About

Mohit Randeria is a professor in the Department of Physics at The Ohio State University. His areas of expertise include Condensed Matter Theory, Strong Correlations in Solids and Cold Atoms, High Temperature Superconductivity, Ultracold atomic gases such as BCS-BEC Crossover and Optical Lattices, as well as Magnetism, Disorder, and Nanoscale Inhomogeneity in Oxides. He holds a Ph.D. in Physics from Cornell University obtained in 1987, a Master's degree in Physics from the California Institute of Technology earned in 1982, and a B. Tech. in Electrical Engineering from IIT Delhi, India, completed in 1980. Randeria is recognized as a Fellow of the American Physical Society since 2008. His research focuses on understanding complex phenomena in condensed matter physics, particularly related to superconductivity and ultracold atomic gases, contributing to the broader understanding of strongly correlated systems.

Research topics

• Condensed matter physics
• Physics
• Materials science
• Quantum mechanics
• Statistical physics

Selected publications

• Understanding insulating ferromagnetism in LaCoO3 films under tensile strain

  arXiv (Cornell University) · 2026-04-06

  preprintOpen access

  LaCoO3 thin films grown under epitaxial tensile strain exhibit a robust ferromagnetic insulating state that is absent in the bulk. Despite many studies, both experimental and computational, the microscopic origin of this phenomenon is not well understood. In this work, density functional theory calculations are used to systematically investigate the magnetic ground state of stoichiometric LaCoO3 under epitaxial strain equivalent to that imposed by a SrTiO3 substrate. The results identify a ferromagnetic insulating ground state characterized by a unique ordered array of high-spin (HS) and low-spin (LS) Co3+ ions. The spin state ordering is best described as 2 x 2 columns that consist of alternating HS and LS Co3+ ions, separated by planes of LS Co3+ ions. This leads to HS-LS-LS repeating sequence of Co3+ ions in both pseudocubic [100] and [010] directions. Analysis of the electronic structure confirms the presence of an insulating gap. Evaluation of the superexchange interactions reveal ferromagnetic interactions between HS Co3+ ions via 90 degree paths, and antiferromagnetic interactions via 180 degree paths, both of which are facilitated by empty sigma* (eg) orbitals on the diamagnetic LS Co3+ ions. The strength and number of 90 degree ferromagnetic interactions are sufficient to overcome the competing 180 degree antiferromagnetic interactions stabilizing a ferromagnetic insulating state.

  PublisherDOI

• Understanding insulating ferromagnetism in LaCoO3 films under tensile strain

  ArXiv.org · 2026-04-06

  articleOpen access

  LaCoO3 thin films grown under epitaxial tensile strain exhibit a robust ferromagnetic insulating state that is absent in the bulk. Despite many studies, both experimental and computational, the microscopic origin of this phenomenon is not well understood. In this work, density functional theory calculations are used to systematically investigate the magnetic ground state of stoichiometric LaCoO3 under epitaxial strain equivalent to that imposed by a SrTiO3 substrate. The results identify a ferromagnetic insulating ground state characterized by a unique ordered array of high-spin (HS) and low-spin (LS) Co3+ ions. The spin state ordering is best described as 2 x 2 columns that consist of alternating HS and LS Co3+ ions, separated by planes of LS Co3+ ions. This leads to HS-LS-LS repeating sequence of Co3+ ions in both pseudocubic [100] and [010] directions. Analysis of the electronic structure confirms the presence of an insulating gap. Evaluation of the superexchange interactions reveal ferromagnetic interactions between HS Co3+ ions via 90 degree paths, and antiferromagnetic interactions via 180 degree paths, both of which are facilitated by empty sigma* (eg) orbitals on the diamagnetic LS Co3+ ions. The strength and number of 90 degree ferromagnetic interactions are sufficient to overcome the competing 180 degree antiferromagnetic interactions stabilizing a ferromagnetic insulating state.

  PublisherOA PDF

• Enhancement of Curie temperature in ferromagnetic insulator-topological insulator heterostructures

  Reports on Progress in Physics · 2026-01-01

  articleOpen accessSenior author

  Abstract We theoretically analyze the topological insulator (TI) surface state mediated interactions between local moments in a proximate 2D ferromagnetic insulator (FMI) motivated by recent experiments that show a significant increase in the Curie temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> of FMI-TI heterostructures. Such interactions have been investigated earlier with a focus on dilute magnetic dopants in TIs. Our problem involves a dense set of moments for which we find that the short range Bloembergen–Rowland interaction, arising from virtual particle-hole transitions between the valence and conduction bands, dominates over the oscillatory Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction. We show that the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> enhancement is proportional to the Van Vleck susceptibility and that the spin-momentum locking of surface states leads to out-of-plane ferromagnetic order in the FMI. We investigate how the hybridization between top and bottom surfaces in a thin TI film impacts <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> enhancement, and show how our results can help understand recent experiments on atomically thin Cr 2 Te 3 -(Bi,Sb) 2 Te 3 . Our results advance the understanding of magnetic interactions relevant for TI-based spintronic and magnonic devices.

  PublisherDOI

• Andreev versus tunneling spectroscopy of unconventional flat-band superconductors

  Proceedings of the National Academy of Sciences · 2025-11-13 · 2 citations

  articleOpen accessCorresponding

  Andreev spectroscopy is one of the few phase-sensitive experiments done on moiré graphene superconductors (SC) that can shed light on the pairing symmetry. Its interpretation however is unclear, as Scanning tunneling microscopy (STM) experiments in the Andreev and tunneling regimes show two distinct energy scales whose origin is mysterious. We show using a Green's function formulation that the two energy scales cannot be understood as a SC gap in the Andreev spectra and a pseudogap in tunneling. We also show that the ballistic Andreev regime can never be realized in moire SCs as the large mismatch in the Fermi velocity [Formula: see text] of the flat-band SC and the STM tip renormalizes a transparent interface toward the tunneling regime. We discuss self-energy corrections to [Formula: see text] that determines the conductance. Finally, we model the Andreev experiment as a circular metallic disc embedded in an unconventional SC. With strong [Formula: see text] mismatch the low bias conductance is dominated by tip-induced Andreev bound states, responsible for the low energy scale distinct from the SC gap seen in tunneling.

  PublisherDOI

• Transition of Néel‐Type and Bloch‐Néel Hybrid Skyrmion in a Metallic Multilayer Material System

  Advanced Materials · 2025-10-17 · 2 citations

  articleOpen access

  Magnetic skyrmions, which are stable, topologically protected spin structures, have garnered significant interest for their potential in revolutionizing spintronic applications. This study reveals the room-temperature coexistence of Néel-type and Bloch-Néel hybrid skyrmions in [Pt/Co/Cu] multilayers grown by molecular beam epitaxy (MBE). Pulse current is used to switch the skyrmion type and modulate the stability of the skyrmions. The thermal effect on the stability of the skyrmions due to the current pulse is also investigated. The work unveils a broad magnetic phase space, offering unprecedented control over skyrmion states in metallic multilayers with broken inversion symmetry. These findings pave the way for diverse applications in spintronics, including binary data encoding, and provide a novel framework for the manipulation of multi-type skyrmions.

  PublisherOA PDFDOI

• Andreev versus Tunneling Spectroscopy of Unconventional Flat Band Superconductors

  ArXiv.org · 2025-03-10

  preprintOpen access

  STM experiments in the tunneling and Andreev regimes on graphene-based moire superconductors (SC) show two distinct energy scales whose origin is mysterious. We express the conductance of a normal-SC interface in terms of Green's functions, which allows us to sharpen the issues in two ways. First, we show that the two distinct energy scales cannot be understood in terms of a pseudogap in tunneling and a superconducting gap in the Andreev spectra. Second, the large Fermi velocity vF mismatch between the STM tip and the at band SC renormalizes a transparent interface towards the tunneling regime, and the ballistic Andreev regime cannot be realized in moire SCs. We also discuss self energy corrections to vF that determines the conductance. Finally, we offer a resolution to these problems by modeling the Andreev experiment as a circular metallic disc embedded in an unconventional SC. We show that with strong vF mismatch the low bias conductance is dominated by Andreev bound states induced by the tip at the interface with the unconventional SC. The ABS give rise to the low energy scale seen in Andreev experiments, smaller than the SC gap in tunneling spectroscopy.

  PublisherOA PDFDOI

• Enhancement of Curie Temperature in Ferromagnetic Insulator-Topological Insulator Heterostructures

  ArXiv.org · 2025-10-23

  preprintOpen accessSenior author

  We theoretically analyze the topological insulator (TI) surface state mediated interactions between local moments in a proximate 2D ferromagnetic insulator (FMI) motivated by recent experiments that show a significant increase in the Curie temperature Tc of FMI-TI heterostructures. Such interactions have been investigated earlier with a focus on dilute magnetic dopants in TIs. Our problem involves a dense set of moments for which we find that the short range Bloembergen-Rowland interaction, arising from virtual particle-hole transitions between the valence and conduction bands, dominates over the oscillatory Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. We show that the Tc enhancement is proportional to the Van Vleck susceptibility and that the spin-momentum locking of surface states leads to out-of-plane ferromagnetic order in the FMI. We investigate how the hybridization between top and bottom surfaces in a thin TI film impacts Tc enhancement, and show how our results can help understand recent experiments on atomically thin Cr2Te3-(Bi,Sb)2Te3.

  PublisherOA PDFDOI

• Emergent Ferromagnetism at LaFeO₃/SrTiO₃ Interface Arising from a Strain‐Induced Spin‐State Transition

  Advanced Materials Interfaces · 2025-05-22 · 4 citations

  articleOpen access

  Abstract Creating new interfacial magnetic states with desired functionalities is attractive for fundamental studies and spintronics applications. The emergence of interfacial magnetic phases demands the fabrication of pristine interfaces and the characterization and understanding of atomic structure as well as electronic, magnetic, and orbital degrees of freedom at the interface. Here, a novel interfacial insulating ferromagnetic order in epitaxial films of LaFeO 3 grown on SrTiO 3 characterized by a combination of electron microscopy and spectroscopy, magnetometry, and density functional theory, is reported. The epitaxial strain drives a spin‐state disproportionation in the interfacial layer of LaFeO 3 , which leads to a checkerboard arrangement of low‐ and high‐spin Fe 3+ ions inside smaller and larger FeO 6 octahedra, respectively. Ferromagnetism at the interface arises from superexchange interactions between the low‐ and high‐spin Fe 3+ . Moving away from the interface the structure relaxes and the antiferromagnetic order seen in bulk LaFeO 3 is restored. It demonstrates how strain‐induced spin‐state disproportionation at the interface creates a novel ferromagnetic superexchange interaction in magnetic insulators, offering a new pathway to engineer interfacial magnetism for spintronic applications.

  PublisherOA PDFDOI

• Enhanced ferromagnetism in monolayer Cr₂Te₃ via topological insulator coupling

  Reports on Progress in Physics · 2025-05-27 · 9 citations

  articleOpen accessCorresponding

  Abstract Exchange-coupled interfaces are pivotal in exploiting two-dimensional (2D) ferromagnetism. Due to the extraordinary correlations among charge, spin, orbital and lattice degrees of freedom, layered magnetic transition metal chalcogenides (TMCs) bode well for exotic topological phenomena. Here we report the realization of wafer-scale Cr 2 Te 3 down to monolayer (ML) on insulating SrTiO 3 (111) and/or Al 2 O 3 (001) substrates using molecular beam epitaxy. Robust ferromagnetism persists in the 2D limit. In particular, the Curie temperature T C of 2 ML Cr 2 Te 3 increases from 100 K to ∼120 K when proximitized to topological insulator (TI) (Bi,Sb) 2 Te 3 , with substantially boosted magnetization as observed via polarized neutron reflectometry. Our experiments and theory strongly indicate that the Bloembergen–Rowland interaction is likely universal underlying T C enhancement in TI-coupled magnetic heterostructures. The topological-surface-enhanced magnetism in 2D TMC enables further exchange coupling physics and quantum hybrid studies, including paving the way to realize interface-modulated topological electronics.

  PublisherDOI

• Anomalous and Topological Hall Effects with Phase-Space Berry Curvatures: Electric, Thermal, and Thermoelectric Transport in Magnets

  arXiv (Cornell University) · 2024-09-06

  preprintOpen accessSenior author

  We develop a theory for the electrical and thermal transverse linear response functions such as the Hall, Nernst and thermal Hall effects in magnetic materials that harbor topological spin textures like skyrmions. In addition to the ordinary transverse response that arises from the Lorentz force due to the external magnetic field, there is an anomalous and a topological response. The intrinsic anomalous response derives from the momentum space Berry curvature arising from the spin-orbit coupling (SOC) in a system with a nonzero magnetization, while the topological response arises from real space Berry curvature related to the the topological charge density of the spin texture. To take into account all these effects on an equal footing, we develop a semiclassical theory that incorporates all phase-space Berry curvatures. We show within a controlled, semiclassical approach that all conductivities -- electrical, thermoelectric, and thermal Hall -- can be written as the sum of three contributions: ordinary, anomalous and topological, when the conduction electron SOC is weaker than the exchange coupling to the spin texture. All other contributions, including those arising from mixed real-momentum space Berry curvature, are negligible in the regime where our calculations are controlled. We derive various general relations that remain valid at low temperatures including the Weidemann-Franz relation between the electrical and thermal conductivities and the Mott relation between the thermoelectric and electrical conductivities. We also discuss how an in-plane Hall response arises in three-dimensional materials with sufficiently low symmetry. Finally, the Hall response is qualitatively different when the conduction electron SOC is stronger than the exchange coupling to the spin texture, where we find that the anomalous term dominates and the topological term vanishes.

  PublisherOA PDFDOI

Recent grants

• Strongly Interacting Fermions in Ultracold Atomic Gases and Correlated Materials

  NSF · $180k · 2010–2013

• Theoretical Investigations of Low Dimensional Quantum Materials

  NSF · $282k · 2014–2018

• Strong Correlations in Atomic Gases and Complex Materials

  NSF · $270k · 2007–2011

Frequent coauthors

• Nandini Trivedi

  137 shared

• M. R. Norman

  67 shared

• J. C. Campuzano

  56 shared

• J. C. Campuzano

  University of Illinois Chicago

  55 shared

• Adam Kaminski

  Ames National Laboratory

  47 shared

• Hong Ding

  47 shared

• H. M. Fretwell

  Iowa State University

  36 shared

• Amit Kanigel

  Technion – Israel Institute of Technology

  27 shared

Education

• PhD, Physics

  Cornell University

Awards & honors

• Fellow, American Physical Society - 2008