Resistive phase transition of the superconducting Si(111)-( )-In surface

Nanoscale Research Letters, Aug 2013

Recently, superconductivity was found on semiconductor surface reconstructions induced by metal adatoms, promising a new field of research where superconductors can be studied from the atomic level. Here we measure the electron transport properties of the Si(111)-( 7 × 3 )-In surface near the resistive phase transition and analyze the data in terms of theories of two-dimensional (2D) superconductors. In the normal state, the sheet resistances (2D resistivities) R□ of the samples decrease significantly between 20 and 5 K, suggesting the importance of the electron-electron scattering in electron transport phenomena. The decrease in R□ is progressively accelerated just above the transition temperature (T c ) due to the direct (Aslamazov-Larkin term) and the indirect (Maki-Thompson term) superconducting fluctuation effects. A minute but finite resistance tail is found below T c down to the lowest temperature of 1.8 K, which may be ascribed to a dissipation due to free vortex flow. The present study lays the ground for a future research aiming to find new superconductors in this class of materials.

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Resistive phase transition of the superconducting Si(111)-( )-In surface

Nanoscale Research Letters Resistive phase transition of the √ superconducting Si(111)-( 7 × Takashi Uchihashi 0 Puneet Mishra 0 Tomonobu Nakayama 0 0 International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS) , 1-1, Namiki, Tsukuba, Ibaraki 305-0044 , Japan Recently, superconductivity was found on semiconductor surface reconstructions induced by metal adatoms, promising a new field of research where superconductors can be studied from the atomic level. Here we measure the electron transport properties of the Si(111)-(√7 × √3)-In surface near the resistive phase transition and analyze the data in terms of theories of two-dimensional (2D) superconductors. In the normal state, the sheet resistances (2D resistivities) R of the samples decrease significantly between 20 and 5 K, suggesting the importance of the electron-electron scattering in electron transport phenomena. The decrease in R is progressively accelerated just above the transition temperature (Tc) due to the direct (Aslamazov-Larkin term) and the indirect (Maki-Thompson term) superconducting fluctuation effects. A minute but finite resistance tail is found below Tc down to the lowest temperature of 1.8 K, which may be ascribed to a dissipation due to free vortex flow. The present study lays the ground for a future research aiming to find new superconductors in this class of materials. Surface reconstruction; Silicon; Indium; Superconductivity; Electron transport; Fluctuation effects; Vortex flow - Background Semiconductor surface reconstructions induced by metal adatoms constitute a class of two-dimensional (2D) materials with an immense variety [1,2]. They are considered one form of atomic layer materials which can possess novel electronic properties and device applications [3,4]. Recently, superconductivity was measured by scanning tunneling microscopy (STM) for atomically thin Pb films [5,6] and three kinds of Si(11√1) surface reconstructions: √ √ √ SIC-Pb, ( 7 × 3)-Pb, and ( 7 × 3)-In [7]. This discovery was followed by a demonstration√of ma√croscopic superconducting currents on Si(111)-( 7 × 3)-In by direct electron transport measurements [8]. These findings are important because they enable us to create superconductors from the atomic level using state-of-the-art nanotechnology. In addition, the space inversion symmetry breaking due to the presence of surface naturally leads to the Rashba spin splitting [9,10] and may consequently help realize exotic superconductors [11]. In reference[8], we√have unambiguously clarified the √ √ p√resence of Si(111)-( 7 × 3)-In (referred to as ( 7 × 3)-In here) superconductivity. However, systematic analysis on electron transport properties above and below the transition temperature (Tc) is still lacking. For example, 2D superconductors are known to exhibit the precursor of phase transition due to the thermal fluctuation effects just above Tc [12-14]. Superconductivity is established below Tc, but vortices can be thermally excited in a 2D system. Their possible motions can cause the phase fluctuation and limit the ideal superconducting property of perfect zero resistance [15]. These fundamental properties should be revealed before one proceeds to search for new superconductors in this class of 2D materials. √ √In this paper, the resistive phase transition of the ( 7 × 3)-In surface is studied in detail for a series of samples. In the normal state, the sheet resistances (2D resistivities) R of the samples decrease significantly between 20 and 5 K, which amounts to 5% to 15% of the residual resis tivity Rn,res. Their characteristic temperature dependence suggests the importance of electron-electron scattering in electron transport phenomena, which are generally marginal for conventional metal thin films. Tc is determined to be 2.64 to 2.99 K and is found to poorly correlate with Rn,res. The decrease in R is progressively accelerated just above Tc due to the superconducting fluctuation effects. Quantitative analysis indicates the parallel contributions of fluctuating Cooper pairs due to the direct (Aslamazov-Larkin term) and the indirect (MakiThompson term) effects. A minute but finite resistance tail is found below Tc down to the lowest temperature of 1.8 K, which may be ascribed to a dissipation due to free vortex flow. Methods The experimental method basically follows the procedure described in reference [8] but includes some modifications. The whole procedure from the sample preparation through the transport measurement was performed in a home-built ultrahigh vacuum (UHV) apparatus wi√thout breaking vacuum (see Figure 1a) [16,17]. First, the ( 7 × √ 3)-In surface was prepared by thermal evaporation of In onto a clean Si(111) substrate, followed by annealing at around 300°C for approximately 10 s in UHV [18-20], and was subsequently confirmed by low-energy electron diffraction and STM. The sample was then patterned by Ar+ sputtering through a shadow (...truncated)


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Takashi Uchihashi, Puneet Mishra, Tomonobu Nakayama. Resistive phase transition of the superconducting Si(111)-( )-In surface, Nanoscale Research Letters, 2013, pp. 167, Volume 8, Issue 1, DOI: 10.1186/1556-276X-8-167