@article{389,
  abstract     = {The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter. The strong time-periodic potential of intense laser light can be used to generate hybrid photon-electron states. Interaction of light with Bloch states leads to Floquet-Bloch states, which are essential in realizing new photo-induced quantum phases. Similarly, dressing of free-electron states near the surface of a solid generates Volkov states, which are used to study nonlinear optics in atoms and semiconductors. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use time- and angle-resolved photoemission spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi2Se3. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet-Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light-matter interaction.},
  author       = {Mahmood, Fahad and Chan, Ching and Alpichshev, Zhanybek and Gardner, Dillon and Lee, Young and Lee, Patrick and Gedik, Nuh},
  issn         = {1745-2481},
  journal      = {Nature Physics},
  pages        = {306 -- 310},
  publisher    = {Springer nature},
  title        = {{Selective scattering between Floquet Bloch and Volkov states in a topological insulator}},
  doi          = {10.1038/nphys3609},
  volume       = {12},
  year         = {2016},
}

@article{18201,
  abstract     = {Owing to thermal fluctuations, two-dimensional (2D) systems cannot undergo a conventional phase transition associated with the breaking of a continuous symmetry1. Nevertheless they may exhibit a phase transition to a state with quasi-long-range order via the Berezinskii–Kosterlitz–Thouless (BKT) mechanism2. A paradigm example is the 2D Bose fluid, such as a liquid helium film3, which cannot condense at non-zero temperature although it becomes superfluid above a critical phase space density. The quasi-long-range coherence and the microscopic nature of the BKT transition were recently explored with ultracold atomic gases4,5,6. However, a direct observation of superfluidity in terms of frictionless flow is still missing for these systems. Here we probe the superfluidity of a 2D trapped Bose gas using a moving obstacle formed by a micrometre-sized laser beam. We find a dramatic variation of the response of the fluid, depending on its degree of degeneracy at the obstacle location.},
  author       = {Desbuquois, Rémi and Chomaz, Lauriane and Yefsah, Tarik and Leonard, Julian and Beugnon, Jérôme and Weitenberg, Christof and Dalibard, Jean},
  issn         = {1745-2481},
  journal      = {Nature Physics},
  number       = {9},
  pages        = {645--648},
  publisher    = {Springer Nature},
  title        = {{Superfluid behaviour of a two-dimensional Bose gas}},
  doi          = {10.1038/nphys2378},
  volume       = {8},
  year         = {2012},
}