scholarly journals Isospin magnetism and spin-polarized superconductivity in Bernal bilayer graphene

Science ◽  
2022 ◽  
Author(s):  
Haoxin Zhou ◽  
Ludwig Holleis ◽  
Yu Saito ◽  
Liam Cohen ◽  
William Huynh ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Order Parameter ◽  
Degrees Of Freedom ◽  
Bilayer Graphene ◽  
Zero Magnetic Field ◽  
Cooper Pairing ◽  
Two Dimensional ◽  
Van Hove Singularity ◽  
Spin Polarized ◽  
Spin Triplet

In conventional superconductors, Cooper pairing occurs between electrons of opposite spin. We observe spin-polarized superconductivity in Bernal bilayer graphene when doped to a saddle-point van Hove singularity generated by large applied perpendicular electric field. We observe a cascade of electrostatic gate-tuned transitions between electronic phases distinguished by their polarization within the isospin space defined by the combination of the spin and momentum-space valley degrees of freedom. Although all of these phases are metallic at zero magnetic field, we observe a transition to a superconducting state at finite B ‖ ≈ 150mT applied parallel to the two-dimensional sheet. Superconductivity occurs near a symmetry breaking transition, and exists exclusively above the B ‖ -limit expected of a paramagnetic superconductor with the observed transition temperature T C ≈ 30mK, consistent with a spin-triplet order parameter.

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.

THE SUPERFLUID PHASES OF LIQUID 3He: BCS THEORY

2010 ◽  
Vol 24 (25) ◽  
pp. 2525-2539 ◽  
Author(s):  
A. J. LEGGETT
Keyword(s):  
Magnetic Field ◽  
Wave Function ◽  
Weak Interactions ◽  
Spin Fluctuation ◽  
Zero Magnetic Field ◽  
Bcs Theory ◽  
Neutral System ◽  
Cooper Pairing ◽  
Pair Wave Function

Following the success of the original BCS theory as applied to superconductivity in metals, it was suggested that the phenomenon of Cooper pairing might also occur in liquid 3- He , though unlike the metallic case the pairs would most likely form in an anisotropic state, and would then lead in this neutral system to superfluidity. However, what had not been anticipated was the richness of the phenomena which would be revealed by the experiments of 1972. In the first place, even in a zero magnetic field there is not one but two superfluid phases, and the explanation of this involves ideas concerning "spin fluctuation feedback" which have no obvious analog in metals. Secondly, the anisotropic nature of the pair wave function, which in the case of the B phase is quite subtle, and the fact that the orientation must be the same for all the pairs, leads to a number of qualitatively new effects, in particular to a spectacular amplification of ultra-weak interactions seen most dramatically in the NMR behavior. In this chapter I review the application of BCS theory to superfluid 3- He with emphasis on these novel features.

scholarly journals Transport gap in suspended bilayer graphene at zero magnetic field

2012 ◽  
Vol 85 (15) ◽  
Author(s):  
A. Veligura ◽  
H. J. van Elferen ◽  
N. Tombros ◽  
J. C. Maan ◽  
U. Zeitler ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Bilayer Graphene ◽  
Zero Magnetic Field

FREE AND DONOR-BOUND CHARGED MAGNETOEXCITONS IN QUANTUM WELLS

2007 ◽  
Vol 21 (08n09) ◽  
pp. 1563-1567 ◽  
Author(s):  
ALEXANDER B. DZYUBENKO ◽  
DIANA A. COSMA ◽  
ANDREY Yu. SIVACHENKO
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Quantum Wells ◽  
Singlet State ◽  
Optical Transitions ◽  
Two Dimensional ◽  
Spin Singlet ◽  
Spin Triplet ◽  
Distinct Features ◽  
The Magnetic Field

We consider eigenstates and magneto-optical transitions of free and donor-bound spin-singlet and spin-triplet charged magnetoexcitons in quasi-two-dimensional quantum wells. We show that the bright singlet state remains always bound while spin-triplet dark and bright states become unbound when the distance to the donor ion becomes smaller than certain critical values, which depend on the magnetic field strength. We demonstrate that main magneto-photoluminescence lines of free and donor-bound charged excitons exhibit very similar features. However, shake-up processes in photoluminescence of free trions are strictly prohibited. Therefore, shake-up transitions are distinct features indicating that symmetry-breaking mechanisms are present in the system.

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