About

Raymond Ashoori is a Professor of Physics and Division Head of Atomic, Biophysical, and Condensed Matter Physics at MIT. His research focuses on the study of interacting electronic systems in low-dimensional electronic structures, such as semiconductor samples, graphene, and transition-metal dichalcogenide layers. He has developed novel pulsed methods that enable contactless measurement of electron tunneling spectra in isolated conducting and insulating samples, leading to discoveries such as a sharp feature in tunneling spectra originating from the vibrations of an electronic crystal. His group also employs highly sensitive capacitance measurements to investigate electronic systems, including detecting spectral features from the Hofstadter Butterfly in graphene and correlated insulating states of twisted bilayer graphene. His work involves understanding the complex behavior of many trapped electrons, which exhibit unusual and counterintuitive correlations due to their indistinguishability and mutual repulsion. Professor Ashoori earned his B.A. from the University of California at San Diego in 1984 and his Ph.D. from Cornell University in 1991. He joined MIT faculty in 1993 after a postdoctoral position at AT&T Bell Laboratories, and was promoted to full Professor in 2004. His awards include the David and Lucille Packard Fellowship, NSF Young Investigator Award, Sloan Fellowship, and APS Fellowship, among others.

Research topics

• Physics
• Materials science
• Condensed matter physics
• Physical medicine and rehabilitation
• Optics
• Chemistry
• Crystallography
• Quantum mechanics
• Medicine

Selected publications

• Evidence of Metallic Wigner Crystal in Rhombohedral Graphene

  ArXiv.org · 2026-03-31

  articleOpen access

  When the Coulomb interaction dominates over kinetic energy, electrons can crystallize into a Wigner crystal (WC). This paradigmatic correlated electronic phase has been realized in two-dimensional electron gases with parabolic band dispersion and completely flat Landau levels under high magnetic fields. Beyond these conventional contexts of electron crystallization, more exotic electron crystals have been postulated but remain unexplored. For example, a metallic Wigner crystal (mWC), in which itinerant carriers coexist with a pinned electron lattice, has been proposed theoretically but considered difficult to realize. Non-parabolic electron bands and quantum geometry may facilitate mWC and other novel topological electron crystals. Here we report transport evidence for WC and mWC in rhombohedral tetra-, penta-, and hexalayer graphene in the charge density range 0.3-0.5x10^12 cm^-2. By flattening the conduction band with a gate-controlled displacement field D, we observe an insulating state at nonzero charge density that shows nonlinear, hysteretic current-voltage relations, signatures of a pinned WC, that are absent from the lower-density insulator. Further increasing D reveals transport dominated by hole-like carriers with density up to only 15% of the nominal electron density, consistent with mWC. This mWC state is closely tied to the WC state, as both collapse simultaneously with increasing temperature or bias voltage. The mWC state shows quantum Hall onset near 0.4 T and disobeys the Streda relation, indicating compressible charge exchange between itinerant holes and the transport-inert WC background. Our results establish rhombohedral graphene as a platform for exploring novel electron crystals, as well as possible nontrivial topology, and new collective modes.

  PublisherOA PDF

• Evidence of Metallic Wigner Crystal in Rhombohedral Graphene

  arXiv (Cornell University) · 2026-03-31

  preprintOpen access

  When the Coulomb interaction dominates over kinetic energy, electrons can crystallize into a Wigner crystal (WC). This paradigmatic correlated electronic phase has been realized in two-dimensional electron gases with parabolic band dispersion and completely flat Landau levels under high magnetic fields. Beyond these conventional contexts of electron crystallization, more exotic electron crystals have been postulated but remain unexplored. For example, a metallic Wigner crystal (mWC), in which itinerant carriers coexist with a pinned electron lattice, has been proposed theoretically but considered difficult to realize. Non-parabolic electron bands and quantum geometry may facilitate mWC and other novel topological electron crystals. Here we report transport evidence for WC and mWC in rhombohedral tetra-, penta-, and hexalayer graphene in the charge density range 0.3-0.5x10^12 cm^-2. By flattening the conduction band with a gate-controlled displacement field D, we observe an insulating state at nonzero charge density that shows nonlinear, hysteretic current-voltage relations, signatures of a pinned WC, that are absent from the lower-density insulator. Further increasing D reveals transport dominated by hole-like carriers with density up to only 15% of the nominal electron density, consistent with mWC. This mWC state is closely tied to the WC state, as both collapse simultaneously with increasing temperature or bias voltage. The mWC state shows quantum Hall onset near 0.4 T and disobeys the Streda relation, indicating compressible charge exchange between itinerant holes and the transport-inert WC background. Our results establish rhombohedral graphene as a platform for exploring novel electron crystals, as well as possible nontrivial topology, and new collective modes.

  PublisherDOI

• Moiré band structure engineering using a twisted boron nitride substrate

  Nature Communications · 2025-01-02 · 26 citations

  articleOpen access

  Applying long wavelength periodic potentials on quantum materials has recently been demonstrated to be a promising pathway for engineering novel quantum phases of matter. Here, we utilize twisted bilayer boron nitride (BN) as a moiré substrate for band structure engineering. Small-angle-twisted bilayer BN is endowed with periodically arranged up and down polar domains, which imprints a periodic electrostatic potential on a target two-dimensional (2D) material placed on top. As a proof of concept, we use Bernal bilayer graphene as the target material. The resulting modulation of the band structure appears as superlattice resistance peaks, tunable by varying the twist angle, and Hofstadter butterfly physics under a magnetic field. Additionally, we demonstrate the tunability of the moiré potential by altering the dielectric thickness underneath the twisted BN. Finally, we find that near-60°-twisted bilayer BN also leads to moiré band features in bilayer graphene, which may come from the in-plane piezoelectric effect or out-of-plane corrugation effect. Tunable twisted BN substrate may serve as versatile platforms to engineer the electronic, optical, and mechanical properties of 2D materials and van der Waals heterostructures.

  PublisherOA PDFDOI

• Displacement Field-Controlled Fractional Chern Insulators and Charge Density Waves in a Graphene/hBN Moiré Superlattice

  Physical Review X · 2025-06-11 · 8 citations

  preprintOpen accessSenior author

  Rhombohedral stacked graphene (RSG) contains two key ingredients for the realization of correlated topological phases of matter: flat electronic bands and concentrated Berry curvature. The fractional quantum anomalous Hall effect was recently observed in an RSG-hexagonal boron nitride (hBN) moiré heterostructure when the conduction electrons were pushed away from the moiré interface by an applied electric displacement field. The question then arises about whether such topological states can also develop in RSG-hBN in a strong moiré potential. Here, we explore the physics in the moiré-proximal limit through capacitance measurements that allow us to determine the electronic compressibility and extract energy gaps of incompressible states. We report the observation of integer and fractional Chern insulator states at low magnetic field in this limit at filling factors <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>ν</a:mi><a:mo>=</a:mo><a:mn>1</a:mn></a:math>, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>2</c:mn><c:mo>/</c:mo><c:mn>3</c:mn></c:math>, and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>1</e:mn><e:mo>/</e:mo><e:mn>3</e:mn></e:math> in addition to numerous trivial and topological charge density waves. We map out a correlated phase diagram that is highly sensitive to both displacement and magnetic fields, establishing the moiré-proximal regime as a tunable platform for studying the interplay between band topology and strong lattice effects.

  PublisherDOI

• Creating and Probing Large Gap 2D Topological Insulators for Quantum Computing (Final Report)

  2025-04-28

  reportOpen access

  Research under this award focused on experimental and theoretical efforts in developing and characterizing 2D topological insulators (TIs). Key areas of investigation included materials synthesis, device fabrication and characterization, and theoretical advancements. The team synthesized ZrTe5, a material with potential for TI phases. Additionally, the team pursued the synthesis of elemental thin films like Indene and Bismuthene, known for their large TI gaps. Indene was successfully stabilized on SiC. Another approach involved stacking and twisting transition metal dichalcogenides (TMDs) to engineer desired TI band structures. On the theoretical front, advancements made under this award predicted remarkable topological properties in twisted WSe2 bilayers, motivating experimental efforts to realize these states. Regarding device fabrication and characterization, significant progress was made in reducing contact resistance, crucial for reliable transport measurements. Contactless Pulsed Tunneling Spectroscopy (CPTS) was employed to study the electronic properties of WTe2 and WSe2. However, challenges in device fabrication and electrode material selection hampered efforts to obtain desired spectra. Ancillary work, utilizing pulsed electrical methods, on the study of sliding ferroelectrics yielded impactful results demonstrating high speed operation and lack of degradation of devices after many billions of cycles.

  PublisherOA PDFDOI

• Ultrafast high-endurance memory based on sliding ferroelectrics

  Science · 2024 · 154 citations

  Senior authorCorresponding
  • Materials science
  • Physical medicine and rehabilitation
  • Medicine

  switching cycles, comparable to state-of-the-art FeFET devices. These characteristics highlight the potential of 2D sliding ferroelectrics for inspiring next-generation nonvolatile memory technology.

  PublisherDOI

• Band structure engineering using a moiré polar substrate

  arXiv (Cornell University) · 2024-05-06

  preprintOpen access

  Applying long wavelength periodic potentials on quantum materials has recently been demonstrated to be a promising pathway for engineering novel quantum phases of matter. Here, we utilize twisted bilayer boron nitride (BN) as a moiré substrate for band structure engineering. Small-angle-twisted bilayer BN is endowed with periodically arranged up and down polar domains, which imprints a periodic electrostatic potential on a target two-dimensional (2D) material placed on top. As a proof of concept, we use Bernal bilayer graphene as the target material. The resulting modulation of the band structure appears as superlattice resistance peaks, tunable by varying the twist angle, and Hofstadter butterfly physics under a magnetic field. Additionally, we demonstrate the tunability of the moiré potential by altering the dielectric thickness underneath the twisted BN. Finally, we find that near-60°-twisted bilayer BN provides a unique platform for studying the moiré structural effect without the contribution from electrostatic moiré potentials. Tunable moiré polar substrates may serve as versatile platforms to engineer the electronic, optical, and mechanical properties of 2D materials and van der Waals heterostructures.

  PublisherOA PDFDOI

• Superconductivity and strong interactions in a tunable moiré quasiperiodic crystal

  arXiv (Cornell University) · 2023-02-01 · 8 citations

  preprintOpen access

  Electronic states in quasiperiodic crystals generally preclude a Bloch description, rendering them simultaneously fascinating and enigmatic. Owing to their complexity and relative scarcity, quasiperiodic crystals are underexplored relative to periodic and amorphous structures. Here, we introduce a new type of highly tunable quasiperiodic crystal easily assembled from periodic components. By twisting three layers of graphene with two different twist angles, we form two moiré patterns with incommensurate moiré unit cells. In contrast to many common quasiperiodic structures that are defined on the atomic scale, the quasiperiodicity in our system is defined on moiré length scales of several nanometers. This novel "moiré quasiperiodic crystal" allows us to tune the chemical potential and thus the electronic system between a periodic-like regime at low energies and a strongly quasiperiodic regime at higher energies, the latter hosting a large density of weakly dispersing states. Interestingly, in the quasiperiodic regime we observe superconductivity near a flavor-symmetry-breaking phase transition, the latter indicative of the important role electronic interactions play in that regime. The prevalence of interacting phenomena in future systems with in situ tunability is not only useful for the study of quasiperiodic systems, but it may also provide insights into electronic ordering in related periodic moiré crystals. We anticipate that extending this new platform to engineer quasiperiodic crystals by varying the number of layers and twist angles, and by using different two-dimensional components, will lead to a new family of quantum materials to investigate the properties of strongly interacting quasiperiodic crystals.

  PublisherOA PDFDOI

• Time, momentum, and energy resolved pump-probe tunneling spectroscopy of two-dimensional electron systems

  Figshare · 2023-01-01

  datasetOpen accessSenior author

  Tunneling spectra data and calculated spectral functions.

  PublisherDOI

• Superconductivity and strong interactions in a tunable moiré quasicrystal

  Nature · 2023 · 143 citations

  • Condensed matter physics
  • Physics
  • Materials science
  PublisherDOI

Frequent coauthors

• L. N. Pfeiffer

  53 shared

• K. W. West

  Princeton University

  37 shared

• Kenji Watanabe

  National Institute for Materials Science

  23 shared

• Pablo Jarillo‐Herrero

  22 shared

• Takashi Taniguchi

  20 shared

• Nikolai B. Zhitenev

  16 shared

• Heun Mo Yoo

  University of California, Santa Barbara

  13 shared

• Benjamin Hunt

  13 shared

Awards & honors

• David and Lucille Packard Fellowship (1993)
• NSF Young Investigator Award (1993)
• Sloan Fellow (1993)
• McMillan Award (1994)
• APS Fellow (2009)