arXiv subjects

Zekang Zhou

Publications and source records attributed to Zekang Zhou.

9 recordsLinked to original sources

arXiv2026

Surface-Selective Probe of Spin-Triplet Superconductivity in Rhombohedral Graphene

Superconductivity in rhombohedral graphene has been observed across many layer numbers, with mounting evidence pointing toward spin-triplet pairing, yet complementary probes of the superconducting spin structure remain needed. Here we use one-sided WS$_2$ proximity in rhombohedral pentalayer graphene (R5G) as a surface-selective spin-orbit probe. The induced Ising spin-orbit coupling is strongest for carriers localized near the WS$_2$ interface, allowing the displacement field to tune the overlap between superconducting carriers and the spin-orbit perturbation. We observe a strongly asymmetric superconducting landscape: two robust pockets, SC1 and SC2, survive only on mutually opposite signs of displacement field, while a third pocket, SC3, is substantially weaker. Gate-tracking features, quantum oscillations, and self-consistent band-structure calculations identify the layer polarization and Fermi-surface character of the relevant carriers. The robust superconducting states are absent or strongly weakened when the active high-DOS carriers are polarized toward the WS$_2$ interface. Since Ising spin-orbit coupling is compatible with time-reversed spin-singlet pairing but competes with same-spin intervalley triplet pairing by canting or pinning the parent spin texture, this surface-selective suppression provides additional evidence for spin-triplet superconductivity involving both hole-like and electron-like carriers. Our results establish one-sided TMD proximity as a displacement-field-tunable probe of superconducting spin structure in rhombohedral graphene.

cond-mat.mes-hall↗

arXiv2026

Competing Orders Driven by Wigner Crystal Phase in Rhombohedral Graphene

Rhombohedral graphene systems provide a unique platform where strong electronic interactions and nontrivial band topology coexist at low carrier densities and high displacement fields, giving rise to a rich landscape of emergent electronic phases. Here, we report that the highly insulating state on the low-density side of chiral superconductivity in rhombohedral pentalayer graphene (R5G) corresponds to a Wigner crystal (WC) phase. In addition, a hole-doped metallic Wigner crystal (h-mWC) phase emerges near the WC boundary. Under an out-of-plane magnetic field, the system hosts competing magnetic-field-stabilized superconductivity (fSC) and unconventional reentrant quantum Hall (RIQH) states. These emergent phases are closely connected to the underlying WC and mWC states and evolve continuously across phase boundaries. Our results establish that WC phase plays an important role in the phase diagram of rhombohedral multilayer graphene and highlight its connection to a rich landscape of emergent phases.

cond-mat.mes-hall↗

arXiv2026

Correlated Insulating States in Twisted Double Bilayer Graphene Enhanced by Interfacial Effect on CrOCl

Interaction between different two dimensional materials can give rise to many exotic physical phenomena which are rarely observed in intrinsic materials. Recently, several theoretical and experimental works have revealed that magnetic proximity effect between pristine graphene and magnetic substrates can lead to the emergence of quantum anomalous Hall states and quantum spin Hall states. However, interplay between correlated states in graphene-based systems and magnetic materials has seldom been studied. Here we perform the transport measurement at ultrahigh magnetic field of twisted double bilayer graphene (TDBG) on CrOCl (COC) substrate, which is an antiferromagnetic material. Instead of a magnetic-exchange effect on graphene, we observe an enhanced correlated insulating state at half-filling factor of TDBG as a result of the charge-transfer process between TDBG and COC. The temperature and magnetic field dependence of this enhanced state are further studied. Our results demonstrate the influence of charge-related effect at the interface, and shed a light on a new route for manipulating the correlated states in graphene-based moir\'e systems using interfacial engineering.

cond-mat.mes-hall↗

arXiv2025

Strong Correlations and Superconductivity in the Supermoir\'e Lattice

The supermoir\'e lattice, arising from the interference of multiple moir\'e patterns, dramatically reshapes the electronic band structure by introducing new minibands and modifying band dispersion. Concurrently, strong electronic interactions within moir\'e flat bands lead to the emergence of various correlated states. However, the impact of the supermoir\'e lattice on the flat band systems with strong interactions remains largely unexplored. Here, we report the existence of the supermoir\'e lattice in the mirror-symmetry-broken twisted trilayer graphene, elucidating its role in generating mini-flat bands and mini-Dirac bands. Furthermore, we demonstrate interaction-induced symmetry-broken phases in the supermoir\'e mini-flat bands alongside the cascade of superconductor-insulator transitions enabled by the supermoir\'e lattice. Our work shows that robust superconductivity can exist in the mirror-symmetry-broken TTG and underscores the significance of the supermoir\'e lattice as an additional degree of freedom for tuning the electronic properties in twisted multilayer systems, sheds light on the correlated quantum phases such as superconductivity in the original moir\'e flat bands, and highlights the potential of using the supermoir\'e lattice to design and simulate novel quantum phases.

cond-mat.str-el↗

arXiv2025

Quantum Hall Antidot as a Fractional Coulombmeter

The detection of fractionally charged quasiparticles, which arise in the fractional quantum Hall regime, is of fundamental importance for probing their exotic quantum properties. While electronic interferometers have been central to probe their statistical properties, their interpretation is often complicated by bulk-edge interactions. Antidots, potential hills in the quantum Hall regime, are particularly valuable in this context, as they overcome the geometric limitations of conventional designs and act as controlled impurities within a quantum point contact. Furthermore, antidots allow for quasiparticle charge detection through straightforward conductance measurements, replacing the need for more demanding techniques. In this work, we employ a gate-defined bilayer graphene antidot operating in the Coulomb-dominated regime to study quasiparticle tunneling in both integer and fractional quantum Hall states. We show that the gate-voltage period and the oscillation slope directly reveal the charge of the tunneling quasiparticles, providing a practical method to measure fractional charge in graphene. We report direct measurements of fractional charge, finding $q = e/3$ at $ν= 4/3$, 5/3 and 7/3, $q = 2e/3$ at $ν= 2/3$ and $q = 3e/5$ at $ν= 3/5$, while at $ν= 8/3$ we observe signatures of both $e/3$ and $2e/3$ tunneling charge. The simplicity and tunability of this design open a pathway to extend antidot-based charge measurements to other van der Waals materials, establishing antidots as a powerful and broadly applicable platform to study the quantum Hall effect.

cond-mat.mes-hall↗

arXiv2025

Tunable Inter-Edge Interactions in a Bilayer Graphene Quantum Hall Antidot

Electronic interferometers in the quantum Hall regime are one of the best tools to study the statistical properties of localized quasiparticles in the topologically protected bulk. However, since their behavior is probed via chiral edge modes, bulk-to-edge and inter-edge interactions are two important effects that affect the observations. Moreover, almost all kinds of interferometers heavily rely on a pair of high-quality quantum point contacts where the presence of impurities significantly modifies the behavior of such constrictions, which in turn can alter the outcome of the measurements. Antidots, potential hills in the quantum Hall regime, are particularly valuable in this context, as they overcome the geometric limitations of conventional geometries and act as controlled impurities within a quantum point contact. Furthermore, antidots allow for quasiparticle charge detection through simple conductance measurements, replacing the need for complex techniques such as shot noise. Here, we use a gate-defined bilayer graphene antidot, operated in the Coulomb-dominated regime. By varying the antidot potential, we can tune inter-edge interactions, enabling a crossover from a single-dot to a double-dot behavior. In the latter, strong coupling between the two edge states leads to edge-state pairing, resulting in a measured doubling of the tunneling charge. We find that in certain regimes, the inter-edge coupling completely dominates over other energy scales of the system, overshadowing the interference effects these devices are mainly designed to probe. These results highlight the significant role of inter-edge interactions and establish antidots as a versatile platform for exploring quantum Hall interferometry.

cond-mat.mes-hall↗

arXiv2024

Strongly correlated Hofstadter subbands in minimally twisted bilayer graphene

Moiré superlattice in twisted bilayer graphene has been proven to be a versatile platform for exploring exotic quantum phases. Extensive investigations have been invoked focusing on the zero-magnetic-field phase diagram at the magic twist angle around $θ=1.1\degree$, which has been indicated to be an exclusive regime for exhibiting flat band with the interplay of strong electronic correlation and untrivial topology in the experiment so far. In contrast, electronic bands in non-magic-angle twisted bilayer graphene host dominant electronic kinetic energy compared to Coulomb interaction. By quenching the kinetic energy and enhancing Coulomb exchange interactions by means of an applied perpendicular magnetic field, here we unveil gapped flat Hofstadter subbands at large magnetic flux that yield correlated insulating states in minimally twisted bilayer graphene at $θ=0.41\degree$. These states appear with isospin symmetry breaking due to strong Coulomb interactions. Our work provides a platform for studying the phase transition of the strongly correlated Hofstadter spectrum.

cond-mat.mes-hall↗

arXiv2024

Featuring nuanced electronic band structure in gapped multilayer graphene

Moiré systems featuring flat electronic bands exhibit a vast landscape of emergent exotic quantum states, making them one of the resourceful platforms in condensed matter physics in recent times. Tuning these systems via twist angle and the electric field greatly enhances our comprehension of their strongly correlated ground states. Here, we report a technique to investigate the nuanced intricacies of band structures in dual-gated multilayer graphene systems. We utilize the Landau levels of a decoupled monolayer graphene to extract the electric field-dependent bilayer graphene charge neutrality point gap. Then, we extend this method to analyze the evolution of the band gap and the flat bandwidth in twisted mono-bilayer graphene. The band gap maximizes at the same displacement field where the flat bandwidth minimizes, indicating the strongest electron-electron correlation, which is supported by directly observing the emergence of a strongly correlated phase. Moreover, we extract integer and fractional gaps to further demonstrate the strength of this method. Our technique gives a new perspective and paves the way for improving the understanding of electronic band structure in versatile flat band systems.

cond-mat.mes-hall↗

arXiv2024

Double-dome Unconventional Superconductivity in Twisted Trilayer Graphene

Graphene moir\'e systems are ideal environments for investigating complex phase diagrams and gaining fundamental insights into the mechanisms underlying exotic states of matter, as they permit controlled manipulation of electronic properties. Magic-angle twisted trilayer graphene (MATTG) has emerged as a key platform to explore moir\'e superconductivity, owing to the robustness of its superconducting order and the displacement-field tunability of its energy bands. Recent measurements strongly suggest that superconductivity in MATTG is unconventional. Here, we report the first direct observation of double-dome superconductivity in MATTG. The temperature, magnetic field, and bias current dependence of the superconductivity of doped holes collectively show that it is significantly suppressed near moir\'e filling $\nu^* = -2.6$, leading to a double dome in the phase diagram within a finite window of the displacement field. The temperature dependence of the normal-state resistance and the $I-V$ curves straddling $\nu^*$ are suggestive of a phase transition and the potentially distinct nature of superconductivity in the two domes. Hartree-Fock calculations incorporating mild strain yield an incommensurate Kekul\'e spiral state whose effective spin polarization peaks in the regime where superconductivity is suppressed in experiments. This allows us to draw conclusions about the normal state as well as the unconventional nature of the superconducting order parameter.

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