Superconductors with excess quasiparticles

Elesin, V. F.; Kopaev, Yurii V.

doi:10.1070/pu1981v024n02abeh004631

Cited by 71 publications

(49 citation statements)

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“…1(b)]. These so-called light-induced gaps [1][2][3][4][5] are the analog of the induced doublets, split by the Rabi frequency R , in a resonantly excited two-level system [ Fig. 1(a)].…”

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confidence: 99%

Light-Induced Gaps in Semiconductor Band-to-Band Transitions

Haug

Mücke

et al. 2004

Phys. Rev. Lett.

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We observe a triplet around the third harmonic of the semiconductor band gap when exciting 50 -100 nm thin GaAs films with 5 fs pulses at 3 10 12 W=cm 2 . The comparison with solutions of the semiconductor Bloch equations allows us to interpret the observed peak structure as being due to a twoband Mollow triplet. This triplet in the optical spectrum is a result of light-induced gaps in the band structure, which arise from coherent band mixing. The theory is formulated for full tight-binding bands and uses no rotating-wave approximation. DOI: 10.1103/PhysRevLett.92.217403 PACS numbers: 78.20.Bh, 42.50.Md, 42.65.Re, 78.47.+p When an intense light field at frequency ! 0 excites band-to-band transitions in a semiconductor, additional energy gaps can evolve within the original bands [ Fig. 1(b)]. These so-called light-induced gaps [1][2][3][4][5] are the analog of the induced doublets, split by the Rabi frequency R , in a resonantly excited two-level system [ Fig. 1(a)]. Here, two out of the four possible optical transitions are energetically degenerate. Hence, the optical spectrum consists of three peaks -the famous Mollow triplet for atoms [6,7] or excitons [8,9]. In the semiconductor band case, the light-induced gap in, e.g., the conduction band arises because the original conduction band and the one-photon sideband of the valence band lead to an avoided crossing. The corresponding Hopfield coefficients [1] determine the amount of conduction band admixture. It is crucial to note that this admixture can be finite even far away from the fictitious crossing point. This statement becomes particularly important for Rabi energies h R approaching the photon energy h! 0 , while it can be neglected for small Rabi energies. The latter case is tacitly assumed in previous graphical representations of calculated light-induced gaps. Importantly, as a result of this finite admixture, optical transitions between the induced bands are possible throughout an appreciable fraction of momentum space. Consequently, the transitions acquire considerable spectral weight. Again, two out of the four sets of possible optical transitions are energetically degenerate and a triplet results, which we will refer to as the two-band Mollow triplet in what follows.Light-induced gaps in semiconductor bands have not unambiguously been observed yet. In order to observe the splitting, it clearly has to be larger than the damping. As typical electron dephasing times under relevant conditions are on the order of 10 fs or less, the Rabi oscillation period has to be shorter than this value. This brings one close to Rabi frequencies approaching the frequency of light -a regime which has previously been referred to as carrier-wave Rabi flopping [10]. In this regime, a splitting in the third-harmonic spectra has been observed [11]. However, as the measurements have been compared only with calculations on the basis of two-level systems [11], skepticism has been expressed whether this interpretation was correct indeed. Furthermore, later theoretical work [12...

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“…1(b)]. These so-called light-induced gaps [1][2][3][4][5] are the analog of the induced doublets, split by the Rabi frequency R , in a resonantly excited two-level system [ Fig. 1(a)].…”

mentioning

confidence: 99%

Light-Induced Gaps in Semiconductor Band-to-Band Transitions

Haug

Mücke

et al. 2004

Phys. Rev. Lett.

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“…We note that this behavior is qualitatively similar ͑as is to be expected͒ to that of a driven bulk superconductor in which the electron-phonon interaction is responsible for relaxation. 16,17 As explained in Sec. I, quantitative differences are accounted for by the different relaxation mechanism ͑tunneling͒ that operates in the present system.…”

Section: ͑319͒mentioning

confidence: 99%

“…It is a common feature of superconductors outside equilibrium. 16,17 ͒ For a symmetric coupling to the source and drain leads, one of the two states we find is superconducting ͑characterized by a nonzero order parameter͒ and the other is normal. Since we are in the regime of high tunnel barriers, at a given voltage, the superconducting island allows less current to flow between the leads than the island in the normal state.…”

Section: Introductionmentioning

confidence: 99%

“…The stability of these states strongly depend on the nature of the quasiparticle distribution function and the relaxation mechanism. 16,17,19 Proper account of superconducting fluctuations may be required to understand the transitions between the stable states and eventually to recover adiabaticity of the superconductor dynamics in the low-frequency limit. 20 In distinction from previous work, we assume that the relaxation is provided by tunneling to/from the leads rather than by inelastic processes in the bulk.…”

Section: Introductionmentioning

confidence: 99%

“…The latter forbids the use of the Boltzmann equation for the distribution function implemented in earlier studies. 16,17 Therefore our work is based on a Green's function technique.…”

Section: Introductionmentioning

confidence: 99%

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Bistability in voltage-biased normal-metal/insulator/superconductor/insulator/normal-metal structures

Snyman

Nazarov

2009

Phys. Rev. B

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As a generic example of a voltage-driven superconducting structure, we study a short superconductor connected to normal leads by means of low transparency tunnel junctions with a voltage bias V between the leads. The superconducting order parameter ⌬ is to be determined self-consistently. We study the stationary states as well as the dynamics after a perturbation. The system is an example of a dissipative driven nonlinear system. Such systems generically have stationary solutions that are multivalued functions of the system parameters. It was discovered several decades ago that superconductors outside equilibrium conform to this general rule in that the order parameter as a function of driving may be multivalued. The main difference between these previous studies and the present work is the different relaxation mechanisms involved. This does not change the fact that there can be several stationary states at a given voltage. It can however affect their stability as well as the dynamics after a perturbation. We find a region in parameter space where there are two stable stationary states at a given voltage. These bistable states are distinguished by distinct values of the superconducting order parameter and of the current between the leads. We have evaluated ͑1͒ the multivalued superconducting order parameter ⌬ at given V, ͑2͒ the current between the leads at a given V, and ͑3͒ the critical voltage at which superconductivity in the island ceases. With regards to dynamics, we find numerical evidence that only the stationary states are stable and that no complicated nonstationary regime can be induced by changing the voltage. This result is somewhat unexpected and by no means trivial, given the fact that the system is driven out of equilibrium. The response to a change in the voltage is always gradual even in the regime where changing the interaction strength induces rapid anharmonic oscillations of the order parameter.

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Dynamic Optical Bistability, Switching and Control of Self-Pulsations of Excitons and Biexcitons

Tronciu

Rotaru

1999

phys. stat. sol. (b)

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The β‐glucuronidase (GUS) gene is a widely used reporter gene in transgenic research. This study shows that although histochemical localisation of GUS activity may be very specific, differences in incubation conditions and tissue status can lead to artificial localisations that are independent of gene activity. The objective of the current studies was to evaluate the factors that affect the in‐situ localisation of β‐glucuronidase using transgenic tobacco plants as model tissues. The aspects considered include tissue size as well as and the addition of surfactants, vacuum infiltration and chemical fixatives. Transgenic tobacco plants exhibited variable staining patterns dependent on the size of tissue assayed and the treatments that affected the infiltration of substrate. A gradient of blue staining was observed in larger tissue pieces (10 mm2), where staining in central areas was light blue in contrast to edges, which stained deep indigo. More intense staining was associated with peripheral cell layers and regions adjacent to leaf veins. Thinner tissue strips incubated under similar conditions exhibited intense and even X‐Gluc staining. Addition of Triton X‐100 (1%) surfactant and vacuum infiltration (2 min) produced considerably quicker and more uniform staining (intense and consistent indigo blue colour) of the examined tissue after a 4 to 6‐h incubation. Chemical fixation of tissues before GUS assay resulted in quantitative and histochemical differences in enzyme activity that were dependent on the fixative type and duration. Quantitative measurements using the MUG fluorometric assay showed that Histochoice™ provided the highest retention of GUS activity, maintaining more than 80 and 50% of the activity after fixation for 15 and 30 min, respectively. Activity in decreasing order was obtained with paraformaldehyde, glutaraldehyde, ethanol and FAA. GUS activity was affected not only by the type of fixative, but also by the duration of fixation with longer fixation producing lower GUS activity. From the experiments performed it can be concluded that those treatments that enhance substrate penetration, i.e., the addition of surfactant and vacuum infiltration, improve the consistency and speed of X‐Gluc staining.

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Superconductors with excess quasiparticles

Cited by 71 publications

References 2 publications

Light-Induced Gaps in Semiconductor Band-to-Band Transitions

Light-Induced Gaps in Semiconductor Band-to-Band Transitions

Bistability in voltage-biased normal-metal/insulator/superconductor/insulator/normal-metal structures

Dynamic Optical Bistability, Switching and Control of Self-Pulsations of Excitons and Biexcitons

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