Direct Observation of the Coulomb Correlation Gap in a Nonmetallic Semiconductor, Si: B

Massey, J. G.; Lee, Mark

doi:10.1103/physrevlett.75.4266

Cited by 136 publications

(133 citation statements)

References 28 publications

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“…In the last ten years, several tunneling experiments on weakly insulating samples provided direct evidence for a pseudogap in the density of states around the Fermi level 40,41,42,43,44,45,46,47 . However, such experiments are restricted to the regime relatively close to the metalinsulator transition.…”

Section: B Coulomb Gap and Hopping Transportmentioning

confidence: 99%

Memory effect in electron glasses: Theoretical analysis via a percolation approach

Lebanon

Müller

2005

Phys. Rev. B

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We present a theory for the memory effect in electron glasses. In fast gate voltage sweeps it is manifested as a dip in the conductivity around the equilibration gate voltage. We show that this feature, also known as anomalous field effect, arises from the long-time persistence of correlations in the electronic configuration. We argue that the gate voltage at which the memory dip saturates is related to an instability caused by the injection of a critical number of excess carriers. This saturation threshold naturally increases with temperature. On the other hand, we argue that the gate voltage beyond which memory is erased, is temperature independent. Using standard percolation arguments, we calculate the anomalous field effect as a function of gate voltage, temperature, carrier density and disorder. Our results are consistent with experiments, and in particular, they reproduce the observed scaling of the width of the memory dip with various parameters.

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Section: B Coulomb Gap and Hopping Transportmentioning

confidence: 99%

Memory effect in electron glasses: Theoretical analysis via a percolation approach

Lebanon

Müller

2005

Phys. Rev. B

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“…The experimental trace of the Coulomb interactions between the electrons is the depletion of the single-particle density of states ͑DOS͒ N͑E͒ at the Fermi energy. [2][3][4][5][6][7][8][9] For a dirty three-dimensional system it is found that N͑E͒ϳ ͱ E in the metallic regime, 3,4 whereas N͑E͒ϳE 2 in the insulating regime 2 recently observed in different localized systems, [5][6][7] including magnetically doped materials. 8 Recently, using conductance measurements across the metal-insulator-transition, Lee 9 constructed the phase diagram shown in Fig.…”

mentioning

confidence: 99%

Correlation effects in the density of states of annealedGa1−xMnxAs

et al. 2007

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We report on an experimental study of low-temperature tunneling in hybrid NbTiN/ GaMnAs structures. The conductance measurements display a ͱ V dependence, consistent with the opening of a correlation gap ͑⌬ C ͒ in the density of states of Ga 1−x Mn x As. Our experiment shows that low-temperature annealing is a direct empirical tool that modifies the correlation gap and thus the electron-electron interaction. Consistent with previous results on boron-doped silicon we find, as a function of voltage, a transition across the phase boundary delimiting the direct and exchange correlation regime. DOI: 10.1103/PhysRevB.75.033308 PACS number͑s͒: 75.50.Pp, 73.40.Gk, 71.30.ϩh The new class of ferromagnetic semiconductors Ga 1−x Mn x As is known 1 to display a metal-insulator transition ͑MIT͒ as function of Mn doping. In conventional doped semiconductors the MIT, which occurs as a function of carrier density, is widely studied and considered to be a prime example of a quantum phase transition. It is understood that the spatial localization of charge carriers, which drives the MIT, reduces the ability of the system to screen charges, leading to a prominent role of the electron-electron interactions. The experimental trace of the Coulomb interactions between the electrons is the depletion of the single-particle density of states ͑DOS͒ N͑E͒ at the Fermi energy. 2-9 For a dirty three-dimensional system it is found that N͑E͒ϳ ͱ E in the metallic regime, 3,4 whereas N͑E͒ϳE 2 in the insulating regime 2 recently observed in different localized systems, 5-7 including magnetically doped materials. 8 Recently, using conductance measurements across the metal-insulator-transition, Lee 9 constructed the phase diagram shown in Fig. 1͑a͒. At low enough temperatures, 10 mK, the energy is controlled by the voltage at which the differential conductance is measured. For low energies, i.e., very close to the Fermi energy where the theory for the MIT is valid, the system is a Coulomb gap insulator below the critical density and a correlated metal above the critical density. For higher energies a mixed state develops around the critical density, in which the density of states on both sides of the transition have a common functional dependence on energies masking the existence of a critical density. The "pure" state at low densities is the regime where exchange correlations describe the Coulomb interactions, whereas above the critical density the direct Coulomb interactions rule. At low energies the DOS is clearly distinct for metallic and insulating samples and the system is in the "pure" state. At high energies the insulating and metallic states are indistinguishable from DOS measurements.The new material system GaMnAs is for low Mn doping an insulator and the resistivity diverges for T → 0, indicating localization effects. In the metallic regime this ͑III, V͒ Mn is characterized by a decreasing resistivity which eventually saturates for T → 0, although these resistivity values remain relatively high ͓ϳ10 −3 ⍀ cm, see Fig. 4͑c͔͒. Thus GaMnAs...

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“…7 The presence of the features due to the Coulomb interactions in the conductivity and DOS in disordered systems near the MIT has been well established experimentally. These effects have been mostly observed in experiments performed using the discrete sets of crystalline 8 and amorphous samples 9 with different dopant concentrations close to the critical one.…”

Section: Introductionmentioning

confidence: 99%

Variation of the density of states in amorphous GdSi at the metal-insulator transition

et al. 2004

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We have performed detailed conductivity and tunneling measurements on the amorphous, magnetically doped material ␣-Gd x Si 1−x , which can be driven through the metal-insulator transition by the application of an external magnetic field. Low temperature conductivity increases linearly with field near the transition and slightly slower on the metallic side. The tunneling conductance, proportional to the density of states N͑E͒, undergoes a gradual change with increasing field, from insulating, showing a soft gap at low bias, with a slightly slower than parabolic energy dependence, i.e., N͑E͒ϳE c , c Շ 2, towards metallic behavior, with E d , 0.5Ͻ d Ͻ 1 energy dependence. The density of states at the Fermi level in a sample, which shows already a small, but metal-like conductivity, appears to be zero at low fields, as in an insulator. We speculate that this behavior is due to the microscopic percolation nature of transport near the transition.

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Direct Observation of the Coulomb Correlation Gap in a Nonmetallic Semiconductor, Si: B

Cited by 136 publications

References 28 publications

Memory effect in electron glasses: Theoretical analysis via a percolation approach

Memory effect in electron glasses: Theoretical analysis via a percolation approach

Correlation effects in the density of states of annealedGa1−xMnxAs

Variation of the density of states in amorphous GdSi at the metal-insulator transition

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