Phase coherence length of electron waves in narrow AlGaAs/GaAs quantum wires fabricated by focused ion beam implantation

Abstract

The phase coherence length Lφ of electron waves in the one-dimensional weak localization regime was studied in selectively doped AlGaAs/GaAs quantum wires fabricated by focused ion beam implantation. Estimated Lφ by fitting the modified weak localization theory to the data is ∼1.2 μm at 0.3 K, nine times longer than in the n-GaAs wires. This difference is well explained by the mobility dependence of Lφ, and shows the advantage of selectively doped structures to obtain long Lφ. Lφ increased with decreasing temperature and saturated below ∼3 K, indicating the existence of temperature-independent phase breaking mechanisms.

Intrinsic Decoherence in Mesoscopic Systems

“…Theoretically, this measured t f ͑T ͒ should increase with decreasing temperature becoming infinite in very large systems at T 0 because both the EP and EE interactions produce a t f ϳ 1͞T p where p varies between 0.5 and 3 [2, 3,5,6]. Yet in every published experiment performed down to very low temperatures, the phase coherence time is universally found to approach a temperature independent and finite value [7][8][9][10]. The temperature at which this saturation occurs varies by orders of magnitude ranging from 10 K in some GaAs devices to as low as 20 mK in a 2D Au film.…”

Dephasing of conduction electrons due to zero-point fluctuation

“…6 In fact, saturated dephasing time ͑length͒ of conduction electrons was universally found in many early experiments. [10][11][12][13] Those early experiments were explained by the heating or the magnetic impurity effect. The recent extensive experiments by MJW ruled out the popular extrinsic effects, [10][11][12][13] and pointed toward the intrinsic dephasing of conduction electrons at zero temperature.…”

“…[10][11][12][13] Those early experiments were explained by the heating or the magnetic impurity effect. The recent extensive experiments by MJW ruled out the popular extrinsic effects, [10][11][12][13] and pointed toward the intrinsic dephasing of conduction electrons at zero temperature. 5,6 This work has been drawing great attention in the condensed-matter physics community because there will be profound consequences if the proposal of zero-temperature dephasing is correct.…”

Phase-coherence time saturation in mesoscopic systems: Wave-function collapse

“…So, at very low temperature (T → 0), the density operator ρ, usually a mixture at non zero temperature, would be a pure state ( ρ = ρ 2 ) with minimal lineal entropy S = 1 − T r ρ 2 . Surprisingly, in recent experiments in mesoscopic systems, it was observed a complete saturation of τ φ at low temperature regime [3][4][5][6][7][8][9][10]. This behavior seems quite general, observed in different experimental realizations, and suggesting an intrinsic mechanism of decoherence.…”

“…The first order calculation on (17) coincides with (12) and showing the independence of the initial state l 0 . W In conclusion, we have considered an iterative model of measurement (3,5) onto an observable of a given quantum system. In the limit of small intervals of time ∆t (ii) and hopping between nearest neighbor (8), the master equation associated to the evolution probability (7) allows to define the phase-coherence time τ meas φ (12).…”