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Evidence for a Monolayer Excitonic Insulator | | Yanyu Jia
; Pengjie Wang
; Cheng-Li Chiu
; Zhida Song
; Guo Yu
; Berthold Jäck
; Shiming Lei
; Sebastian Klemenz
; F. Alexandre Cevallos
; Michael Onyszczak
; Nadezhda Fishchenko
; Xiaomeng Liu
; Gelareh Farahi
; Fang Xie
; Yuanfeng Xu
; Kenji Watanabe
; Takashi Taniguchi
; B. Andrei Bernevig
; Robert J. Cava
; Leslie M. Schoop
; Ali Yazdani
; Sanfeng Wu
; | | Date: |
12 Oct 2020 | | Abstract: | The interplay between topology and correlations can generate a variety of
unusual quantum phases, many of which remain to be explored. Recent advances
have identified monolayer WTe2 as a promising material for exploring such
interplay in a highly tunable fashion. The ground state of this two-dimensional
(2D) crystal can be electrostatically tuned from a quantum spin Hall insulator
(QSHI) to a superconductor. However, much remains unknown about the nature of
these ground states, including the gap-opening mechanism of the insulating
state. Here we report systematic studies of the insulating phase in WTe2
monolayer and uncover evidence supporting that the QSHI is also an excitonic
insulator (EI). An EI, arising from the spontaneous formation of electron-hole
bound states (excitons), is a largely unexplored quantum phase to date,
especially when it is topological. Our experiments on high-quality transport
devices reveal the presence of an intrinsic insulating state at the charge
neutrality point (CNP) in clean samples. The state exhibits both a strong
sensitivity to the electric displacement field and a Hall anomaly that are
consistent with the excitonic pairing. We further confirm the correlated nature
of this charge-neutral insulator by tunneling spectroscopy. Our results support
the existence of an EI phase in the clean limit and rule out alternative
scenarios of a band insulator or a localized insulator. These observations lay
the foundation for understanding a new class of correlated insulators with
nontrivial topology and identify monolayer WTe2 as a promising candidate for
exploring quantum phases of ground-state excitons. | | Source: | arXiv, 2010.05390 | | Services: | Forum | Review | PDF | Favorites | |
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