Publications by Yulin Chen

Strong spin-orbit coupling and Dirac nodal lines in the three-dimensional electronic structure of metallic rutile IrO2

PHYSICAL REVIEW B 99 (2019) ARTN 195106

X Xu, J Jiang, WJ Shi, V Suess, C Shekhar, SC Sun, YJ Chen, S-K Mo, C Felser, BH Yan, HF Yang, ZK Liu, Y Sun, LX Yang, YL Chen

Topological Lifshitz transitions and Fermi arc manipulation in Weyl semimetal NbAs.

Nature communications 10 (2019) 3478-

HF Yang, LX Yang, ZK Liu, Y Sun, C Chen, H Peng, M Schmidt, D Prabhakaran, BA Bernevig, C Felser, BH Yan, YL Chen

Surface Fermi arcs (SFAs), the unique open Fermi-surfaces (FSs) discovered recently in topological Weyl semimetals (TWSs), are unlike closed FSs in conventional materials and can give rise to many exotic phenomena, such as anomalous SFA-mediated quantum oscillations, chiral magnetic effects, three-dimensional quantum Hall effect, non-local voltage generation and anomalous electromagnetic wave transmission. Here, by using in-situ surface decoration, we demonstrate successful manipulation of the shape, size and even the connections of SFAs in a model TWS, NbAs, and observe their evolution that leads to an unusual topological Lifshitz transition not caused by the change of the carrier concentration. The phase transition teleports the SFAs between different parts of the surface Brillouin zone. Despite the dramatic surface evolution, the existence of SFAs is robust and each SFA remains tied to a pair of Weyl points of opposite chirality, as dictated by the bulk topology.

Unveiling Electronic Correlation and the Ferromagnetic Superexchange Mechanism in the van der Waals Crystal CrSiTe_{3}.

Physical review letters 123 (2019) 047203-

J Zhang, X Cai, W Xia, A Liang, J Huang, C Wang, L Yang, H Yuan, Y Chen, S Zhang, Y Guo, Z Liu, G Li

The recent discovery of intrinsic ferromagnetic order in the atomically thin van der Waals crystal CrXTe_{3} (X=Si, Ge) stimulates intensive studies on the nature of low-dimensional magnetism because the presence of long-range magnetic order in two-dimensional systems with continuous symmetry is strictly prohibited by thermal fluctuations. By combining advanced many-body calculations with angle-resolved photoemission spectroscopy we investigate CrSiTe_{3} single crystals and unveil the pivotal role played by the strong electronic correlations at both high- and low-temperature regimes. Above the Curie temperature (T_{c}), Coulomb repulsion (U) drives the system into a charge transfer insulating phase. In contrast, below T_{c} the crystal field arranges the Cr-3d orbitals such that the ferromagnetic superexchange profits, giving rise to the bulk ferromagnetic ground state with which the electronic correlations compete. The excellent agreement between theory and experiment establishes CrSiTe_{3} as a prototype low-dimensional crystal with the cooperation and interplay of electronic correlation and ferromagnetism.

Chiral topological semimetal with multifold band crossings and long Fermi arcs

NATURE PHYSICS 15 (2019) 759-+

NBM Schroter, D Pei, MG Vergniory, Y Sun, K Manna, F De Juan, JA Krieger, V Suess, M Schmidt, P Dudin, B Bradlyn, TK Kim, T Schmitt, C Cacho, C Felser, VN Strocov, Y Chen

Measurement of the bulk and surface bands in Dirac line-node semimetal ZrSiS

CHINESE PHYSICS B 27 (2018) ARTN 017105

G-H Hong, C-W Wang, J Jiang, C Chen, S-T Cui, H-F Yang, A-J Liang, S Liu, Y-Y Lv, J Zhou, Y-B Chen, S-H Yao, M-H Lu, Y-F Chen, M-X Wang, L-X Yang, Z-K Liu, Y-L Chen

Ultrafast and highly sensitive infrared photodetectors based on two-dimensional oxyselenide crystals.

Nature Communications 9 (2018) 3311-

J Yin, Z Tan, H Hong, J Wu, H Yuan, Y Liu, C Chen, C Tan, F Yao, T Li, Y Chen, Z Liu, K Liu, H Peng

Infrared light detection and sensing is deeply embedded in modern technology and human society and its development has always been benefitting from the discovery of various photoelectric materials. The rise of two-dimensional materials, thanks to their distinct electronic structures, extreme dimensional confinement and strong light-matter interactions, provides a material platform for next-generation infrared photodetection. Ideal infrared detectors should have fast respond, high sensitivity and air-stability, which are rare to meet at the same time in one two-dimensional material. Herein we demonstrate an infrared photodetector based on two-dimensional Bi2O2Se crystal, whose main characteristics are outstanding in the whole two-dimensional family: high sensitivity of 65 AW-1 at 1200 nm and ultrafast photoresponse of ~1 ps at room temperature, implying an intrinsic material-limited bandwidth up to 500 GHz. Such great performance is attributed to the suitable electronic bandgap and high carrier mobility of two-dimensional oxyselenide.

Observation of topological surface states and strong electron/hole imbalance in extreme magnetoresistance compound LaBi


J Jiang, NBM Schroter, S-C Wu, N Kumar, C Shekhar, H Peng, X Xu, C Chen, HF Yang, C-C Hwang, S-K Mo, C Felser, BH Yan, ZK Liu, LX Yang, YL Chen

Giant anomalous Hall effect in a ferromagnetic Kagomé-lattice semimetal.

Nature physics 14 (2018) 1125-1131

E Liu, Y Sun, N Kumar, L Müchler, A Sun, L Jiao, S-Y Yang, D Liu, A Liang, Q Xu, J Kroder, V Süß, H Borrmann, C Shekhar, Z Wang, C Xi, W Wang, W Schnelle, S Wirth, Y Chen, STB Goennenwein, C Felser

Magnetic Weyl semimetals with broken time-reversal symmetry are expected to generate strong intrinsic anomalous Hall effects, due to their large Berry curvature. Here, we report a magnetic Weyl semimetal candidate, Co3Sn2S2, with a quasi-two-dimensional crystal structure consisting of stacked Kagomé lattices. This lattice provides an excellent platform for hosting exotic topological quantum states. We observe a negative magnetoresistance that is consistent with the chiral anomaly expected from the presence of Weyl nodes close to the Fermi level. The anomalous Hall conductivity is robust against both increased temperature and charge conductivity, which corroborates the intrinsic Berry-curvature mechanism in momentum space. Owing to the low carrier density in this material and the significantly enhanced Berry curvature from its band structure, the anomalous Hall conductivity and the anomalous Hall angle simultaneously reach 1130 Ω-1 cm-1 and 20%, respectively, an order of magnitude larger than typical magnetic systems. Combining the Kagomé-lattice structure and the out-of-plane ferromagnetic order of Co3Sn2S2, we expect that this material is an excellent candidate for observation of the quantum anomalous Hall state in the two-dimensional limit.

How to probe the spin contribution to momentum relaxation in topological insulators (vol 8, 2017)


M-S Nam, BH Willams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

Surface Structure and Reconstructions of HgTe (111) Surfaces


X-Y Yang, G-Y Wang, C-X Zhao, Z Zhu, L Dong, A-M Li, Y-Y Lv, S-H Yao, Y-B Chen, D-D Guan, Y-Y Li, H Zheng, D Qian, C Liu, Y-L Chen, J-F Jia

Electronic structures and unusually robust bandgap in an ultrahigh-mobility layered oxide semiconductor, Bi2O2Se.

Science Advances 4 (2018) eaat8355-

C Chen, M Wang, J Wu, H Fu, H Yang, Z Tian, T Tu, H Peng, Y Sun, X Xu, J Jiang, NBM Schröter, Y Li, D Pei, S Liu, SA Ekahana, H Yuan, J Xue, G Li, J Jia, Z Liu, B Yan, H Peng, Y Chen

Semiconductors are essential materials that affect our everyday life in the modern world. Two-dimensional semiconductors with high mobility and moderate bandgap are particularly attractive today because of their potential application in fast, low-power, and ultrasmall/thin electronic devices. We investigate the electronic structures of a new layered air-stable oxide semiconductor, Bi2O2Se, with ultrahigh mobility (~2.8 × 105 cm2/V⋅s at 2.0 K) and moderate bandgap (~0.8 eV). Combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we mapped out the complete band structures of Bi2O2Se with key parameters (for example, effective mass, Fermi velocity, and bandgap). The unusual spatial uniformity of the bandgap without undesired in-gap states on the sample surface with up to ~50% defects makes Bi2O2Se an ideal semiconductor for future electronic applications. In addition, the structural compatibility between Bi2O2Se and interesting perovskite oxides (for example, cuprate high-transition temperature superconductors and commonly used substrate material SrTiO3) further makes heterostructures between Bi2O2Se and these oxides possible platforms for realizing novel physical phenomena, such as topological superconductivity, Josephson junction field-effect transistor, new superconducting optoelectronics, and novel lasers.

Visualizing electronic structures of quantum materials by angle-resolved photoemission spectroscopy


H Yang, A Liang, C Chen, C Zhang, NBM Schroeter, Y Chen

Quantum oscillations of electrical resistivity in an insulator.

Science (New York, N.Y.) 362 (2018) 65-69

Z Xiang, Y Kasahara, T Asaba, B Lawson, C Tinsman, L Chen, K Sugimoto, S Kawaguchi, Y Sato, G Li, S Yao, YL Chen, F Iga, J Singleton, Y Matsuda, L Li

In metals, orbital motions of conduction electrons on the Fermi surface are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators. Here, we report a notable exception in an insulator-ytterbium dodecaboride (YbB12). The resistivity of YbB12, which is of a much larger magnitude than the resistivity in metals, exhibits distinct quantum oscillations. These unconventional oscillations arise from the insulating bulk, even though the temperature dependence of the oscillation amplitude follows the conventional Fermi liquid theory of metals with a large effective mass. Quantum oscillations in the magnetic torque are also observed, albeit with a lighter effective mass.

Single crystalline electronic structure and growth mechanism of aligned square graphene sheets

APL MATERIALS 6 (2018) ARTN 036107

HF Yang, C Chen, H Wang, ZK Liu, T Zhang, H Peng, NBM Schroter, SA Ekahana, J Jiang, LX Yang, V Kandyba, A Barinov, CY Chen, J Avila, MC Asensio, HL Peng, ZF Liu, YL Chen

How to probe the spin contribution to momentum relaxation in topological insulators.

Nature communications 9 (2018) 56-

M-S Nam, BH Williams, Y Chen, S Contera, S Yao, M Lu, Y-F Chen, GA Timco, CA Muryn, REP Winpenny, A Ardavan

Topological insulators exhibit a metallic surface state in which the directions of the carriers' momentum and spin are locked together. This characteristic property, which lies at the heart of proposed applications of topological insulators, protects carriers in the surface state from back-scattering unless the scattering centres are time-reversal symmetry breaking (i.e. magnetic). Here, we introduce a method of probing the effect of magnetic scattering by decorating the surface of topological insulators with molecules, whose magnetic degrees of freedom can be engineered independently of their electrostatic structure. We show that this approach allows us to separate the effects of magnetic and non-magnetic scattering in the perturbative limit. We thereby confirm that the low-temperature conductivity of SmB6 is dominated by a surface state and that the momentum of quasiparticles in this state is particularly sensitive to magnetic scatterers, as expected in a topological insulator.

Folded superstructure and degeneracy-enhanced band gap in the weak-coupling charge density wave system 2H-TaSe2

PHYSICAL REVIEW B 97 (2018) ARTN 115118

YW Li, J Jiang, HF Yang, D Prabhakaran, ZK Liu, LX Yang, YL Chen

Topological surface state of α-Sn on InSb(001) as studied by photoemission

Physical review B: Condensed matter and materials physics American Physical Society 97 (2018) 075101

MR Scholz, L Dudy, F Reis, F Adler, J Aulbach, LJ Collins-McIntyre, LB Duffy, HF Yang, YL Chen, T Hesjedal, ZK Liu, M Hoesch, S Muff, JH Dil, J Schaefer, R Claessen

Dirac line nodes and effect of spin-orbit coupling in the nonsymmorphic critical semimetals MSiS (M = Hf, Zr)

PHYSICAL REVIEW B 95 (2017) ARTN 125126

C Chen, X Xu, J Jiang, S-C Wu, YP Qi, LX Yang, MX Wang, Y Sun, NBM Schroeter, HF Yang, LM Schoop, YY Lv, J Zhou, YB Chen, SH Yao, MH Lu, YF Chen, C Felser, BH Yan, ZK Liu, YL Chen

ARPES study of the epitaxially grown topological crystalline insulator SnTe(111)


Y Zhang, Z Liu, B Zhou, Y Kim, L Yang, H Ryu, C Hwang, Y Chen, Z Hussain, Z-X Shen, S-K Mo

Signature of type-II Weyl semimetal phase in MoTe2.

Nature communications 8 (2017) 13973-

J Jiang, ZK Liu, Y Sun, HF Yang, CR Rajamathi, YP Qi, LX Yang, C Chen, H Peng, C-C Hwang, SZ Sun, S-K Mo, I Vobornik, J Fujii, SSP Parkin, C Felser, BH Yan, YL Chen

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.