scholarly journals Imaging orbital ferromagnetism in a moiré Chern insulator

Science ◽  
2021 ◽  
pp. eabd3190
Author(s):  
C. L. Tschirhart ◽  
M. Serlin ◽  
H. Polshyn ◽  
A. Shragai ◽  
Z. Xia ◽  
...  
Keyword(s):  
Quantum Interference ◽  
Chemical Potential ◽  
Hexagonal Boron Nitride ◽  
Large Change ◽  
Anomalous Hall Effect ◽  
Structural Disorder ◽  
Flat Band ◽  
Edge States ◽  
Superconducting Quantum Interference Device ◽  
Break Time

Electrons in moiré flat band systems can spontaneously break time reversal symmetry, giving rise to a quantized anomalous Hall effect. Here we use a superconducting quantum interference device to image stray magnetic fields in twisted bilayer graphene aligned to hexagonal boron nitride. We find a magnetization of several Bohr magnetons per charge carrier, demonstrating that the magnetism is primarily orbital in nature. Our measurements reveal a large change in the magnetization as the chemical potential is swept across the quantum anomalous Hall gap consistent with the expected contribution of chiral edge states to the magnetization of an orbital Chern insulator. Mapping the spatial evolution of field-driven magnetic reversal, we find a series of reproducible micron scale domains pinned to structural disorder.

scholarly journals Holographic superconducting quantum interference device

2015 ◽  
Vol 30 (09) ◽  
pp. 1550040 ◽  
Author(s):  
Shingo Takeuchi
Keyword(s):  
Quantum Interference ◽  
Cooper Pair ◽  
Chemical Potential ◽  
Gravitational Theory ◽  
De Sitter ◽  
Scalar Model ◽  
Superconducting Quantum Interference Device ◽  
Complex Scalar ◽  
Superconducting Quantum Interference

We present a holographic model of the SQUID (Superconducting QUantum Interference Device) in the external magnetic field. The model of the gravitational theory considered in this paper is the Einstein–Maxwell-complex scalar model on the four-dimensional anti-de Sitter Schwarzschild black brane geometry, where one space direction is compacted into a circle and we arrange the coefficient of the time components profile so that we can model the SQUID, where the profile plays the role of the chemical potential for the Cooper pair.

scholarly journals Towards holographic flat bands

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Nicolás Grandi ◽  
Vladimir Juričić ◽  
Ignacio Salazar Landea ◽  
Rodrigo Soto-Garrido
Keyword(s):  
Chemical Potential ◽  
Condensed Matter ◽  
Anomalous Hall Effect ◽  
Spectral Weight ◽  
Flat Band ◽  
Dirac Fermion ◽  
Holographic Model ◽  
Quantum Phases ◽  
Flat Bands ◽  
Dirac Systems

Abstract Motivated by the phenomenology in the condensed-matter flat-band Dirac systems, we here construct a holographic model that imprints the symmetry breaking pattern of a rather simple Dirac fermion model at zero chemical potential. In the bulk we explicitly include the backreaction to the corresponding Lifshitz geometry and compute the dynamical critical exponent. Most importantly, we find that such a geometry is unstable towards a nematic phase, exhibiting an anomalous Hall effect and featuring a Drude-like shift of its spectral weight. Our findings should motivate further studies of the quantum phases emerging from such holographic models.

High-Resolution Backside GMR Magnetic Current Imaging on a Contour-Milled Globally Ultrathin Die

2014 ◽  
Author(s):  
D. Vallett ◽  
J. Gaudestad ◽  
C. Richardson
Keyword(s):  
Quantum Interference ◽  
Flip Chip ◽  
Milling Process ◽  
Dramatic Improvement ◽  
Superconducting Quantum Interference Device ◽  
Density Peak ◽  
Magnetic Current ◽  
Gmr Sensors ◽  
Silicon Thickness ◽  
A Current

Abstract Magnetic current imaging (MCI) using superconducting quantum interference device (SQUID) and giant-magnetoresistive (GMR) sensors is an effective method for localizing defects and current paths [1]. The spatial resolution (and sensitivity) of MCI is improved significantly when the sensor is as close as possible to the current paths and associated magnetic fields of interest. This is accomplished in part by nondestructive removal of any intervening passive layers (e.g. silicon) in the sample. This paper will present a die backside contour-milling process resulting in an edge-to-edge remaining silicon thickness (RST) of < 5 microns, followed by a backside GMR-based MCI measurement performed directly on the ultra-thin silicon surface. The dramatic improvement in resolving current paths in an ESD protect circuit is shown as is nanometer scale resolution of a current density peak due to a power supply shortcircuit defect at the edge of a flip-chip packaged die.

scholarly journals Edge channels of broken-symmetry quantum Hall states in graphene visualized by atomic force microscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sungmin Kim ◽  
Johannes Schwenk ◽  
Daniel Walkup ◽  
Yihang Zeng ◽  
Fereshte Ghahari ◽  
...  
Keyword(s):  
Atomic Force Microscopy ◽  
Chemical Potential ◽  
Quantum Hall ◽  
Broken Symmetry ◽  
Topological Order ◽  
Edge States ◽  
Force Microscopy ◽  
Atomic Force ◽  
Intimate Relation ◽  
Boundary Measurements

AbstractThe quantum Hall (QH) effect, a topologically non-trivial quantum phase, expanded the concept of topological order in physics bringing into focus the intimate relation between the “bulk” topology and the edge states. The QH effect in graphene is distinguished by its four-fold degenerate zero energy Landau level (zLL), where the symmetry is broken by electron interactions on top of lattice-scale potentials. However, the broken-symmetry edge states have eluded spatial measurements. In this article, we spatially map the quantum Hall broken-symmetry edge states comprising the graphene zLL at integer filling factors of $${{\nu }}={{0}},\pm {{1}}$$ ν = 0 , ± 1 across the quantum Hall edge boundary using high-resolution atomic force microscopy (AFM) and show a gapped ground state proceeding from the bulk through to the QH edge boundary. Measurements of the chemical potential resolve the energies of the four-fold degenerate zLL as a function of magnetic field and show the interplay of the moiré superlattice potential of the graphene/boron nitride system and spin/valley symmetry-breaking effects in large magnetic fields.

scholarly journals Chemical potential and quantum Hall ferromagnetism in bilayer graphene

Science ◽  
2014 ◽  
Vol 345 (6192) ◽  
pp. 58-61 ◽  
Author(s):  
Kayoung Lee ◽  
Babak Fallahazad ◽  
Jiamin Xue ◽  
David C. Dillen ◽  
Kyounghwan Kim ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Chemical Potential ◽  
Hexagonal Boron Nitride ◽  
Quantum Hall ◽  
Bilayer Graphene ◽  
Zero Magnetic Field ◽  
High Magnetic Fields ◽  
Complex Interplay ◽  
Electron Hole ◽  
Quantum Hall State

Bilayer graphene has a distinctive electronic structure influenced by a complex interplay between various degrees of freedom. We probed its chemical potential using double bilayer graphene heterostructures, separated by a hexagonal boron nitride dielectric. The chemical potential has a nonlinear carrier density dependence and bears signatures of electron-electron interactions. The data allowed a direct measurement of the electric field–induced bandgap at zero magnetic field, the orbital Landau level (LL) energies, and the broken-symmetry quantum Hall state gaps at high magnetic fields. We observe spin-to-valley polarized transitions for all half-filled LLs, as well as emerging phases at filling factors ν = 0 and ν = ±2. Furthermore, the data reveal interaction-driven negative compressibility and electron-hole asymmetry in N = 0, 1 LLs.

Sign in / Sign up

Export Citation Format

Share Document