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A. Prinz

Publications and source records attributed to A. Prinz.

17 recordsLinked to original sources
arXiv2002

On the two-dimensional metallic state in silicon-on-insulator structures

It is shown that the electronic conduction in silicon-on-insulator (SOI) layers exhibits a metallic regime which is very similar to that in high-mobility Si-metal oxide semiconductor structures (MOS). The peak in the electron mobility versus density, the strong drop in resistivity and the critical concentration for the metal-insulator transition are all consistent. On the basis of our SOI data for the temperature and in-plane magnetic field dependence of the resistivity, we discuss several models for the metallic state in two dimensions. We find that the observed behavior can be well described by the theory on the interaction corrections in the ballistic regime. For the investigated regime, the temperature dependent screening of scattering potentials gives also a good description of the data.

cond-mat.str-el↗
arXiv2002

Interaction Effects in Conductivity of Si Inversion Layers at Intermediate Temperatures

We compare the temperature dependence of resistivity ρ(T) of Si MOSFETs with the recent theory by Zala et al. This comparison does not involve any fitting parameters: the effective mass m* and g*-factor for mobile electrons have been found independently. An anomalous increase of ρwith temperature, which has been considered a signature of the "metallic" state, can be described quantitatively by the interaction effects in the ballistic regime. The in-plane magnetoresistance ρ(B) is qualitatively consistent with the theory; however, the lack of quantitative agreement indicates that the magnetoresistance is more susceptible to the sample-specific effects than ρ(T).

cond-mat.str-el↗
arXiv2001

The low-density spin susceptibility and effective mass of mobile electrons in Si inversion layers

We studied the Shubnikov-de Haas (SdH) oscillations in high-mobility Si-MOS samples over a wide range of carrier densities $n\simeq (1-50) \times 10^{11}$cm$^{-2}$, which includes the vicinity of the apparent metal-insulator transition in two dimensions (2D MIT). Using a novel technique of measuring the SdH oscillations in superimposed and independently controlled parallel and perpendicular magnetic fields, we determined the spin susceptibility $χ^*$, the effective mass $m^*$, and the $g^*$-factor for mobile electrons. These quantities increase gradually with decreasing density; near the 2D MIT, we observed enhancement of $χ^*$ by a factor of $\sim 4.7$.

cond-mat.mes-hall↗
arXiv2001

Exclusion of quantum coherence as the origin of the 2D metallic state in high-mobility silicon inversion layers

The temperature and density dependence of the phase coherence time $τ_ϕ$ in high-mobility silicon inversion layers was determined from the magnetoresistivity due to weak localization. The upper temperature limit for single-electron quantum interference effects was delineated by comparing $τ_ϕ$ with the momentum relaxation time $τ$. A comparison between the density dependence of the borders for quantum interference effects and the strong resistivity drop reveals that theses effects are not related to each other. As the strong resistivity drop occurs in the Drude regime, the apparent metallic behavior can not be caused by quantum coherent effects.

cond-mat.mes-hall↗
arXiv2001

Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high mobility (100) Si-inversion layers

We report studies of the magnetoresistance (MR) in a two-dimensional electron system in (100) Si-inversion layers, for perpendicular and parallel orientations of the current with respect to the magnetic field in the 2D-plane. The magnetoresistance is almost isotropic; this result does not support the suggestion of the orbital origin of the MR in Si-inversion layer. In the hopping regime, however, the MR contains a weak anisotropic component that is non-monotonic in magnetic field. We found that the field, at which the MR saturates, for different samples varies by a factor of two, being lower or higher than the field of complete spin polarization of free carriers. Therefore, the saturation of the MR can not be identified with the spin polarization of free carriers.

cond-mat.str-el↗
arXiv2001

Effect of the In-Plane Magnetic Field on Conduction of the Si-inversion Layer: Magnetic Field Driven Disorder

We compare the effects of temperature, disorder and parallel magnetic field on the metallic-like temperature dependence of the resistivity. We found a similarity between the effects of disorder and parallel field: the parallel field weakens the metallic-like conduction in high mobility samples and make it similar to that for low-mobility samples. We found a smooth continuous effect of the in-plane field on conduction, without any threshold. While conduction remains non-activated, the parallel magnetic field restores the same resistivity value as the high temperature does. This matching sets substantial constraints on the choice of the theoretical models developed to explain the mechanism of the metallic conduction and parallel field magnetoresistance in 2D carrier systems. We demonstrate that the data for magneto- and temperature dependence of the resistivity of Si-MOS samples in parallel field may be well described by a simple model of the magnetic field dependent disorder.

cond-mat.str-el↗
arXiv2001

Valley Splitting in Si-Inversion Layers at Low Magnetic Fields

We report novel manifestation of the valley splitting for the two valley electron system in (100) Si-inversion layers at low carrier density. We found that valley splitting causes almost 100% modulation of the Shubnikov de Haas oscillations in very low magnetic fields, almost on the bound of the quantum interference peak of the negative magnetoresistance. From the interference pattern of oscillations we determined the valley splitting in the B=0 limit which appears to vary only within a factor of 1.3 over the density range (3-7)x10^{11}/cm^2. We found also that level broadenings in both electron valleys differ only by < 3%. The latter result shows that the inter-valley scattering is not responsible for the strong (six fold) `metallic-like' changes of the resistivity with temperature.

cond-mat.str-el↗
arXiv2000

Weak-localization type description of conduction in the "anomalous" metallic state

This paper is devoted to the temperature dependence of the resistivity in Si- MOS samples over the wide range of densities in the ``metallic phase'' (n>n_c) but not too close to the critical density n_c. Three domains of different behavior in ρ(T) are identified. These are: [i] quantum domain of `low-temperatures', where a logarithmic T-dependence of ρ(with $dρ/dT<0$) dominates; [ii] semi-classical domain of `high-temperatures', in which Drude resistivity strongly varies with T (with dρ/dT>0); and [ii] crossover between the former two, where a linear T-dependence dominates (with dρ/dT>0). In the crossover regime and at higher densities (n>20x10^{11}/cm^2), ρ(T) goes through a minimum at temperature T_{min}. Both the absolute value of T_{min} and its dependence on density are found to be in an agreement with the conventional weak-localization theory. For n smaller than \sim 20x10^{11}/cm^2, the theoretical estimate for T_{min} falls outside the experimentally accessible temperature range. This explains the absence of the minimum at these densities in the data. In total, over the two decades in the temperature (domains [ii] and [iii]), the two semiclassical effects mimic the metallic like transport properties. Our analysis shows that the behaviour of ρ(T) in the region of ρ<< h/e^2 can be described phenomenologically in terms of the conventional weak-localization theory.

cond-mat.str-el↗
arXiv1999

Weak localization in the 2D metallic regime of Si-MOS

The negative magnetoresistance due to weak localization is investigated in the two-dimensional metallic state of Si-MOS structures for high conductance values between 35 and 120 e^2/h. The extracted phase coherence time is equal to the momentum relaxation time at 10 K but nearly 100 times longer at the lowest temperature. Nevertheless, only weak logarithmic corrections to the conductivity are present in the investigated temperature and concentration range thus proving the absence of strong quantum effects due to electron-electron interaction. From saturation effects of the phase coherence time a lower boundary for spin-orbit scattering of about 200 ps is estimated.

cond-mat.mes-hall↗
arXiv1999

Time-dependent Effects in the Metallic Phase in Si-MOS: Evidence for Non-Diffusive Transport

We have found that the conduction in Si-MOS structures has a substantial imaginary component in the metallic phase for the density range 6 \times n_c > n > n_c, where n_c is the critical density of the metal-insulator transition. For high mobility samples, the corresponding delay (or advance) time equals approximately to 0.1 - 10ms and increases exponentially as density and temperature decrease. In very low mobility samples, at temperature of 0.3K, the time-lag in establishing the equilibrium resistance reaches hundreds of seconds. The delay (advance) times are approximately 10^2-10^8 times larger than the overall RC-time of the gated structure. These results give evidence for a non-Boltzmann character of the transport in the low-density metallic phase. We relate the time-dependent effects to tunneling of carries between the 2D bulk and localized states.

cond-mat.str-el↗
arXiv1999

Weak Field Hall Resistance and Effective Carrier Density Through Metal-Insulator Transition in Si-MOS Structures

We studied the weak field Hall voltage in 2D electron layers in Si-MOS structures with different mobilities, through the metal-insulator transition. In the vicinity of the critical density on the metallic side of the transition, we have found weak deviations (about 6-20 %) of the Hall voltage from its classical value. The deviations do not correlate with the strong temperature dependence of the diagonal resistivity rho_{xx}(T). The smallest deviation in R_{xy} was found in the highest mobility sample exhibiting the largest variation in the diagonal resistivity ρ_{xx} with temperature (by a factor of 5).

cond-mat.str-el↗
arXiv1998

Maximum Metallic Conductivity in Si-MOS Structures

We found that the conductivity of the two-dimensional electron system in Si-MOS structures is limited to a maximum value, G_{max}, as either density increases or temperature decreases. This value G_{max} is weakly disorder dependent and ranging from 100 to 140 e^2/h for samples whose mobilities differ by a factor of 4.

cond-mat.str-el↗
arXiv1998

Logarithmic Temperature Dependence of the Conductivity and Lack of Universal One-Parameter Scaling in the Two-Dimensional Metal

We show that the two-dimensional metallic state in Si-MOS samples persists over a wide range of temperatures (16 mK to 8 K), sample peak mobilities (varying by a factor of 8), carrier densities (0.8 to $35\times 10^{11}$ cm$^{-2}$) and conductances from 0.3 to $120 e^2/h$. Our data reveal a failure of the universal one-parameter scaling. We have found a weak delocalizing logarithmic correction to the conductivity, which governs a weak increase in the conductivity of the 2D metal as $T$ approaches zero.

cond-mat.str-el↗
arXiv1997

Interaction effects at the magnetic-field induced metal-insulator transition in Si/SiGe superlattices

A metal-insulator transition was induced by in-plane magnetic fields up to 27 T in homogeneously Sb-doped Si/SiGe superlattice structures. The localisation is not observed for perpendicular magnetic fields. A comparison with magnetoconductivity investigations in the weakly localised regime shows that the delocalising effect originates from the interaction-induced spin-triplet term in the particle-hole diffusion channel. It is expected that this term, possibly together with the singlet particle-particle contribution, is of general importance in disordered n-type Si bulk and heterostructures.

cond-mat.mes-hall↗
arXiv1997

Instability of the Two-Dimensional Metallic Phase to Parallel Magnetic Field

We report on magnetotransport studies of the unusual two-dimensional metallic phase in high mobility Si-MOS structures. We have observed that the magnetic field applied in the 2D plane suppresses the metallic state, causing the resistivity to increase dramatically by more than 30 times. Over the total existence range of the metallic state, we have found three distinct types of the magnetoresistance, related to the corresponding quantum corrections to the conductivity. Our data suggest that the unusual metallic state is a consequence of both spin- and Coulomb-interaction effects.

cond-mat.str-el↗