公海555000kk线路检测・(中国)有限公司

摘要

After giving a brief introduction to the application of ultrashort laser pulses in novel quantum material and the technique of time- and angle-resolved photoemission (trARPES), I will present two examples of my recent studies on cuprate high temperature superconductor by trARPES. 1) Ultrafast studies of high Tc superconductor reveal a softening of the electron-boson interaction in concomitance with a softening/closure of the superconducting gap. The effect is negligible in the normal state and for a metallic compound, suggesting that the electron-boson interaction might be a booster for pairing in cuprates. 2) We study the initial response of a high-temperature superconductor for both coherent pairing and non-equilibrium quasiparticle recombination following perturbation with an ultrashort infrared pulse. At temperature far below the superconducting transition temperature, the build-up of maximum response in electronic states takes as long as 0.9 ps, while at high excitation density, in the normal states, and outside of the Fermi arc in the Brillouin zone, the electronic states respond the photon pulse immediately. These observations demonstrate a much slower build-up of the maximum response in perturbing a coherent pairing system than would occur if pumping a metal or non-coherently gapped state, indicating that fast stimulated emission of Cooper pairs plays an important role in governing the quasiparticles recombination in superconductors.

报告人简介

    张文涛，2005年本科毕业于中国科学技术大学物理系，2010年于中国科学院物理研究所获博士学位。2010-2013年在美国劳伦兹伯克利国家实验室做博士后研究。2013年底至今为加州福尼亚大学伯克利分校物理系Assistant Researcher。
　　主要利用基于真空紫外激光光源的超高分辨角分辨光电子谱和超快激光的时间分辨光电子能谱等尖端实验技术，在高温铜氧化物超导体的电子能谱及动态过程研究等方面作出了多项重要的工作。利用超高分辨ARPES，从实验上观察到铜氧化物超导体中存在一种新的耦合模式，并对高能色散的物理起源做了解释，而且第一次从光电子谱抽取出铜氧化物超导体的动量分辨电子配对自能函数；利用超短、超强脉冲，用具有时间分辨功能的角分辨光电子能谱仪探测到铜氧化物相图中三个不同的温度尺度并且发现结点区电子色散上的扭折与超导能隙存在着密切关系。发表文章30多篇，包括Nature, Science, Nature Communications, Physcal Review Letters文章近十篇。