We show that superconducting interlayer coupling, which coexists with and is depressed by stripe order in La1.885Ba0.115CuO4, can be enhanced by excitation with near-infrared laser pulses. For temperatures lower than Tc = 13 K, we observe a blue-shift of the equilibrium Josephson plasma resonance, detected by terahertzfrequency reflectivity measurements. Key to this measurement is the ability to probe the optical properties at frequencies as low as 150 GHz, detecting the weak interlayer coupling strengths. For T > Tc a similar plasma resonance, absent at equilibrium, is induced up to the spin-ordering temperature TSO ≃ 40 K. These effects are reminiscent but qualitatively different from the light-induced superconductivity observed by resonant phonon excitation in La1.675Eu0.2Sr0.125CuO6.5. Importantly, enhancement of the below-Tc interlayer coupling and its appearance above Tc are preferentially achieved when the nearinfrared pump light is polarized perpendicular to the superconducting planes, likely due to more effective melting of stripe order and the less effective excitation of quasiparticles from the Cooper pair condensate when compared to in-plane excitation.
Josephson plasma waves are linear electromagnetic modes that propagate along the planes of cuprate superconductors, sustained by interlayer tunnelling supercurrents. For strong electromagnetic fields, as the supercurrents approach the critical value, the electrodynamics become highly nonlinear. Josephson plasma solitons (JPSs) are breather excitations predicted in this regime, bound vortex-antivortex pairs that propagate coherently without dispersion. We experimentally demonstrate the excitation of a JPS in La 1.84 Sr 0.16 CuO 4 , using intense narrowband radiation from an infrared free-electron laser tuned to the 2-THz Josephson plasma resonance. The JPS becomes observable as it causes a transparency window in the opaque spectral region immediately below the plasma resonance. Optical control of magnetic-flux-carrying solitons may lead to new applications in terahertz-frequency plasmonics, in information storage and transport and in the manipulation of high-T c superconductivity.T erahertz-frequency nonlinear optics holds great potential for device applications in data storage and manipulation at high bit rates, as well as for applications in the coherent control of matter. New tabletop and accelerator-based sources, which generate electric fields at megavolt per centimetre strengths, are opening up new opportunities in this area. Recent advances have relied on direct control of selected vibrational resonances 1-6 or on the use of field enhancement in metamaterial structures 7 . In cuprate superconductors, direct excitation of the order-parameter phase has been shown to modulate the superfluid density on the ultrafast timescale 8 , effectively demonstrating non-dissipative routes to control the macroscopic state of the solid.Here, the terahertz nonlinear optics of cuprate superconductors is studied experimentally and theoretically in the general case in which nonlinear propagation effects are combined with the local response of ref. 8. The intrinsic nonlinearity of interlayer tunnelling is shown to generate solitonic modes that concentrate the electromagnetic energy in space and time, propagating without distortion inside the material.The terahertz-frequency electrodynamics of cuprate superconductors are, for fields polarized perpendicular to the planes, dominated by superconducting tunnelling between layers 9 . Cuprates are in fact stacks of extended Josephson junctions 10,11 , with distributed tunnelling inductance L J (x, y, t ) between capacitively coupled planes (x and y are the spatial coordinates in the planes and t is time).For low fields, L J is independent of space and time and a single Josephson plasma resonance (JPR) is found at ω JPR = 2π/ √ L J C (C is the equivalent capacitance of the planes, which is assumed to be constant in space and time). In most cuprates, ω JPR ranges between gigahertz (refs 12,13) and terahertz (ref. 14) frequencies. As characteristic for a plasmonic response, the superconductor is transparent and frequency dispersive for ω > ω JPR and has unity reflectivity for ω < ω JPR ....
Many applications in photonics require all-optical manipulation of plasma waves1, which can concentrate electromagnetic energy on sub-wavelength length scales. This is difficult in metallic plasmas because of their small optical nonlinearities. Some layered superconductors support Josephson plasma waves (JPWs)2,3, involving oscillatory tunneling of the superfluid between capacitively coupled planes. Josephson plasma waves are also highly nonlinear4, and exhibit striking phenomena like cooperative emission of coherent terahertz radiation5,6, superconductor-metal oscillations7 and soliton formation8. We show here that terahertz JPWs can be parametrically amplified through the cubic tunneling nonlinearity in a cuprate superconductor. Parametric amplification is sensitive to the relative phase between pump and seed waves and may be optimized to achieve squeezing of the order parameter phase fluctuations9 or single terahertz-photon devices.
We analyze the pump wavelength dependence for the photo-induced enhancement of interlayer coupling in La 1.885 Ba 0.115 CuO 4 , which is promoted by optical melting of the stripe order. In the equilibrium superconducting state (T < T C = 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 CuO 2 planes. In the striped, nonsuperconducting state (T C < T < T SO ≃ 40 K) a transient plasma resonance similar to that seen below T C appears from a featureless equilibrium reflectivity. Most strikingly, both these effects become stronger upon tuning of the pump wavelength from the mid-infrared to the visible, underscoring an unconventional competition between stripe order and superconductivity, which occurs on energy scales far above the ordering temperature.
SignificanceWe present measurements of transient photoconductivity in BaPb1−xBixO3 (BPBO)––a poorly understood material belonging to the bismuthate family, which has been coined “the other high-temperature superconductor.” The phase diagram of BPBO encompasses charge-density-wave (CDW) order in BaBiO3 (x = 1), through superconductivity for intermediate compositions, to bad metal behavior in BaPbO3 (x = 0). We present evidence for the coexistence of CDW order and superconductivity for underdoped compositions of BPBO––something that has been discussed previously, but never definitively established. These results are especially timely given that CDW correlations have recently been found in some underdoped cuprate superconductors, pointing toward a surprising commonality between some aspects of these materials. Our measurements also put energy scales on the associated charge order.
We demonstrate that the polarization states of higher harmonics emitted from crystalline solids (here silicon, quartz) are determined by both crystal symmetry and nonperturbative dynamics, opening the door to strong-field control of the harmonics' polarization states. Extending attoscience from atoms and molecules to condensed matter and nanosystems is currently one of the most fascinating frontiers of ultrafast physics. Adapting attosecond metrology techniques to observe and control electronic dynamics on sub-optical-cycle time scales opens up unprecedented opportunities for PHz electronic signal processing.Since its first observation by Ghimire et al.[1], the physics underlying high-harmonic generation (HHG) in solids has extensively been investigated (for a comprehensive review, see [2]). Recent studies have, for example, demonstrated isolated attosecond XUV pulses emitted from thin SiO 2 films [3], HHG from amorphous fused silica [4], graphene (enhanced by driving ellipticity) [5], or 2D transition metal dichalcogenides [5,6].A striking observation is the asymmetric driver-ellipticity dependence of the HHG yield for certain crystal orientations in MgO [7]. The asymmetric, non-Gaussian-shaped ellipticity profiles are in strong contrast to the ellipticity dependence in gas-phase HHG. Later works reported the generation of circularly polarized harmonics from single-color driver pulses [8,9]. To understand this peculiar behavior, we recently introduced an ab-initio time-dependent densityfunctional theory (TDDFT) framework that allows us to investigate the complex interplay between the coupled intraand interband dynamics giving rise to HHG without making a-priori assumptions [10], and we theoretically investigated the ellipticity dependence of the HHG yield in Si and MgO [11]. Here, we show that the polarization states of higher harmonics emitted from crystalline Si and quartz samples are determined by both crystal symmetry [8,9,[11][12][13] and nonperturbative dynamics [11], opening the door to strong-field control of the harmonics' polarization states.We irradiated free-standing, 2-µm-thin, (100)-cut crystalline silicon samples with 120-fs, 2.1-µm pulses from a Ti:sapphire-pumped OPA with a maximum peak intensity of 0.7 TW cm −2 (in vacuum). The driver pulse ellipticity ε was varied from ε = 0 (linear) to |ε| = 1 (circular) using a combination of quarter-wave plate (QWP) and half-wave plate (HWP) to keep the major axis of the polarization ellipse constant. Fig. 1(a)-(c) shows the harmonic ellipticities
In cuprate high-Tc superconductors, superconducting layers are separated by insulating layers. Cooper pairs can go through the insulating layer via coherent quantum tunnelling. Such structure can be considered as stacks of Josephson junctions, and its spatial and temporal characteristics are described by a nonlinear equation known as the sine-Gordon equation. With a weak electromagnetic driving field, the layered structure shows a typical plasma response which allows the propagation of linear electromagnetic waves (known as Josephson plasma waves) with frequencies only above the Josephson plasma resonance (in the THz region). When the driving field increases, the tunnelling supercurrent approaches its critical value, and the electrodynamics becomes highly nonlinear
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.