Ultrafast Dynamics Evidence of High Temperature Superconductivity in Single Unit Cell FeSe onSrTiO3

Abstract

We report the time-resolved excited state ultrafast dynamics of single unit cell (1 UC) thick FeSe films on SrTiO_{3} (STO), with FeTe capping layers. By measuring the photoexcited quasiparticles' density and lifetime, we unambiguously identify a superconducting (SC) phase transition, with a transition temperature T_{c} of 68 (-5/+2) K and a SC gap of Δ(0)=20.2±1.5 meV. The obtained electron-phonon coupling strength λ is as large as 0.48, demonstrating the likely crucial role of electron-phonon coupling in the high temperature superconductivity of the 1 UC FeSe on STO systems. We further find a 0.05 THz coherent acoustic phonon branch in the capping layer, which provides an additional decay channel to the gluing bosons.

Comparative Review on Thin Film Growth of Iron-Based Superconductors

“…They estimated the electron-phonon coupling constant, λ, to be 0.5 from the relative intensity of replica bands. Large electron-phonon coupling to STO substrates was also suggested by some other experimental results [151,159,160]. However, at present, there are no experimental results that demonstrate the direct relation between the electron-phonon coupling and the enhancement of the superconductivity.…”

Experimental observation of copper oxide layers in cuprates by scanning tunneling microscopy

“…温超导电性也能在其他异质结中实现, 尽管这些异质 结所涉及的材料的化学组成和结构存在很大的不同. 单层FeSe/SrTiO 3 异质结 [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] 就是这一类结构体系的代 表, 而且该体系的研究工作已经在国际超导界引起了 重大反响, 被认为是开辟了高温超导领域的一个全新 研究方向 [37][38][39] 的工作. 体相FeSe在常压下的超导转变温度为9.4 K左右, 对应的超导能隙为2.2 meV [40,41] .…”

“…原位四探针电输运测 量结果则初步表明, 该体系具有超过100 K的超导转 变温度 [27] . 目前, 大多数的实验结果认为, 单层FeSe/ SrTiO 3 体系的高温超导电性是由界面电荷转移和界面 增强电声耦合共同作用的结果 [22,24,28,[32][33][34][35][36]42] . 这些研究 开启了通过界面工程设计高温超导体的新时代, 也为 理解铜氧化物和铁基超导体高温超导机理提供了新的 思路 [43] .…”

Coherent helix vacancy phonon and its ultrafast dynamics waning in topological Dirac semimetal Cd3As2

“…Ultrafast spectroscopy has been employed in observing quantum phase transitions [9][10][11][12][13] and topological properties [14][15][16]. Owing to its advantages in coherent generation and detection, ultrafast spectroscopy has been also widely used to probe the coherent phonon dynamics in quantum materials [9,[17][18][19][20][21]. Other than the helix vacancyinduced phonon modes (abbreviated as HVP), our major * Corresponding author: jmzhao@iphy.ac.cn discovery is a clear waning (with increasing temperature) behavior in its ultrafast dynamics that is "superimposed" on a regular anharmonic phonon-phonon scattering.…”

“…Our experimental setup is similar to that in Refs. [9,10] and the details are given in the Supplemental Material in Ref. [22].…”