Stanford Advisors

All Publications

  • Thermodynamic evidence for a two-component superconducting order parameter in Sr2RuO4 NATURE PHYSICS Ghosh, S., Shekhter, A., Jerzembeck, F., Kikugawa, N., Sokolov, D. A., Brando, M., Mackenzie, A. P., Hicks, C. W., Ramshaw, B. J. 2021; 17 (2): 199-+
  • One-component order parameter in URu2Si2 uncovered by resonant ultrasound spectroscopy and machine learning SCIENCE ADVANCES Ghosh, S., Matty, M., Baumbach, R., Bauer, E. D., Modic, K. A., Shekhter, A., Mydosh, J. A., Kim, E., Ramshaw, B. J. 2020; 6 (10): eaaz4074


    The unusual correlated state that emerges in URu2Si2 below T HO = 17.5 K is known as "hidden order" because even basic characteristics of the order parameter, such as its dimensionality (whether it has one component or two), are "hidden." We use resonant ultrasound spectroscopy to measure the symmetry-resolved elastic anomalies across T HO. We observe no anomalies in the shear elastic moduli, providing strong thermodynamic evidence for a one-component order parameter. We develop a machine learning framework that reaches this conclusion directly from the raw data, even in a crystal that is too small for traditional resonant ultrasound. Our result rules out a broad class of theories of hidden order based on two-component order parameters, and constrains the nature of the fluctuations from which unconventional superconductivity emerges at lower temperature. Our machine learning framework is a powerful new tool for classifying the ubiquitous competing orders in correlated electron systems.

    View details for DOI 10.1126/sciadv.aaz4074

    View details for Web of Science ID 000519001400039

    View details for PubMedID 32181367

    View details for PubMedCentralID PMC7060057

  • Strong increase in ultrasound attenuation below T-c in Sr2RuO4: Possible evidence for domains PHYSICAL REVIEW B Ghosh, S., Kiely, T. G., Shekhter, A., Jerzembeck, F., Kikugawa, N., Sokolov, D. A., Mackenzie, A. P., Ramshaw, B. J. 2022; 106 (2)
  • Elastocaloric determination of the phase diagram of Sr2RuO4. Nature Li, Y., Garst, M., Schmalian, J., Ghosh, S., Kikugawa, N., Sokolov, D. A., Hicks, C. W., Jerzembeck, F., Ikeda, M. S., Hu, Z., Ramshaw, B. J., Rost, A. W., Nicklas, M., Mackenzie, A. P. 2022; 607 (7918): 276-280


    One of the main developments in unconventional superconductivity in the past two decades has been the discovery that most unconventional superconductors form phase diagrams that also contain other strongly correlated states. Many systems of interest are therefore close to more than one instability, and tuning between the resultant ordered phases is the subject of intense research1. In recent years, uniaxial pressure applied using piezoelectric-based devices has been shown to be a particularly versatile new method of tuning2,3, leading to experiments that have advanced our understanding of the fascinating unconventional superconductor Sr2RuO4 (refs.4-9). Here we map out its phase diagram using high-precision measurements of the elastocaloric effect in what we believe to be the first such study including both the normal and the superconducting states. We observe a strong entropy quench on entering the superconducting state, in excellent agreement with a model calculation for pairing at the Van Hove point, and obtain a quantitative estimate of the entropy change associated with entry to a magnetic state that is observed in proximity to the superconductivity. The phase diagram is intriguing both for its similarity to those seen in other families of unconventional superconductors and for extra features unique, so far, to Sr2RuO4.

    View details for DOI 10.1038/s41586-022-04820-z

    View details for PubMedID 35831597

  • Strong magnetoelastic coupling in Mn3X (X = Ge, Sn) PHYSICAL REVIEW B Theuss, F., Ghosh, S., Chen, T., Tchernyshyov, O., Nakatsuji, S., Ramshaw, B. J. 2022; 105 (17)
  • Role of correlations in determining the Van Hove strain in Sr2RuO4 PHYSICAL REVIEW B Barber, M. E., Lechermann, F., Streltsov, S., Skornyakov, S. L., Ghosh, S., Ramshaw, B. J., Kikugawa, N., Sokolov, D. A., Mackenzie, A. P., Hicks, C. W., Mazin, I. I. 2019; 100 (24)
  • Spatial control of heavy-fermion superconductivity in CeIrIn5 SCIENCE Bachmann, M. D., Ferguson, G. M., Theuss, F., Meng, T., Putzke, C., Helm, T., Shirer, K. R., Li, Y., Modic, K. A., Nicklas, M., Koenig, M., Low, D., Ghosh, S., Mackenzie, A. P., Arnold, F., Hassinger, E., McDonald, R. D., Winter, L. E., Bauer, E. D., Ronning, F., Ramshaw, B. J., Nowack, K. C., Moll, P. W. 2019; 366 (6462): 221-+


    Although crystals of strongly correlated metals exhibit a diverse set of electronic ground states, few approaches exist for spatially modulating their properties. In this study, we demonstrate disorder-free control, on the micrometer scale, over the superconducting state in samples of the heavy-fermion superconductor CeIrIn5 We pattern crystals by focused ion beam milling to tailor the boundary conditions for the elastic deformation upon thermal contraction during cooling. The resulting nonuniform strain fields induce complex patterns of superconductivity, owing to the strong dependence of the transition temperature on the strength and direction of strain. These results showcase a generic approach to manipulating electronic order on micrometer length scales in strongly correlated matter without compromising the cleanliness, stoichiometry, or mean free path.

    View details for DOI 10.1126/science.aao6640

    View details for Web of Science ID 000490014700039

    View details for PubMedID 31601766

  • Quadratic Magneto-Optic Kerr Effect Investigations of Fe(100) Grown on Ir(100) Pradeep, A. V., Ghosh, S., Ajesh, K. G., Kumar, P. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. 2017
  • Simple quadratic magneto-optic Kerr effect measurement system using permanent magnets REVIEW OF SCIENTIFIC INSTRUMENTS Pradeep, A. V., Ghosh, S., Kumar, P. 2017; 88 (1): 013901


    In recent times, quadratic magneto-optic Kerr effect (QMOKE) is emerging as an important experimental tool to investigate higher-order spin-orbit interactions in magnetic thin films and heterostructures. We have designed and constructed a simple, cost-effective QMOKE measurement system using permanent magnets. The permanent magnets are mounted on the inner surface of a cylindrical ferromagnetic yoke which can be rotated about its axis. Our system is sensitive to both the quadratic and linear MOKE signals. We use rotating field method to extract the QMOKE components in saturation. This system is capable of extracting the QMOKE signal from single crystals and thin film samples. Here we present the construction and working of the QMOKE measurement system using permanent magnets and report, for the first time, the QMOKE signal from Fe3O4 single crystal.

    View details for DOI 10.1063/1.4973419

    View details for Web of Science ID 000395396900032

    View details for PubMedID 28147657