# Prof. Dr. Ming Shi

Senior Scientist

Spectroscopy of Novel Materials group

Forschungsstrasse 111

5232 Villigen PSI

Suisse

**Professorship**

Adjunct Professor of the Institute of Physics, Chinese Academy of Sciences

## Biography

Ming Shi is a senior scientist at the Photon Science Division (PSD) of Paul Scherrer Institute (PSI). He received his PhD degree in Physics at the University of Geneva in 1996. Since then he worked at PSI as a postdoc (1996), a staff scientist (1998) and senior scientist (2009). Ming Shi became an adjunct professor in the Institute of Physics, Chinese Academy of Sciences in 2012. In 2004 – 2005 he worked as a visiting professor in the group of Prof. Juan Carlos Campuzano at the Department of Physics, University of Illinois at Chicago, USA.

## Institutional Responsibilities

Along with the research activities in condensed matter physics, Ming Shi is the responsible of Surface/Interface Spectroscopy beamline (SIS) at Swiss Light Source (SLS) for the operation and development to maintain its position as one of the leading angle-resolved photoemission beamlines worldwide. He has also made significant contributions in establishing institutional partnerships between PSI and research institutes/universities in China for the researches in condensed matter physics and materials science. Since 2010 he has organized/co-organized 8 Swiss-Sino workshops which services as a platform for collaborative researches using large facilities. Ming Shi is a group leader of National Centre of Competence in Research (NCCR) for Computation Design and Discovery of Novel Materials (MARVEL).

## Scientific Research

Ming Shi’s research focuses on the behavior of electrons in novel quantum materials and strongly correlated systems. The primary interest is to explore the electronic excitations and properties associated with various emergent and/or macroscopic quantum phenomena, such as quantum (spin) Hall state and superconducting state. Combining photoemission spectroscopy with other experimental means we attempt to unveil the micro mechanism of various instabilities and phenomena, e.g. high-temperature superconductivity and fractional quantum Hall effect, arising from electron-electron correlation effects, the coupling between electrons and collective excitations, and the interplay of the charge, spin, orbital and lattice in solids.

## Selected Publications

For an extensive overview we kindly refer you to our publication repository DORA.

**Emergence of nontrivial Dirac fermions in antiferromagnet EuCd2As2 with broken parity-time symmetry,** J.-Z. Ma, H. Wang, S.-M. Nie, C-J.Yi, Y.-F. Xu, H. Li, J. Jandke, W. Wulfhekel, Y.-B. Huang, D. West, P. Richard, A. Chikina, V. N. Strocov, J. Mesot, H.-M. Weng, S.-B. Zhang, Y.-G. Shi*, T. Qian*, ** M. Shi***, and H. Ding.

**Advanced Materials 32, 1907565 (2020).**(* corresponding author)

Parity‐time symmetry plays an essential role for the formation of Dirac states in Dirac semimetals. The realization of magnetic topological Dirac semimetals (DSMs) remains a major issue in topological material research. Here we show that the magnetic order breaks time reversal symmetry in EuCd

_{2}As

_{2}which can be an ideal DSM. The double degeneracy of the Dirac bands is protected by a combination of inversion, time‐reversal, and an additional translation operation. We further show that a deviation of the magnetic moments from the c‐axis leads to the breaking of C3 rotation symmetry and results in a novel state containing three different types of topological insulator: axion insulator, topological crystalline insulator, and higher order topological insulator.

**Spin Fluctuation induced Weyl semimetal state in the paramagnetic phase of EuCd2As2**.** **J.-Z. Ma, S. M. Nie, C. J. Yi, J. Jandke, T. Shang, M. Y. Yao, M. Naamneh, L. Q. Yan, Y. Sun, A. Chikina, V. N. Strocov, M. Medarde, M. Song, Y.-M. Xiong, G. Xu, W. Wulfhekel, J. Mesot, M. Reticcioli, C. Franchini, C. Mudry, M. Müller, Y. G. Shi*, T. Qian*, H. Ding, * M. Shi**.

**Science Adv. 5, eaaw4718 (2019)**

In the quest of Weyl fermions induced by time-reversal symmetry breaking, we observed that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd

_{2}As

_{2}. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi–long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Fermi level. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not essential requirements for WSM states in centrosymmetric systems and that WSM states can emerge in a wider range of condensed matter systems than previously thought.

**Observation of Weyl Nodes in Robust Type-II Weyl Semimetal WP _{2},** M. -Y. Yao*, N. Xu*, Q. S. Wu, G. Autès, N. Kumar, V. N. Strocov, N. C. Plumb, M. Radovic, O. V. Yazyev, C. Felser, J. Mesot, and

***,**

*M. Shi***Phys. Rev. Lett. 122, 176402 (2019)**(Editors’ Suggestion)

**.**

Using angle-resolved photoemission spectroscopy supported by the first-principles calculations, we determined the tilted Weyl cone bands in the bulk electronic structure of WP

_{2}, which are at the origin of Fermi arcs at the surfaces and transport properties related to the chiral anomaly in type-II WSMs. Our results ascertain that, due to the spin-orbit coupling, the Weyl nodes originate from the splitting of fourfold degenerate band-crossing points with Chern numbers

*C*= ±2 induced by the crystal symmetries of WP

_{2}, which is unique among all the discovered WSMs. Our finding also provides a guiding line to observe the chiral anomaly that could manifest in novel transport properties.

**Evidence of a Coulomb-Interaction-Induced Lifshitz Transition and Robust Hybrid Weyl Semimetal in Td-MoTe_{2},** N. Xu*, Z. W. Wang, A. Magrez, P. Bugnon, H. Berger, C. E. Matt, V. N. Strocov, N. C. Plumb, M. Radovic, E. Pomjakushina, K. Conder, J. H. Dil, J. Mesot, R. Yu, H. Ding*, and

***,**

*M. Shi***Phys. Rev. Lett. 121, 136401 (2018).**

In revealing the bulk electronic structure of

*Td*-MoTe

_{2}we found that on-site Coulomb interaction leads to a Lifshitz transition, which is essential for a precise description of the electronic structure. A hybrid Weyl semimetal state with a pair of energy bands touching at both type-I and type-II Weyl nodes is indicated by comparing the experimental data with theoretical calculations. Unveiling the importance of Coulomb interaction opens up a new route to comprehend the unique properties of MoTe

_{2}, and is significant for understanding the interplay between correlation effects, strong spin-orbit coupling and superconductivity in this van der Waals material.

**Distinct Evolutions of Weyl Fermion Quasiparticles and Fermi Arcs with Bulk Band Topology in Weyl Semimetals****,** N. Xu*, G. Autès, C. E. Matt, B. Q. Lv, M. Y. Yao, F. Bisti, V. N. Strocov, D. Gawryluk, E. Pomjakushina, K. Conder, N. C. Plumb, M. Radovic, T. Qian, O. V. Yazyev, J. Mesot, H. Ding*,and ** M. Shi***,

**Phys. Rev. Lett. 118, 106406 (2017**

**).**

We demonstrate that Weyl fermion quasiparticles and Fermi arcs show distinct evolutions with the bulk band topology. While Weyl fermion quasiparticles exist only when the chemical potential is located between two saddle points of the Weyl cone features, the Fermi arc states extend in a larger energy scale. The findings not only provide insight into the relationship between the exotic physical phenomena and the intrinsic bulk band topology in Weyl semimetals, but also resolve the apparent puzzle of the different magnetotransport properties observed in TaAs, TaP, and NbP, where the Fermi arc states are similar.

**Rotation Symmetry Breaking in La _{2−x}Sr_{x}CuO_{4} Revealed by Angle-Resolved Photoemission Spectroscopy**

**,**E. Razzoli, C. E. Matt, Y. Sassa, M. Månsson, O. Tjernberg, G. Drachuck, M. Monomo, M. Oda, T. Kurosawa, Y. Huang, N. C. Plumb, M. Radovic, A. Keren, L. Patthey, J. Mesot, and

*M. Shi**,**Phys. Rev. B 95, 224504 (2017**

**).**

Using angle-resolved photoemission spectroscopy it is revealed that in the vicinity of optimal doping the electronic structure of La

_{2−x}Sr

_{x}CuO

_{4}cuprate undergoes an electronic reconstruction associated with a wave vector

*q*_{a}*= (π,0). The reconstructed Fermi surface and folded band are distinct to the shadowbands observed in BSCCO cuprates and in underdoped La*

_{2−x}Sr

_{x}CuO

_{4}with x = 0.12, which shift the primary band along the zone diagonal direction. Furthermore, the folded bands appear only with

*q*_{a}*= (π,0) vector, but not with*

*q*_{b}*= (0,π), which indicates the fourfold symmetry is broken in the system.*

**NaFe _{0.56}Cu_{0.44}As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction**

**,**C. E. Matt*, N. Xu, B. Lv, J. Ma, F. Bisti, J. Park, T. Shang, C. Cao, Y. Song,6 Andriy H. Nevidomskyy, P. Dai, L. Patthey, N. C. Plumb, M. Radovic, J. Mesot, and

***,**

*M. Shi***Phys. Rev. Lett. 117, 097001 (2016**

**).**

In the studies of iron pnictides, a key question is whether their bad-metal state from which the superconductivity emerges lies in close proximity with a magnetically ordered insulating phase. We identified that the ground state of NaFe

_{1-x}Cu

_{x}As (x = 0.44) is a narrow-gap insulator. We show that the on-site Coulombic (Hubbard) and Hund’s coupling energies play crucial roles in the formation of the band gap about the chemical potential. Our study provides a basis for investigating the evolution of the electronic structure of a Mott insulator transforming into a bad metallic phase and eventually forming a superconducting state in iron pnictides.

**Observation of Weyl Nodes and Fermi Arcs in Tantalum Phosphide****,** N. Xu*, H.M. Weng, B.Q. Lv, C.E. Matt, J. Park, F. Bisti, V.N. Strocov, D. Gawryluk, E. Pomjakushina, K. Conder, N.C. Plumb, M. Radovic, G. Autès, O.V. Yazyev, Z. Fang, X. Dai, T. Qia, J. Mesot, H. Ding*, ** M. Shi***,

**Nature Communications 7:11006 (2016**

**).**

To have the transport properties dominated by Weyl fermions in a semimetal, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Here, we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications.

**Camelback-shaped band reconciles heavy-electron behavior with weak electronic Coulomb correlations in superconducting TlNi _{2}Se_{2},** N. Xu*, C. E. Matt, P. Richard, A. van Roekeghem, S. Biermann, X. Shi, S.-F. Wu,H. W. Liu, D. Chen, T. Qian, N. C. Plumb, M. Radovic, H. Wang, Q. Mao, J. Du, M. Fang, J. Mesot, H. Ding, and

***,**

*M. Shi***Phys. Rev. B 92, 081116 (2015**

**).**

Combining photoemission spectroscopy, Raman spectroscopy, and first-principles calculations, we characterize superconducting TlNi

_{2}Se

_{2}as a material with weak electronic Coulomb correlations leading to a bandwidth renormalization of 1.4. We identify a camelback-shaped band, whose energetic position strongly depends on the selenium height. While this feature is universal in transition metal pnictides, in TlNi

_{2}Se

_{2}it lies in the immediate vicinity of the Fermi level, giving rise to a pronounced van Hove singularity. The resulting heavy band mass resolves the apparent puzzle of a large normal-state Sommerfeld coefficient in this weakly correlated compound.

**Observation of Weyl nodes in TaAs**, B. Q. Lv, N. Xu, H. M. Weng, J. Z. Ma, P. Richard, X. C. Huang, L. X. Zhao, G. F. Chen, C. E. Matt, F. Bisti, V. N. Strocov, J. Mesot, Z. Fang, X. Dai, T. Qian*, ** M. Shi*** and H. Ding*,

**Nature Physics 11, 724 (2015**)

In 1929, H. Weyl proposed that the massless solution of the Dirac equation represents a pair of a new type of particles, the so-called Weyl fermions. However, their existence in particle physics remains elusive after more than eight decades. Here we report the direct observation in TaAs of the long-sought-after Weyl nodes by performing bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy measurements. The projected locations at the nodes on the (001) surface match well to the Fermi arcs, providing undisputable experimental evidence for the existence of Weyl fermionic quasiparticles in TaAs.

## Books

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