Young Lab

Two dimensional electrons in a flat dispersion are highly susceptible to interaction driven instabilities based on broken symmetries (such as superconductivity and ferromagnetism) and emergent topology (such a fractionally quantized hall effets). 

Driven by a string of technical advances in the field of two dimensional layered materials [1-2], including recently in our group [3-4], graphene heterostructures are now among the best material platforms for studying these effects, combining pristine sample quality, in situ control of electronic structure and band dispersion, and a rich landscape of broken symmetry orders arising from spin, valley, and orbital quasi-degeneracies.

Using these materials, our group has reported a number of key discoveries, including the experimental discovery of fractional Chern insulators [5], the observation of an intrinsic quantized anomalous Hall effect arising from the interplay of Stoner ferromagnetism and band topology[6], the discovery of field-effect actuated magnetic switching [7], and the discovery of magnetism and superconductivity in simple crystalline graphene allotropes [8-9].

Ongoing projects include using these devices to experimentally detect nonabelian statistics using both interferometric and thermodynamic probes, engineering nonabelian defect states in abelian fractional quantum Hall phases, and revealing the mechanisms for superconductivity in crystalline graphene systems.

[1] Dean et al., Nature Nanotechnology, 5:722-726 (2010).
[2] Wang et al., Science, 342:614-617 (2013).
[3] Zibrov et al., Nature 549:360-364 (2017).
[4] Cohen et al., Nature Physics 19:1502-1508 (2023).
[5] Spanton et al., Science 360:62-66 (2018).
[6] Serline et al., Science 367:900-903 (2020)
[7] Polshyn et al., Nature 488:66-70 (2020).
[8] Zhou et al., Nature 598:429-433 (2021).
[9] Zhou et al., Nature 598:434-438 (2021).

Understanding the nature of electronic states requires access to a variety of fundamental observables. Some can be extracted directly from a well designed sample using, resistance and density of states measurements, but others require specialized tools.  We build and operate nanoSQUID-on-tip microscopes [1] that allow nanoscale mapping of magnetic and thermal properties. These microscopes are based on a superconducting quantum interference device fabricated at the tip of a quartz pipette, and enable world-leading combination of spatial resolution (down to ~40 nm), magnetic sensitivity, and thermal sensitivity[] in the the cryogenic temperature range.

Our lab operates three nanoSQUID-on-tip based microscope spanning the 20mK to 7K temperature range with access to vector magnetic field and variable pressure sample environments. Scientific achievements to date using these tools include direct imaging of orbital magnetism in graphene and transition metal dichalcogenide heterostructures [3-5], including the first magnetic imaging of fractional quantum anomalous Hall phases. Ongoing work includes direct imaging of electron flow in strongly correlated electron systems and investigating the nature of heat transport on the nanoscale in superfluid helium.

[1] Vasyukov et al., Nature Nanotechnology 8:639-644 (2013).
[2] Halbertal et al., Nature 539:407-410 (2016).
[3] C. L. Tschirhart et al., Science 372, 1323-1327 (2021).
[4] C. L. Tschirhart et al., Nature Physics (in press, 2023).
[5] E. Redekop et al., Nature (in press).

The condition of equilibrium puts constraints on what types of matter can exist, and on their quantitative characteristics.  It has been proposed that strong electromagnetic drive can induce new phases not available as ground states, or quantitatively favor one or more competing ground states under a set of similar equilibrium conditions (temperature, magnetic field, etc.).  Accessing such phases with electrical measurements, however, is limited by the short timescales during which electromagnetic drive can be applied, itself limited both by the availability of pulsed laser sources and limits on power dissipation within the sample itself.  We have developed a versatile THz spectrometer-on-a-chip technique, allowing us to probe the excitation spectrum of deeply sub-diffraction limit sized samples—including van der Waals heterostructures—in the THz frequency range and on picosecond time scales [1]. Critically, our design features both cryogenic compatibility and fast sample exchange, allowing us to bring this technique to bear on highly tunable, complex heterostructures hosting a wide array of correlation driven electronic ground states.

[1] A. Potts, A. Nayak, AFY et. al., “On-chip time-domain terahertz spectroscopy of superconducting films below the diffraction limit.” arXiv:2302.05434