1
|
Belopolski I, Chang G, Cochran TA, Cheng ZJ, Yang XP, Hugelmeyer C, Manna K, Yin JX, Cheng G, Multer D, Litskevich M, Shumiya N, Zhang SS, Shekhar C, Schröter NBM, Chikina A, Polley C, Thiagarajan B, Leandersson M, Adell J, Huang SM, Yao N, Strocov VN, Felser C, Hasan MZ. Observation of a linked-loop quantum state in a topological magnet. Nature 2022; 604:647-652. [PMID: 35478239 DOI: 10.1038/s41586-022-04512-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 02/03/2022] [Indexed: 11/09/2022]
Abstract
Quantum phases can be classified by topological invariants, which take on discrete values capturing global information about the quantum state1-13. Over the past decades, these invariants have come to play a central role in describing matter, providing the foundation for understanding superfluids5, magnets6,7, the quantum Hall effect3,8, topological insulators9,10, Weyl semimetals11-13 and other phenomena. Here we report an unusual linking-number (knot theory) invariant associated with loops of electronic band crossings in a mirror-symmetric ferromagnet14-20. Using state-of-the-art spectroscopic methods, we directly observe three intertwined degeneracy loops in the material's three-torus, T3, bulk Brillouin zone. We find that each loop links each other loop twice. Through systematic spectroscopic investigation of this linked-loop quantum state, we explicitly draw its link diagram and conclude, in analogy with knot theory, that it exhibits the linking number (2, 2, 2), providing a direct determination of the invariant structure from the experimental data. We further predict and observe, on the surface of our samples, Seifert boundary states protected by the bulk linked loops, suggestive of a remarkable Seifert bulk-boundary correspondence. Our observation of a quantum loop link motivates the application of knot theory to the exploration of magnetic and superconducting quantum matter.
Collapse
Affiliation(s)
- Ilya Belopolski
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA. .,RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, Japan.
| | - Guoqing Chang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - Tyler A Cochran
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Zi-Jia Cheng
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Xian P Yang
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Cole Hugelmeyer
- Department of Mathematics, Princeton University, Princeton, NJ, USA
| | - Kaustuv Manna
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.,Department of Physics, Indian Institute of Technology Delhi, New Delhi, India
| | - Jia-Xin Yin
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Guangming Cheng
- Princeton Institute for Science and Technology of Materials, Princeton University, Princeton, NJ, USA
| | - Daniel Multer
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Maksim Litskevich
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Nana Shumiya
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Songtian S Zhang
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA
| | - Chandra Shekhar
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | | | - Alla Chikina
- Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland
| | - Craig Polley
- MAX IV Laboratory, Lund University, Lund, Sweden
| | | | | | - Johan Adell
- MAX IV Laboratory, Lund University, Lund, Sweden
| | - Shin-Ming Huang
- Department of Physics, National Sun Yat-sen University, Kaohsiung City, Taiwan
| | - Nan Yao
- Princeton Institute for Science and Technology of Materials, Princeton University, Princeton, NJ, USA
| | | | - Claudia Felser
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - M Zahid Hasan
- Laboratory for Topological Quantum Matter and Spectroscopy, Department of Physics, Princeton University, Princeton, NJ, USA. .,Princeton Institute for Science and Technology of Materials, Princeton University, Princeton, NJ, USA. .,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. .,Quantum Science Center, Oak Ridge, TN, USA.
| |
Collapse
|
2
|
Wu Z, Fang Y, Su H, Xie W, Li P, Wu Y, Huang Y, Shen D, Thiagarajan B, Adell J, Cao C, Yuan H, Steglich F, Liu Y. Revealing the Heavy Quasiparticles in the Heavy-Fermion Superconductor CeCu_{2}Si_{2}. Phys Rev Lett 2021; 127:067002. [PMID: 34420319 DOI: 10.1103/physrevlett.127.067002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 02/28/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
The superconducting order parameter of the first heavy-fermion superconductor CeCu_{2}Si_{2} is currently under debate. A key ingredient to understand its superconductivity and physical properties is the quasiparticle dispersion and Fermi surface, which remains elusive experimentally. Here, we present measurements from angle-resolved photoemission spectroscopy. Our results emphasize the key role played by the Ce 4f electrons for the low-temperature Fermi surface, highlighting a band-dependent conduction-f electron hybridization. In particular, we find a very heavy quasi-two-dimensional electron band near the bulk X point and moderately heavy three-dimensional hole pockets near the Z point. Comparison with theoretical calculations reveals the strong local correlation in this compound, calling for further theoretical studies. Our results provide the electronic basis to understand the heavy-fermion behavior and superconductivity; implications for the enigmatic superconductivity of this compound are also discussed.
Collapse
Affiliation(s)
- Zhongzheng Wu
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Yuan Fang
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Hang Su
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Wu Xie
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Peng Li
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Yi Wu
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Yaobo Huang
- Shanghai Institute of Applied Physics, Chinese Academy of Science, Shanghai 210800, China
| | - Dawei Shen
- State Key Laboratory of Functional Materials for Informatics and Center for Excellence in Superconducting Electronics, SIMIT, Chinese Academy of Science, Shanghai 200050, China
| | | | - Johan Adell
- MAX IV Laboratory, Lund University, P.O. Box 118, 221 00 Lund, Sweden
| | - Chao Cao
- Department of Physics, Hangzhou Normal University, Hangzhou 311121, China
| | - Huiqiu Yuan
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310058, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Frank Steglich
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Yang Liu
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
- Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou 310058, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| |
Collapse
|
6
|
Laverock J, Chen B, Smith KE, Singh RP, Balakrishnan G, Gu M, Lu JW, Wolf SA, Qiao RM, Yang W, Adell J. Resonant soft-X-ray emission as a bulk probe of correlated electron behavior in metallic SrxCa1-xVO3. Phys Rev Lett 2013; 111:047402. [PMID: 23931404 DOI: 10.1103/physrevlett.111.047402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Indexed: 06/02/2023]
Abstract
The evolution of electron correlation in SrxCa1-xVO3 has been studied using a combination of bulk-sensitive resonant soft x-ray emission spectroscopy, surface-sensitive photoemission spectroscopy, and ab initio band structure calculations. We show that the effect of electron correlation is enhanced at the surface. Strong incoherent Hubbard subbands are found to lie ∼20% closer in energy to the coherent quasiparticle features in surface-sensitive photoemission spectroscopy measurements compared with those from bulk-sensitive resonant soft x-ray emission spectroscopy, and a ∼10% narrowing of the overall bandwidth at the surface is also observed.
Collapse
Affiliation(s)
- J Laverock
- Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Laukkanen P, Punkkinen MPJ, Komsa HP, Ahola-Tuomi M, Kokko K, Kuzmin M, Adell J, Sadowski J, Perälä RE, Ropo M, Rantala TT, Väyrynen IJ, Pessa M, Vitos L, Kollár J, Mirbt S, Johansson B. Anomalous bismuth-stabilized (2x1) reconstructions on GaAs(100) and InP(100) surfaces. Phys Rev Lett 2008; 100:086101. [PMID: 18352637 DOI: 10.1103/physrevlett.100.086101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2007] [Revised: 12/14/2007] [Indexed: 05/26/2023]
Abstract
First-principles phase diagrams of bismuth-stabilized GaAs- and InP(100) surfaces demonstrate for the first time the presence of anomalous (2x1) reconstructions, which disobey the common electron counting principle. Combining these theoretical results with our scanning-tunneling-microscopy and photoemission measurements, we identify novel (2x1) surface structures, which are composed of symmetric Bi-Bi and asymmetric mixed Bi-As and Bi-P dimers, and find that they are stabilized by stress relief and pseudogap formation.
Collapse
Affiliation(s)
- P Laukkanen
- Optoelectronics Research Centre, Tampere University of Technology, FIN-33101 Tampere, Finland.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|