Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 34: Metal Substrates: Structure, Epitaxy and Growth

O 34.7: Poster

Tuesday, March 17, 2015, 18:15–21:00, Poster A

Temperature-dependent surface structure of in-situ cleaved TlNi₂Se₂ investigated by STM — •Martin Schmitt¹, Tobias Mauerer¹, Paolo Sessi¹, Hangdong Wang², Qianhui Mao², Minghu Fang², and Matthias Bode¹ — ¹Physikalisches Institut, Experimentelle Physik II, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany — ²Department of Physics, Zhejiang University, Hangzhou 310027, People’s Republic of China

Recently, the Ni-chalcogenide TlNi₂Se₂ has been identified as a heavy-fermion multiband superconductor with a critical temperature T_C = 3.7 K [1]. We have investigated the temperature-dependent surface structure of in-situ cleaved TlNi₂Se₂ by means of low- and variable-temperature scanning tunneling microscopy. The cleaving process leads to large atomically flat (001) surfaces with typical terrace width that exceed 100 nm. These terraces are separated by step edges which—in the vast majority of cases—are multiples of the Tl–Tl layer spacing, d_Tl−Tl = c/2 = 6.72 Å. Our results indicate that the TlNi₂Se₂ surface structure at T ≤ 120 K critically depends on the sample temperature during the cleaving process. Low-temperature cleavage leads to a surface which is dominated by a square-shaped (√2 × √2) superstructure and coexisting stripes of a (2 × 1) structure. In contrast, samples cleaved at room temperature exhibit a more irregular “worm-like” superstructure. Temperature-dependent STM data show an irreversible transition from the former to the latter at a temperature above of about 130 K upon heating.
Hangdong Wang et al., Phys. Rev. Lett.111, 207001 (2013).