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Register a new userEnergy dissipation in the time domain governed by bosons in a correlated material
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In complex materials various interactions play important roles in determining the material properties. Angle Resolved Photoelectron Spectroscopy (ARPES) has been used to study these processes by resolving the complex single particle self energy $Sigma(E)$ and quantifying how quantum interactions modify bare electronic states. However, ambiguities in the measurement of the real part of the self energy and an intrinsic inability to disentangle various contributions to the imaginary part of the self energy often leave the implications of such measurements open to debate. Here we employ a combined theoretical and experimental treatment of femtosecond time-resolved ARPES (tr-ARPES) and show how measuring the population dynamics using tr-ARPES can be used to separate electron-boson interactions from electron-electron interactions. We demonstrate the analysis of a well-defined electron-boson interaction in the unoccupied spectrum of the cuprate Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ characterized by an excited population decay time constant $tau_{QP}$ that maps directly to a discrete component of the equilibrium self energy not readily isolated by static ARPES experiments.
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In quasi-two dimensional Ce(Ir,Rh)In$_5$ system, it has been suggested that the phase diagram contains two distinct domes with different heavy fermion superconducting states. We here report the systematic pressure dependence of the electron transport properties in the normal state of CeRh$_{0.2}$Ir$_{0.8}$In$_{5}$ and CeIrIn$_{5}$, which locates in first and second superconducting dome, respectively. We observed non-Fermi liquid behavior at low temperatures in both compounds, including non-quadratic $T-$dependence of the resistivity, large enhancement of the Hall coefficient, and the violation of the Kohlers rule in the magnetoresistance. We show that the cotangent of Hall angle $cot Theta_H$ varies as $T^2$, and the magnetoresistance is quite well scaled by the Hall angle as $Delta rho_{xx}/rho_{xx}propto tan^2Theta_H$. The observed transport anomalies are common features of Ce$M$In$_{5}$ ($M$=Co, Rh, and Ir) and high-$T_c$ cuprates, suggesting that the anomalous transport properties observed in CeIrIn$_{5}$ are mainly governed by the antiferromagnetic spin fluctuations, not by the Ce-valence fluctuations which has been proposed to be the possible origin for the second superconducting dome.
We investigate the origin of ubiquitous low energy kinks found in Angle Resolved Photoemission (ARPES) experiments in a variety of correlated matter. Such kinks are unexpected from weakly interacting electrons and hence identifying their origin should lead to fundamental insights in strongly correlated matter. We devise a protocol for extracting the kink momentum and energy from the experimental data which relies solely on the two asymptotic tangents of each dispersion curve, away from the feature itself. It is thereby insensitive to the different shapes of the kinks as seen in experiments. The body of available data is then analyzed using this method. We proceed to discuss two alternate theoretical explanations of the origin of the kinks. Some theoretical proposals invoke local Bosonic excitations (Einstein phonons or other modes with spin or charge character), located exactly at the energy of observed kinks, leading to a momentum independent self energy of the electrons. A recent alternate is the theory of extremely correlated Fermi liquids (ECFL). This theory predicts kinks in the dispersion arising from a momentum dependent self energy of correlated electrons. We present the essential results from both classes of theories, and identify experimental features that can help distinguish between the two mechanisms. The ECFL theory is found to be consistent with currently available data on kinks in the nodal direction of cuprate superconductors, but conclusive tests require higher resolution energy distribution curve data.
We report neutron scattering measurements, which reveal spin-liquid polymorphism in a 11 iron chalcogenide superconductor, a poorly-metallic magnetic FeTe tuned towards superconductivity by substitution of a small amount of Tellurium with iso-electronic Sulphur. We observe liquid-like magnetic dynamics, which is described by a competition of two phases with different local structure, whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in the non-superconducting FeTe, which preserves the C$_4$ symmetry of the underlying square lattice and is favored at high temperatures. The other is the antiferromagnetic plaquette phase with broken C$_4$ symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest a first-order liquid-liquid phase transition in the electronic spin system of FeTe$_{1-x}$(S,Se)$_x$. We thus discover remarkable new physics of competing spin liquid polymorphs in a correlated electron system approaching superconductivity. Our results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors.
We study conductance spectroscopy of a two-dimensional junction between a normal metal and a strongly-correlated superconductor in an applied magnetic field in the Pauli limit. Depending on the field strength the superconductor is either in the Bardeen-Cooper-Schrieffer (BCS), or in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state of the Fulde-Ferrell (FF) type. The strong correlations are accounted for by means of the Gutzwiller method what leads naturally to the emergence of the spin-dependent masses (SDM) of quasiparticles when the system is spin-polarized. The case without strong correlations (with the spin-independent masses, SIM) is analyzed for comparison. We consider both the s-wave and the d-wave symmetries of the superconducting gap and concentrate on the parallel orientation of the Cooper pair momentum Q with respect to the junction interface. The junction conductance is presented for selected barrier strengths (i.e., in the contact, intermediate, and tunneling limits). The conductance spectra in the cases with and without strong correlations differ essentially. Our analysis provides thus an experimentally accessible test for the presence of strong-correlations in the superconducting state. Namely, correlations alter the distance between the conductance peaks (or related conductance features) for carriers with spin-up and spin-down. In the uncorrelated case, this distance is twice the Zeeman energy. In the correlated case, the corresponding distance is about 30-50% smaller, but other models may provide even stronger difference, depending on details of the system electronic structure. It turns out that the strong correlations manifest themselves most clearly in the case of the junction with the BCS, rather than the FFLO superconductor, what should make the experimental verification of the present results simpler.
Metastable self-organized electronic states in quantum materials are of fundamental importance, displaying emergent dynamical properties that may be used in new generations of sensors and memory devices. Such states are typically formed through phase transitions under non-equilibrium conditions and the final state is reached through processes that span a large range of timescales. By using time-resolved optical techniques and femtosecond-pulse-excited scanning tunneling microscopy (STM), the evolution of the metastable states in the quasi-two-dimensional dichalcogenide 1T-TaS2 is mapped out on a temporal phase diagram using the photon density and temperature as control parameters on timescales ranging from 10^(-12) to 10^3 s. The introduction of a time-domain axis in the phase diagram enables us to follow the evolution of metastable emergent states created by different phase transition mechanisms on different timescales, thus enabling comparison with theoretical predictions of the phase diagram and opening the way to understanding of the complex ordering processes in metastable materials.
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