Impact of disorder in the charge density wave state of Pd-intercalated ErTe 3 revealed by the electrodynamic response
Not Available
Corasaniti, M. (ORCID:0000000198371552)↗
Engineering topics
Fisher, I. R.
Publications and source records attributed to Fisher, I. R..
Evidence for Realignment of the Charge Density Wave State in ErTe 3 and TmTe 3 under Uniaxial Stress via Elastocaloric and Elastoresistivity Measurements
Not Available
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Observation of the non-linear Meissner effect
A long-standing theoretical prediction is that in clean, nodal unconventional superconductors the magnetic penetration depth λ, at zero temperature, varies linearly with magnetic field. This non-linear Meissner effect is an equally important manifestation of the nodal state as the well studied linear-in-T dependence of λ, but has never been convincingly experimentally observed. Here we present measurements of the nodal superconductors CeCoIn 5 and LaFePO which clearly show this non-linear Meissner effect. We further show how the effect of a small dc magnetic field on λ(T) can be used to distinguish gap nodes from non-nodal deep gap minima. Our measurements of KFe 2 As 2 suggest that this material has such a non-nodal state.
36 MATERIALS SCIENCE↗
Nonequilibrium charge-density-wave order beyond the thermal limit
The interaction of many-body systems with intense light pulses may lead to novel emergent phenomena far from equilibrium. Recent discoveries, such as the optical enhancement of the critical temperature in certain superconductors and the photo-stabilization of hidden phases, have turned this field into an important research frontier. Here, we demonstrate nonthermal charge-density-wave (CDW) order at electronic temperatures far greater than the thermodynamic transition temperature. Using time- and angle-resolved photoemission spectroscopy and time-resolved X-ray diffraction, we investigate the electronic and structural order parameters of an ultrafast photoinduced CDW-to-metal transition. Tracking the dynamical CDW recovery as a function of electronic temperature reveals a behaviour markedly different from equilibrium, which we attribute to the suppression of lattice fluctuations in the transient nonthermal phonon distribution. A complete description of the system’s coherent and incoherent order-parameter dynamics is given by a time-dependent Ginzburg-Landau framework, providing access to the transient potential energy surfaces.
36 MATERIALS SCIENCE↗
Anisotropic quasiparticle coherence in nematic BaFe 2 As 2 studied with strain-dependent ARPES
The hallmark of nematic order in iron-based superconductors is a resistivity anisotropy but it is unclear to which extent quasiparticle dispersions, lifetimes, and coherence contribute. While the lifted degeneracy of the Fe d xz and d yz dispersions has been studied extensively, only little is known about the two other factors. In this work, we combine in situ strain tuning with ARPES and study the nematic response of the spectral weight in BaFe 2 As 2 . The symmetry analysis of the ARPES spectra demonstrates that the d xz band gains quasiparticle spectral weight compared to the d yz band for negative antisymmetric strain Δε yy suggesting the same response inside the nematic phase. Our results are compatible with a different coherence of the d xz and d yz orbital within a Hund's metal picture. We also discuss the influence of orbital mixing.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Ultrafast formation of domain walls of a charge density wave in SmTe 3
We study ultrafast x-ray diffraction on the charge density wave (CDW) of SmTe 3 using an x-ray free-electron laser. The high momentum and time resolution afforded by the x-ray laser enabled capturing fine wave-vector and time-dependent features of the CDW that originate from fast (in time) and sharp (in real space) variations of the CDW lattice distortion, which we attribute to an inversion of the order parameter. These domain inversions occur near the surface and are caused by the short penetration depth of the near-infrared pump with the wavelength centered at 800 nm, resulting in CDW domain walls perpendicular to the sample surface. These domain walls break the CDW long-range order on the scale of the x-ray probe depth, controlled experimentally by the x-ray incidence angle and suppress the diffraction intensity of the CDW for times much longer than the ~1–ps recovery of the electronic gap observed in time and angle-resolved photoemission spectroscopy. We model the spatial and temporal dependences of the order parameter using a simple Ginzburg-Landau model with all the parameters obtained from the published literature. We find reasonable agreement between the calculated and the measured diffraction across the momentum, time, fluence, and incidence angle dependence without adjusting any parameters. In conclusion, we reconstruct the spatial and temporal dependences of the lattice order parameter and find that at long times, depending on the pump fluence, multiple domain walls remain at distances of a few nanometers from the surface.
36 MATERIALS SCIENCE↗
Frequency-dependent sensitivity of AC elastocaloric effect measurements explored through analytical and numerical models
We present a comprehensive study of the frequency-dependent sensitivity for measurements of the AC elastocaloric effect by applying both exactly soluble models and numerical methods to the oscillating heat flow problem. These models reproduce the finer details of the thermal transfer functions observed in experiments, considering here representative data for single-crystal Ba(Fe1−xCox)2As2. Based on our results, we propose a set of practical guidelines for experimentalists using this technique. This work establishes a baseline against which the frequency response of the AC elastocaloric technique can be compared and provides intuitive explanations of the detailed structure observed in experiments.
Straquadine, J. A. W. (ORCID:0000000165309541)↗
Magnetic breakdown and charge density wave formation: A quantum oscillation study of the rare-earth tritellurides
The rare-earth tritellurides (RTe 3 , where R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y) form a charge density wave state consisting of a single unidirectional charge density wave for lighter R, with a second unidirectional charge density wave, perpendicular and in addition to the first, also present at low temperatures for heavier R. In this paper, we present a quantum oscillation study in magnetic fields up to 65T that compares the single charge density wave state with the double charge density wave state both above and below the magnetic breakdown field of the second charge density wave. In the double charge density wave state it is observed that there remain several small, light pockets with the largest occupying around 0.5% of the Brillouin zone. By applying magnetic fields above the independently determined magnetic breakdown field, the quantum oscillation frequencies of the single charge density wave state are recovered, as expected in a magnetic breakdown scenario. Measurements of the electronic effective mass do not show any divergence or significant increase on the pockets of Fermi surface observed here as the putative quantum phase transition between the single and double charge density wave states is approached.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Low work function in the 122-family of iron-based superconductors
Herein we determine the work functions of the iron arsenic compounds A Fe 2 As 2 ( A = Ca , Ba , Cs ) using photoemission spectroscopy to be 2.7 eV for CaFe 2 As 2 , 1.8 eV for BaFe 2 As 2 , and 1.3 eV for CsFe 2 As 2 . The work functions of these 122 iron-based superconductors track those of the elementary metal A but are substantially smaller. The most likely explanation of this observation is that the cleaving surface exposes only half an A -layer. The low work function and good photoemission cross section of BaFe 2 As 2 and CsFe 2 As 2 enable photoemission even from a common white LED light.
36 MATERIALS SCIENCE↗