Dephasing of electrons in mesoscopic metal wires

Abstract

We have extracted the phase coherence time τ φ of electronic quasiparticles from the low field magnetoresistance of weakly disordered wires made of silver, copper and gold. In samples fabricated using our purest silver and gold sources, τ φ increases as T −2/3 when the temperature T is reduced, as predicted by the theory of electron-electron interactions in diffusive wires. In contrast, samples made of a silver source material of lesser purity or of copper exhibit an apparent saturation of τ φ starting between 0.1 and 1 K down to our base temperature of 40 mK. By implanting manganese impurities in silver wires, we show that even a minute concentration of magnetic impurities having a small Kondo temperature can lead to a quasi saturation of τ φ over a broad temperature range, while the resistance increase expected from the Kondo effect remains hidden by a large background. We also measured the conductance of Aharonov-Bohm rings fabricated using a very pure copper source and found that the amplitude of the h/e conductance oscillations increases strongly with magnetic field. This set of experiments suggests that the frequently observed "saturation" of τ φ in weakly disordered metallic thin films can be attributed to spin-flip scattering from extremely dilute magnetic impurities, at a level undetectable by other means. I. MOTIVATIONSThe time τ φ during which the quantum coherence of an electron is maintained is of fundamental importance in mesoscopic physics. The observability of many phenomena specific to this field relies on a long enough phase coherence time. 1 Amongst these are the weak localization correction to the conductance (WL), the universal conductance fluctuations (UCF), the Aharonov-Bohm (AB) effect, persistent currents in rings, the proximity effect near the interface between a superconductor and a normal metal, and others. Hence it is crucial to find out what mechanisms limit the quantum coherence of electrons.In metallic thin films, at low temperature, electrons experience mostly elastic collisions from sample boundaries, defects of the ion lattice and static impurities in the metal. These collisions do not destroy the quantum coherence of electrons. Instead they can be pictured as resulting from a static potential on which the diffusivelike electronic quantum states are built.What limits the quantum coherence of electrons are inelastic collisions. These are collisions with other electrons through the screened Coulomb interaction, with phonons, and also with extrinsic sources such as magnetic impurities or two level systems in the metal. Whereas above about 1 K electron-phonon interactions are known to be the dominant source of decoherence, 2 electron-electron interactions are expected to be the leading inelastic process at lower temperatures in samples without extrinsic sources of decoherence. 3 The theory of electron-electron interactions in the diffusive regime was worked out in the early 1980's (for a review see 4 ). It predicts a power law divergence of τ φ when the temperature T goes to zero....

Sensitivity Measurements of a Transition-Edge Hot-Electron Microbolometer for Millimeter-Wave Astrophysical Observations

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“…The fitted e-p values and conductances for both models are listed in Table 1. The disconnected model fits to values only slightly lower than literature values [12,13]. In all cases the ep conductance is substantially greater than the e-e conductance along the absorber, further supporting a disconnected model for this test device.…”

Emulating weak localization using a solid-state quantum circuit

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Low-temperature dephasing saturation from elastic magnetic spin disorder and interactions

“…13 . The situation here is to be contrasted with the absence of spin disorder, where it has been shown that…”

“…Decoherence arises from coulombic interactions, scattering by phonons, magnetic fluctuations etc. The saturation of the dephasing rate at low temperature T seen in numerous experiments [1][2][3][4][5][6][7][8][9][10][11][12][13] has attracted a vigorous interest, especially given the longstanding theoretical prediction for a vanishing τ −1 φ as the temperature T → 0. [14][15][16][17][18][19][20][21] .…”