- Email: [email protected]
High-resolution angle-resolved resonant-photoemission spectroscopy of FexTiTe2
ARTICLE IN PRESS
Physica B 351 (2004) 262–264
High-resolution angle-resolved resonant-photoemission spectroscopy of FexTiTe2 K. Yamazakia,*, K. Shimadab, H. Negishic, F. Xud, A. Inoa, M. Higashiguchia, H. Namatameb, M. Taniguchia,b, M. Sasakie, S. Titovaf, A. Titovg, Yu.M. Yarmoshenkog a
Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan Hiroshima Synchrotron Radiation Center, Hiroshima University, Kagamiyama 2-313, Higashi-Hiroshima 739-8526, Japan c Advanced Department of Science and Material, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan d National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, PR China e Department of Physics, Faculty of Science, Yamagata University, Kojirakawa-machi 1-4-12, Yamagata 990-8560, Japan f Institute of Metallurgy, Urals Division of RAS, 620219 Yekaterinburg GSP-170, Russia g Institute of Metal Physics, Urals Division of RAS, 620219 Yekaterinburg GSP-170, Russia b
Abstract The electronic band structures of 1T-TiTe2 and Fe0.25TiTe2 have been clarified by angle-resolved resonantphotoemission spectroscopy. Upon Fe intercalation, while most of the band structure is unchanged, two new flat bands appear at the Fermi level and at EB0.5 eV. Constant-initial-state spectra indicate that these states are derived from both Ti 3d and Fe 3d states. While the Fermi wave number of the electron pocket around M point is reduced by Fe intercalation, those of hole pockets around G point are almost unchanged, suggesting that the additional electrons are accommodated by the new flat band at 0.5 eV. r 2004 Elsevier B.V. All rights reserved. PACS: 71.20.b; 79.60.i; 71.20.Tx Keywords: Intercalation compounds; Angle-resolved photoemission; Resonant photoemission; Fermi surface
Semi-metallic 1T-TiTe2 has a layered crystal structure of the CdI2 type, and the Te–Te parts are coupled by a weak van der Waals force [1]. Upon Fe intercalation into 1T-TiTe2, the lattice parameter c decreases [2], and the electrical conductivity is lowered, showing anomalous temperature *Corresponding author. Fax: +81-824-24-0719. E-mail address: [email protected] (K. Yamazaki).
dependence [3,4]. We report high-resolution lowtemperature angle-resolved resonant-photoemission (ARPES) experiments of 1T-TiTe2 and Fe0.25TiTe2 using synchrotron radiation, and discuss the effect of intercalant atoms on the electronic structure. The ARPES measurements were performed at the undulator beamline BL-1 and the bending magnet beamline BL-7 on 700 MeV electronstorage ring (HiSOR) at Hiroshima University.
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.06.020
ARTICLE IN PRESS K. Yamazaki et al. / Physica B 351 (2004) 262–264
263
The intensity of constant-initial-state (CIS) spectra was normalized to the photon flux. Fig. 1(a) shows the ARPES spectra of Fe0.25TiTe2 taken at hn=56 eV along G2M direction, and Fig. 1(b) shows its intensity plot, where white regions correspond to the highspectral intensity. Two bands crossing the Fermi level (EF) near G point form ‘‘hole pockets’’ and another band crossing EF near M point forms an ‘‘electron pocket’’ as observed by ARPES of TiTe2 [6–8]. The hole pockets and the electron pocket are mainly derived from the Te 5p states and the Ti 3dz2 states, respectively [6–8]. Upon Fe intercalation two additional bands appear at EB0.1 eV (BEF) and B0.5 eV. Since the 0.5-eV band shows no appreciable dispersion along the G–A, G–M and G–K directions, the electrons in this band have localized nature. Fig. 2 shows the CIS spectra of Fe0.25TiTe2. The Ti 3p-3d and Fe 3p-3d resonance energies are at hnB48 and B56 eV, respectively. Since the CIS spectra have a broad peak from hnB48 eV to B56 eV for E ¼ 0:1 and 0.5 eV, both Fe 3d and Ti 3d states contribute to these flat bands. On the other hand, the spectral feature at 1.8 eV is mainly derived from Ti 3d states, because the CIS
E = -0.1 eV E = -0.5 eV
Single crystalline 1T-TiTe2 and Fe0.25TiTe2 were grown by chemical vapor transport using I2 as a carrier [5]. Clean surfaces were obtained by cleaving in situ at a base pressure better than 3 1010 Torr. The samples were cooled to 17 K during measurements using a He-flow-type cryostat and a He refrigerator for BL-1 and BL-7, respectively. Total energy resolution was set at 40 and 150 meV for BL-1 and BL-7, respectively. The angular resolution is B0.3 , which gives a wave( 1 at hn =40 eV. vector resolution Dk||B0.02 A
Intensity (arb. units)
E = -1.8 eV Fig. 1. (a) ARPES spectra of Fe0.25TiTe2 taken at hn=56 eV along G–M direction. (b) Intensity plot of the ARPES spectra shown in (a).
45
50
55 60 65 Photon Energy (eV)
70
75
Fig. 2. CIS spectra of Fe0.25TiTe2 at E=0.1, 0.5, and 1.8 eV.
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spectrum has higher intensity at hnB48 eV than at hnB56 eV. We found that the Fermi wave number of the electron pocket around M point is reduced by the Fe intercalation, while those of the hole pockets around G point are unchanged. Thus, the effect of the intercalated 3d-transition-metal atoms on the electronic structure of 1T-TiTe2 cannot be understood by a rigid-band model. The result indicates that the intercalant atoms affect strongly on the Ti 3dz2 states, not on the Te 5p states. It has been claimed that the reduction of the c-axis lattice constant on Fe intercalation is due to the formation of the local Ti–Fe–Ti covalent bond along c-axis [2–4]. The present result indicates that the additional electrons introduced by Fe intercalation are accommodated by the new 0.5-eV flat band instead of increasing the area enclosed by Fermi surface. This is in agreement with that the electrical conductivity is reduced on Fe intercalation.
Acknowledgements This work was partly supported by a Grant-inAid for COE Research (13CE2002) by the
Ministry of Education, Science, and Culture of Japan. We thank the Cryogenic Center, Hiroshima University for supplying liquid helium. The synchrotron radiation experiments have been done under the approval of HSRC (Proposal No. 02-A-43).
References [1] R.H. Friend, A.D. Yoffe, Adv. Phys. 36 (1987) 1. [2] V.G. Pleshchev, A.N. Titov, S.G. Titova, A.V. Kuranov, Neorg. Mater. 33 (11) (1997) 1333. [3] A.N. Titov, Fiz. Met. Metalloved. 81 (6) (1996) 75. [4] A.N. Titov, T.B. Popova, S.G. Titova, Phys. Solid State 41 (1999) 613. [5] A. Titov, S. Titova, M. Neumann, V. Pleschov, Yu. Yarmoshenko, L. Krasavin, A. Dolgoshein, A. Kuranov, Mol. Crystallogr. Liq. Crystallogr. 311 (1998) 161. [6] R. Claessen, R.O. Anderson, G.-H. Gweon, J.W. Allen, W.P. Ellis, C. Janowitz, C.G. Olson, Z.X. Shen, V. Eyert, M. Skibowski, K. Friemelt, E. Bucher, S. Hufner, . Phys. Rev. B 54 (1996) 2453. [7] K. Rossnagel, L. Kipp, M. Skibowski, C. Solterbeck, T. Strasser, W. Schattke, D. VoX, P. Kruger, . A. Mazur, J. Pollmann, Phys. Rev. B 63 (2001) 125104. [8] Th. Straub, R. Claessen, P. Steiner, S. Hufner, . V. Eyert, K. Friemelt, E. Bucher, Phys. Rev. B 55 (1997) 13473.
Physica B 351 (2004) 262–264
High-resolution angle-resolved resonant-photoemission spectroscopy of FexTiTe2 K. Yamazakia,*, K. Shimadab, H. Negishic, F. Xud, A. Inoa, M. Higashiguchia, H. Namatameb, M. Taniguchia,b, M. Sasakie, S. Titovaf, A. Titovg, Yu.M. Yarmoshenkog a
Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan Hiroshima Synchrotron Radiation Center, Hiroshima University, Kagamiyama 2-313, Higashi-Hiroshima 739-8526, Japan c Advanced Department of Science and Material, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan d National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, PR China e Department of Physics, Faculty of Science, Yamagata University, Kojirakawa-machi 1-4-12, Yamagata 990-8560, Japan f Institute of Metallurgy, Urals Division of RAS, 620219 Yekaterinburg GSP-170, Russia g Institute of Metal Physics, Urals Division of RAS, 620219 Yekaterinburg GSP-170, Russia b
Abstract The electronic band structures of 1T-TiTe2 and Fe0.25TiTe2 have been clarified by angle-resolved resonantphotoemission spectroscopy. Upon Fe intercalation, while most of the band structure is unchanged, two new flat bands appear at the Fermi level and at EB0.5 eV. Constant-initial-state spectra indicate that these states are derived from both Ti 3d and Fe 3d states. While the Fermi wave number of the electron pocket around M point is reduced by Fe intercalation, those of hole pockets around G point are almost unchanged, suggesting that the additional electrons are accommodated by the new flat band at 0.5 eV. r 2004 Elsevier B.V. All rights reserved. PACS: 71.20.b; 79.60.i; 71.20.Tx Keywords: Intercalation compounds; Angle-resolved photoemission; Resonant photoemission; Fermi surface
Semi-metallic 1T-TiTe2 has a layered crystal structure of the CdI2 type, and the Te–Te parts are coupled by a weak van der Waals force [1]. Upon Fe intercalation into 1T-TiTe2, the lattice parameter c decreases [2], and the electrical conductivity is lowered, showing anomalous temperature *Corresponding author. Fax: +81-824-24-0719. E-mail address: [email protected] (K. Yamazaki).
dependence [3,4]. We report high-resolution lowtemperature angle-resolved resonant-photoemission (ARPES) experiments of 1T-TiTe2 and Fe0.25TiTe2 using synchrotron radiation, and discuss the effect of intercalant atoms on the electronic structure. The ARPES measurements were performed at the undulator beamline BL-1 and the bending magnet beamline BL-7 on 700 MeV electronstorage ring (HiSOR) at Hiroshima University.
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.06.020
ARTICLE IN PRESS K. Yamazaki et al. / Physica B 351 (2004) 262–264
263
The intensity of constant-initial-state (CIS) spectra was normalized to the photon flux. Fig. 1(a) shows the ARPES spectra of Fe0.25TiTe2 taken at hn=56 eV along G2M direction, and Fig. 1(b) shows its intensity plot, where white regions correspond to the highspectral intensity. Two bands crossing the Fermi level (EF) near G point form ‘‘hole pockets’’ and another band crossing EF near M point forms an ‘‘electron pocket’’ as observed by ARPES of TiTe2 [6–8]. The hole pockets and the electron pocket are mainly derived from the Te 5p states and the Ti 3dz2 states, respectively [6–8]. Upon Fe intercalation two additional bands appear at EB0.1 eV (BEF) and B0.5 eV. Since the 0.5-eV band shows no appreciable dispersion along the G–A, G–M and G–K directions, the electrons in this band have localized nature. Fig. 2 shows the CIS spectra of Fe0.25TiTe2. The Ti 3p-3d and Fe 3p-3d resonance energies are at hnB48 and B56 eV, respectively. Since the CIS spectra have a broad peak from hnB48 eV to B56 eV for E ¼ 0:1 and 0.5 eV, both Fe 3d and Ti 3d states contribute to these flat bands. On the other hand, the spectral feature at 1.8 eV is mainly derived from Ti 3d states, because the CIS
E = -0.1 eV E = -0.5 eV
Single crystalline 1T-TiTe2 and Fe0.25TiTe2 were grown by chemical vapor transport using I2 as a carrier [5]. Clean surfaces were obtained by cleaving in situ at a base pressure better than 3 1010 Torr. The samples were cooled to 17 K during measurements using a He-flow-type cryostat and a He refrigerator for BL-1 and BL-7, respectively. Total energy resolution was set at 40 and 150 meV for BL-1 and BL-7, respectively. The angular resolution is B0.3 , which gives a wave( 1 at hn =40 eV. vector resolution Dk||B0.02 A
Intensity (arb. units)
E = -1.8 eV Fig. 1. (a) ARPES spectra of Fe0.25TiTe2 taken at hn=56 eV along G–M direction. (b) Intensity plot of the ARPES spectra shown in (a).
45
50
55 60 65 Photon Energy (eV)
70
75
Fig. 2. CIS spectra of Fe0.25TiTe2 at E=0.1, 0.5, and 1.8 eV.
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spectrum has higher intensity at hnB48 eV than at hnB56 eV. We found that the Fermi wave number of the electron pocket around M point is reduced by the Fe intercalation, while those of the hole pockets around G point are unchanged. Thus, the effect of the intercalated 3d-transition-metal atoms on the electronic structure of 1T-TiTe2 cannot be understood by a rigid-band model. The result indicates that the intercalant atoms affect strongly on the Ti 3dz2 states, not on the Te 5p states. It has been claimed that the reduction of the c-axis lattice constant on Fe intercalation is due to the formation of the local Ti–Fe–Ti covalent bond along c-axis [2–4]. The present result indicates that the additional electrons introduced by Fe intercalation are accommodated by the new 0.5-eV flat band instead of increasing the area enclosed by Fermi surface. This is in agreement with that the electrical conductivity is reduced on Fe intercalation.
Acknowledgements This work was partly supported by a Grant-inAid for COE Research (13CE2002) by the
Ministry of Education, Science, and Culture of Japan. We thank the Cryogenic Center, Hiroshima University for supplying liquid helium. The synchrotron radiation experiments have been done under the approval of HSRC (Proposal No. 02-A-43).
References [1] R.H. Friend, A.D. Yoffe, Adv. Phys. 36 (1987) 1. [2] V.G. Pleshchev, A.N. Titov, S.G. Titova, A.V. Kuranov, Neorg. Mater. 33 (11) (1997) 1333. [3] A.N. Titov, Fiz. Met. Metalloved. 81 (6) (1996) 75. [4] A.N. Titov, T.B. Popova, S.G. Titova, Phys. Solid State 41 (1999) 613. [5] A. Titov, S. Titova, M. Neumann, V. Pleschov, Yu. Yarmoshenko, L. Krasavin, A. Dolgoshein, A. Kuranov, Mol. Crystallogr. Liq. Crystallogr. 311 (1998) 161. [6] R. Claessen, R.O. Anderson, G.-H. Gweon, J.W. Allen, W.P. Ellis, C. Janowitz, C.G. Olson, Z.X. Shen, V. Eyert, M. Skibowski, K. Friemelt, E. Bucher, S. Hufner, . Phys. Rev. B 54 (1996) 2453. [7] K. Rossnagel, L. Kipp, M. Skibowski, C. Solterbeck, T. Strasser, W. Schattke, D. VoX, P. Kruger, . A. Mazur, J. Pollmann, Phys. Rev. B 63 (2001) 125104. [8] Th. Straub, R. Claessen, P. Steiner, S. Hufner, . V. Eyert, K. Friemelt, E. Bucher, Phys. Rev. B 55 (1997) 13473.