Half- and quarter-metals in rhombohedral trilayer graphene

Zhou, Haomin; Xie, Tian; Ghazaryan, Areg; Holder, Tobias; Ehrets, James R.; Spanton, Eric; Taniguchi, Takashi; Berg, Erez; Serbyn, Maksym; Young, Andrea

doi:10.1038/s41586-021-03938-w

Cited by 206 publications

(165 citation statements)

References 39 publications

Supporting

Mentioning

153

Contrasting

Unclassified

Order By: Relevance

“…The symmetry breaking transitions move to higher |n e | with increasing |D|, as expected from a Stoner picture given that increasing D enhances the size of the van Hove singularity favoring isospin symmetry breaking states at higher carrier concentration [24]. This behavior is analogous to that observed in RTG [25], but the observed phases differ between the two systems. For example, we find no signatures of the annu-lar Fermi seas that host superconductivity in the trilayer, nor do we find a spin-polarized half-metal state.…”

supporting

confidence: 65%

Isospin magnetism and spin-triplet superconductivity in Bernal bilayer graphene

Zhou,

Holleis,

Saito

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

We report the observation of 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. While 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 TC ≈ 30mK, implying a spin-triplet order parameter.

show abstract

supporting

confidence: 65%

Isospin magnetism and spin-triplet superconductivity in Bernal bilayer graphene

Zhou,

Holleis,

Saito

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…3) is also a feasible way to identify the half metallic phase. Considering that the correlated half metallic phase in rhombohedral stacked graphene trilayer has been observed in experiment very recently 41,42 , we expect that the proposed half metallic phase in 4L-BGM can be confirmed in future experiments.…”

Section: A Half Metallic State In 4l-bgmsupporting

confidence: 63%

“…Actually, such half metallic state based on antiferromagnetic spin order is a general phenomenon in the Hubbard lattice models 39,40 . Note that the interaction induced half metallic phase in rhombohedral stacked graphene trilayer has been observed in recent experiments 41,42 .…”

Section: Introductionmentioning

confidence: 56%

Gate-induced half-metals in Bernal stacked graphene multilayer

Liang,

Li,

Gao

2021

Preprint

View full text Add to dashboard Cite

Recent experiments indicate that the Bernal stacked graphene multilayer (BGM) have an interaction induced gapped (or pseudo gapped) ground state. Here, we propose that, due to the electron correlation, the BGM can be induced into a half metallic phase by applying a vertical electric field and doping. The half metallic states in even-layer and odd-layer BGMs have totally different behaviors, due to their different band structures. We systematically calculate the graphene tetralayer (4L-BGM) and trilayer (3L-BGM) as the typical examples of the even-layer and odd-layer BGMs, respectively. In 4L-BGM, we find an interesting phenomenon of electric field induced inversion of the spin-polarized bands. Namely, in the half metallic phase, the spin polarization of the conducting channel and the net magnetic moment are inversed when the applied electric field exceeds a critical value. In 3L-BGM, a remarkable feature is that the inequivalence of the the two sublattices will intrinsically break the degeneracy of the the spin-up and spin-down bands even in the zero electric field case. Our results suggest that 4L-BGM should be an ideal platform to detect the proposed half metallic phase in BGM systems.

show abstract

“…Bernal-stacked bilayer graphene, equivalent to R-stacking, is the simplest member of this family of structures, however, to date reports of symmetry-broken states in bilayer graphene have generally required large magnetic fields [21][22][23][24] or involved subtle gapped states at charge neutrality [25][26][27][28][29][30]. Intriguingly, R-stacked (ABC) trilayer graphene was recently shown to exhibit spontaneous itinerant spin and valley polarization at zero magnetic field, displaying a series of phase transitions, hysteresis, anomalous Hall, and superconductivity at millikelvin temperatures in carefully prepared samples [31,32]. R-stacking is crucial for these phenomena, however this stacking arrangement is not stable in trilayers, inhibiting experimental efforts.…”

mentioning

confidence: 99%

“…If the primary effect of B is to introduce a Zeeman splitting of the spin states in the system, we can interpret the reduction in density of the A-B transition point as resulting from the difference in Zeeman energy between the two phases with B [31]. From fixed field measurements (Fig.…”

mentioning

confidence: 99%

Cascade of isospin phase transitions in Bernal bilayer graphene at zero magnetic field

de la Barrera,

Aronson,

Zheng

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

Emergent phenomena arising from the collective behavior of electrons is generally expected when Coulomb interactions dominate over the kinetic energy, as in delocalized quasiparticles in highly degenerate flat bands. Bernal-stacked bilayer graphene intrinsically supports a pair of flat bands predicted to host a variety of spontaneous broken-symmetry states arising from van Hove singularities and a four-fold spin-valley (isospin) degeneracy [1][2][3][4][5][6]. Here, we show that ultra-clean samples of bilayer graphene display a cascade of symmetry-broken states with spontaneous and spin and valley ordering at zero magnetic field. Using capacitive sensing in a dual-gated geometry, we tune the carrier density and electric displacement field independently to explore the phase space of transitions and probe the character of the isospin order. Itinerant ferromagnetic states emerge near the conduction and valence band edges with complete spin and valley polarization and a high degree of displacement field tunability. At larger hole densities, two-fold degenerate quantum oscillations manifest in an additional broken symmetry state that is enhanced by the application of an in-plane magnetic field. Both types of symmetry-broken states display enhanced layer polarization at low temperatures, suggesting a coupling to the layer pseudospin degree of freedom in the electronic wavefunctions [1,6]. Notably, the zero-field spontaneous symmetry breaking reported here emerges in the absence of a moiré superlattice and is intrinsic to natural graphene bilayers. Thus, we demonstrate that the tunable bands of bilayer graphene represent a related, but distinct approach to produce flat band collective behavior, complementary to engineered moiré structures.

show abstract

Half- and quarter-metals in rhombohedral trilayer graphene

Cited by 206 publications

References 39 publications

Isospin magnetism and spin-triplet superconductivity in Bernal bilayer graphene

Isospin magnetism and spin-triplet superconductivity in Bernal bilayer graphene

Gate-induced half-metals in Bernal stacked graphene multilayer

Cascade of isospin phase transitions in Bernal bilayer graphene at zero magnetic field

Contact Info

Product

Resources

About