high-temperature superconductivity; angle-resolved photoemission (ARPES); electronic structure; condensed matter physics; iron pnictide
Ribak Amit, Chashka Khanan B., Lahoud Elias, Naamneh Muntaser, Rinott Shahar, Ein-Eli Yair, Plumb Nicholas C., Shi Ming, Rienks Emile, Kanigel Amit (2016), Internal pressure in superconducting Cu intercalated Bi2Se3, in Phys. Rev. B
, 93, 064505.
Shi Xun, RichardP., Wang Kefeng, Liu M., Matt C. E., Xu Nan, DhakaR. S., Ristic Z., Qian T., Yang Y. -F., Petrovic C., Shi Ming, Ding Hong (2016), Observation of Dirac-like band dispersion in LaAgSb2, in Phys. Rev. B
, 93, 081105.
Xu Nan, Weng H. M., Lv B. Q., Matt C. E., Park J., Bisti F., Strocov V. N., Gawryluk D., Pomjakushina E., Conder K., Plumb N. C., Radovic M., Autes G., Yazyev O. V., Fang Z., Dai X., Qian T., Mesot J., Ding H., Shi Ming (2016), Observation of Weyl nodes and Fermi arcs in tantalum phosphide, in Nature Communications
, 7, 11006.
Xu Nan, Matt Christian Egon, Richard Pierre, Roekeghem A. van, Biermann S., Shi Xun, Wu S. -F, Liu H. W., Chen D., Qian Tian, Plumb Nicholas Clark, Radovic Milan, Wang Hangdong, Mao Qianhui, Du Jianhua, Fang Minghu, Mesot Joel, Ding. Hong, Shi Ming (2015), Camelback-shaped band reconciles heavy-electron behavior with weak electronic Coulomb correlations in superconducting TiNi2Se2, in Phys. Rev. B
, 92, 081116.
Matt Christian Egon, Fatuzzo C. G., Sassa Y., Mansson Martin, Fatale S., Bitetta V., Shi Xun, Pailhes S., Berntsen M. H., Kurosawa T., Oda M, Momono N., Lipscombe O. J., Hayden S. M., Yan J. -Q., Zhou J. -S., Goodenough J. B., Pyon S., Takauama T., Takagi H., Patthey Luc, Bendounan A., Razzoli Elia, Shi Ming, Plumb Nicholas Clark (2015), Electron scattering, charge order, and pseudogap physics in La1.6-xNd0.4SrxCuO4: An angle-resolved photoemission spectroscopy study, in Phys. Rev. B
, 92, 134524.
Charnukha A., Evtushinsky D. V., Matt Christian Egon, Xu N., Shi Ming, Buchner B., Zhigadlo N. D., Batlogg B., Borisenko S. V. (2015), High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides, in Scientific Reports
, 5, 18273.
Lv B. Q., Muff S., Qian T., Song Z. D., Nie S. M., Xu Nan, Richard P., Matt Christian Egon, Plumb N. C., Zhao L. X., Chen G. F., Fang Z., Dai X., Dil J. H., Mesot J., Shi Ming, Weng H. M., Ding H. (2015), Observation of Fermi-Arc Spin Texture in TaAs, in Phys. Rev. Lett.
, 115, 217601.
Lv Baiqing, Xu Nan, Weng Hongming, Ma Junzhang, Richard Pierre, Zhao L. X., Chen G. -F., Matt Christian Egon, Bisti F., Strocov V. N., Mesot Joel, Fang Zhong, Dai Xi, Qian Tian, Shi Ming, Ding Hong (2015), Observation of Weyl nodes in TaAs, in Nature Physics
, 11, 724.
Razzoli Elia, Matt Christian Egon, Kobayashi M., Wang Xiaoping, Strocov V. N., Roekeghem A. van, Biermann S., Plumb Nicholas Clark, Radovic Milan, Schmitt Thorsten, Capan C., Fisk Z., Richard Pierre, Ding Hong, Aebi Philipp, Mesot Joel, Shi Ming (2015), Tuning electronic correlations in transition metal pnictides: Chemistry beyond the valence count, in Phys. Rev. B
, 91, 214502.
Xu Nan, Biswas Pabitra Kumar, Dil Jan Hugo, Dhaka R. S., Landolt Gabriel, Muff Stefan, Matt Christian Egon, Shi Xun, Plumb Nicholas Clark, Radovic Milan, Pomjakushina Ekaterina, Conder Kazimierz, Amato Alex, Borisenko S. V., Yu R, Weng H. -M, Fang Zhong, Dai Xi, Mesot Joel, Ding Hong, Shi Ming (2014), Direct observation of the spin texture in SmB6 as evidence of the topological Kondo insulator, in Nature Communications
, 5, 4566.
Xu Nan, Matt Christian Egon, Pomjakushina Ekaterina, Shi Xun, Dhaka R. S., Plumb Nicholas Clark, Radovic Milan, Biswas Pabitra Kumar, Evtushinsky D., Zabolotnyy V., Dil Jan Hugo, Conder Kazimierz, Mesot Joel, Ding Hong, Shi Ming (2014), Exotic Kondo crossover in a wide temperature region in the topological Kondo insulator SmB6 revealed by high-resolution ARPES, in Phys. Rev. B
, 90, 085148.
Xu Nan, Richard Pierre, Shi Xun, Roekeghem. A. van, Qian Tian, Razzoli Elia, Rienks E., Chen G. -F., Ieki E., Nakayama K., Sato T., Takahashi T., Shi Ming, Ding Hong (2013), Possible nodal superconducting gap and Lifshitz transition in heavily hole-doped Ba0.1K0.9Fe2As2, in Phys. Rev. B
, 88, 220508.
Xu Nan, Shi Ming (2013), Surface and bulk electronic structure of the strongly correlated system SmB6 and implications for a topological Kondo insulator, in PHYSICAL REVIEW B
, 88, 121102.
Monney M., Schmitt T., Matt Christian Egon, Mesot Joel, Strocov V. N., Lipscombe O. J., Hayden S. M., Chang J., A resonant inelastic x-ray scattering study of the spin and charge excitations in the overdoped superconductor La1.77Sr0.23CuO4, in Phys. Rev. B
The aim of this project is to study the electronic structure and the low-energy electronic excitations of 1111 iron-pnictides (Fe-pnictides), which have the highest superconducting transition temperature (Tc) among the newly discovered iron-based superconductors. This will advance our understanding of various exotic properties of this class of materials and shed light on the microscopic origin of the high-temperature superconductivity in Fe-pnictides.Since the discovery of superconductivity in F-doped LaFeAsO with Tc = 26 K in early 2008, significant attention has been paid to ZrCuSiAs-type compounds. Further studies on RFeAsO1-xFx (R, rare-earth metal) have shown that Tc is extremely sensitive to the lanthanide, exceeding 50 K for the Nd- and Sm-containing oxypnictides. The experimental evidence accumulated so far has shown that intriguing couplings between superconductivity, magnetism, and structural features are present. The magnetic phase appears to be associated with a distortion of the crystal lattice from a tetragonal to an orthorhombic structure. In some materials the antiferromagnetic order persists into the superconducting phase (e.g. SmOFeAs). In other cases the antiferromagnetic and superconducting phases are completely separated. Increasing fluorine content suppresses both the magnetic order and the structural distortion, and the superconductivity emerges.Because many physical properties in solids are governed by the electronic states, an essential piece of knowledge is how the electronic structure and excitation spectra change from one phase to another. A systematic study of the momentum-resolved electronic structure of RFeAsO1-xFx as a function of doping and temperature is still lacking in the current literature. One of the main reasons is lack of high quality large-size single-crystal samples in 1111 systems for the spectroscopic techniques that probe the charge excitation spectra of single-particle spectral function. In collaboration with Dr. J. Karpinski’s group at ETHZ, we successfully made preliminary angle-resolved photoemission (ARPES) measurements on the newly grown NdFeAsO1-xFx samples. This progress opens the door for us to explore the electron excitations in the momentum-resolved manner for the important 1111 systems of Fe-based superconductors.In the proposed project we shall concentrate our studies on two 1111 families NdFeAsO1-xFx and SmFeAsO1-xFx. Although both systems have Tc beyond 50 K, their temperature-doping phase diagrams are apparently different (Fig. 1). By using high-resolution ARPES and soft X-ray ARPES stations at Swiss Light Source (SLS), we will investigate how the electronic structure evolves under the structural transition from a tetragonal structure to an orthorhombic one, and under phase transitions from an antiferromagnetically ordered phase (AFM) to a superconducting state, and from a normal state to a superconducting state. We shall investigate whether there is a connection between Fermi surface nesting and a spin-density-wave (SDW) instability that has been proposed to account for the small Fe moments in rare-earth oxypnictides, and how the different Fe moments are related to the difference in band structures of different materials. Along with studies of electron correlation effects, we shall measure the superconducting gap and its momentum-dependence as function of F-doping and temperature. Knowledge of the electron pairing strength and the shape in momentum-space of the superconducting order parameters will provide essential ingredients for uncovering the pairing mechanism for the emergence of the high-temperature superconductivity.