Quantum System Theory Research Team

Principal Investigator

PI Name

Daniel Loss

Degree

Ph.D.

Title

Team Leader

Brief Resume

1985	Ph.D. in Theoretical Physics, University of Zurich, Switzerland
1985	Postdoctoral Research Associate, University of Zurich, Switzerland
1989	Postdoctoral Research Fellow, University of Illinois at Urbana-Champaign, USA
1991	Research Scientist, IBM T. J. Watson Research Center, USA
1993	Assistant/Associate Professor, Simon Fraser University, Canada
1996	Professor, Department of Physics, University of Basel, Switzerland (-present)
2012	Team Leader, Emergent Quantum System Research Team, RIKEN
2013	Team Leader, Quantum System Theory Research Team, Quantum Information Electronics Division, RIKEN Center for Emergent Matter Science (-present)
2021	Team Leader, Semiconductor Quantum Information Device Theory Research Team, RIKEN Center for Quantum Computing (-present)

Outline

Our team works on the quantum theory of condensed matter with a focus on spin and topological phenomena in semiconducting and magnetic nanostructures. In particular, we investigate novel mechanisms and seek new platforms hosting topological or spin phases in solid-state systems, including helical spin texture, topological insulators and topological superconductors, which have potential hosting topological quantum states, such as Majorana fermions and parafermions. Moreover, we also investigate (quasi-)one-dimensional Tomonaga-Luttinger liquid, nuclear spins in semiconductors, many-body effects in low-dimensional systems, (fractional) quantum Hall effect, strongly correlated electron systems, spin-orbit interaction, and quantum transport phenomena.

Research Fields

Theoretical Physics, Quantum Theory of Condensed Matter

Keywords

Strongly correlated electron system
Nanodevice
Spin-orbit interaction
Topological quantum matter
Majorana fermions and parafermions

Results

Majorana Kramers pairs in higher-order topological insulators

Higher order topological insulators are systems which realize the most recent flavor of topological matter. While being insulating in the bulk and on the surface, they host propagating states at the edges (hinges), where two facets meet. We designed a tune-free scheme to realize Kramers pairs of Majorana bound states in higher-order topological insulators with proximity-induced superconductivity.

Our scheme is an experimentally accessible setup, which proposes to use a bismuth wire half-covered by a superconductor. Namely, we find that when two hinges with the same helicity of the wire are in contact to an s-wave superconductor, moderate electron-electron interactions favor the inter-hinge pairing over the intra-hinge pairing, leading to formation of Majorana Kramers pairs. As a result, the proposed scheme does not require a magnetic field or local voltage gates, which is a highly desired property in the quest for topological states.

Left panel: Higher order topological insulator realized using a superconductor (yellow) and a wire (green). Right panel: The phase diagram of the model shown in the Left panel.
Chen-Hsuan Hsu, Peter Stano, Jelena Klinovaja, and Daniel Loss, “Majorana Kramers Pairs in Higher-Order Topological Insulators,” Phys. Rev. Lett. 121, 196801 (2018) © APS

Members

Daniel Loss	Team Leader	loss.daniel[at]riken.jp
Peter Stano	Senior Research Scientist	peter.stano[at]riken.jp
Chen-Hsuan Hsu	Research Scientist	chen-hsuan.hsu[at]riken.jp
Ognjen Malkoc	Postdoctoral Researcher
Yuusuke Takeshige	Student Trainee

Publications

C.-H. Hsu, F. Ronetti, P. Stano, J. Klinovaja, and D. Loss

Universal conductance dips and fractional excitations in a two-subband quantum wire

Phys. Rev. Research 2, 043208 (2020)
C.-H. Hsu, P. Stano, Y. Sato, S. Matsuo, S. Tarucha, and D. Loss

Charge transport of a spin-orbit-coupled Luttinger liquid

Phys. Rev. B 100, 195423 (2019)
P. P. Aseev, P. Marra, P. Stano, J. Klinovaja, and D. Loss

Degeneracy lifting of Majorana bound states due to electron-phonon interactions

Phys. Rev. B 99, 205435 (2019)
C.-H. Hsu, P. Stano, J. Klinovaja, and D. Loss

Majorana Kramers Pairs in Higher-Order Topological Insulators

Phys. Rev. Lett. 121, 196801 (2018)
J. Klinovaja, P. Stano, and D. Loss

Topological Floquet Phases in Driven Coupled Rashba Nanowires

Phys. Rev. Lett. 116, 176401 (2016)