About

Professor James N. Eckstein received his bachelor's degree in physics from St. Olaf College in 1973 and his Ph.D. in physics from Stanford University in 1978. He joined the Department of Physics at the University of Illinois in 1997 after spending 15 years as a senior scientist and research manager at Varian Associates in Palo Alto, California. He is widely recognized as a pioneer in developing techniques for growing high-quality oxide thin films, which are used to investigate the fundamental properties of cuprate superconductors and oxide magnetic materials. His development of atomic layer-by-layer molecular beam epitaxy (MBE) has enabled research on oxide films at new levels of precision and sophistication. Professor Eckstein's work, in collaboration with researchers at Illinois, Stanford, and Berkeley, has been central to recent advances in superconductor research, including measurements of angle-resolved photoemission and terahertz conductivity. His group has also developed some of the best planar tunneling junctions with oxide superconductors and oxide magnets. His studies of magnetic tunneling in oxides have provided insights into the role of defects in limiting the temperature range over which such junctions exhibit significant magnetotransport effects. His research program on thin-film manganites has contributed significantly to understanding these complex materials. He holds six U.S. patents and has made substantial contributions to the fields of superconducting and magnetic materials, focusing on colossal magnetoresistance, tunneling phenomena, and spin-valve structures using molecular beam epitaxy.

Research topics

• Condensed matter physics
• Physics
• Quantum mechanics
• Optoelectronics
• Materials science
• Geometry
• Geology
• Optics
• Chemistry
• Combinatorics
• Mathematics
• Nuclear magnetic resonance

Selected publications

• Molecular beam epitaxy—a path to novel high T _c superconductors?

  WORLD SCIENTIFIC eBooks · 2025-10-01

  book-chapter
  PublisherDOI

• Topological Surface Superconductivity via Josephson Coupling in Bi ₂ Te ₃ /Nb

  Nano Letters · 2025-11-08

  articleOpen access

  Since discoveries of protected conducting surface states, topological superconducting qubits have enchanted quantum science as prime elements in future fault-tolerant devices, particularly those based on Josephson junctions containing topological insulators. Still, Josephson coupling is often eclipsed by other proximity effects that can dilute topological superconducting pairing at the nontrivial insulator’s boundaries. Here, however, using an ultra-low-temperature scanning tunneling microscope, we detect Josephson physics in topological Bi2Te3 films on superconducting Nb. At low temperatures, a previously undetected proximity gap varies little with Bi2Te3 thickness and the density of states exhibits normal and superconducting components. Such observations are rationalized via Josephson pair tunneling through the (nearly) insulating Bi2Te3 bulk, creating a rare, pure topological superconducting sheet. Our findings establish routes toward accessible topological superconducting states in qubits.

  PublisherDOI

• Uniform Diffusion of Cooper Pairing Mediated by Hole Carriers in Topological Sb ₂ Te ₃ /Nb

  ACS Nano · 2024-10-29 · 4 citations

  articleOpen access

  Spin-helical Dirac Fermions at a doped topological insulator’s boundaries can support Majorana quasiparticles when coupled with s-wave superconductors, but in n-doped systems, the requisite induced Cooper pairing in topological states is often buried at heterointerfaces or complicated by degenerate coupling with bulk conduction carriers. Rarely probed are p-doped topological structures with nondegenerate Dirac and bulk valence bands at the Fermi level, which may foster long-range superconductivity without sacrificing Majorana physics. Using ultrahigh-resolution photoemission, we report proximity pairing with a large decay length in p-doped topological Sb2Te3 on superconducting Nb. Despite no momentum-space degeneracy, the topological and bulk states of Sb2Te3/Nb exhibit the same isotropic superconducting gaps at low temperatures. Our results unify principles for realizing accessible pairing in Dirac Fermions relevant to topological superconductivity.

  PublisherOA PDFDOI

• Terahertz-mediated microwave-to-optical transduction

  Physical review. A/Physical review, A · 2024-04-10 · 2 citations

  article

  Transduction of quantum signals between the microwave and the optical ranges will unlock powerful hybrid quantum systems enabling information processing with superconducting qubits and low-noise quantum networking through optical photons. Most microwave-to-optical quantum transducers suffer from thermal noise due to pump absorption. We analyze the coupled thermal and wave dynamics in electro-optic transducers that use a two-step scheme based on an intermediate frequency state in the THz range. Our analysis, supported by numerical simulations, shows that the two-step scheme operating with a continuous pump offers near-unity external efficiency with a multiorder noise suppression compared to single-step transduction. As a result, two-step electro-optic transducers may enable quantum-noise-limited interfacing of superconducting quantum processors with optical channels at MHz-scale bit rates.

  PublisherDOI

• Terahertz-Mediated Microwave-to-Optical Transduction

  arXiv (Cornell University) · 2023-07-07

  preprintOpen access

  Transduction of quantum signals between the microwave and the optical ranges will unlock powerful hybrid quantum systems enabling information processing with superconducting qubits and low-noise quantum networking through optical photons. Most microwave-to-optical quantum transducers suffer from thermal noise due to pump absorption. We analyze the coupled thermal and wave dynamics in electro-optic transducers that use a two-step scheme based on an intermediate frequency state in the THz range. Our analysis, supported by numerical simulations, shows that the two-step scheme operating with a continuous pump offers near-unity external efficiency with a multi-order noise suppression compared to direct transduction. As a result, two-step electro-optic transducers may enable quantum noise-limited interfacing of superconducting quantum processors with optical channels at MHz-scale bitrates.

  PublisherOA PDFDOI

• Interference, diffraction, and diode effects in superconducting array based on bismuth antimony telluride topological insulator

  Communications Physics · 2023 · 15 citations

  • Physics
  • Optics
  • Optoelectronics

  Abstract It is well-known in optics that the spectroscopic resolution of a diffraction grating is much better compared to an interference device having just two slits, as in Young’s famous double-slit experiment. On the other hand, it is well known that a classical superconducting quantum interference device (SQUID) is analogous to the optical double-slit experiment. Here we report experiments and present a model describing a superconducting analogue to the diffraction grating, namely an array of superconducting islands positioned on a topological insulator film Bi 0.8 Sb 1.2 Te 3 . In the limit of an extremely weak field, of the order of one vortex per the entire array, such devices exhibit a critical current peak that is much sharper than the analogous peak of an ordinary SQUID. Therefore, such arrays can be used as sensitive absolute magnetic field sensors. A key finding is that the device acts as a superconducting diode, controlled by magnetic field.

  PublisherOA PDFDOI

• Erratum: “Thermoelectric transport contribution from topological surface states vs 2D-electron gas in 10 nm Bi2Se3” [J. Appl. Phys. 132, 164301 (2022)]

  Journal of Applied Physics · 2023-10-13

  erratumOpen access

  Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Lakshmi Amulya Nimmagadda, Yang Bai, Manjunath C. Rajagopal, Soorya Suresh Babu, James N. Eckstein, Sanjiv Sinha; Erratum: “Thermoelectric transport contribution from topological surface states vs 2D-electron gas in 10 nm Bi2Se3” [J. Appl. Phys. 132, 164301 (2022)]. J. Appl. Phys. 14 October 2023; 134 (14): 149901. https://doi.org/10.1063/5.0174773 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioJournal of Applied Physics Search Advanced Search |Citation Search

  PublisherOA PDFDOI

• Interference, diffraction, and diode effects in superconducting array based on Bi0.8Sb1.2Te3 topological insulator

  arXiv (Cornell University) · 2022-09-28 · 1 citations

  preprintOpen access

  It is a well known phenomenon in optics that spectroscopic resolution of a diffraction grating is much better compared to an interference device having just two slits, as in the Young's famous double-slit experiment. On the other hand, it is well known that a classical superconducting quantum interference device (SQUID) is analogous to the optical double-slit experiment. Here we report experiments and present a model describing a superconducting analogue to the diffraction grating, namely an array of superconducting islands positioned on a topological insulator (TI) film Bi0.8Sb1.2Te3. In the limit of extremely weak field, of the order of one vortex per the entire array, such devices exhibit a critical current peak that is much sharper than the analogous peak of an ordinary SQUID. Because of this, such arrays can be used as sensitive absolute magnetic field sensors. An important finding is that, due to the inherent asymmetry of such arrays, the device also acts as a superconducting diode.

  PublisherOA PDFDOI

• Thermoelectric transport contribution from topological surface states vs 2D-electron gas in 10 nm Bi2Se3

  Journal of Applied Physics · 2022-10-24 · 2 citations

  article

  Topological surface states (TSSs) coexist with a rapidly formed two-dimensional electron gas (2DEG) at the surface of Bi2Se3. While this complex band structure has been widely studied for its interactions between the two states in terms of electrical conductivity and carrier density, the resulting thermopower has not been investigated as thoroughly. Here, we report measurements of the temperature dependent Seebeck coefficient (S) and electrical conductivity (σ) on an undoped 10 nm thin Bi2Se3 film over the temperature range of 100–300 K to find an overall metal-like behavior. The measured S is consistent with the theory when assuming that both the TSS and the 2DEG contribute to thermoelectric transport. Our analysis further shows that the coefficient corresponds to a Fermi level situated well above the conduction band minima of the 2DEG, resulting in comparable contributions from the TSS and the 2DEG. The thermoelectric power factor (S2σ) at 300 K increases by 10%–30% over the bulk. This work provides insights into understanding and enhancing thermoelectric phenomena in topological insulators.

  PublisherDOI

• Quantifying superconducting proximity pairing in topological (Bi 1-x Sb x ) 2 Te 3 films on niobium substrates

  Bulletin of the American Physical Society · 2021-03-16

  article
  Publisher

Recent grants

• ITR: Toward Agile Information Networks: Electro-Optic Frequency Shifter

  NSF · $268k · 2000–2003

• Topological Insulator to Superconductor Junctions

  NSF · $345k · 2011–2015

Frequent coauthors

• I. Božović

  Brookhaven National Laboratory

  56 shared

• Xiaofang Zhai

  38 shared

• Seongshik Oh

  Rutgers, The State University of New Jersey

  37 shared

• Jian‐Min Zuo

  30 shared

• Maitri Warusawithana

  University of North Florida

  28 shared

• Anand Bhattacharya

  Argonne National Laboratory

  26 shared

• J. Orenstein

  University of California, Berkeley

  25 shared

• J. O’Donnell

  University of Oxford

  21 shared