Hidden states of matter may be created if a system out of equilibrium follows a trajectory to a state that is inaccessible or does not exist under normal equilibrium conditions. We found such a hidden (H) electronic state in a layered dichalcogenide crystal of 1T-TaS2 (the trigonal phase of tantalum disulfide) reached as a result of a quench caused by a single 35-femtosecond laser pulse. In comparison to other states of the system, the H state exhibits a large drop of electrical resistance, strongly modified single-particle and collective-mode spectra, and a marked change of optical reflectivity. The H state is stable until a laser pulse, electrical current, or thermal erase procedure is applied, causing it to revert to the thermodynamic ground state.

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We use ultrashort intense laser pulses to study superconducting state vaporization dynamics in La2-xSrxCuO4 (x=0.1 and 0.15) on the femtosecond time scale. We find that the energy density required to vaporize the superconducting state is 2.0+/-0.8 and 2.6+/-1.0 K/Cu for x=0.1 and 0.15, respectively. This is significantly greater than the condensation energy density, indicating that the quasiparticles share a large amount of energy with the boson glue bath on this time scale. Considering in detail both spin and lattice energy relaxation pathways which take place on the relevant time scale of approximately 10(-12) s, the experiments appear to favor phonon-mediated pair-breaking mechanisms over spin-mediated pair breaking.

A. Sample preparationThe YBa 2 Cu 3 O 6.5 (YBCO) single crystal used here was grown by top-seeded solution growth using a Ba 3 Cu 5 O solvent [1]. The as-grown single crystal was first annealed at 700°C for 70 h with flowing oxygen and quenched down to room temperature. The La 1.85 Sr 0.15 CuO 4 (LSCO) single crystal was synthesised by a travelling-solvent-floating-zone method utilizing infrared radiation furnaces (Crystal system, FZ-T-4000) and annealed in oxygen gas under ambient pressure at 600°C for 7 days[2]. B. Femtosecond pump-probe set-upA detailed description of the set-up used is found in [3]. In a "pump-probe" experiment, a "pump" pulse excites the sample and the induced change in transmission or reflection of a delayed probe pulse monitors the relaxation behaviour. In the linear approximation ∆R R directly tracks the electronic relaxation processes, and the time constants obtained from fits of its dynamics are the characteristic times of the underlying relaxation processes. In our data, this approximation is justified by two essential characteristics: (i) the ∆R R amplitude is linear in the excitation intensity (see Figure 1a for LSCO), and (ii) the same decay times appear independently of the probe wavelength, only with different spectral weights of the individual components.In order to resolve the dynamics of fast processes very short pulses are necessary, since the instrumental response function is given by the cross correlation between the pump and probe pulses. We use sub-10 fs probe pulses from an ultrabroadband (covering a spectral range from 500 to 700 nm) non-collinear optical parametric amplifier (NOPA) and ∼15 fs pump pulses from a narrower band (wavelength tunable, in our case centred at 530 nm) NOPA. The seed pulses for the NOPAs and the amplified pulses are steered and focussed exclusively with reflecting optics to avoid pulse chirping.A schematic of the experimental apparatus is shown in Fig. 1. The laser source is a regeneratively amplified modelocked Ti:sapphire laser (Clark-MXR Model CPA-1), delivering pulses at 1 kHz repetition rate with 780 nm center wavelength, 150 fs duration, and 500 µJ energy. Both NOPAs are pumped by the second harmonic of the Ti:sapphire laser, which is generated in a 1-mm-thick lithium triborate crystal (LBO), cut for type-I phase matching in the XY plane (θ = 90°, ϕ = 31.68°, Shandong Newphotons).The ultrabroadband visible NOPA that generates the probe pulses has been described in detail before[4]; a schematic of it is shown in Fig. 2. The white light continuum seed pulses are generated by a small fraction of the fundamental

We report on a spectroscopic study of surface plasmon damping and group velocity in polycrystalline silver and gold nanowires. By comparing to single-crystalline wires and by using different substrates, we quantitatively deduce the relative damping contributions due to metal crystallinity and absorption in the substrate. Compared to absorbing substrates, we find strongly reduced plasmonic damping for polycrystalline nanowires on quartz substrates, enabling the application of such wires for plasmonic waveguide networks.