scholarly journals Topological valley currents via ballistic edge modes in graphene superlattices near the primary Dirac point

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Yang Li ◽  
Mario Amado ◽  
Timo Hyart ◽  
Grzegorz. P. Mazur ◽  
Jason W. A. Robinson
Keyword(s):  
Magnetic Field ◽  
Boron Nitride ◽  
Dirac Point ◽  
Hexagonal Boron Nitride ◽  
Zero Magnetic Field ◽  
Decay Length ◽  
Topological Phase ◽  
Show Evidence ◽  
Nonlocal Transport

AbstractGraphene on hexagonal boron nitride (hBN) can exhibit a topological phase via mutual crystallographic alignment. Recent measurements of nonlocal resistance (Rnl) near the secondary Dirac point (SDP) in ballistic graphene/hBN superlattices have been interpreted as arising due to the quantum valley Hall state. We report hBN/graphene/hBN superlattices in which Rnl at SDP is negligible, but below 60 K approaches the value of h/2e2 in zero magnetic field at the primary Dirac point with a characteristic decay length of 2 μm. Furthermore, nonlocal transport transmission probabilities based on the Landauer-Büttiker formalism show evidence for spin-degenerate ballistic valley-helical edge modes, which are key for the development of valleytronics.

scholarly journals Observation of fractional Chern insulators in a van der Waals heterostructure

Science ◽  
2018 ◽  
Vol 360 (6384) ◽  
pp. 62-66 ◽  
Author(s):  
Eric M. Spanton ◽  
Alexander A. Zibrov ◽  
Haoxin Zhou ◽  
Takashi Taniguchi ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Boron Nitride ◽  
Symmetry Breaking ◽  
Hexagonal Boron Nitride ◽  
Landau Levels ◽  
Topological Order ◽  
Hall Conductance ◽  
Van Der Waals Heterostructure ◽  
Ordered Phases ◽  
Chern Insulators

Topologically ordered phases are characterized by long-range quantum entanglement and fractional statistics rather than by symmetry breaking. First observed in a fractionally filled continuum Landau level, topological order has since been proposed to arise more generally at fractional fillings of topologically nontrivial Chern bands. Here we report the observation of gapped states at fractional fillings of Harper-Hofstadter bands arising from the interplay of a magnetic field and a superlattice potential in a bilayer graphene–hexagonal boron nitride heterostructure. We observed phases at fractional filling of bands with Chern indices C=−1, ±2, and ±3. Some of these phases, in C=−1 and C=2 bands, are characterized by fractional Hall conductance—that is, they are known as fractional Chern insulators and constitute an example of topological order beyond Landau levels.

scholarly journals Non-local terahertz photoconductivity in the topological phase of Hg1−xCdxTe

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
A. S. Kazakov ◽  
A. V. Galeeva ◽  
A. I. Artamkin ◽  
A. V. Ikonnikov ◽  
L. I. Ryabova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Laser Pulses ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Topological Phase ◽  
Non Local ◽  
Dark Signal ◽  
The Magnetic Field

AbstractWe report on observation of strong non-local photoconducitivity induced by terahertz laser pulses in non-zero magnetic field in heterostructures based on Hg1−xCdxTe films being in the topological phase. While the zero-field non-local photoconductivity is negligible, it is strongly enhanced in magnetic fields ~ 0.05 T resulting in appearance of an edge photocurrent that exceeds the respective dark signal by orders of magnitude. This photocurrent is chiral, and the chirality changes every time the magnetic field or the electric bias is reversed. Appearance of the non-local terahertz photoconductivity is attributed to features of the interface between the topological film and the trivial buffer.

Interplay of orbital hopping and perpendicular magnetic field in anisotropic phase transitions for Bernal bilayer graphene and hexagonal boron-nitride

2019 ◽  
Vol 21 (1) ◽  
pp. 238-245 ◽  
Author(s):  
P. T. T. Le ◽  
M. Davoudiniya ◽  
M. Yarmohammadi
Keyword(s):  
Magnetic Field ◽  
Phase Transitions ◽  
Boron Nitride ◽  
Hexagonal Boron Nitride ◽  
Bilayer Graphene ◽  
Perpendicular Magnetic Field ◽  
Magnetic Field Effects ◽  
Field Effects ◽  
Electronic Phase ◽  
Anisotropic Phase

We theoretically address the perpendicular magnetic field effects on the orbital electronic phase of Bernal bilayer graphene and hexagonal boron-nitride (h-BN).

scholarly journals Localization to delocalization probed by magnetotransport of hBN/graphene/hBN stacks in the ultra-clean regime

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Takuya Iwasaki ◽  
Satoshi Moriyama ◽  
Nurul Fariha Ahmad ◽  
Katsuyoshi Komatsu ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Elastic Scattering ◽  
Boron Nitride ◽  
High Temperatures ◽  
Low Temperatures ◽  
Dirac Point ◽  
Hexagonal Boron Nitride ◽  
Monolayer Graphene ◽  
Scattering Mechanism ◽  
High Quality ◽  
Dirac Materials

AbstractWe report on magnetotransport in a high-quality graphene device, which is based on monolayer graphene (Gr) encapsulated by hexagonal boron nitride (hBN) layers, i.e., hBN/Gr/hBN stacks. In the vicinity of the Dirac point, a negative magnetoconductance is observed for high temperatures >  ~ 40 K, whereas it becomes positive for low temperatures ≤  ~ 40 K, which implies an interplay of quantum interferences in Dirac materials. The elastic scattering mechanism in hBN/Gr/hBN stacks contrasts with that of conventional graphene on SiO2, and our ultra-clean graphene device shows nonzero magnetoconductance for high temperatures of up to 300 K.

scholarly journals Intrinsic quantized anomalous Hall effect in a moiré heterostructure

Science ◽  
2019 ◽  
Vol 367 (6480) ◽  
pp. 900-903 ◽  
Author(s):  
M. Serlin ◽  
C. L. Tschirhart ◽  
H. Polshyn ◽  
Y. Zhang ◽  
J. Zhu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energy Gap ◽  
Hexagonal Boron Nitride ◽  
Magnetic Ordering ◽  
Anomalous Hall Effect ◽  
Zero Magnetic Field ◽  
Strong Interactions ◽  
Hall Resistance ◽  
Magnetic Memory ◽  
Electrical Currents

The quantum anomalous Hall (QAH) effect combines topology and magnetism to produce precisely quantized Hall resistance at zero magnetic field. We report the observation of a QAH effect in twisted bilayer graphene aligned to hexagonal boron nitride. The effect is driven by intrinsic strong interactions, which polarize the electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1. In contrast to magnetically doped systems, the measured transport energy gap is larger than the Curie temperature for magnetic ordering, and quantization to within 0.1% of the von Klitzing constant persists to temperatures of several kelvin at zero magnetic field. Electrical currents as small as 1 nanoampere controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.

scholarly journals Magnetic-field-dependent quantum emission in hexagonal boron nitride at room temperature

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Annemarie L. Exarhos ◽  
David A. Hopper ◽  
Raj N. Patel ◽  
Marcus W. Doherty ◽  
Lee C. Bassett
Keyword(s):  
Magnetic Field ◽  
Boron Nitride ◽  
Room Temperature ◽  
Hexagonal Boron Nitride ◽  
Field Dependent
Sign in / Sign up

Export Citation Format

Share Document