@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{978,
  abstract     = {The newly discovered topological crystalline insulators feature a complex band structure involving multiple Dirac cones, and are potentially highly tunable by external electric field, temperature or strain. Theoretically, it has been predicted that the various Dirac cones, which are offset in energy and momentum, might harbour vastly different orbital character. However, their orbital texture, which is of immense importance in determining a variety of a materialâ €™ s properties remains elusive. Here, we unveil the orbital texture of Pb 1â ̂'x Sn x Se, a prototypical topological crystalline insulator. By using Fourier-transform scanning tunnelling spectroscopy we measure the interference patterns produced by the scattering of surface-state electrons. We discover that the intensity and energy dependences of the Fourier transforms show distinct characteristics, which can be directly attributed to orbital effects. Our experiments reveal a complex band topology involving two Lifshitz transitions and establish the orbital nature of the Dirac bands, which could provide an alternative pathway towards future quantum applications.},
  author       = {Zeljkovic, Ilija and Okada, Yoshinori and Huang, Chengyi and Sankar, Raman and Walkup, Daniel and Zhou, Wenwen and Serbyn, Maksym and Chou, Fangcheng and Tsai, Wei and Lin, Hsin and Bansil, Arun and Fu, Liang and Hasan, Md and Madhavan, Vidya},
  issn         = {1745-2481},
  journal      = {Nature Physics},
  number       = {8},
  pages        = {572 -- 577},
  publisher    = {Nature Publishing Group},
  title        = {{Mapping the unconventional orbital texture in topological crystalline insulators}},
  doi          = {10.1038/nphys3012},
  volume       = {10},
  year         = {2014},
}

@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},
}