ac method for measuring low-frequency resistance fluctuation spectra

Scofield, John

doi:10.1063/1.1139587

Cited by 219 publications

(135 citation statements)

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“…As a result we do not use the exact number of wires in any of our calculation. The noise measurement was carried out using a digital signal processing (DSP) based a.c technique (using a lock-in-amplifier) which allows simultaneous measurement of the background noise as well as the bias dependent noise from the sample [8,9]. The apparatus was calibrated down to a spectral power density S V (f ) = 10 −20 V 2 /Hz by measuring the 4k B T R Nyquist noise at a known temperature T of a calibrated resistor.…”

Section: Pacs Numbersmentioning

confidence: 99%

Observation of large low-frequency resistance fluctuations in metallic nanowires: Implications on its stability

2005

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We have measured the low frequency (1mHz ≤ f ≤ 10Hz) resistance fluctuations in metallic nanowires (diameter 15nm to 200nm) in the temperature range 77K to 400K. The nanowires were grown electrochemically in polycarbonate membranes and the measurements were carried out in arrays of nanowires by retaining them in the membrane. A large fluctuation in excess of conventional 1/f noise which peaks beyond a certain temperature was found. The fluctuations with a significant low frequency component (≃ 1/f 3/2 ) arise when the diameter of the wire ≃ 15nm and vanishes rapidly as the diameter is increased. We argue that Rayleigh-Plateau instability is the likely cause of this excess noise.

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Section: Pacs Numbersmentioning

confidence: 99%

Observation of large low-frequency resistance fluctuations in metallic nanowires: Implications on its stability

2005

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“…Low-frequency noise measurements were done using the ac noise measurement technique [23]. The measured noise power (S V ) showed 1/f α dependence for either gate (top or back) voltage with values of α close to 1 ( Fig.…”

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confidence: 99%

Quantum interference noise near the Dirac point in graphene

2014

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Effects of disorder on the electronic transport properties of graphene are strongly affected by the Dirac nature of the charge carriers in graphene. This is particularly pronounced near the Dirac point, where relativistic charge carriers cannot efficiently screen the impurity potential. We have studied time-dependent conductance fluctuations and magnetoresistance in graphene in the close vicinity of the Dirac point. We show that the fluctuations are due to the quantum interference effects due to scattering on impurities, and find an unusually large reduction of the relative noise power in magnetic field, possibly indicating that an additional symmetry plays an important role in this regime.In disordered electronic systems, quantum corrections to the conductance arise due to quantum interference between paths of electrons scattered on random impurities. In the absence of a magnetic field, the electron paths that traverse the loops in a clockwise fashion interfere constructively with the counterclockwise paths through the same loops, resulting in a small change in the conductance. Specifically, the backscattered paths (the paths that return to their origin) lead to a correction to the average conductance of the system, known as weak localization (WL) [1][2][3]. Magnetic field adds a different phase factor to the paths that are identical, but traversed in the opposite sense, removing the WL corrections, but one still observes the universal conductance fluctuations (UCF) as a function of magnetic field or chemical potential, which arise from adding the interference contributions from all possible paths [4,5]. The quantum interference contribution to the conductance also fluctuates if the impurity configuration changes over time, leading to time-dependent conductance fluctuations that are expected to cause 1/f noise [6][7][8].In graphene, the quantum interference phenomena are affected by the pseudospin and valley degrees of freedom [9,10]. Conservation of pseudospin precludes backscattering, suppressing WL and causing weak antilocalization (WAL) [11], while intervalley scattering restores the WL [12][13][14]. Additional effects, such as defects and corrugations, can completely suppress the quantum corrections [15]. Depending on the carrier density and the nature of the disorder, all three regimes (WL, WAL and the suppression of quantum corrections) are observed experimentally [16,17]. UCF in graphene depend on the carrier density and the nature of the impurity scattering, but can also depend on the details and the geometry of the sample [18][19][20]. In particular, strong intervalley scattering is found to suppress UCF [18,19], in contrast to its effect on WL. However, the majority of the theoretical and experimental work on quantum corrections has focused on the regime away from the Dirac point. In the close vicinity to the Dirac point (at low doping and low temperatures), the relativistic Dirac quasiparticles are unable to screen the long-range Coulomb interactions in the usual way, altering electron-electron inte...

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“…In general, we expect the following relation between the cut-off frequency, f c , the correlation length, ξ, and T : f c ∼ ξ −z ∼ T νz , where ν is the correlation length exponent and z is the dynamical critical exponent. Ideally, one measures the noise using a sensitive bridge setup [24] in which the large and non-fluctuating resistance background is eliminated, rather than the simple four-terminal methods used in this study. In addition, the fluctuations should be measured when the system is in a steady-state, instead of in the initial relaxation process as shown in Fig.…”

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confidence: 99%

Electron Glass in Ultrathin Granular Al Films at Low Temperatures

Bielejec

2001

Phys. Rev. Lett.

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Quench-condensed granular Al films, with normal-state sheet resistance close to 10 kΩ/✷, display strong hysteresis and ultraslow, non-exponential relaxation in the resistance when temperature is varied below 300 mK. The hysteresis is nonlinear and can be suppressed by a dc bias voltage. The relaxation time does not obey the Arrhenius form, indicating the existence of a broad distribution of low energy barriers. Furthermore, large resistance fluctuations, having a 1/f -type power spectrum with a low-frequency cut-off, are observed at low temperatures. With decreasing temperature, the amplitude of the fluctuation increases and the cut-off frequency decreases. These observations combine to provide a coherent picture that there exists a new glassy electron state in ultrathin granular Al films, with a growing correlation length at low temperatures.PACS numbers: 72.80. Ng, 64.60.My, The electron glass was first predicted to exist in disordered interacting systems nearly two decades ago [1]. Such nonergodic behavior is very interesting because one normally expects electron systems to relax rather rapidly. Over the years, a number of studies have been reported in which electrons display glassy dynamics that are often associated with non-exponential relaxation extending over many decades in time, such as the field-effect conductance measurements in compensated GaAs [2], amorphous indium-oxide films [3], and ultrathin Bi/Ge and Pb/Ge films [4]. The glassy behavior is believed to arise from the electron-electron (e-e) interactions and the Coulomb gap [5][6][7]. Recently, the electron glass has received renewed interest [8] as the subject of e-e interactions has become a central topic in understanding the metal-insulator transition in two-dimensions [9]. However, the precise role that the Coulomb gap plays in the observed glassy behavior is not clear since there is no simultaneous measurement of the conductance relaxation and the single particle density of states. In addition, there is no direct experimental effort to probe the correlation length in the glassy phase.In this Letter we report glassy behavior in the normal state of quench-condensed weakly insulating granular Al films of sheet resistance, R ✷ , of about 10 kΩ/✷ at 300 mK. We measure the relaxation of R ✷ after the temperature was varied. We have focused on weakly insulating films because R ✷ on the order of 10 kΩ/✷ is easy to measure using sensitive ac lock-in techniques, which turn out to be crucial in measuring the resistance fluctuations described below. We observed that, below 300 mK, the resistance was strongly hysteretic and displayed ultraslow, non-exponential relaxation as the temperature was varied. We have also observed strong nonlinear behavior in the hysteretic regime. What was unique to our work was the first observation in quench-condensed metal films of large resistance fluctuations below 100 mK. We argue that these observations indicate the existence of a glassy electron state in ultrathin granular Al films with a growing correlation length at l...

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ac method for measuring low-frequency resistance fluctuation spectra

Cited by 219 publications

References 28 publications

Observation of large low-frequency resistance fluctuations in metallic nanowires: Implications on its stability

Observation of large low-frequency resistance fluctuations in metallic nanowires: Implications on its stability

Quantum interference noise near the Dirac point in graphene

Electron Glass in Ultrathin Granular Al Films at Low Temperatures

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