Assistant Professor
Hsu, Yu-Te

Field:   Condensed Matter (Exp.)
Office: 42535 (PHYS R224）
Lab: 42552 (PHYS R218)
Group website

E-mail: ythsu@phys.nthu.edu.tw

Education

PhD in Physics, University of Cambridge, UK (2013/10-2018/01)
MSc in Physics, Linköping Univeristy, Sweden (2008/09-2010/06)
BSc in Materials Science and Engineering, National Tsing Hua University, Taiwan (2005/09-2008/06, 2010/09-2011/06)

Current position：

Assistant Professor, Department of Physics, National Tsing Hua University, Taiwan (2024/02-)
Assistant Professor, Department of Materials Science and Engineering, National Tsing Hua University, Taiwan (joint appointment; 2024/06-)

Experience：

Visiting scientist, Institute of Physics, University of Amsterdam, The Netherlands (2023/09-2024/01)
Visiting scientist, High Field Magnet Laboratory, Radboud University, The Netherlands (2023/08-2024/01)
Postdoctoral researcher, Center for Theory and Computation, National Tsing Hua University, Taiwan (2023/07-2024/01)
Research scientist, High Field Magnet Laboratory, Radboud University, The Netherlands (2022/03-2023/03)
Postdoctoral researcher,High Field Magnet Laboratory, Radboud University, The Netherlands (2018/10-2022/03)
Research assistant, Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan (2012/09-2013/08)

Research Fields

Strongly correlated electron systems
Quantum materials
Superconductivity
High magnetic field sciences

Research Interests

My current research focuses on exploring emergent properties in quantum materials that lie beyond the single-particle theoretical framework. Quantum materials are of both fundamental and technological importance and have emerged as one of the key areas in condensed matter research.

Unconventional superconductivity
The discovery of high-transition-temperature (T_c) cuprate superconductors is an important milestone in quantum materials research. After over three decades of intense research, the microscopic mechanism of high-temperature superconductivity has yet to reach a consensus. Therefore, a complete description of the mechanism realizing high-T_c superconductivity in the cuprates is regarded as one of the most important outstanding issues in condensed matter physics. Recent efforts in this field have focused on building a complete description of the electronic ground state in its non-superconducting state, including the pseudogap state and strange metal phase occupying the specific regions of its phase diagram, and understanding how superconductivity arises from these strongly correlated electronic ground state. The physics community has devoted a long-standing effort to searching for material systems with similar lattice and electronic properties to the cuprates in order to gain better insights into the key ingredients for high-T_c superconductivity. The recently discovered superconducting nickelates with an infinite layer crystal structure and the square-lattice iridate Mott insulator with strong electron-orbital coupling have extremely similar properties to the cuprates, and provide new opportunities for the understanding of high-T_c superconductivity. My recent research in this area will focus on two main directions: 1) Through a comparative study of three closely related but distinct material systems (copper, nickel and iridium oxide), I will aim to clarify the key factors that determine the realization of the superconducting state in a two-dimensional Mott lattice; 2) Leveraging the developments in synthesizing novel materials with atomic precision and inducing carriers with ultra-high concentrations, I will explore the possibility of further optimizing the superconducting properties of the cuprates and achieving an even higher T_c.

Narrow-band insulator
In materials with strong electronic interactions, a metal-insulator transition due to varying temperatures can often be observed, which can be used as a useful indicator of potential novel quantum phenomena. Kondo insulators from the rare-earth boride family represent an archetypal case study. In samarium hexaboride (SmB₆), its 4f and 5d electronic bands are hybridized due to the Kondo effect, resulting in the opening of a narrow energy gap of ≈ 5 meV at its Fermi level. At the Kondo temperature ≈ 40 K, the metal-insulator transition occurs and a high resistivity exceeding 10 Ω-cm is found in SmB₆ below 4 K. However, the material shows prominent quantum oscillations in magnetization measurements at low temperatures, manifesting the Fermi surface characteristics of a metallic ground state according to the conventional electronic band theory. Furthermore, SmB₆ also exhibits thermal conductivity and specific-heat characteristics typical of a metallic ground state, indicating that the material has the characteristics of both an electrical insulator and a good thermal conductor and possibly realizing a novel state of quantum matter. Similar phenomena were later discovered in related materials (YbB₁₂, YbIr₃Si₇, etc.), thus opening up an emerging research field in condensed matter research. However, materials systems in which such dual metal-insulator character can be observed are highly limited, which hinders progress in this field. In this research direction, I will conduct low-temperature electrical, magnetic and thermal measurements on narrow-band iron-based insulating materials (FeSi and FeGa₃) with similar electrical transport characteristics and explore the existence of an unconventional Fermi surface in iron-based correlated insulators.

Experimental techniques
My expertise is the high-sensitivity measurements on the transport and thermodynamic properties of quantum materials, operating in extreme conditions of high magnetic fields and low temperatures. Transport experiments (electrical, thermal, and thermo-electric) are highly sensitive to the electronic state near or at the Fermi level, and have proven to be a powerful tool to reveal the existence of an electronic phase transition. On the other hand, thermodynamic experiments (magnetization and specific heat) can provide key information about the nature of the phase transition and the interaction therefore, which cannot be obtained by alternative means. The combination of electronic transport and thermodynamic experiments can provide indispensable information for understanding the electronic ground state of novel materials. My experiments are often conducted in international high magnetic field laboratories, such as the National High Magnetic Field Laboratory in the United States, which can generate a steady-state high magnetic field of 45 T, and the European High Magnetic Field Laboratory, which can generate an ultra-high high magnetic field of 90+ T under non-destructive pulsed condition.

Students who are interested in joining our research team are welcome to contact me by email.

Selected Publications

1. Y.-T. Hsu, K. Lee, S. Badoux, C. Duffy, A. Cuoghi, B. Y. Wang, A. Kool, I. Haïk-Dunn, H. Y. Hwang, N. E. Hussey
"Transport phase diagram and anomalous metallicity in superconducting infinite-layer nickelates"
Nature Communications 15:9863 (2024)

2. Y.-T. Hsu, A. Rydh, M. Berben, C. Duffy, A. de la Torre, R. S. Perry, N. E. Hussey
"Carrier density crossover and quasiparticle mass ehnancement in a doped 5d Mott insulator"
Nature Physics 20, 1596 (2024)

3. Y.-T. Hsu, B. Y. Wang, M. Berben, D. Li, K. Lee, C. Duffy, T. Ottenbros, W. J. Kim, M. Osada, S. Wiedmann, H. Y. Hwang, N. E. Hussey
"Insulator-to-metal crossover near the edge of the superconducting dome in Nd1-xSrxNiO2"
Physical Review Research 3, L042015 (2021)

4. Y.-T. Hsu, D. Prishchenko, M. Berben, M. Čulo, S. Wiedmann, E. C. Hunter, P. Tinnermans, T. Takayama, V. Mazurenko, N. E. Hussey, R. S. Perry
“Evidence of strong electron correlations in a non-symmorphic Dirac semimetal”
npj Quantum Materials 6:92 (2021)

5. Y.-T. Hsu, M. Berben, M. Čulo, S. Adachi, T. Kondo, T. Takeuchi, Y. Wang, S. Wiedmann, S. M. Hayden, N. E. Hussey
“Anomalous vortex liquid in charge-ordered cuprate superconductors”
Proceedings of the National Academy of Sciences 118, e2016275118 (2021)

6. Y.-T. Hsu, M. Hartstein, A. J. Davies, A. J. Hickey, M. K. Chan, J. Porras, T. Loew, S. V. Taylor, H. Liu, A. G. Eaton, M. Le Tacon, H. Zuo, J. Wang, Z. Zhu, G. G. Lonzarich, B. Keimer, N. Harrison, S. E. Sebastian
“Unconventional quantum vortex matter state hosts quantum oscillations in the underdoped high-temperature cuprate superconductors”
Proceedings of the National Academy of Sciences 118, e2021216118 (2021)

7. M. Hartstein, Y.-T. Hsu, K. A. Modic, J. Porras, T. Loew, M. Le Tacon, H. Zuo, J. Wang, Z. Zhu, M. K. Chan, R. D. McDonald, G. G. Lonzarich, B. Keimer, S. E. Sebastian, N. Harrison
"Hard antidnodal gap revealed by quantum oscillations in the pseudogap regime of underdoped high-T_c superconductors"
Nature Physics 16, 841 (2020)

8. M. Hartstein^*, W. H. Toews^*, Y.-T. Hsu^*, B. Zeng, X. Chen, M. Ciomaga Hatnean, Q. R. Zhang, S. Nakamura, A. S. Padgett, G. Rodway-Gant, J. Berk, M. K. Kingston, G. H. Zhang, M. K. Chan, S. Yamashita, T. Sakakibara, Y. Takano, J.-H. Park, L. Balicas, N. Harrison, N. Shitsevalova, G. Balakrishnan, G. G. Lonzarich, R. W. Hill, M. Sutherland, S. E. Sebastian (^*equal contribution)
“Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB₆” 
Nature Physics 14, 166 (2018)

9. B. S. Tan, Y.-T. Hsu, B. Zeng, M. Ciomaga Hatnean, N. Harrison, Z. Zhu, M. Hartstein, M. Kiourlappou, A. Srivastava, M. D. Johannes, T. P. Murphy, J.-H. Park, J. Balicas, G. G. Lonzarich, G. Balakrishnan, S. E. Sebastian
“Unconventional Fermi surface in an insulating state”
Science 349, 287 (2015)