Far-infrared photoresponse of quasi-two-dimensional granular NbN/BN films

Strom, U.; Culbertson, J. C.; Sa, Wolf; Perkowitz, Sidney; Gl, Carr

doi:10.1103/physrevb.42.4059

Phys. Rev. B

1990

DOI: 10.1103/physrevb.42.4059

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Far-infrared photoresponse of quasi-two-dimensional granular NbN/BN films

U. Strom

J. C. Culbertson

Wolf Sa

et al.

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Cited by 18 publications

(3 citation statements)

References 22 publications

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“…The relaxation rates r 2 and r 3 suggest the occurance of three lines one each at UJ andu> ± 2A/7L The temperature dependence in the pair breaking process is a bit stronger than T 6 at low temperatures. The calculations of T~1 involves ]T fc k , which for a three dimensional solid is equivalent to / / 2(m/h 2 )3 €kd€kdtk' oc e 3 in agreement with the E 3 dependence suggested by Kraus et al 5 . The resolution of the detector is limited by the line width determined from the life time of the x-ray (40).The thermal and non-equilibrium response of superconductors as radiation detectors Theory of detection of x-rays.…”

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confidence: 83%

“…Space Agency requires a highly theoretical approach combined with advanced device process developement. The latest work demonstrates an exceptional energy resolution of 53 eV when cooled to 1.5 K. The superconducting films of NbN/BN have been shown to exhibit photoresponse to visible light [3]. It has been pointed out by Jochum et al [4] that new detectors have initiated important discoveries.…”

mentioning

confidence: 99%

“…It has been pointed out by Jochum et al [4] that new detectors have initiated important discoveries. Kraus et al [5] have pointed out that the rate of relaxation of particles down to the gap edge is, t<xE 3…”

mentioning

confidence: 99%

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Theory of Detection of X-Rays by Superconductors

1997

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Two new processes occur in a superconducting film when it is used as a detector of X-rays. One of these processes is the scattering of the X-ray by a single electron which gives rise to the broadening of the X-ray line. Another process describes the breaking of a Cooper pair by the X-ray which also contributes to the width of the X-ray. The line arising from the single electron process depends on T4 whereas that arising from the pair breaking process varies almost as T6 at low temperatures. Lines occur at ℏωq ± 2Δ, and at ℏωq where ℏωq is the energy of the X-ray and 2Δ is the gap of the superconductor.

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confidence: 83%

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confidence: 99%

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Theory of Detection of X-Rays by Superconductors

1997

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Far infrared response of thin film Bi2Sr2CaCu2O8 using a free electron laser

Prettl

Lengfellner

Kaminski

et al. 1992

Int J Infrared Milli Waves

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The far infrared response of granular thin-film Bi2Sr~.CaCu208 superconductor has been investigated using long (~ 5/ts) but sharply truncated free electron laser pulses in the fi'equency range between 50 cm -1 and 125cm -1. Under constant current bias, a fast response and a slow bolometric signal component could be identified in this energy range, which is below the BCS energy gap (~ 200 cm-1). Measurements of the power dependences of the signal voltages showed that both the fast and the thermal responses are consistent with the predictions of the resistively shunted Josephson junction model. 1660 Prettl and Lengfellner IntroductionThere has been considerable interest in understanding the optical and infrared response of high-To superconductors.In previous investigations of thin granular films a wide range of response times have been observed. Slow signals, with time constants in the range of microseconds to milliseconds, were identified as a bolometric response arising from heating of the film. Fast signals in the far infrared (FIR), with time constants of nanoseconds, were attributed to several non-thermal mechanisms: an optical destruction of wave function coherence [1], the depairing of vortex-antivortex pairs [2], an optically induced charge imbalance in neighbouring superconducting grains [3] or infrared radiation generated currents in Josephson junctions inherent in granular films [4,5]. A drastic variation of the response time with frequency were found in T12Ba2CalCu208 films using FIR molecular lasers pumped by TEA CO2 lasers [6]. Below a critical frequency uc ~ 100cm -1 only fast signals, with a time constant in the order of lns, were observed. In contrast, above uc a slow response of bolometric character occurred. The transition frequency uc was identified with the energy gap value at the surface of superconducting grains. Recently non-thermal processes have been questioned by an investigation of the thermal boundary resistance of YBa2CuaOT-x films and their substrate materials [7]. It was shown that a bolometric response may occur on a nanosecond time scale: thus thermal and nonthermal effects cannot be distinguished by the time constant alone.In the present paper we report on measurements of the FIR response of thin granular film Bi2Sr2CaCu2Os using the University of California, Santa Barbara,(UCSB) Free Electron Laser (FEL). The sample was irradiated by long laser pulses truncated at the trailing edge by a rapid optical switch. Our results demonstrate that in the FIR both fast and slow signals of very different time constants are present at high powers, indicating two distinct signal generation mechanisms. The slow signal is readily identified as a bolometric response by the non -exponential decay which follows from one dimensional heat flow through the substrate to the cold finger [8]. Both types of signals show a nonlinear dependence on intensity which may be explained by the model of an effective resistively shunted Josephson junction which has the properties of a random array of junctions [9,...

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Current-driven effects in disordered arrays of Josephson junctions

Leath

1996

Physica B: Condensed Matter

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Far-infrared photoresponse of quasi-two-dimensional granular NbN/BN films

Cited by 18 publications

References 22 publications

Theory of Detection of X-Rays by Superconductors

Theory of Detection of X-Rays by Superconductors

Far infrared response of thin film Bi2Sr2CaCu2O8 using a free electron laser

Current-driven effects in disordered arrays of Josephson junctions

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