Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S8: Electronic Structure (Photoemission and Transport) |
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Sponsoring Units: DCMP Chair: Shuolong Yang, Cornell University Room: 267 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S8.00001: Electronic properties of topological materials studied by angle-resolved photoemission spectroscopy Y. Wu, T. Kong, N.H. Jo, L.-L. Wang, D. Mou, L. Huang, B. Schrunk, K. Sun, E. Mun, Y. Lee, D.D. Johnson, S.L. Bud'ko, P.C. Canfield, A. Kaminski We use ultrahigh resolution, tunable, vacuum ultraviolet laser-based angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of topological materials. In PtSn${}_{4}$, we have discovered Dirac node arc states where Dirac dispersions extend along arcs in the momentum space. In topological semimetal LaBi, we have observed Dirac surface states that are buried deeply in the bulk states with asymmetric mass acquisition. In type-II Weyl semimetal candidate WTe${}_{2}$, we have observed the Fermi arc surface states which are very sensitive to pressure/strain. These results are experimental confirmations of theoretical predictions and band structure calculations. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S8.00002: Measurement of the Atomic Orbital Composition of the Near-Fermi-Level Electronic States in the Lanthanum Monopnictides LaBi and LaSb Thomas Nummy, Justin Waugh, Stephen Parham, Haoxiang Li, Xiaoqing Zhou, Nick Plumb, Fazel Tafti, Daniel Dessau Angle resolved photoemission spectroscopy (ARPES) is used to measure the electronic structure of the Extreme Magnetoresistance (XMR) topological semimetal candidates LaBi and LaSb. Using a wide range of photon energies the true bulk states are cleanly disentangled from the various types of surface states, which may exist due to surface projections of bulk states as well as for topological reasons. The orbital content of the near-$E_F$ states are extracted using varying photon polarizations. The measured bulk bands are somewhat lighter and are energy shifted compared to the results of Density Functional calculations, which is a minor effect in LaBi and a more serious effect in LaSb. This bulk band structure puts LaBi in the $v=1$ class of Topological Insulators (or semimetals), consistent with the measured Dirac-like surface states. LaSb on the other hand is at the verge of a topological band inversion, with a less-clear case for any distinctly topological surface states. The low-dimensional cigar-shaped bulk Fermi surfaces for both compounds are separated out by orbital content, with a crossover from pnictide $d$ orbitals to La $p$ orbitals around the Fermi surface, which through strong spin-orbit coupling may be relevant for the Extreme Magnetoresistance. [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S8.00003: Topologically entangled Rashba-split Shockley states on the surface of grey arsenic Peng Zhang, Yukiaki Ishida, Junzhang Ma, Lingxiao Zhao, Qiunan Xu, Baiqing Lv, Genfu Chen, Hongming Weng, Xi Dai, Zhong Fang, Koichiro Yaji, Xingqiu Chen, Liang Fu, Tian Qian, Hong Ding, Shik Shin Topological surface states (SSs) and Shockley SSs are two kinds of typical SSs. The relationship between them has been theoretically proposed while convincing experimental evidence is still absent. Here we discover a pair of spin-polarized surface bands on the (111) face of grey arsenic by using angle-resolved photoemission spectroscopy (ARPES). In the occupied side, the pair resembles typical nearly-free-electron Shockley states observed on noble-metal surfaces. However, pump-probe ARPES reveals that the spin-polarized pair traverses the bulk band gap and that the crossing of the pair at $\Gamma $ is topologically unavoidable. First-principles calculations well reproduce the bands and their non-trivial topology; it also supports that the surface states are of Shockley type because they arise from a band inversion caused by crystal field. The results provide compelling evidence that topological Shockley states are realized on As(111). [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S8.00004: Experimental Evidence of the First Nonsymmorphic Topological Insulator KHgSb. Junzhang Ma, C.J Yi, B.Q Lv, S.M Nie, L Wang, L.Y Kong, P Richard, H.M Weng, Y.G Shi, T Qian, Hong Ding, Z.J Wang, B.A Bernevig, P Zhang, K Yaji, K Kuroda, S Shin, Y.B Huang Topological insulators (TIs) host novel states of quantum matter characterized by nontrivial conducting boundary states connecting valence and conduction bulk bands. All TIs discovered experimentally so far rely either on time reversal or mirror crystal symmorphic symmetries to protect massless Dirac-like boundary states. Several materials were recently proposed to be TIs with nonsymmorphic symmetry, where a glide-mirror protects exotic surface fermions with hourglass-shaped dispersion. However, an experimental confirmation of such new fermion is missing. Using angle- resolved photoemission spectroscopy, we provide experimental evidence of hourglass fermions on the (010) surface of crystalline KHgSb while the (001) surface has no boundary state, in agreement with first-principles calculations. Our study will stimulate further research activities of topological properties of nonsymmorphic materials. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S8.00005: Signature of Type-II Weyl Semimetal Phase in MoTe$_{2}$ Juan Jiang, Zhongkai Liu, Haifeng Yang, Lexian Yang, Cheng Chen, Han Peng, Chan-Cuk Hwang, Sung-Kwan Mo, Yulin Chen Topological Weyl semimetal (TWS) is a new state of quantum matter, which has sparked enormous research interest recently. Possessing unique Weyl fermions in the bulk and Fermi arcs on the surface, TWSs offer a rare platform for realizing many exotic physical phenomena. Here, by using angle-resolved photoemission spectroscopy, we directly visualize the electronic structure of MoTe$_{2}$, a recently proposed type-II TWS, which do not respect Lorentz symmetry compared with type-I TWS. Furthermore, we unravel the unique surface Fermi arcs, in good agreement with our ab-initio calculations, which have non-trivial topological nature. Our work not only leads to new understandings of the unusual properties discovered in this family of compounds, but also allows for the further exploration of exotic properties and practical applications of type-II TWSs, as well as the interplay between superconductivity and their topological order. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S8.00006: Revealing the ultrafast light-to-matter energy conversion before heat diffusion in a layered Dirac semimetal Yukiaki Ishida, Hidetoshi Masuda, Hideaki Sakai, Shintaro Ishiwata, Shik Shin There is still no general consensus on how one can describe the out-of-equilibrium phenomena in matter induced by an ultrashort light pulse. We investigate the pulse-induced dynamics in a layered Dirac semimetal SrMnBi$_{\mathrm{2}}$ by pump-and-probe photoemission spectroscopy [1]. At \textless 1 ps, the electronic recovery slowed upon increasing the pump power. Such a bottleneck-type slowing is expected in a two-temperature model (TTM) scheme, although opposite trends have been observed to date in graphite and in cuprates. Subsequently, an unconventional power-law cooling took place at \textasciitilde 100 ps, indicating that spatial heat diffusion is still ill defined at \textasciitilde 100 ps. We identify that the successive dynamics before the emergence of heat diffusion is a canonical realization of a TTM scheme. Criteria for the applicability of the scheme is also provided. [1] Phys. Rev. B 93, 100302(R) (2016). [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S8.00007: Temperature-Induced Lifshitz Transition in Weak Topological Insulator Candidates ZrTe$_{5}$ and HfTe$_{5}$ Yan Zhang, Chenlu Wang, Guodong Liu, Jianwei Huang, Genfu Chen, Li Yu, Shaolong He, Lin Zhao, Chuangtian Chen, Zuyan Xu, Xingjiang Zhou The transition metal pentatellurides ZrTe$_{5}$ and HfTe$_{5}$ have attracted consideration attention since the 70s, due to their unusual transport properties like resistivity peak at \textasciitilde 135K/\textasciitilde 65K and the sign change of the Hall coefficient and thermopower. The origin of the most peculiar transport properties remains controversial. Lately, ZrTe$_{5}$ and HfTe$_{5}$ have ignited renewed interest because it is predicted that single-layer ZrTe$_{5}$ and HfTe$_{5}$ are two-dimensional topological insulators and there is possibly a topological phase transition in bulk ZrTe$_{5}$ and HfTe$_{5}$. In this talk we will present temperature dependent Fermi surface and band structure of ZrTe$_{5}$ and HfTe$_{5}$, by using our super-high resolution angle-resolved photoemission system equipped with the VUV laser and the time-of-flight (TOF) electron energy analyzer. Upon cooling down, we found a gradual transition from hole-like band into electron-like band around the Brillouin zone center. Such an electron state transition forms the underlying physics for the abnormal transport properties. We will also discuss on the topological nature of ZrTe$_{5}$ and HfTe$_{5¡£}$ [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S8.00008: Sn-doped Bi$_{\mathrm{1.1}}$Sb$_{\mathrm{0.9}}$Te$_{\mathrm{2}}$S: An ideal bulk topological insulator SK Kushwaha, I Pletikosic, T Liang, A Gyenis, SH Lapidus, Y Tian, H Zhao, KS Burch, J Lin, W Wang, H Ji, AV Fedorov, A Yazdani, NP Ong, T Valla, RJ Cava In the recent decade the topological insulators have been of significant importance for the condensed matter community. However, so far no real materials could fulfill all the requirements. Here, we present the Bridgman growth of slightly Sn-doped Bi$_{\mathrm{1.1}}$Sb$_{\mathrm{0.9}}$Te$_{\mathrm{2}}$S (with bulk band gap of \textasciitilde 350) single crystals and characterization by electronic transport, STM and ARPES. The results on the crystals exhibit an intrinsic semiconducting behavior with the Fermi level and Dirac energies lie in bulk gap and high quality 2D surface states are detangled from the bulk states, and it fulfils all the requirements to be an ideal topological insulator. Reference: S K Kushwaha et al., NATURE COMM., 7:11456 (2016). [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S8.00009: Electronic structure of Ba(Zn$_{0.875}$Mn$_{0.125}$)$_{2}$As$_{2}$ studied by angle-resolved photoemission spectroscopy Dong Qian, Fengfeng Zhu, Weidong Luo, Jinfeng Jia Electronic structure of single crystalline Ba(Zn$_{0.875}$Mn$_{0.125}$)$_{2}$As$_{2}$, parent compound of the recently founded high-temperature ferromagnetic semiconductor, was studied by high-resolution photoemission spectroscopy (ARPES). Through systematically photon energy and polarization dependent measurements, the energy bands along the out-of-plane and in-plane directions were experimentally determined. Except the localized states of Mn, the measured band dispersions agree very well with the first-principle calculations of undoped BaZn$_{2}$As$_{2}$. A new feature related to Mn 3d states was identified at the binding energies of about -1.6 eV besides the previously observed feature at about -3.3 eV. We suggest that the hybridization between Mn and As orbitals strongly enhanced the density of states around -1.6 eV. Although our resolution is much better compared with previous soft X-ray photoemission experiments, no clear hybridization gap between Mn 3d states and the valence bands proposed by previous model calculations was detected. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S8.00010: d$_{xz/yz}$ subband structure and Chiral Orbital Angular Momentum of Nb doped SrTiO$_{3}$ surface states Shoresh Soltani, Soohyun Cho, Hanyoung Ryu, Garam Han, Timur Kim, Moritz Hoesch, Changyoung Kim Using angle resolved photoemission spectroscopy (ARPES), we investigate subband structure and chiral orbital angular momentum (OAM) texture on the surface of lightly electron doped SrTiO$_{3}$ single crystals. Our linearly polarized light ARPES data taken with 51 eV photons, reveal additional subbands for out-of-plane d$_{xz/yz\, }$orbitals in addition to the previously reported ones. Our CD-ARPES data reveal a chiral OAM structure which we use as a clue to explain the origin of linear Rashba-like surface band splitting of Ti 3d t$_{2g}$ orbitals. The observed CD signal is enhanced near crossing points, where different orbitals hybridize, compatible with a linear Rashba-like surface band splitting. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S8.00011: Electronic phase separation and dramatic inverse band renormalisation in the mixed valence cuprate LiCu$_2$O$_2$ Simon Moser, Yusuke Nomura, Luca Moreschini, Gianmarco Gatti, Helmuth Berger, Philippe Bugnon, Arnaud Magrez, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Silke Biermann, Marco Grioni We measured by ARPES the electronic structure of LiCu$_2$O$_2$, a mixed valence cuprate where planes of formally Cu(I) ($3d^{10}$) ions are sandwiched between layers containing one-dimensional edge-sharing Cu(II) ($3d^{9}$) chains. We find that the Cu(I)- and Cu(II)-derived electronic states form separate electronic subsystems, in spite of being coupled by bridging O ions. The valence band, of Cu(I) character, disperses within the charge-transfer gap of the strongly correlated Cu(II) states. This anomalous electronic structure produces an unexpected and unprecedented 250\% $broadening$ of the valence band with respect to the predictions of density functional theory. Our observation is at odds with two widely accepted tenets of many-body theory, namely that correlation effects are weak in filled bands, and that they generally yield narrower bands and larger electron masses. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S8.00012: Renormalization of electronic energy scales by electron-phonon interactions in the spin-chain cuprate Li$_2$CuO$_2$ Steven Johnston, C. Monney, V. Bisogni, K. J. Khou, R. Kraus, G. Behr, V. N. Strocov, J. Malek, S.-L. Drechsler, J. Geck, T. Schmitt, J. van den Brink Recent advances in resonant inelastic x-ray scattering has improved energy resolution to the point that phonon excitations are now regularly observed in low-dimensional correlated materials. This observation provides a new way to study the electron-phonon interaction in these materials. I will discuss the observations of phonon excitations in the quasi-1D spin-chain cuprate Li$_2$CuO$_2$. Through detailed modeling of the RIXS spectra over a wide energy range we are able to determine the strength of this interaction. Importantly, we are also able to determine how several fundamental electronic energy scales such as the charge transfer energy and Cu-Cu exchange coupling are renormalized by interactions with the lattice. Our results point to the strong interplay between the lattice, charge, and magnetic excitations in Li$_2$CuO$_2$ and other low-dimensional cuprates. Ref: S. Johnston {\em et al}., Nature Commun. {\bf 7}, 10563 (2016). [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S8.00013: In situ ARPES on Sr2IrO4 thin films electron and hole-doped via cation substitution Jocienne Nelson, Brendan Faeth, Jason Kawasaki, Celesta Chang, David Muller, Darrell Schlom, Kyle Shen Sr$_2$IrO$_4$, a Mott insulator with spin-orbit coupling, has garnered much attention due to its similarities to the prototypical cuprate superconductor La$_2$CuO$_4$ and its predicted high temperature superconductivity. It is thus essential to explore the full phase diagram of Sr2IrO4. We grow carrier doped Sr$_2$IrO$_4$ epitaxial thin films by oxide molecular beam epitaxy, and characterize the films using in situ angle-resolved photoemission. We present methods for both electron and hole-doping Sr$_2$IrO$_4$ using substitutional doping on the Sr site, thus maintaining the structure of the IrO2 planes, and minimizing the strong disorder scattering which occurs when substituting on the Ir site. We describe the subsequent evolution of the electronic structure by ARPES and transport. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S8.00014: Distinct Electronic Structure for the Extreme Magnetoresistance in YSb Junfeng He, Chaofan Zhang, Nirmal Ghimire, Tian Liang, Chunjing Jia, Juan Jiang, Shujie Tang, Sudi Chen, Yu He, S.-K. Mo, C. C. Hwang, M. Hashimoto, D. H. Lu, B. Moritz, T. P. Devereaux, Y. L. Chen, J. F. Mitchell, Z.-X. Shen An extreme magnetoresistance (XMR) has recently been observed in several non-magnetic semimetals. Increasing experimental and theoretical evidence indicates that the XMR can be driven by either topological protection or electron-hole compensation. Here, by investigating the electronic structure of a XMR material, YSb, we present spectroscopic evidence for a special case which lacks topological protection and perfect electron-hole compensation. Further investigations reveal that a cooperative action of a substantial difference between electron and hole mobility and a moderate carrier compensation might contribute to the XMR in YSb. [Preview Abstract] |
Thursday, March 16, 2017 2:03PM - 2:15PM |
S8.00015: Influence of the cubic-tetragonal structural transition on the k-resolved band structure of CH$_{3}$NH$_{3}$PbI$_{3}$ hybrid organic-inorganic perovskite Min-I LEE, A. Barragan, M. Nair, V. Jacques, D. Le Bolloch, P. Fertey, K. Jemli, F. Ledee, G. Trippe-Allard, E. Deleporte, A. Taleb-Ibrahimi, A. Tejeda Hybrid organic-inorganic halide perovskites have become a promising material for photovoltaics due to their high performance of energy conversion efficiencies. The most outstanding performance (22\%) is contributed by methylammonium lead halide perovskite (CH$_{3}$NH$_{3}$PbI$_{3}$, MAPI), which is also compatible with a low-temperature and low-cost fabrication in solution. A requirement to further improve the performances is the better understanding of the electronic band structure, which has remained experimentally elusive until now. Also, the impact of the structural phase transitions on the band structure in the operation temperature range of solar cells must be elucidated. Herein, we present the first experimental determination of the band structure of MAPI with k resolution. Our results show that the electronic periodicity in the tetragonal phase of MAPI (below $50^{\circ}$C) corresponds to the high-temperature cubic phase. This will lead to the insensitivity of solar cells in the usual range of operating temperatures despite the cubic-tetragonal structural transition. [Preview Abstract] |
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