be a WTI candidate at the early stage of exploring WTIs [2], inwhich there is no surface state on the top surface, while on the side surface there is
topological surface state, as shown in Fig. 1(a). It has a quasi-1D crystal structure. Along thelattice b direction, the layers are stacked by van der Waals forces, and a clean surface can beeasily obtained by cleavage. Instead, Te–Te bonding exists between adjacent layers along thelattice c direction, causing much more difficulty in cleaving the side a-b surface. Due to thedifficulty to cleave the side surface, all the previous surface-sensitive studies were carried out
Figure 1 ARPES measurement on
the side surface of ZrTe5. (a) Band
structure of a WTI on the top
surface and side surface. (b)Intensity mapping in the real space
for the cleaved area of the sidesurface from a nano-ARPES. (c)Band structure measured at theposition indicated by red cross in(b). (d) Fermi surface measured
with laser ARPES. The red and blue
arrows indicated the spin direction
measured with a spin-resolved
ARPES.

on the top surface. Whether or not this material is topological, which relies on the measurementfrom side surface, has not been determined beyond speculation. We successfully prepared theside surface of this sample [3]. With a synchrotron-based nano-ARPES (spot size < 1 μm), we
took real space maps of photoemission intensity on several samples, as sketched in Fig. 1(b). It
is found that the typical dimension of cleaved areas is around or smaller than 50 μm. Alonglattice a direction, the band shows a hole-like dispersion (Fig. 1(c)). In k-space, a quasi-1D
Fermi surface is exhibited by plotting ARPES intensities about the Fermi level, which shows
no dispersion along lattice b direction (Fig. 1(d)). We further observed a clear spin polarization
along lattice b direction. In contrast, the spin polarization is almost zero along the lattice a andc directions, as sketched by red and blue arrows in Fig. 1(d). Therefore, the band is spinpolarized along the b-direction with spin-momentum locking, consistent with the spin-textureof WTIs with a quasi-1D dispersion.
Strain-tuned topological phase transition observed on the top surface
First-principles calculations predict that ZrTe5 is close to a topological phase transition,
which may be tuned by external strain. We used a strain device shown in Fig. 2(a) to apply
both compressive and tensile strain. On the top surface, without strain we observed a smallbulk gap (~ 28 meV), as shown in the middle panel of Fig. 2(b). The small bulk gap indicatesthat the WTI state in ZrTe5 is protected only marginally from external perturbations. Withtensile strain, the band gap is enlarged to ~ 51 meV. In contrast, we could reduce the band gap
by compressive strain, even realizing a Dirac semimetal state with no band gap. The
corresponding first-principles calculations are displayed in Fig. 2(c), which is consistent withthe experimental results. In Fig. 2(d), we summarized the topological phase diagram of ZrTe5.
Figure2
Strain-tuned
topological phase transitionin ZrTe5. (a) Strain device we
used
to
apply
both
compressive and tensile
strain. (b) Band structure
measured from top surface
with both compressive andtensilestrain.
(c)Corresponding
band
structuresfromfirstprinciples calculations. (d)Phase diagram of ZrTe5 withdifferent strain.

References:[1] R. Noguchi et al., Nature, 566, 518 (2019).
[2] H. Weng, X. Dai & Z. Fang, Phys. Rev. X 4, 011002 (2014).
[3] P. Zhang et al., Nature Commun. 12, 406 (2021).

ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY OFGALLIUM SINGLE CRYSTAL SURFACE
1

Koichiro Yaji1, Kenta Kuroda2, Fumio Komori2
Research Center for Advanced Measurement and Characterization,
National Institute for Material Science
2

Institute for Solid State Physics, The University of Tokyo

Topological insulators have been intensively studied in last decade, where the spin-polarized
surface states on the topological insulators can be understood with the topology of the
wavefunctions of an electron. A concept common to the topological insulator is applicable tothe superconductor, so-called a topological superconductor. The topological superconductor ispredicted that the surface states host the emergence of Majorana bound states. Recently, we
revealed that an iron-based superconductor FeSe0.55Te0.45 is the topological superconductor [1].
Here, it is important to clarify the Fermi surface and the energy band dispersion to identify if
the material is the topological superconductor.
An elemental gallium is a pure metal. The bulk gallium crystals have a rich phase diagram.
Among them, only the orthorhombic phase, so-called a-gallium (a-Ga), is stable at atmosphericpressure. The a-Ga exhibits giant magnetoresistance though that is a non-magnetic material,
which can be originating from topological property [2]. Moreover, the superconductivity wasconfirmed by both specific heat and resistivity measurements [2]. Therefore, the a-Ga would
offer an interesting platform for understanding coexistence of non-trivial electronic states andsuperconductivity in the pure metal. In our previous study using synchrotron radiation, we haveclearly observed the surface state of a-Ga. The aim of the present study is the investigation of
the spin structure of the surface states with spin-resolved ARPES.
The a-Ga single crystal was prepared from super-cooled Ga [2]. Due to the low melting
temperature, the special care was needed when we treated the crystal during polishing and insitu cleaning procedures. The a-Ga(010) surface was mechanically polished using diamondpaste. Subsequently, the surface was then cleaned by repeated cycles of 0.7 keV Ne+ sputtering
at 273 K and annealing up to 273 K in the ultra-high vacuum chamber. The clean surface waschecked by low energy electron diffraction (LEED).
Figure 1 shows a LEED pattern from a-Ga(010) at 0 ℃. We
find sharp LEED spots, indicating that a high-quality single
crystal surface has been obtained. Here, the a-Ga(010) surface
has a glide plane in [100] direction. Thus, the odd-number spots
in the [100] direction disappear, which is in good agreementwith former study [4].
The ARPES measurements were performed at E-building in
ISSP. Photoelectrons were excited by a 7-eV laser light. The
sample temperature was kept at 35 K during the measurements.
However, unfortunately, photoelectron intensity with 7-eV Fig. 1. LEED pattern of aphotons was not enough to observe the band of a-Ga(010) due Ga(010) with the primaryenergy of 31 eV at 273 K.
to the low photoionization cross section.
REFERENCES[1] P. Zhang et al., Science 360, 182 (2018).
[2] B. Chen et al., npj Quantum Materials 3, 40 (2018).
[3] K. Yaji et al., Rev. Sci. Instrum. 87, 053111 (2016).
[4] Ch. Søndergaard et al., Phys. Rev. B 67, 205105 (2003).

STUDY ON THE SPIN TEXTURE OF THE TOPOLOGICAL STATES INQUASI-ONE-DIMENSIONAL MATERIAL
Deyang Wang1, Mao Ye1, Kenta Kuroda2, Koichiro Yaji2, Ayumi Harasawa2, Takeshi Kondo2
1

State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem andInformation Technology, Chinese Academy of Science, Shanghai 200050, People’s Republic of China
2

Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.

The reducing of dimensionality in materials significantly increases electrons’ anisotropy.
This is especially important for topological materials, where the backscattering is prohibited
due to the protection of time-reversal-symmetry. For quasi-one-dimensional (quasi-1D)
materials, the occurrence of scattering is even more strictly prohibited than that in materials
with higher dimensionality, because quasi-1D materials only possess one dimensional
conductive channel. Therefore, the topological states in quasi-1D materials are considered to
be a promising platform for the development and application of spintronics devices with low
energy consumption.
TaNiTe5 is predicted to be a candidate for quasi-1D topological materials, in which the highly
anisotropic transport properties and nontrivial Berry phases have been confirmed [1]. However,the direct experimental observation of the topological surface states in TaNiTe5 are still missing.
Thus, the band topology in this quasi-1D materials remains unclear. In this study, weunambiguously reveal the topological surface states in TaNiTe5 by means of high resolution
laser spin- and angle-resolved photoemission spectroscopy (laser-SARPES) combined with
DFT calculations.
High quality single crystalline TaNiTe5 samples were grown by self-flux method, and thencharacterized by the X-ray Diffraction and Energy Dispersive Spectroscopy. The highresolution laser- SARPES experiments were conducted at the Institute for Solid State Physics,
University of Tokyo, equipped with 6.994 eV photons laser and ScientaOmicron DA30L
analyzer [2]. The density functional theory (DFT) calculations were performed via Vienna ab
initio Simulation Package [3] for bulk bands and WannierTools [4] for surface states.
The crystal structure of TaNiTe5 is shown in Figure 1(a), where the NiTe2 quasi-1D atomic
chains extend along a direction. The Van der Waals layers stack along b direction, where thecrystal can be easily cleaved. Figure 1(b) shows the corresponding bulk Brillouin zone (BZ)
and surface projected BZ for the cleaved plane. The Fermi surface measured by laser-ARPES
is shown in Figure 1(c), showing strong anisotropic properties, which shows good agreementwith the calculated Fermi surface obtained by DFT method as shown in Figure 1 (d). Figure 1(e) shows the spin-resolved band structure along Z-Γ-Z direction. Two sets of Dirac-typesurface bands (denoted as α and β) near the Fermi energy, and one set of Rashba-type bands(denoted as γ) located at binding energy around 0.4 eV are clearly resolved. The spin-resolved
results reveal that both α and β bands possess spin-momentum-locking spin texture, and are
well reproduced by our DFT calculations [Figure 1(f)], indicting the existence of topologically
non-trivial surface states.

Figure 1 (a) Crystal structure and cleaved plane of TaNiTe5. (b) Three-dimensional (3D) bulk Brillouin zone (BZ)
and the projected surface BZ for cleaved plane. (c) Spin-integrated Fermi surface intensity measured by 7-eV laserARPES. (d) Fermi surface obtained by DFT calculations. (e) Spin-resolved band structure along Z-Γ-Z direction
measured by spin-ARPES, while red and blue stands for spin-up and spin-down in ka direction, black and white
represents the intensity distribution. (f) Spin-resolved band structure along Z-Γ-Z direction obtained by DFT
calculations.

In summary, we observed the surface states and its spin-texture of the qusi-1D material
TaNiTe5 through high-resolution laser- SARPES experiments, and further confirmed by thecomparison with DFT calculations. Further examination of the band topology, as well as theexperimental measurements on other cleaved planes would benefit the determination of the
topological properties in the qusi-1D TaNiTe5 materials.

REFERENCES[1] Xu, Chunqiang, et al. "Anisotropic transport and quantum oscillations in the quasi-one-dimensional
TaNiTe5: Evidence for the nontrivial band topology." The Journal of Physical Chemistry Letters 11.18(2020): 7782-7789.
[2] Yaji, Koichiro, et al. "High-resolution three-dimensional spin-and angle-resolved photoelectron
spectrometer using vacuum ultraviolet laser light." Review of Scientific Instruments 87.5 (2016): 053111.
[3] Kresse, Georg, and Jürgen Furthmüller. "Efficiency of ab-initio total energy calculations for metals
and semiconductors using a plane-wave basis set." Computational materials science 6.1 (1996): 15-50.
[4] Wu, QuanSheng, et al. "WannierTools: An open-source software package for novel topologicalmaterials." Computer Physics Communications 224 (2018): 405-416.