Academic Appointments

2023-24 Courses

Stanford Advisees

All Publications

  • Fermi surface reconstruction in electron-doped cuprates without antiferromagnetic long-range order. Proceedings of the National Academy of Sciences of the United States of America He, J., Rotundu, C. R., Scheurer, M. S., He, Y., Hashimoto, M., Xu, K., Wang, Y., Huang, E. W., Jia, T., Chen, S., Moritz, B., Lu, D., Lee, Y. S., Devereaux, T. P., Shen, Z. 2019; 116 (9): 3449–53


    Fermi surface (FS) topology is a fundamental property of metals and superconductors. In electron-doped cuprate Nd2-x Ce x CuO4 (NCCO), an unexpected FS reconstruction has been observed in optimal- and overdoped regime (x = 0.15-0.17) by quantum oscillation measurements (QOM). This is all the more puzzling because neutron scattering suggests that the antiferromagnetic (AFM) long-range order, which is believed to reconstruct the FS, vanishes before x = 0.14. To reconcile the conflict, a widely discussed external magnetic-field-induced AFM long-range order in QOM explains the FS reconstruction as an extrinsic property. Here, we report angle-resolved photoemission (ARPES) evidence of FS reconstruction in optimal- and overdoped NCCO. The observed FSs are in quantitative agreement with QOM, suggesting an intrinsic FS reconstruction without field. This reconstructed FS, despite its importance as a basis to understand electron-doped cuprates, cannot be explained under the traditional scheme. Furthermore, the energy gap of the reconstruction decreases rapidly near x = 0.17 like an order parameter, echoing the quantum critical doping in transport. The totality of the data points to a mysterious order between x = 0.14 and 0.17, whose appearance favors the FS reconstruction and disappearance defines the quantum critical doping. A recent topological proposal provides an ansatz for its origin.

    View details for PubMedID 30808739

  • Enhancement and destruction of spin-Peierls physics in a one-dimensional quantum magnet under pressure PHYSICAL REVIEW B Rotundu, C. R., Wen, J., He, W., Choi, Y., Haskel, D., Lee, Y. S. 2018; 97 (5)
  • Synthesis dependent properties of barlowite and Zn-substituted barlowite Journal of Solid State Chemistry Smaha, R. W., He, W., Sheckelton, J. P., Wen, J., Lee, Y. S. 2018; 268: 123-129
  • Infrared phonons as a probe of spin-liquid states in herbertsmithite ZnCu3(OH)(6)Cl-2 JOURNAL OF PHYSICS-CONDENSED MATTER Sushkov, A. B., Jenkins, G. S., Han, T., Lee, Y. S., Drew, H. D. 2017; 29 (9)


    We report on temperature dependence of the infrared reflectivity spectra of a single crystalline herbertsmithite in two polarizations-parallel and perpendicular to the kagome plane of Cu atoms. We observe anomalous broadening of the low frequency phonons possibly caused by fluctuations in the exotic dynamical magnetic order of the spin liquid.

    View details for DOI 10.1088/1361-648X/aa5566

    View details for Web of Science ID 000394595900001

  • Correlated impurities and intrinsic spin-liquid physics in the kagome material herbertsmithite PHYSICAL REVIEW B Han, T., Norman, M. R., Wen, J., Rodriguez-Rivera, J. A., Helton, J. S., Broholm, C., Lee, Y. S. 2016; 94 (6)
  • Do quantum spin liquids exist? PHYSICS TODAY Imai, T., Lee, Y. S. 2016; 69 (8): 30-36
  • Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet SCIENCE Fu, M., Imai, T., Han, T., Lee, Y. S. 2015; 350 (6261): 655-658


    The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χ(kagome), deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χ(kagome) that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.

    View details for DOI 10.1126/science.aab2120

    View details for Web of Science ID 000364162800044

    View details for PubMedID 26542565

  • Thermal Hall Effect of Spin Excitations in a Kagome Magnet PHYSICAL REVIEW LETTERS Hirschberger, M., Chisnell, R., Lee, Y. S., Ong, N. P. 2015; 115 (10)


    At low temperatures, the thermal conductivity of spin excitations in a magnetic insulator can exceed that of phonons. However, because they are charge neutral, the spin waves are not expected to display a thermal Hall effect. However, in the kagome lattice, theory predicts that the Berry curvature leads to a thermal Hall conductivity κ_{xy}. Here we report observation of a large κ_{xy} in the kagome magnet Cu(1-3, bdc) which orders magnetically at 1.8 K. The observed κ_{xy} undergoes a remarkable sign reversal with changes in temperature or magnetic field, associated with sign alternation of the Chern flux between magnon bands. The close correlation between κ_{xy} and κ_{xx} firmly precludes a phonon origin for the thermal Hall effect.

    View details for DOI 10.1103/PhysRevLett.115.106603

    View details for Web of Science ID 000360528200005

    View details for PubMedID 26382691