Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session V1: Non-Equilibrium Aspects of Electron-Boson Coupling in High Temperature SuperconductorsInvited
|
Hide Abstracts |
Sponsoring Units: DCMP DMP Chair: Zhi-Xun Shen, Stanford University Room: Ballroom I |
Thursday, March 17, 2016 2:30PM - 3:06PM |
V1.00001: Understanding electron-boson coupling in high temperature superconductors using time-resolved photoemission. Invited Speaker: Shuolong Yang Time- and angle-resolved photoelectron spectroscopy (trARPES) is a powerful technique for studying non-equilibrium properties of high temperature superconductors. The access to electronic band structure upon optical excitation enables a detailed investigation of the temporal evolution of photo-excited carriers. With strong optical excitations changing electronic properties non-adiabatically, coherent phonon modes can also be launched and detected. We employed trARPES to study both the copper- and iron-based high temperature superconductors. In optimally doped Bi2212, we find that the trARPES-derived population lifetimes deviate from the ARPES-derived single-particle lifetimes by one to two orders of magnitude [1]. This disparity can only be understood if processes beyond electron-phonon interactions play a significant role in the electron dynamics. In FeSe/SrTiO3 systems, we observe an abrupt phonon frequency renormalization in the monolayer FeSe as compared to thicker films [2]. This result sets the basis to quantitatively understand the interfacial lattice strain. Combining the collective response of the electronic bands with information about the underlying coherent lattice motion measured by time-resolved X-ray diffraction, we develop a fundamental understanding of the electron-phonon coupling in FeSe [3]. These examples demonstrate some remarkable microscopic insights on electronic and phononic properties which can only be accessed by trARPES. [1] S.-L. Yang et al. Phys. Rev. Lett. 114, 247001 (2015) [2] S.-L. Yang et al. Nano Lett. 15, 4150 (2015) [3] S. Gerber et al. in preparation (2015) [Preview Abstract] |
Thursday, March 17, 2016 3:06PM - 3:42PM |
V1.00002: Femtosecond snapshots of the electron-boson coupling in copper oxides and other correlated materials Invited Speaker: Claudio Giannetti One of the pivotal questions in the physics of unconventional superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This issue has remained elusive as electronic correlations are expected to greatly accelerate the electron--boson scattering processes, confining them to the very femtosecond timescale. Recent advances in ultrafast spectroscopy allowed us to simultaneously push the time resolution and frequency range of transient reflectivity measurements, up to the point of direct observing the effective electron--boson interaction in doped copper oxides. The extremely fast timescale ($\sim $15 fs) is in agreement with numerical calculations based on the $t-J$ model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations with an energy spectrum extending up to $\sim $300 meV. Our results support a scenario in which the strong local magnetic correlations provide a dissipative channel that is effective on the 10 fs timescale. Secondly, we will present very recent results on the model system Na$_2$IrO$_3$, in which the interplay of the spin-orbit coupling, the onsite Coulomb repulsion and the hopping within the Ir hexagons gives rise to a complex magnetic ground state, characterized by strong antiferromagnetic correlations below 100 K and the emergence of a zig-zag magnetic phase at T$=$12 K. The energy exchange between the photoexcited charge carriers and the antiferromagnetic background is observed by monitoring a specific high-energy quasi-molecular orbital, which turns out to be sensitive to the magnetization of the system. [Preview Abstract] |
Thursday, March 17, 2016 3:42PM - 4:18PM |
V1.00003: Signatures of electron-boson coupling in the time domain: beyond the equilibrium interpretation Invited Speaker: Alexander Kemper A powerful method to study the interactions between electrons and bosons in high-Tc superconductors is the measurement of the single-particle spectral function. The recent development of time-resolved ARPES (tr-ARPES) has allowed this measurement of be performed out of equilibrium, where the material is driven by an ultrafast laser pump pulse. We have developed a theoretical framework to complement to these experiments, and here we report on several aspects of electron-boson coupling out of equilibrium. First, we will illustrate how time-resolved spectroscopy can be used to study the coupling between electrons and phonons observing the decay rate of the transient signals as a function of energy, momentum, and time. A sufficiently strongly coupled phonon will exhibit a signature in the tr-ARPES spectra as both a kink in the dispersion as well as a sharp change of the decay rates, and we will discuss how these effects appear out of equilibrium. [1][2]\\ \\ Second, we will focus on the return to equilibrium in systems with multiple interaction types, and show that there are two distinct types of scattering processes: those types of interactions that conserve the energy within a subsystem, and those that do not. While in equilibrium these two contribute equally to the linewidth, we will show that out of equilibrium they behave differently -- the first type are mainly responsible for thermalization within the electronic subsystem, whereas the second type drain the energy out. As a result, the scattering rates out of equilibrium can be vastly different from the linewidth, and the features of the second type of interactions can be clearly observed.[3][4]\\ \\ 1. M. Sentef et al., Phys. Rev. X 3, 041033 (2013)\\ 2. A.F. Kemper et al., Phys. Rev. B 90, 075126 (2014)\\ 3. S.L. Yang et al., Phys. Rev. Lett. 114, 247001 (2015)\\ 4. J. Rameau et al., arXiv:1505.07055 [Preview Abstract] |
Thursday, March 17, 2016 4:18PM - 4:54PM |
V1.00004: Time-resolved study of Higgs mode in superconductors Invited Speaker: Ryo Shimano The behavior of superconductors far from equilibrium has been intensively studied over decades. Goals of these studies are the elucidation of bosonic fluctuations essential for the pairing mechanisms, the manifestation of competing orders or hidden phases, and the optical manipulation of superconductivity. The study of collective modes is crucially important for these perspectives as it provides the information on the dynamics of order parameters in non-equilibirium states. Generally, collective modes in ordered phases associated with spontaneous symmetry breaking are classified into 1) gapless phase modes and 2) gapped amplitude modes. In superconductors, the phase mode is eaten by gauge field, according to the Anderson-Higgs mechanism. The remaining amplitude mode is recently termed as Higgs mode from its analogy to the Higgs boson in particle physics. Despite its long history of investigation, unambiguous observation of Higgs mode has remained elusive. This is because the Higgs mode does not have a charge nor electric dipole and therefore it does not couple directly to the electromagnetic field. Here we report on our recent observation of Higgs mode in s-wave superconductors by using THz-pump and THz-probe spectroscopy technique. After nonadiabatic excitation near the superconducting gap energy with monocycle THz pulses, Higgs mode was observed as oscillations in the transmission of THz probe pulse. The resonant nonlinear coupling between the Higgs mode and coherent radiation field was also discovered, resulting in an efficient third order harmonic generation of the incident THz radiation. The extension of experiments to multiband superconductors and unconventional superconductors will be discussed. [Preview Abstract] |
Thursday, March 17, 2016 4:54PM - 5:30PM |
V1.00005: Optical probes of symmetry breaking in magnetic and superconducting BaFe$_{2}$(As$_{1-x}$P$_{x})_{2}$ Invited Speaker: Joseph Orenstein The discovery of iron pnictide superconductors has opened promising new directions in the effort to fully understand the phenomenon of high-$T_{c}$, with a focus on the connections between superconductivity, magnetism, and electronic nematicity. The BaFe$_{2}$(As$_{1-x}$P$_{x})_{2}$ (P:Ba122) system in particular has received attention because isovalent substitution of As for P generates less disorder than doping on the Fe site. The phase diagram of P:Ba122 is characterized by a line of simultaneous antiferromagnetic (AF) and tetragonal-to-orthorhombic transitions, $T_{s}(x)$, that penetrates the superconducting dome at x$=$0.28, just below optimal doping ($x_{opt}=$0.30). In this work, we use spatially-resolved optical polarimetry and photomodulated reflectance to detect linear birefringence and therefore breaking of 4-fold rotational (C$_{4})$ symmetry. In underdoped ($x$\textless 0.28) samples, birefringence appears at $T $\textgreater $T_{s} $and grows continuously with decreasing $T$ . The birefringence is unidirectional in a large (300 $\mu $m x300 $\mu $m) field of view, suggesting that C$_{4}_{\, }$breaking in this range of $T$ is caused by residual strain that couples to a diverging nematic susceptibility. Birefringence maps just below $T_{s}(x)$ show the appearance of domains, indicating the onset of spontaneous symmetry breaking to an AF ground state. Surprisingly, in samples with $x$\textgreater 0.28, in which the low $T$ phase is superconducting/ tetragonal rather than AF/orthorhombic, C$_{4}_{\, }$breaking is observed as well, with an abrupt onset and domain formation at 55 K. We tentatively associate these features with a transition to an AF phase induced by residual strain, as previously proposed [H.-H. Kuo et al. Phys. Rev. B86, 134507 (2012)] to account for structure in resistivity vs. $T$. Time-resolved photomodulation allow us to follow the amplitude of the AF order with time following pulsed photoexcitation. Below $T_{c}$ the AF order at first weakens , but then strengthens in response to the photoinduced weakening of superconductivity. This complex time evolution is accounted for quantitatively by a model based on the coexistence and competition of AF and superconducting order. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700