Surface structure and multigap superconductivity of V3Si (111) revealed by scanning tunneling microscopy
Shuyue Ding, Dongming Zhao, Tianxing Jiang, Haitao Wang, Donglai Feng, Tong Zhang
Abstract
Abstract V 3 Si, a classical silicide superconductor with relatively high $T_{\mathrm{C}}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>C</mml:mi> </mml:msub> </mml:math> (∼16 K), is promising for constructing silicon-based superconducting devices and hetero-structures. However, real space characterization on its surfaces and superconducting properties are still limited. Here we report the first low-temperature scanning tunnelling microscopy (STM) study on cleaned V 3 Si (111) single crystal surface. We observed a $\sqrt{3} \times \sqrt{3}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> <mml:mo>×</mml:mo> <mml:msqrt> <mml:mn>3</mml:mn> </mml:msqrt> </mml:math> superstructure which displays mirror symmetry between adjacent terraces, indicating the surface is V-terminated and reconstructed. The tunneling spectrum shows full superconducting gap with double pairs of coherence peaks, but has a relatively small gap size with comparing to bulk $T_{\mathrm{C}}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>C</mml:mi> </mml:msub> </mml:math> . Impurity induced in-gap state is absent on surface defects but present on introduced magnetic adatoms. Upon applying magnetic field, a hexagonal vortex lattice is visualized. Interestingly, the vortex size is found to be field dependent, and the coherence length measured from single vortex at low field is significantly larger than estimated value from bulk $H_{c2}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>H</mml:mi> <mml:mrow> <mml:mi>c</mml:mi> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> . These results reflect V 3 Si is a multi-band, s -wave superconductor.