Tunable quantum interferometer for correlated moiré electrons.

Magic-angle twisted bilayer graphene can host a variety of gate-tunable correlated states - including superconducting and correlated insulator states. Recently, junction-based superconducting moiré devices have been introduced, enabling the study of the charge, spin and orbital nature of superconductivity, as well as the coherence of moiré electrons in magic-angle twisted bilayer graphene. Complementary fundamental coherence effects-in particular, the Little-Parks effect in a superconducting ring and the Aharonov-Bohm effect in a normally conducting ring - have not yet been reported in moiré devices.

Kagome Quantum Oscillations in Graphene Superlattices.

Electronic spectra of solids subjected to a magnetic field are often discussed in terms of Landau levels and Hofstadter-butterfly-style Brown-Zak minibands manifested by magneto-oscillations in two-dimensional electron systems. Here, we present the semiclassical precursors of these quantum magneto-oscillations which appear in graphene superlattices at low magnetic field near the Lifshitz transitions and persist at elevated temperatures. These oscillations originate from Aharonov-Bohm interference of electron waves following open trajectories that belong to a kagome-shaped network of paths characteristic for Lifshitz transitions in the moire superlattice minibands of twistronic graphenes.

A tunable monolithic SQUID in twisted bilayer graphene.

Magic-angle twisted bilayer graphene (MATBG) hosts a number of correlated states of matter that can be tuned by electrostatic doping. Transport and scanning-probe experiments have shown evidence for band, correlated and Chern insulators along with superconductivity. This variety of in situ tunable states has allowed for the realization of tunable Josephson junctions.

Gate-Defined Electron Interferometer in Bilayer Graphene.

We present an electron interferometer defined purely by electrostatic gating in an encapsulated bilayer graphene. This minimizes possible sample degradation introduced by conventional etching methods when preparing quantum devices. The device quality is demonstrated by observing Aharonov-Bohm (AB) oscillations with a period of /, /2, /3, and /4, witnessing a coherence length of many microns.

Scattering between Minivalleys in Twisted Double Bilayer Graphene.

A unique feature of the complex band structures of moiré materials is the presence of minivalleys, their hybridization, and scattering between them. Here, we investigate magnetotransport oscillations caused by scattering between minivalleys-a phenomenon analogous to magnetointersubband oscillations-in a twisted double bilayer graphene sample with a twist angle of 1.94°.

Correlated electron-hole state in twisted double-bilayer graphene.

When twisted to angles near 1°, graphene multilayers provide a window on electron correlation physics. Here, we report the discovery of a correlated electron-hole state in double-bilayer graphene twisted to 2.37°.

Gate-defined Josephson junctions in magic-angle twisted bilayer graphene.

In situ electrostatic control of two-dimensional superconductivity is commonly limited due to large charge carrier densities, and gate-defined Josephson junctions are therefore rare. Magic-angle twisted bilayer graphene (MATBG) has recently emerged as a versatile platform that combines metallic, superconducting, magnetic and insulating phases in a single crystal. Although MATBG appears to be an ideal two-dimensional platform for gate-tunable superconductivity, progress towards practical implementations has been hindered by the need for well-defined gated regions.

Combined Minivalley and Layer Control in Twisted Double Bilayer Graphene.

Control over minivalley polarization and interlayer coupling is demonstrated in double bilayer graphene twisted with an angle of 2.37°. This intermediate angle is small enough for the minibands to form and large enough such that the charge carrier gases in the layers can be tuned independently.

Gap Opening in Twisted Double Bilayer Graphene by Crystal Fields.

Crystal fields occur due to a potential difference between chemically different atomic species. In van der Waals heterostructures such fields are naturally present perpendicular to the planes. It has been realized recently that twisted graphene multilayers provide powerful playgrounds to engineer electronic properties by the number of layers, the twist angle, applied electric biases, electronic interactions, and elastic relaxations, but crystal fields have not received the attention they deserve.