About

Pallab Goswami is an Assistant Professor in the Department of Physics and Astronomy at Northwestern University. He earned his PhD from the University of California Los Angeles in 2008. His research focuses on condensed matter physics, specifically on studying emergent low temperature phases in correlated and disordered materials. His work involves developing theoretical tools to address emergent quantum phases and quantum phase transitions in strongly correlated and disordered materials, with an emphasis on their topological properties. Goswami's research is motivated by recent progress in quantum material science, which enables the study of the interplay between strong electronic interactions and spin orbit coupling in various compounds such as iridium-based oxides, Heusler, and heavy fermion systems. His studies explore phase diagrams that display competing orders, topological properties, and exotic quantum critical phenomena. He enjoys working on abstract theoretical problems and collaborates closely with experimental groups. His contributions include investigating magnetic Weyl fermions, topological quantum phase transitions, and the effects of disorder in quantum materials.

Research topics

• Condensed matter physics
• Physics
• Quantum mechanics
• Chemistry
• Mathematics
• Optics
• Metallurgy
• Nanotechnology
• Chemical physics
• Optoelectronics
• Materials science

Selected publications

• Entangling Power: A Probe of Symmetry and Integrability in Quantum Many-Body Systems

  arXiv (Cornell University) · 2026-05-20

  preprintOpen accessSenior author

  The entangling power of a unitary operator quantifies its ability to generate entanglement from product states and provides a natural probe of quantum many-body dynamics. Entanglement extremization at points of enhanced symmetry has previously been observed in high-energy scattering. In this work we compute the time-averaged entangling power of anisotropic Heisenberg spin chains across two-site models and finite-size systems, as well as the entangling power of the two-magnon $S$-matrix in the thermodynamic limit. For two-site models we establish a monotonic hierarchy: the entangling power decreases as the symmetry group grows, reaching its minimum at the $SU(2)$ XXX point. Finite-size XXZ chains exhibit sharp dips at the $SU(2)$ points $Δ=\pm 1$ and the free-fermion point $Δ=0$, with the free-fermion dip decaying much more slowly with system size. In the thermodynamic limit, we decompose the two-magnon $S$-matrix into quantum logic gates -- Identity, SWAP, and $σ_z\otimesσ_z$ -- and show that the entangling power vanishes for all scattering energies at the $SU(2)$ points, where the $S$-matrix reduces to the Identity gate, while the free-fermion point achieves the maximum -- the opposite of the finite-size many-body behavior. The entangling power can serve as an {\em operator} diagnostic for symmetry and selected aspects of integrability in quantum simulations of spin-chain dynamics.

  PublisherDOI

• Entangling Power: A Probe of Symmetry and Integrability in Quantum Many-Body Systems

  ArXiv.org · 2026-05-20

  articleOpen accessSenior author

  The entangling power of a unitary operator quantifies its ability to generate entanglement from product states and provides a natural probe of quantum many-body dynamics. Entanglement extremization at points of enhanced symmetry has previously been observed in high-energy scattering. In this work we compute the time-averaged entangling power of anisotropic Heisenberg spin chains across two-site models and finite-size systems, as well as the entangling power of the two-magnon $S$-matrix in the thermodynamic limit. For two-site models we establish a monotonic hierarchy: the entangling power decreases as the symmetry group grows, reaching its minimum at the $SU(2)$ XXX point. Finite-size XXZ chains exhibit sharp dips at the $SU(2)$ points $Δ=\pm 1$ and the free-fermion point $Δ=0$, with the free-fermion dip decaying much more slowly with system size. In the thermodynamic limit, we decompose the two-magnon $S$-matrix into quantum logic gates -- Identity, SWAP, and $σ_z\otimesσ_z$ -- and show that the entangling power vanishes for all scattering energies at the $SU(2)$ points, where the $S$-matrix reduces to the Identity gate, while the free-fermion point achieves the maximum -- the opposite of the finite-size many-body behavior. The entangling power can serve as an {\em operator} diagnostic for symmetry and selected aspects of integrability in quantum simulations of spin-chain dynamics.

  PublisherOA PDF

• Investigation of the Two-Dimensional Non-Hermitian Su–Schrieffer–Heeger Model

  Acta Physica Polonica A · 2025-08-19

  articleOpen accessSenior author

  This article presents an examination of a two-dimensional, non-Hermitian Su–Schrieffer–Heeger model, which differs from its conventional Hermitian counterpart by incorporating gain and/or loss terms, mathematically represented by imaginary on-site potentials. The time-reversal symmetry is disrupted due to these on-site potentials. Exceptional points in a non-Hermitian system feature eigenvalue coalescence and non-trivial eigenvector degeneracies. Utilization of the rank-nullity theorem and graphical analysis of the phase rigidity factor enables identification of true exceptional points. Furthermore, this investigation achieves vectorized Zak phase quantization and examines a topolectric resistors–inductors–capacitors circuit to derive the corresponding topological boundary resonance condition and the quantum Hall susceptance. Although Chern number quantization is not feasible, staggered hopping amplitudes corresponding to unit-cell lattice sites lead to broken inversion symmetry with non-zero Berry curvature, resulting in finite anomalous Nernst conductivity.

  PublisherOA PDFDOI

• Intrinsic magnetism in KTaO3 heterostructures

  Applied Physics Letters · 2024-02-26 · 13 citations

  articleOpen access

  There has been intense recent interest in the two-dimensional electron gases (2DEGs) that form at the surfaces and interfaces of KTaO3 (KTO), with the discovery of superconductivity at temperatures significantly higher than those of similar 2DEGs based on SrTiO3 (STO). Like STO heterostructures, these KTO 2DEGs are formed by depositing an overlayer on top of appropriately prepared KTO surfaces. Some of these overlayers are magnetic, and the resulting 2DEGs show signatures of this magnetism, including hysteresis in the magnetoresistance (MR). Here, we show that KTO 2DEGs fabricated by depositing AlOx on top of KTO also show hysteretic MR, indicative of long-range magnetic order, even though the samples nominally contain no intrinsic magnetic elements. The hysteresis appears in both the transverse and longitudinal resistance in magnetic fields both perpendicular to and in the plane of the 2DEG. The hysteretic MR has different characteristic fields and shapes for surfaces of different crystal orientations and vanishes above a few Kelvin. Density functional theory (DFT) calculations indicate that the magnetism likely arises from Ta4+ local moments created in the presence of oxygen vacancies.

  PublisherOA PDFDOI

• Real-space screening of quantum spin-Hall insulators

  Physical Review Materials · 2024-12-23

  articleSenior author

  It was shown by Prodan in 2009 that both magnetic and nonmagnetic two-dimensional insulators can support quantized spin-Chern number in the absence of spin-rotation symmetry as a bulk topological invariant, which is robust against impurity effects. Recent studies on higher-order and fragile topological insulators further demonstrate that the spin-Chern number can exist without gapless edge states. Therefore, the presence of generalized quantum spin-Hall states in real materials can be difficult to identify using only symmetry-based indicators and Wannier obstruction. Such phases require more sophisticated probes of bulk topology. Magnetic flux tube has emerged as one such singular real-space probe that leads to spin-charge separation and allows for a precise diagnosis of the spin-Chern number. In this paper, we develop an automated workflow to scan the database of experimentally relevant, large band-gap, two-dimensional insulators using magnetic flux tubes. The results reveal many material candidates of higher-order topological insulators possessing double spin-Chern number, including the 1H-${MX}_{2}$ family of transition metal dichalcogenides. Our paper has broad implications for current efforts to employ these materials for new platforms of moir\'e systems.

  PublisherDOI

• Nonlinear Hall Effect in KTaO$_3$ Two-Dimensional Electron Gases

  arXiv (Cornell University) · 2024-11-14

  preprintOpen access

  The observation of a Hall effect, a finite transverse voltage induced by a longitudinal current, usually requires the breaking of time-reversal symmetry, for example through the application of an external magnetic field or the presence of long range magnetic order in a sample. Recently it was suggested that under certain symmetry conditions, the presence of finite Berry curvatures in the band structure of a system with time-reversal symmetry but without inversion symmetry can give rise to a nonlinear Hall effect in the presence of a probe current. In order to observe the nonlinear Hall effect, one requires a finite component of a so-called Berry dipole along the direction of the probe current. We report here measurements of the nonlinear Hall effect in two-dimensional electron gases fabricated on the surface of KTaO$_3$ with different surface crystal orientations as a function of the probe current, a transverse electric field and back gate voltage. For all three crystal orientations, the transverse electric field modifies the nonlinear Hall effect. We discuss our results in the context of the current understanding of the nonlinear Hall effect as well as potential experimental artifacts that may give rise to the same effects.

  PublisherOA PDFDOI

• In-plane Wilson loop for measurement of quantized non-Abelian Berry flux

  Physical review. B./Physical review. B · 2024-05-15 · 3 citations

  articleOpen accessSenior author

  Band topology of anomalous quantum Hall insulators can be precisely addressed by computing the Chern numbers of constituent nondegenerate bands, describing the presence of quantized, Abelian Berry flux through the two-dimensional Brillouin zone. Can Berry flux be captured for the $SU(2)$ Berry connection of two-fold degenerate bands in spinful materials preserving space-inversion ($\mathcal{P}$) and time-reversal ($\mathcal{T}$) symmetries without detailed knowledge of underlying basis? We address this question by investigating the correspondence between a non-Abelian generalization of Stokes' theorem and the manifestly gauge-invariant eigenvalues of Wilson loops computed along in-plane contours which preserve the underlying crystalline symmetry. The importance of this correspondence is elucidated by performing natural number resolved classification of ab initio band structures of three-dimensional, Dirac materials. Our work underscores how identification of quantized Berry flux, both Abelian and non-Abelian, offers a unified framework for addressing first-order and higher-order topology of insulators and semimetals.

  PublisherOA PDFDOI

• Fundamentals of crystalline Hopf insulators

  arXiv (Cornell University) · 2023-01-19 · 3 citations

  preprintOpen accessSenior author

  Three-dimensional, crystalline Hopf insulators are generic members of unitary Wigner-Dyson class, which can break all global discrete symmetries and point group symmetries. In the absence of first Chern number for any two-dimensional plane of Brillouin zone, the Hopf invariant $N_H \in \mathbb{Z}$. But in the presence of Chern number $N_H \in \mathbb{Z}_{2q}$, where $q$ is the greatest common divisor of Chern numbers for $xy$, $yz$, and $xz$ planes of Brillouin zone. How does $N_H$ affect topological quantization of isotropic, magneto-electric coefficient? We answer this question with calculations of Witten effect for a test, magnetic monopole. Furthermore, we construct $N$-band tight-binding models of Hopf insulators and demonstrate their topological stability against spectral flattening.

  PublisherOA PDFDOI

• Topology of three-dimensional Dirac semimetals and quantum spin Hall systems without gapless edge modes

  Physical Review Research · 2023 · 10 citations

  Senior authorCorresponding
  • Physics
  • Condensed matter physics
  • Quantum mechanics

  A theoretical framework is outlined for calculating the spin-Chern number of topological Dirac semimetals and quantum spin Hall insulators lacking spin-conservation law and gapless edge modes. Spin-charge separation and quantized spin-pumping are probed by inserting a magnetic flux tube.

  PublisherOA PDFDOI

• Spin-charge separation and quantum spin Hall effect of $$\beta$$-bismuthene

  Scientific Reports · 2023 · 13 citations

  Senior authorCorresponding
  • Physics
  • Quantum mechanics
  • Condensed matter physics

  Multiple works suggest the possibility of classification of quantum spin Hall effect with magnetic flux tubes, which cause separation of spin and charge degrees of freedom and pumping of spin or Kramers-pair. However, the proof of principle demonstration of spin-charge separation is yet to be accomplished for realistic, ab initio band structures of spin-orbit-coupled materials, lacking spin-conservation law. In this work, we perform thought experiments with magnetic flux tubes on [Formula: see text]-bismuthene, and demonstrate spin-charge separation, and quantized pumping of spin for three insulating states, that can be accessed by tuning filling fractions. With a combined analysis of momentum-space topology and real-space response, we identify important role of bands supporting even integer invariants, which cannot be addressed with symmetry-based indicators. Our work sets a new standard for the computational diagnosis of two-dimensional, quantum spin-Hall materials by going beyond the [Formula: see text] paradigm and providing an avenue for precise determination of the bulk invariant through computation of quantized, real-space response.

  PublisherOA PDFDOI

Frequent coauthors

• Bitan Roy

  Lehigh University

  35 shared

• Qimiao Si

  30 shared

• Alexander C. Tyner

  Northwestern University

  24 shared

• Sudip Chakravarty

  University of California, Los Angeles

  23 shared

• Sumanta Tewari

  Clemson University

  18 shared

• S. Das Sarma

  Joint Quantum Institute

  16 shared

• Luis Balicas

  16 shared

• Rong Yu

  Renmin University of China

  14 shared

Labs

• Condensed Matter & Materials PhysicsPI

Education

• Ph.D.

  University of California Los Angeles

  2008

Awards & honors

• Dirac Postdoctoral Fellowship, National High Magnetic Field…
• G. K. Walters Postdoctoral Fellowship, Rice University (2008…