Topological Quantum Phenomena Research Unit

Principal Investigator

PI Name

Tian Liang

Degree

Ph.D.

Title

Unit Leader

HP

http://www.phys.tsinghua.edu.cn/phyen/info/1068/1504.htm

Brief Resume

2016	Ph.D. in physics, Princeton University, USA
2016	Postdoctoral associate, Stanford University, USA
2018	Postdoctoral Researcher, Strong Correlation Quantum Transport Research Team, RIKEN Center for Emergent Matter Science
2021	Assistant Professor, Tsinghua University, China
2021	Unit Leader, Topological Quantum Phenomenon Research Unit, Cross-Divisional Materials Research Program, RIKEN Center for Emergent Matter Science (-present)
2023	Associate Professor, Tsinghua University, China (-present)

Outline

In our unit, we aim to investigate the intriguing physical properties in topological phases of matter and strongly correlated electron system, through the research based on the condensed matter experiment. First, from fundamental physics point of view, we pay attention to the nontrivial geometrical properties of the band structure, and aim to measure the novel electrical, thermal, and magnetic quantum effect on the system. In addition, from application point of view, we work on the design of high quality thermoelectric material and devices with low dissipation. In order to achieve the above mentioned goals, we will collaborate with the researchers all over the world and enhance the understanding of physics both from the fundamental and application aspects.

Research Fields

Physics

Keywords

Condensed matter physics
Topological quantum matters
Berry phase physics
Thermoelectric effect
Strongly Correlated electron system

Results

Berry curvature generation detected by Nernst responses in ferroelectric Weyl semimetal

The quest for non-magnetic Weyl semimetals with high tunability of phase has remained a demanding challenge. As the symmetry-breaking control parameter, the ferroelectric order can be steered to turn on/off the Weyl semimetals phase, adjust the band structures around the Fermi level, and enlarge/shrink the momentum separation of Weyl nodes which generate the Berry curvature as the emergent magnetic field. Here, we report the realization of a ferroelectric non-magnetic Weyl semimetal based on indium-doped Pb_1−xSn_xTe alloy where the underlying inversion symmetry as well as mirror symmetries are broken with the strength of ferroelectricity adjustable via tuning indium doping level and Sn/Pb ratio. The transverse thermoelectric effect, i.e., Nernst effect, both for out-of-plane and in-plane magnetic-field geometry, is exploited as a Berry-curvature-sensitive experimental probe to manifest the generation of Berry curvature via the re-distribution of Weyl nodes under magnetic fields. The results demonstrate a clean non-magnetic Weyl semimetal coupled with highly tunable ferroelectric order, providing an ideal platform for manipulating the Weyl fermions in non-magnetic system.

The left panel shows the topological phase transition in the system of In-PbSnTe. Since the spatial inversion symmetry is broken by ferroelectricity, a Weyl semimetal phase appears. The right panel shows anomalous Hall and thermoelectric Hall effect, which originates from the Berry curvature generated by the Weyl nodes.

Members

Tian Liang	Unit Leader	tian.liang[at]riken.jp

Publications

C.-L. Zhang, T. Liang, Y. Kaneko, N. Nagaosa, and Y. Tokura

Giant Berry curvature dipole density in a ferroelectric Weyl semimetal

npj Quantum Mater. 7, 103 (2022)
C.-L. Zhang, T. Liang, M. S. Bahramy, N. Ogawa, V. Kocsis, K. Ueda, Y. Kaneko, M. Kriener, and Y. Tokura

Berry curvature generation detected by Nernst responses in ferroelectric Weyl semimetal

Proc. Natl. Acad. Sci. U.S.A. 118, e2111855118 (2021)
C.-L. Zhang, T. Liang, N. Ogawa, Y. Kaneko, M. Kriener, T. Nakajima, Y. Taguchi, and Y. Tokura

Highly tunable topological system based on PbTe-SnTe binary alloy

Phys. Rev. Mater. 4, 091201 (2020)
J. J. He, T. Liang, Y. Tanaka, and N. Nagaosa

Platform of chiral Majorana edge modes and its quantum transport phenomena

Commun. Phys. 2, 149 (2019)
K. Yasuda, H. Yasuda, T. Liang, R. Yoshimi, A. Tsukazaki, K. S. Takahashi, N. Nagaosa, M. Kawasaki, and Y. Tokura

Nonreciprocal charge transport at topological insulator/superconductor interface

Nat. Commun. 10, 2734 (2019)