Solid State Communications 150 (2010) 1936–1939 Contents lists available at ScienceDirect Solid State Communications journal homepage: www.elsevier.com/locate/ssc Band mapping of CeAg 2 Ge 2 using angle-resolved photoemission spectroscopy Soma Banik a,∗ , Aparna Chakrabarti a , S.K. Deb a , S.N. Jha b , S.V.N. Bhaskara Rao b , Devang A. Joshi c , A. Thamizhavel c , S.K. Dhar c a Raja Ramanna Centre for Advanced Technology, Rajendra Nagar, Indore 452013, India b Spectroscopy Division, Bhabha Atomic Research Center, Mumbai 400085, India c Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India article info Article history: Received 21 May 2010 Accepted 9 July 2010 by S. Das Sarma Available online 17 July 2010 Keywords: A. Metallic single crystal B. Self-flux method E. Angle resolved photoemission and band structure calculation abstract The electronic structure of single-crystal CeAg 2 Ge 2 has been investigated by using angle-resolved photoelectron spectroscopy with synchrotron radiation at different photon energies ranging from 21 eV to 35 eV. Experimental energy bands have been mapped from the normal-emission photoelectron spectra of the CeAg 2 Ge 2 (001) surface along the Γ –Z direction. Four photoemission features are observed to show the dispersion. The experimental spectra have been interpreted with the help of calculations based on the full potential linear augmented plane wave method using density functional theory. Excellent agreement has been obtained between the theory and the experiment. The bands that show dispersion are mainly related to the Ce 4f states and the hybridized Ag 4d with Ge 4p states and the bands that does not show any dispersion along the Γ –Z direction are the hybridized Ce 4f states and the Ag 4d states. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction CeAg 2 Ge 2 is a member of the RT 2 X 2 (R = rare earth, T = transition metal, and X = Si, Ge) family of the ternary rare- earth intermetallic compounds, studied since the early 1980s. Ce-based intermetallics have attracted much attention due to vari- ous ground-state properties such as the magnetism, non-magnetic heavy fermion, and quantum criticality [1–6]. The diverse ground states are due to the competition between the Ruderman–Kittel– Kasuya–Yosida (RKKY) interaction and the Kondo effect [7]. The ground-state properties are believed to be dependent on the strength of hybridization of the f electrons with the delocalized band states. If the hybridization is small, crystal-field effects and RKKY exchange interactions determine the low-temperature prop- erties, yielding magnetic order in most cases. CeAg 2 Ge 2 is an- tiferromagnetic, with a Néel temperature of 4.6 K [8]. Neutron diffraction experiments have shown a sine-modulated structure with a magnetic moment equal to 1.85 μB at T = 1.5K[6]. It is well known that a variety of physical phenomena of crys- talline materials such as transport, optical, magnetic response, and phase transitions rely on the details of the topology of the Fermi surface. Angle-resolved photoemission spectroscopy (ARPES) has emerged as a most powerful tool for directly determining the oc- cupied electronic band structure of solids and their surfaces [9]. ∗ Corresponding author. Tel.: +91 731 2488145; fax: +91 731 2442140. E-mail addresses: somasharath@gmail.com, soma@rrcat.gov.in (S. Banik). Recently, ARPES has been performed on the closely related Ce in- termetallics such as CeCo 2 Ge 2 and CeNi 2 Ge 2 [10,11]. For CeNi 2 Ge 2 , the bands that show dispersion are mainly of Ni 3d and Ce 5d char- acter [11]. On the other hand, for CeCo 2 Ge 2 , the dispersion has been observed for the Ce 4f bands across the 3d–4f resonance [10]. We have earlier investigated the occupied electronic states of CeAg 2 Ge 2 , by a systematic Ce 4d–4f resonant photoemission spec- troscopy study [12]. CeAg 2 Ge 2 shows two resonance features in the valence band region having 4f character, and it exhibits a Fano-like sharp resonance profile. A strong hybridization was observed be- tween the Ce 4f states and the Ag 4d and Ge 4p states. X-ray pho- toemission measurements show that Ce is in the trivalent state in CeAg 2 Ge 2 , and the hybridization parameter obtained between Ce and other atoms is ≈0.19 eV [12]. To understand the momentum- dependent hybridization of Ce, Ag and Ge atoms in CeAg 2 Ge 2 we have performed an angle-resolved photoemission study. In the present work, we have investigated the electronic band structure of the CeAg 2 Ge 2 (001) surface along the Γ –Z direction by record- ing the normal-emission photoelectron spectra at different photon energies. The experimental results are interpreted with the help of theoretical first-principle calculations based on density functional theory. 2. Experimental methods CeAg 2 Ge 2 crystallizes in the ThCr 2 Si 2 structure (space group I 4/mmm), with a body-centered tetragonal lattice. The correspo- nding simple tetragonal unit cell is shown in Fig. 1. The experimen- tal lattice parameters are a = 4.301(8) Å and c = 10.973(7) Å, 0038-1098/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2010.07.019