Temperature and fluence dependence of the 1.55-eV optical transient reflectivity in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ was measured and analysed in the low and high excitation density limit. The effective magnitude of the superconducting gap of $\sim 5$ meV obtained from the low-fluence-data bottleneck model fit is consistent with the ARPES results for the $γ$-hole Fermi surface. The superconducting-state nonthermal optical destruction energy was determined from the fluence dependent data. The in-plane optical destruction energy scales well with T$_{\mathrm{c}}^{2}$ and is found to be similar in a number of different layered superconductors.
Temperature-dependent reflectivity measurements in the frequency range 85 - 7000 cm$^{-1}$ were performed on BaFe$_2$As$_2$ single crystals under pressure up to $\sim$5 GPa. The corresponding pressure- and temperature-dependent optical conductivity was analyzed with the Drude-Lorentz model to extract the coherent and incoherent contributions. The gradual suppression of the spin-density wave (SDW) state with increasing pressure and the appearance of the superconducting phase coexisting with the SDW phase at 3.6~GPa were observed. At 3.6~GPa, the reflectivity reaches unity below $\sim$95~cm$^{-1…
We investigate coherent phonon oscillations of BaFe$_2$As$_2$ using optical pump-probe spectroscopy. Time-resolved optical reflectivity shows periodic modulations due to $A_{1g}$ coherent phonon of $c$-axis arsenic vibrations. Optical probe beams polarized along the orthorhombic $a$- and $b$-axes reveal that the initial phase of coherent oscillations shows a systematic deviation as a function of temperature, although these oscillations arise from the same $c$-axis arsenic vibrations. The oscillation-phase remains anisotropic even in the tetragonal structure, reflecting a nematic response of Ba…
We perform, as a function of uniaxial stress, an optical-reflectivity investigation of the representative 'parent' ferropnictide BaFe$_2$As$_2$ in a broad spectral range, across the tetragonal-to-orthorhombic phase transition and the onset of the long-range antiferromagnetic order (AFM). The infrared response reveals that the $dc$ transport anisotropy in the orthorhombic AFM state is determined by the interplay between the Drude spectral weight and the scattering rate, but that the dominant effect is clearly associated with the metallic spectral weight. In the paramagnetic tetragonal phase, th…
Multi-gap superconductivity in a BaFe1.84Co0.16As2 film from optical measurements at terahertz frequencies
测量了高质量铁基超导体BaFe $_{1.84}$ Co $_{0.16}$ As $_2$外延薄膜的THz反射特性，T_（$_c$）=22.5 K.通过脉冲激光沉积在具有外延SrTiO $_3$中间层的DyScO $_3$衬底上生长膜。测量的$R_S/R_N$谱，即超导和正常状态反射率之间的反射率比，提供了接近15 cm $^{-1}$的超导间隙$Δ_A$的明确证据。详细的数据分析表明，一个两带，两个间隙模型是绝对必要的，以获得一个很好的描述所测量的$R_S/R_N$频谱。低能$Δ_A$能隙结果被很好地确定（$Δ_A$ =15.5 $\pm$ 0.5 cm $^{-1}$），而高能能隙$Δ_B$的值更不确定（$Δ_B$ =55 $\pm$ 7 cm $^{-1}$）.我们的研究结果提供了一个无节点的各向同性双间隙的情况下，与存在的两个光学间隙对应的2 $Δ/kT_c$值接近2和7的证据。
A systematic temperature dependent study of the femtosecond optical superconducting (SC) state destruction and recovery in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ cuprate superconductor by means of the all-optical polarization-sensitive multi-pulse spectroscopy is presented. At low temperatures and a partial SC state suppression an anisotropic SC-gap recovery-timescale is suggested by the data. The SC state destruction and recovery dynamics are compared to the recent TR-ARPES-inferred SC-gap dynamics and a qualitative agreement is found. Using a phenomenological response function the experimental …
Competition between the Pseudogap and Superconducting States of Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+δ}$ Single Crystals Revealed by Ultrafast Broadband Optical Reflectivity
用超快宽带瞬态反射率实验研究了Bi $_{2}$ Sr $_{2}$ Ca $_{0.92}$ Y $_{0.08}$ Cu $_{2}$ O $_{8+δ}$中赝能隙的非平衡动力学与超导相的相互作用.一旦建立了超导电性，赝能隙的弛豫速度就会比正常状态快2倍，而相应的瞬态反射率变化在$\sim$ 0.5 ps后改变符号。$\sim$。结果可以用一组耦合的赝能隙和超导序参量的微分方程来描述。耦合项的符号和强度表明两相之间的竞争非常弱，允许它们共存。
Doping dependence of femtosecond quasi-particle relaxation dynamics in Ba(Fe,Co)_2As_2 single crystals: possible evidence for normal state nematic fluctuations
本文系统地研究了电子掺杂Ba（Fe_{1-x} Co_{x}）_{2} As_{2}单晶的光激发准粒子弛豫和低能电子结构随Co掺杂量（0<= x <=0.11）的变化。$x$的光致反射率瞬态的演变没有突变。在斜方晶系自旋密度波（SDW）状态下，检测到与部分电荷间隙开口相关的瓶颈，类似于以前在不同SDW铁磷属元素化物中的结果。相对电荷间隙幅度随着x的增加而减小。在超导（SC）状态下，由于SC状态在亚0.5皮秒时间尺度上的部分（或完全）破坏，出现了额外的弛豫分量。根据SC组分的饱和行为，确定了最佳掺杂附近的光学SC态破坏能U_p/k_B= 0.3K/Fe。SC状态的随后相对缓慢的恢复指示干净的SC间隙。在正常状态下的瞬态反射率振幅的T-依赖性是一致的QP态密度中的赝能隙的存在。瞬态的极化各向异性表明，赝能隙的行为可能与一个破点对称性所产生的电子涨落持续到T~200 K在任何x。Eliashberg函数的二阶矩，从金属态在较高温度下的弛豫速率获得，表明中等的电子-声子耦合，λ <~0.3，随着掺杂的增加而降低。
Optically induced coherent transport far above Tc in underdoped YBa2Cu3O6+x
本文报道了YBa_2Cu_2O_（6 +x）的光致瞬态，在该瞬态中，垂直于Cu-O平面的输运变得高度相干。这种效应是通过用中红外光脉冲激发来实现的，该中红外光脉冲被调谐到顶端氧振动的共振频率，从而调制晶格和电子性质。在超导转变温度Tc以下，超导层间耦合的平衡特征增强。最引人注目的是，光激发诱导一个新的反射率边缘在更高的频率比平衡约瑟夫森等离子体共振，伴随着增强的低频虚电导率。在Tc以上，非相干平衡电导率变得高度相干，出现反射率边缘和正虚电导率，其随频率降低而增加。在YBa_2Cu_2O_6.45和YBa_2Cu_2O_6.5中观察到这些特征直到室温。高于Tc的数据可以通过假设光仅在固体的一小部分上重新建立瞬态超导状态来拟合，寿命为几皮秒。非超导输运也可以解释这些观测结果，尽管我们必须假设在100 K时瞬态载流子迁移率接近10^4 cm ^2/（V.sec），且载流子密度与低于Tc的超流体密度相似。我们的研究结果表明，高度非常规的非平衡物理和复杂固体的光学控制开辟了新的前景。
We analyze the pump wavelength dependence for the photo-induced enhancement of interlayer coupling in La1.885Ba0.115CuO4, which is promoted by optical melting of the stripe order. In the equilibrium superconducting state (T < Tc = 13 K), in which stripes and superconductivity coexist, time-domain THz spectroscopy reveals a photo-induced blue-shift of the Josephson Plasma Resonance after excitation with optical pulses polarized perpendicular to the CuO2 planes. In the striped, non-superconducting state (Tc < T < T_SO = 40 K) a transient plasma resonance similar to that seen below Tc appears fro…
The polarized femtosecond spectroscopies obtained from well characterized (100) and (110) YBa2Cu3O7-δthin films are reported. This bulk-sensitive spectroscopy, combining with the well-textured samples, serves as an effective probe to quasiparticle relaxation dynamics in different crystalline orientations. The significant anisotropy in both the magnitude of the photoinduced transient reflectivity change and the characteristic relaxation time indicates that the nature of the relaxation channel is intrinsically different in various axes and planes. By the orientation-dependent analysis, d-wave sy…
Optical drives at terahertz and mid-infrared frequencies in quantum materials are increasingly used to reveal the nonlinear dynamics of collective modes in correlated many-body systems and their interplay with electromagnetic waves. Recent experiments demonstrated several surprising optical properties of transient states induced by driving, including the appearance of photo-induced edges in the reflectivity in cuprate superconductors, observed both below and above the equilibrium transition temperature. Furthermore, in other driven materials, reflection coefficients larger than unity have been…
Signatures of three-dimensional photo-induced superconductivity in YBa$_2$Cu$_3$O$_{6.48}$
Max Planck Institute for the Structure and Dynamics of Matter（马普物质结构与动力学研究所）；Physics Department, Politecnico di Milano（米兰理工大学物理系）；Max Planck Institute for Solid State Research（马普固态研究所）；Department of Physics, Clarendon Laboratory, University of Oxford（牛津大学克拉伦登实验室物理系）
