Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z39: Focus Session: Iron Based Superconductors: Spectroscopy II |
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Sponsoring Units: DCMP DMP Chair: Suchitra Sebastian, University of Cambridge Room: F150 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z39.00001: Evolution of Fermi surface nesting of BaFe2(As{1-x}Px)2 revealed by de Haas-van Alphen effect James Analytis, JiunHaw Chu, Ian Fisher, Ross McDonald The iron-pnictide superconductors are a new class of materials with unique superconducting and magnetic properties. Many theoretical frameworks describing these materials rely heavily on the nature of the size and topology of the Fermi surface. The classic method ofdetermining the Fermi surface is by looking at oscillations in the magnetization as a function of field. These oscillations, known as the de Haas-van Alphen effect, is extremely powerful in that it can determine the full three-dimensional topology of the FS, in addition to the quasiparticle renormalization to the effective mass. In the present study we measure the Fermi surface of the superconducting P-doped BaFe2As2. We are able to reveal the curvature of the electron pockets and the size and topology of a corresponding hole pocket, revealing a dramatic enhancement of the nesting for superconducting compounds, in contrast to the non-superconducting compounds. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z39.00002: De Haas-van Alphen Oscillations in KFe$_2$As$_2$ Taichi Terashima, Motoi Kimata, Nobuyuki Kurita, Hidetaka Satsukawa, Atsushi Harada, Kaori Hazama, Motoharu Imai, Akira Sato, Shinya Uji, Kunihiro Kihou, Chul-Ho Lee, Hijiri Kito, Hiroshi Eisaki, Akira Iyo, Hideto Fukazawa, Yoh Kohori, Hisatomo Harima In order to clarify pairing mechanisms and symmetries of the new high-$T_c$ superconductivity in the FeAs compounds, it is necessary to know their Fermi surfaces. We report on de Haas-van Alphen effect in KFe$_2$As$_2$, which is an end member of the high-$T_c$ binary alloy (Ba, K)Fe$_2$As$_2$. It shows no magnetic or structural phase transition down to low temperatures and becomes superconducting below about 3 K. We have observed many dHvA frequencies and their angular dependences are basically 1/cos$\theta$, where $\theta$ is the angle between the $c$ axis and the magnetic field. At the moment, our analysis indicates that three quasi-two-dimensional FS cylinders have been observed and that they occupy about 1, 8, and 12\% of the Brillouin zone, respectively. The effective masses of electrons are fairly heavy, ranging from 6 to 9 times the free electron mass for $B \parallel c$. This seems consistent with previously reported $T^2$ dependence of $\rho$ with a large $A$ coefficient [1] and large Sommerfeld coefficient of the specific heat [2]. [1] T. Terashima \textit{et al}., JPSJ 78, 063702 (2009). [2] H. Fukazawa \textit{et al}., JPSJ 78, 083712 (2009). [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z39.00003: Angle-dependent Magnetoresistance Oscillations in KFe$_{2}$As$_{2}$ Motoi Kimata, Taichi Terashima, Nobuyuki Kurita, Hidetaka Satsukawa, Atsushi Harada, Kouta Kodama, Akira Sato, Motoharu Imai, Shinya Uji, Kunihiro Kihou, Chul-Ho Lee, Hijiri Kito, Hiroshi Eisaki, Akira Iyo, Hideo Fukazawa, Yoh Kohori, Hisatomo Harima We report the results of angular-dependent magnetoresistance oscillations (AMRO) in the Fe-Pnictide superconductor KFe$_{2}$As$_{2}$. The two series of AMRO structures are observed, suggesting the existence of two quasi-two-dimensional Fermi surfaces (Q2D-FSs). The obtained FS cross sectional areas correspond to 11 and 15{\%} of the first Brillouin zone, and our results indicate that the cross sections of the Q2D-FSs are rounded square. The diagonal axes of the rounded squares are parallel to the a-axis in both FSs. These results are essentially consistent with the recent quantum oscillations and photoemission spectroscopy measurements. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:27PM |
Z39.00004: ARPES studies of FeAs-based compounds Invited Speaker: With critical temperatures and 2$\Delta $/k$_{B}T_{c}$ ratios comparable to those of cuprates, the new iron-based superconductors are believed to be the host of an unconventional pairing mechanism. Since these superconductors are multi-band materials, a deep understanding of their electronic properties and of the paring mechanism necessitates a good knowledge of their electronic structure in momentum space, particularly in the vicinity of the Fermi level. Owing to its momentum resolution capability, angle-resolved photoemission spectroscopy (ARPES) is a very powerful tool to characterize precisely the electronic states lying close to the Fermi level, which trigger the electronic behavior of crystals. In this talk, I present recent ARPES results obtained on the so-called $122$ class of materials over a wide range of doping. I show the evolution of the multi-band Fermi surface and the superconducting gap with doping and emphasize on the importance of interband scattering. In particular, I reveal that the occurence of high-temperature superconductivity seems related to ``near-nesting'' of $\Gamma $-centered holelike and M-centered electronlike Fermi surface pockets. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z39.00005: Observation of Dirac Cone Electronic Dispersion in BaFe$_{2}$As$_{2}$ Pierre Richard, K. Nakayama, T. Sato, M. Neupane, Y.-M. Xu, J.H. Bowen, G.F. Chen, J.L. Luo, N.L. Wang, H. Ding, T. Takahashi As with cuprates, it is widely believed that high-$T_{c}$ superconductivity in pnictides emerges by tuning interactions already present in the parent compounds and it is thus imperative to understand their electronic structure. We performed an angle-resolved photoemission spectroscopy study of BaFe$_{2}$As$_{2}$, which is the parent compound of the so-called $122$ phase of the iron-pnictide high-temperature superconductors. We reveal the existence of a Dirac cone in the electronic structure of this material below the spin-density-wave temperature, which is responsible for small spots of high photoemission intensity at the Fermi level. Our analysis suggests that the cone is slightly anisotropic and its apex is located very near the Fermi level, leading to tiny Fermi surface pockets. Moreover, the bands forming the cone show an anisotropic leading edge gap away from the cone that suggests a nodal spin-density-wave description. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z39.00006: Fermi surface and superconducting gap of FeTe$_{1-x}$Se$_{x}$ superconductor studied by high-resolution ARPES Kosuke Nakayama, Takafumi Sato, Takuma Kawahara, Yoichi Sekiba, Pierre Richard, Gen-Fu Chen, Tian Qian, Jian-Lin Luo, Nan-Lin Wang, Hong Ding, Takashi Takahashi The origin of superconductivity in FeTe$_{1-x}$Se$_{x}$ superconductor is a subject of intensive debate, since the parent compound FeTe shows considerably different electronic and magnetic properties compared to FeAs-based families. To clarify the superconducting mechanism, an experimental investigation of the low-energy electronic structure is of particular importance. Here, we report our recent high-resolution ARPES results on FeTe$_{1-x}$Se$_{x}$ superconductor, and demonstrate several universalities in the electronic states between FeTe$_{1-x}$Se$_{x}$ and FeAs-based superconductors. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z39.00007: Fermi surface dichotomy of superconducting gap and pseudogap in underdoped pnictides Y.-M. Xu, P. Richard, K. Nakayama, T. Kawahara, Y. Sekiba, T. Qian, M. Neupane, S. Souma, T. Sato, T. Takahashi, H. Luo, H.-H. Wen, G.-F. Chen, N.-L. Wang, Z. Wang, Z. Fang, X. Dai, H. Ding A systematic angle-resolved photoemission spectroscopy (ARPES) study has been performed on the hole-doped 122-phase (Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2})$ in the underdoped (UD) region. We observe that the superconducting (SC) gap of the UD pnictides scales linearly with the transition temperature, and a distinct pseudogap develops upon underdoping and coexists with the SC gap. Remarkably, this pseudogap occurs mainly on the FS sheets that are connected by the AF wave vector, where the SC pairing is stronger as well. The observed dichotomic behaviour of the pseudogap and the SC gap on different FS sheets in the UD pnictides shares many similarities with those observed in the UD copper oxide superconductors, providing a unifying picture for both families of high- temperature superconductors. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z39.00008: ARPES Study on the Electronic Structure of FeTe Zhongkai Liu, Ming Yi, Yulin Chen, Ruihua He, Donghui Lu, Rob Moore, Sung-Kwan Mo, Tijiang Liu, Zhiqiang Mao, Zahid Hussain, Zhi-Xun Shen Among the iron-based superconductors, iron chalcogenides FeSe$_{x}$Te$_{1-x}$ (T$_{c}\sim $20K) are special for their structural simplicity. FeTe, the parent compound for iron chalcogenides, though without superconducting transition, shows a unique antiferromagnetic order below tetragonal-orthorhombic structural phase transition temperature. Here we present recent ARPES results on this material, including measurements on electronic band structure and Fermi surface topology. We discovered strong k$_{z}$ dispersion of the Fermi surface and observed electronic band evolution through phase transition. The comparison of iron chalcogenides and other iron-based superconductor families helps us identify the governing physics in this new family of superconductors. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z39.00009: Photoemission in Ferropnictides Klaus Koepernik, Helmut Eschrig High resolution angle resolved photo emission spectroscopy yields the most direct and most detailed information on the electronic structure of solids. This opens the oppertunity to really compare theoretical band structures with experiment. However, the method is surface sensitive. For the ferropnictides highly resolved data are available, which are re-evaluated on the basis of density functional calculations. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z39.00010: Ab initio study of de Haas van Alphen effect in LaFe2P2 and CeFe2P2 Simon Blackburn, Michel Cote, Bobby Prevost, Gabriel Seyfarth, Andrea D. Bianchi, Cigdem Capan, Zachary Fisk, Roy G. Goodrich, Marek Bartkowiak, Oleg Ignatchik, Jochen Wosnitza The use of the maximally localized Wannier functions (MLWF) scheme (Marzari {\&} Vanderbilt, \textit{Phys. Rev. B}, 56, 12847, 1997) to interpolate the Hamiltonian on a very dense k-point grid allows an accurate description of the Fermi surface (FS) of a metal. It is then possible to calculate sections of a FS with great precision. These areas are related to de Haas van Alphen (dHvA) frequencies which can be measured experimentally. In this work, we study LaFe2P2 and CeFe2P2, both crystals in the pnictide family. Results of dHvA frequencies for different functionals are compared directly to experimental data. More specifically, we will present the effects of including a Hubbard U term in the calculations in order to take into account strong correlation on the Fe d orbitals. We will also consider another approach to deal with these orbitals by adding a certain amount of exact exchange to the functional. In this case, we used a PBE0 functional which adds 25{\%} of exact exchange (M. Ernzerhof and G.E. Scuseria, \textit{J. Chem. Phys.}, 110, 5029, 1999). [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z39.00011: Quantum oscillation experiments on iron pnictides LaFe$_{2}$P$_{2}$ and CeFe$_{2}$P$_{2}$ Bobby Prevost, Simon Blackburn, Andrea D. Bianchi, Michel Cote, Gabriel Seyfarth, Marek Bartkowiak, Oleg Ignatchik, Jochen Wosnitza, Roy G. Goodrich, Cigdem Capan, Zachary Fisk We investigated the quantum oscillations of the non-superconducting iron pnictides LaFe$_{2}$P$_{2}$ and CeFe$_{2}$P$_{2}$. Those compounds are isostructural to the high-temperature superconductor (Ba$_{1-x}$K$_{x}$)Fe$_{2}$As$_{2}$ [M. Rotter et al., Phys. Rev. Lett. 101, 107006 (2008)]. Measurements have been carried out using a torque cantilever in fields up to 35 T. Angular-dependent observations of the extremal Fermi surface areas shows a good agreement with our density functional theory calculation using GGA+U functional, which has been used to constructed the Fermi surfaces. We found significant differences between the Fermi surfaces of the two compounds, with LaFe$_{2}$P$_{2}$ showing a much more three dimensional Fermi surface. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z39.00012: Fermi surface and electronic structure in iron-based superconductors from Angle-Resolved Photoemission Spectroscopy Haiyun Liu, Xingjiang Zhou We will report our high resolution Angle-Resolved Photoemission measurements on iron-based superconductors. Multiple Fermi pockets are well resolved around the $\Gamma $(0, 0) and M($\pi $, $\pi )$ point. In addition, detailed temperature dependent electronic structures will be shown both above and below magnetic/structural transition (T$_{MS})$. [Preview Abstract] |
Friday, March 19, 2010 2:03PM - 2:15PM |
Z39.00013: ARPES study of the new iron-based superconductor Sr$_{4}$V$_{2}$O$_{6}$Fe$_{2}$As$_{2}$ Tian Qian, Kosuke Nakayama, Takuma Kawahara, Youichi Sekiba, Takafumi Sato, Takashi Takahashi, Haihu Wen, Hong Ding A new FeAs-based compound Sr$_{4}$V$_{2}$O$_{6}$Fe$_{2}$As$_{2}$ was discovered recently to show superconductivity at a relatively high temperature (Tc $\sim $ 37K). We will present ARPES results of band structure and Fermi surface of Sr$_{4}$V$_{2}$O$_{6}$Fe$_{2}$As$_{2}$, and discuss implications to its superconductivity. [Preview Abstract] |
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