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Discovery of Segmented Fermi Surface in Superconductor Published in Science

November 02, 2021      Author:

The research team led by Prof. Zheng Hao and Prof. Jia Jinfeng from the School of Physics and Astronomy, Shanghai Jiao Tong University, produced and detected segmented Fermi surface induced by Cooper pair momentum within the Bi2Te3/NbSe2 heterostructure using a scanning tunneling microscopy (STM) at a low temperature. The paper was accepted by Science and published on its website as a "First Release" on the morning of October 29, 2021 (China Standard Time).

Through molecular beam epitaxy, The team created 4-layer Bi2Te3 thin films, quintessential topological insulators, on top of a bulk crystal NbSe2, an s-wave superconductor. A small applied in-plane magnetic field induces a screening supercurrent, which leads to finite-momentum pairing on the topological surface states of Bi2Te3 and results in the detection of segmented Fermi surface.

Furthermore, the team observed the patterns of standing wave in the real space images using quasiparticle interference (QPI), and also proved the formation of Fermi surface with zero-energy quasiparticles with through Fourier transforms. Notably, this new Fermi surface consists of only segments of the normal state Fermi surface, whose size and location are controlled by the field strength and orientation, which corresponds with a theory predicting the superconducting state of segmented Fermi surface.

The innovative use of topological insulator/particularity of superconductor heterostructure has enabled the team to solve problems in experiments and helped them observe the segmented Fermi surface predicted 50 years ago for the first time in history. The team also discovered that the magnetic field strength and orientation could control the size and location of the new Fermi surface, and that by changing the topological surface state, new topological superconductivity could be constructed. In all, this paper offered new insights into new approaches to change the state of matter.

 

Source: School of Physics and Astrology, SJTU

Editor: Lu Xinyu

Executive Editor: Jin Xue

Translated by Wang Hui

Proofread by Xiao Yangning

 

Paper Link: https://www.science.org/doi/10.1126/science.abf1077

Abstract

A sufficiently large supercurrent can close the energy gap in a superconductor and create gapless quasiparticles through the Doppler shift of quasiparticle energy caused by finite Cooper pair momentum. In this gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal state Fermi surface, whereas the remaining Fermi surface is still gapped. Here we use quasiparticle interference to image the field-controlled Fermi surface of Bi2Te3 thin films proximitized by the superconductor NbSe2. A small applied in-plane magnetic field induces a screening supercurrent, which leads to finite-momentum pairing on the topological surface states of Bi2Te3. We identify distinct interference patterns that indicate a gapless superconducting state with segmented Fermi surface. Our results reveal the strong impact of finite Cooper pair momentum on the quasiparticle spectrum.