Debanjan Chowdhury
Assistant Professor
Overview
Our group works on a variety of problems in theoretical condensed matter Physics. The concept of quasiparticles, the longlived excitations above the ground state of a manybody system, which remain particlelike even in the presence of strong electronelectron interactions, has been immensely successful in describing the phenomenology of electronic systems. However, recent decades have seen an increasing number of challenges to these ideas, following the discovery of phenomena such as the fractional quantum Hall effect, ‘strange’ metals and frustrated quantum magnetism. A central theme of our research is the Physics of such strongly correlated quantum systems, where the effects of interaction can lead to the emergence of dramatic new collective phenomena, not describable in terms of the standard quasiparticlebased framework. Many of these problems are inspired by our quest for understanding experiments on a variety of exotic materials, such as unconventional superconductors, quantum spin liquids and nonFermi liquids, from a fundamental microscopic point of view.
Research Focus
My research is focused primarily on the study of strongly correlated quantum matter, using techniques from quantum field theory and quantum information.
Universal properties of incoherent metals:
There are a plethora of materials, such as the cuprates, the pnictides, the ruthenates, and more recently, twisted bilayers of graphene and transition metal dichalcogenides, that display a strong departure from conventional Fermi liquid behavior. This includes the mysterious observation of an electrical resistivity that scales linearly with temperature over a broad range of energy scales, and often down to shockingly low temperatures. One of the most remarkable empirical facts related to transport across these microscopically distinct systems is their apparent universality of (“Planckian”) scattering rates, controlled only by the ratio of k_{B}T/ℏ. Given the ubiquitous nature of these observations, some of the fundamental questions that I am interested in are (i) Can we formulate a universal effective theory for a subset of these nonFermi liquid metals?, (ii) What controls the emergent universality of the Planckian scattering rate?, and (iii) What is the relationship between chaotic properties of quantum manybody systems and transport, if any?
Superconductivity and quantum criticality in moiré materials:
The discovery of superconductivity and other competing orders in twisted bilayer graphene has ushered a new era of studying correlated quantum phenomena in a highly tunable platform. The key question of interest across these materials is tied to the lowenergy fate of electronic interactions projected to the “flat” bands. The problem is inherently nonperturbative, without any “small” parameter and requires the development of new theoretical tools. Additionally, the observation of continuous metalinsulator transitions and other correlated phenomena in moiré transition metal dichalcogenides allows us to revisit many classic unsolved problems in the field from a fresh perspective. Interestingly, understanding the experimental phenomenology across these platforms often involves analyzing the effects of interaction, disorder and topology in a highly nontrivial setting. The three questions that fascinate me are (i) Can we put universal constraints on the superconducting and transport properties of interacting flatband systems in these highly nonperturbative regimes?, (ii) What is the correct theoretical formulation going beyond the traditional LandauGinzburgWilson paradigm for the experimentally observed quantum phase transitions between metals and correlated insulators?, and (iii) How should we design new experiments that can help probe the frequency and momentumresolved correlation functions in these materials in the absence of many conventional scattering techniques?
Graduate Students
Juan Felipe MendezValderrama, Sunghoon Kim, Xuepeng Wang, Keiran Lewellen
Postdocs
Dan Mao (Bethe/KIC Fellow), Dimitri Pimenov
Publications

J.F. MendezValderrama*, E. Tulipman*, E. Zhakina, A.P. Mackenzie, E. Berg and Debanjan Chowdhury, Tlinear resistivity from magnetoelastic scattering: application to PdCrO2, arXiv:2301.10776.

D. Mao and Debanjan Chowdhury, Diamagnetic response and phase stiffness for interacting isolated narrow bands, Proceedings of the National Academy of Sciences, 120 (11), e2217816120 (2023).

S. Kim, A. Agarwala and Debanjan Chowdhury, Fractionalization and topology in amorphous electronic solids, Phys. Rev. Lett. 130, 026202 (2023).

S. Kim, T. Senthil and Debanjan Chowdhury, Continuous Mott transition in moiré semiconductors: role of longwavelength inhomogeneities, Phys. Rev. Lett. 130, 066301 (2023).

Debanjan Chowdhury, A. Georges, O. Parcollet and S. Sachdev, SachdevYeKitaev Models and Beyond: A Window into NonFermi Liquids, Rev. Mod. Phys. 94, 035004 (2022).

T. Li, S. Jiang, L. Li, Y. Zhang, K. Kang, J. Zhu, K. Watanabe, T. Taniguchi, Debanjan Chowdhury, L. Fu, J. Shan, K.F. Mak, Continuous Mott transition in semiconductor moiré superlattices, Nature 597, 350 (2021).

C. Lewandowski, S. NadjPerge and Debanjan Chowdhury, Does fillingdependent band renormalization aid pairing in twisted bilayer graphene?, npj Quantum Materials 6, 82 (2021).

L. Zou and Debanjan Chowdhury, Deconfined metallic quantum criticality: a U(2) gauge theoretic approach, Phys. Rev. Research 2, 023344 (2020).

J.S. Hofmann, E. Berg and Debanjan Chowdhury, Superconductivity, pseudogap and phase separation in topological flat bands, Phys. Rev. B 102, 201112(R) (2020).

Y. Cao*, Debanjan Chowdhury*, D. RodanLegrain, O. RubiesBigorda, K. Watanabe, T. Taniguchi, T. Senthil and P. JarilloHerrero, Strange metal in magicangle graphene with near Planckian dissipation, Phys. Rev. Lett. 124, 076801 (2020).

Debanjan Chowdhury, Y. Werman, E. Berg and T. Senthil, Translationally invariant nonFermi liquids with critical Fermisurfaces: Solvable models, Phys. Rev. X 8, 031024 (2018).

Debanjan Chowdhury, I. Sodemann and T. Senthil, Mixedvalence insulators with neutral Fermisurfaces, Nature Communications 9, 1766 (2018).

Debanjan Chowdhury and B. Swingle, Onset of manybody chaos in the O(N) model, Phys. Rev. D 96, 065005 (2017).

B. Swingle and Debanjan Chowdhury, Slow scrambling in disordered quantum systems, Phys. Rev. B 95, 060201(R) (2017).
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