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Journal Article
Observation of fractionally quantized anomalous Hall effect
2023
Overview
The integer quantum anomalous Hall (QAH) effect is a lattice analogue of the quantum Hall effect at zero magnetic field
1
–
3
. This phenomenon occurs in systems with topologically non-trivial bands and spontaneous time-reversal symmetry breaking. Discovery of its fractional counterpart in the presence of strong electron correlations, that is, the fractional QAH effect
4
–
7
, would open a new chapter in condensed matter physics. Here we report the direct observation of both integer and fractional QAH effects in electrical measurements on twisted bilayer MoTe
2
. At zero magnetic field, near filling factor
ν
= −1 (one hole per moiré unit cell), we see an integer QAH plateau in the Hall resistance
R
xy
quantized to
h
/
e
2
± 0.1%, whereas the longitudinal resistance
R
xx
vanishes. Remarkably, at
ν
= −2/3 and −3/5, we see plateau features in
R
xy
at
3
2
h
/
e
2
±
1
%
and
5
3
h
/
e
2
±
3
%
, respectively, whereas
R
xx
remains small. All features shift linearly versus applied magnetic field with slopes matching the corresponding Chern numbers −1, −2/3 and −3/5, precisely as expected for integer and fractional QAH states. Additionally, at zero magnetic field,
R
xy
is approximately 2
h
/
e
2
near half-filling (
ν
= −1/2) and varies linearly as
ν
is tuned. This behaviour resembles that of the composite Fermi liquid in the half-filled lowest Landau level of a two-dimensional electron gas at high magnetic field
8
–
14
. Direct observation of the fractional QAH and associated effects enables research in charge fractionalization and anyonic statistics at zero magnetic field.
Transport measurements in twisted bilayer MoTe
2
reveal quantized Hall resistance plateaus and composite Fermi liquid-like behaviour under zero magnetic field, constituting a direct observation of integer and fractional quantum anomalous Hall effects.
Publisher
Nature Publishing Group UK,Nature Publishing Group
Subject
