All Publications

  • Emergent tetragonality in a fundamentally orthorhombic material. Science advances Singh, A. G., Bachmann, M. D., Sanchez, J. J., Pandey, A., Kapitulnik, A., Kim, J. W., Ryan, P. J., Kivelson, S. A., Fisher, I. R. 2024; 10 (21): eadk3321


    Symmetry plays a key role in determining the physical properties of materials. By Neumann's principle, the properties of a material remain invariant under the symmetry operations of the space group to which the material belongs. Continuous phase transitions are associated with a spontaneous reduction in symmetry. Less common are examples where proximity to a continuous phase transition leads to an increase in symmetry. We find signatures of an emergent tetragonal symmetry close to a charge density wave (CDW) bicritical point in a fundamentally orthorhombic material, ErTe3, for which the two distinct CDW phase transitions are tuned via anisotropic strain. We first establish that tension along the a axis favors an abrupt rotation of the CDW wave vector from the c to a axis and infer the presence of a bicritical point where the two continuous phase transitions meet. We then observe a divergence of the nematic elastoresistivity approaching this putative bicritical point, indicating an emergent tetragonality in the critical behavior.

    View details for DOI 10.1126/sciadv.adk3321

    View details for PubMedID 38781340

    View details for PubMedCentralID PMC11114214

  • Emergent Z2 symmetry near a charge density wave multicritical point PHYSICAL REVIEW B Kivelson, S. A., Pandey, A., Singh, A. G., Kapitulnik, A., Fisher, I. R. 2023; 108 (20)
  • Random geometry at an infinite-randomness fixed point PHYSICAL REVIEW B Pandey, A., Mahadevan, A., Cowsik, A. 2023; 108 (6)
  • A stability bound on the [Formula: see text]-linear resistivity of conventional metals. Proceedings of the National Academy of Sciences of the United States of America Murthy, C., Pandey, A., Esterlis, I., Kivelson, S. A. 2023; 120 (3): e2216241120


    Perturbative considerations account for the properties of conventional metals, including the range of temperatures where the transport scattering rate is 1/τtr = 2πλT, where λ is a dimensionless strength of the electron-phonon coupling. The fact that measured values satisfy λ ≲ 1 has been noted in the context of a possible "Planckian" bound on transport. However, since the electron-phonon scattering is quasielastic in this regime, no such Planckian considerations can be relevant. We present and analyze Monte Carlo results on the Holstein model which show that a different sort of bound is at play: a "stability" bound on λ consistent with metallic transport. We conjecture that a qualitatively similar bound on the strength of residual interactions, which is often stronger than Planckian, may apply to metals more generally.

    View details for DOI 10.1073/pnas.2216241120

    View details for PubMedID 36634139

  • Interstitial-Induced Ferromagnetism in a Two-Dimensional Wigner Crystal. Physical review letters Kim, K. S., Murthy, C., Pandey, A., Kivelson, S. A. 2022; 129 (22): 227202


    The two-dimensional Wigner crystal (WC) occurs in the strongly interacting regime (r_{s}≫1) of the two-dimensional electron gas (2DEG). The magnetism of a pure WC is determined by tunneling processes that induce multispin ring-exchange interactions, resulting in fully polarized ferromagnetism for large enough r_{s}. Recently, Hossain et al. [Proc. Natl. Acad. Sci. U.S.A. 117, 32244 (2020)PNASA60027-842410.1073/pnas.2018248117] reported the occurrence of a fully polarized ferromagnetic insulator at r_{s}≳35 in an AlAs quantum well, but at temperatures orders of magnitude larger than the predicted exchange energies for the pure WC. Here, we analyze the large r_{s} dynamics of an interstitial defect in the WC, and show that it produces local ferromagnetism with much higher energy scales. Three hopping processes are dominant, which favor a large, fully polarized ferromagnetic polaron. Based on the above results, we speculate concerning the phenomenology of the magnetism near the metal-insulator transition of the 2DEG.

    View details for DOI 10.1103/PhysRevLett.129.227202

    View details for PubMedID 36493455