Inelastic Scattering Time and Metal-Insulator Transition in Thick Disordered Bismuth Films

The magnetoresistance of TTF-TCNQ has been measured for currents along the crystallographic b axis in static fields of 50 kOe for temperatures between 17 and 98 K. For [Formula: see text] the magnetoresistance Δρ/ρ = [ρ(50 kOe) − ρ(0)]/ρ(0) is less than 0.1% in magnitude. There is a peak of about −1.4% at 52.8 ± 0.2 K. Below 50 K, Δρ/ρ is small and negative and is described reasonably well by the formula Δρ/ρ = −(1/2)(μBH/kT)2. At all temperatures Δρ/ρ was found to be approximately independent of the orientation of the applied field with respect to the current. The high temperature behavior is consistent with that expected for a metal in the short scattering time limit [Formula: see text]. We attribute the peak at 52.8 K to the suppression of the metal–insulator transition by the magnetic field, and we show why such behavior would be expected for a Peierls transition. In the low temperature region the crystal acts like a small gap semiconductor for which the –T−2 dependence of Δρ/ρ is easily understood. We note that the peak in the magnetoresistance at 52.8 K strongly suggests that the electronic energy gap goes to zero at this temperature. One is then led to conclude that the decrease in the conductivity between 58 and 53 K is due to resistive fluctuations above the metal–insulator transition.

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Microwave Evidence for a Size-Induced Metal-Insulator Transition in Mesoscopic Conductors

MRS Proceedings ◽

10.1557/proc-124-155 ◽

1988 ◽

Vol 124 ◽

Cited By ~ 1

Author(s):

P. Marquardt ◽

G. Nimtz ◽

G. Heite ◽

H. Peters

Keyword(s):

Size Variation ◽

Insulator Transition ◽

Interference Effects ◽

Electron Wave ◽

Metal Insulator Transition ◽

Metal Insulator ◽

3 Dimensional ◽

Microelectronic Devices ◽

Scattering Time

ABSTRACTMicrowave investigations on sub-pm (“mesoscopic”) metal crystals revealed a size-induced metal-insulator transition (SIMIT). The microwaves were applied to determine the sizedependent quasi-static conductivity of metal crystals dispersed in an insulating matrix. Choosing an indium colloid for a model system allowed an in-situ particle size variation from 10 nm up to about 1μm. The experiments were carried out in a microwave bridge at 10 GHz, a frequency where the oscillation time is much longer than the elastic scattering time of electrons in a metal (quasi-static limit). The conductivity of metal crystals was found to decrease approximately with their volumes in the above size range. The 3-dimensional confinement of the electron wave packets gives rise to quantum-mechanical interference effects leading to the SIMIT as the crystals become smaller than 1μm. Experimental details and results including the sizeaffected temperature dependence of the conductivity are presented. The universal significance of the SIMIT and its consequences for the engineering of novel materials and the ultimate size-reduction in microelectronic devices are discussed as well.,

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Giant Seebeck effect across the field-induced metal-insulator transition of InAs

npj Quantum Materials ◽

10.1038/s41535-020-00296-0 ◽

2020 ◽

Vol 5 (1) ◽

Author(s):

Alexandre Jaoui ◽

Gabriel Seyfarth ◽

Carl Willem Rischau ◽

Steffen Wiedmann ◽

Siham Benhabib ◽

...

Keyword(s):

Magnetic Field ◽

Insulator Transition ◽

Quantum Limit ◽

Low Density ◽

Phonon Drag ◽

Metal Insulator Transition ◽

Metal Insulator ◽

Order Of Magnitude ◽

Scattering Time ◽

The Magnetic Field

AbstractLightly doped III–V semiconductor InAs is a dilute metal, which can be pushed beyond its extreme quantum limit upon the application of a modest magnetic field. In this regime, a Mott-Anderson metal–insulator transition, triggered by the magnetic field, leads to a depletion of carrier concentration by more than one order of magnitude. Here, we show that this transition is accompanied by a 200-fold enhancement of the Seebeck coefficient, which becomes as large as 11.3 mV K−1$$\approx 130\frac{{k}_{B}}{e}$$ ≈ 130 k B e at T = 8 K and B = 29 T. We find that the magnitude of this signal depends on sample dimensions and conclude that it is caused by phonon drag, resulting from a large difference between the scattering time of phonons (which are almost ballistic) and electrons (which are almost localized in the insulating state). Our results reveal a path to distinguish between possible sources of large thermoelectric response in other low-density systems pushed beyond the quantum limit.

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