Two-dimensional topological effects and emerging many-body phenomena in semiconductor heterostructures
Two-dimensional (2D) topological effects that interplay with electron-electron interactions have attracted lots of attention in the field of condensed matter physics. Quantum spin Hall (QSH) effect is such a typical topological effect. In this talk I will mainly present recent experimental studies of QSH effect in inverted InAs/GaSb quantum wells(QWs). Using charge-neutral point (CNP) density as a tuning parameter, we observed two distinct QSH regimes: I), in dense limit in CNP, a single-particle hybridization gap opens, which hosts time-reversal-symmetry (TRS) QSH effect [1,2]; II), as dilute limit is approached, a spontaneous excitonic gap opens in the bulk, with the emergence of TRS-broken QSH effect where helical edges persist under high magnetic fields [1,3]. To clarify the interesting observation in regime II), we performed transport and THz measurements, and observed conclusive evidence for long-sought-after excitonic insulator(EI) . The TRS-broken property of EI would be discussed. In the rest of my talk, I will discuss recent progresses of artificial graphene (AG) in nanopatterned GaAs QWs [4,5], which could offer exclusive tunability to 2D topological effects.
. Lingjie Du et al, Nature Communications, 8, 1971 (2017)
. Lingjie Du et al, Phys. Rev. Lett. 119, 056803 (2017)
. Lingjie Du et al, Phys. Rev. Lett. 114, 096802 (2015)
. Sheng Wang et al, Nature Nanotechnology, 13, 29 (2017)
. Lingjie Du et al, Nature Communications, 9, 3299 (2018)
Dr. Lingjie Du obtained his bachelor and master degree from Nanjing University in 2008 and 2011, respectively. Afterwards, he moved to Rice University and finished his PhD in 2016. Since then, he worked as a postdoc in Columbia University.