Ruiheng (Ray) Su

Hello there! I am a quantum science and engineering Ph.D. student at Princeton University.

I graduated from the University of British Columbia in 2024, where I spent 3 years in Prof. Joshua Folk's Quantum Devices Group. With Prof. Folk, I led experiments exploring the interplay between topology and electron-electron correlations in 2D materials. ☕

Here, you'll find my highlights of my research, other projects, updates, and my CV.

Correlation and topology in moiré graphene

The ability to systematically assemble 2D materials opens opportunities for designing highly tunable quantum states and electronic devices.

My research has focused on multilayer graphene, often incorporating rotational misalignment between the crystal lattice of neighboring atomic layers. This introduces a new length scale in the system - that of the moiré pattern. The family of such materials is known as twisted M-layer + N-layer graphene. An exemplary example is t2+2, also known as twisted double bilayer graphene.

Generalized anomalous Hall crystal in twisted bilayer-trilayer graphene

In a dilute two-dimensional electron gas, Coulomb interactions can stabilize the formation of a Wigner crystal. Although Wigner crystals are topologically trivial, it has been predicted that electrons in a partially filled band can break continuous translational symmetry and time-reversal symmetry spontaneously to form an anomalous Hall crystal (AHC).

Here, we report the observation of a generalized AHC in twisted bilayer-trilayer graphene (t2+3) whose formation is seeded by the moiré potential. The crystal quadruples the moiré unit-cell area, coinciding with an integer quantum anomalous Hall effect. Recent theories have predicted the generalized AHC to act as a parent state of the fractional quantum anomalous Hall effect, pointing to t2+3 as a promising platform in the search for new correlated and topological phenomena.

Su, R., Waters, D. et al. arXiv:2406.17766 (2024)

Topological flat bands in the Bernal-stacked tM+N graphene family

Moiré materials host a wealth of correlated and topological states of matter arising from flat electronic bands with nontrivial quantum geometry.

Here, we studied the family of twisted graphene multilayers made of twisted sheets of M- and N-layer Bernal-stacked graphene flakes. Our results show that this family of structures is promising for discovering of new topological electronic phenomena, enabled by using the layer number to tune the moiré band and the screening environment.

Waters, D., Su, R., Thompson, E. et al. Nat. Commun. 15, 10552 (2024)

Superconductivity in twisted double bilayer graphene on WSe2

Featured in: News & Views, Nature Materials

In a superconductor, electrons form a macroscopic quantum ground state, allowing charge/current to flow without dissipation.

We discovered that proximal coupling to few-layer WSe2 stabilizes superconductivity in twisted double bilayer graphene (t2+2). Our results contribute to the growing body of evidence in graphitic systems, suggesting a correlation—though not an overlap—between electronic states with a tendency toward isospin polarization and those conducive to superconductivity.

Su, R. et al. Nat. Mater. 22, 1332-1337 (2023)

Recycling robot

This is a robot I designed for a competition to retrieve and deposit the greatest number of scattered soda cans into a recycling bin within 1 minute.

Switching to online classes at the time (2020) meant the entire robot had to be constructed/soldered by hand. This is a video of a prototype in action!

Machined phone holder

I machined this foldable phone holder from brass and aluminum scraps. Unlike typical plastic holders, it's big enough to hold a tablet, built to last, and heavy.

This was a project to become a qualified user of UBC's student machine shop. It involved using the mill, lathe, drill press, water jet, as well as hand tools such as the tap and die.

News 🥂

2024 Dec. 8 Now in Nature Communications, our work reporting topological flatbands in a family of tN+M graphene!
Aug. 19 Our preprint on "Interplay of electronic crystals with integer and fractional Chern insulators in moiré pentalayer graphene" is now on arXiv!
June 25 Our preprint on "Generalized anomalous Hall crystals in twisted bilayer-trilayer graphene" is now on arXiv!
May 29 I graduated from UBC with a Bachelor of Applied Science in Engineering Physics!
May 10 Our work on "Topological flat bands in a family of multilayer graphene moiré lattices" is now on arXiv!
March 5 APS March meeting is in Minneapolis, Minnesota, this year! I reported on a possible observation of a Josephson-like effect in an orbital ferromagnet. Our collaborators from UW reported on topological states in tM+N graphene (Abstracts: Here and Here)
2023 Sept. 29 I won first prize in the poster session at SBQMI’s International Scientific Advisory Board meeting! (Check it out: Here)
Aug. 28 Exciting news! Our superconductivity work was recently published in Nature Materials :)
May 12 I attended the CIFAR Quantum Materials spring school in Montreal, where I learned from graduate students about their research and received valuable feedback on my poster on electronic phases of twisted double bilayer graphene on WSe2. (Check it out: Here)
March 7 I gave a talk at the APS March meeting in Las Vegas, Nevada, reporting our discovery of superconductivity in twisted double bilayer graphene! (Abstract: Here)