Metal–insulator transition in amorphous alloys

Abstract

We focus on the central problem of discriminating between metallic and insulating behaviour in amorphous alloys formed between a semiconductor and a metal. For this, the logarithmic temperature derivative of the conductivity, w = d ln σ/d ln T , has proved over recent years to be very helpful in determining the critical value x c of the metal content x for the metal-insulator transition (MIT). We show that, for various amorphous alloys, recent experimental results on w(T, x) are qualitatively inconsistent with the usual assumptions of continuity of the MIT at T = 0 and of σ(T, x c ) being proportional to a power of T . These results suggest that w(T, x c ) tends to 0 as T → 0, in which case the MIT should be discontinuous at T = 0 (but only there), in agreement with Mott's hypothesis of a finite minimum metallic conductivity. 71.30.+h,71.23.Cq, Typeset using REVT E X Abbreviations EDX: energy dispersive X-ray analysis MIT: metal-insulator transition MOSFET: metal oxide semiconductor field effect transistor RBS: Rutherford backscattering analysis

Numerical Investigations of Scaling at the Anderson Transition

“…The current estimate is ν ≈ 1. The interest in the exact value of ν arises since compensated semiconductors apparently have ν ≈ 1 as do amorphous metals [14,15,8]. On the other hand, for uncompensated semiconductors one had previously found ν ≈ 0.5 [9,8].…”

Semiconductor-Metal Transition in Many-Valley Semiconductors

“…At the same time, randomness in the impurity distribution also increases favouring localization (Anderson regime). However, as experiments show beyond a certain (critical) concentration of impurities the metallic transition occurs [8,9,11,20]. It is therefore clear that because of these competing effects the transitions should occur at a higher concentration than that in a model which omits localization.…”

The metal-insulator transition in disordered solids: How theoretical prejudices influence its characterization A critical review of analyses of experimental data

“…For more than fifty years, localization in disordered systems, in particular the corresponding metal-insulator transition (MIT), has attracted a lot of interest from both theoreticians and experimentalists. [1][2][3][4][5][6][7][8][9][10][11] Milestones on this way have been Anderson noting the absence of diffusion in certain lattices with disorder, 12 Mott's concept of the minimum metallic conductivity, 13 the scaling theory of localization, 14 and the renormalization group approach incorporating electron-electron interaction into localization theory. 15 Experimentally, localization in three-dimensional systems has been studied in a large number of disordered solids, such as heavily doped crystalline semiconductors (in which the disorder arises from the randomly positioned impurities), amorphous transition-metal semiconductor alloys, granular metals, and nanocrystalline substances.…”

“…15 Experimentally, localization in three-dimensional systems has been studied in a large number of disordered solids, such as heavily doped crystalline semiconductors (in which the disorder arises from the randomly positioned impurities), amorphous transition-metal semiconductor alloys, granular metals, and nanocrystalline substances. [7][8][9][10] Many of these solids are or may become application relevant; therefore they are often considered to be among the materials. 3 In various experiments, the MIT has been triggered by diverse control parameters: composition / doping, stress, magnetic field, light, as well as structure, see, for example, Refs.…”

“…Nevertheless, two repeatedly observed phenomena are in conflict with the continuity hypothesis: the scaling of the T dependences of σ in the hopping region 42,43 and the existence of specific low-temperature minima in the T dependences of the logarithmic T derivative of σ, d ln σ/d ln T . 10,21 -Because of the focus on properties of individual samples, we here mostly use total derivative symbols although σ depends not only on T but also on a control parameter. -…”