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Abstract The increase in the resistivity with decreasing temperature followed by a drop by more than one order of magnitude is observed on the metallic side near the zero-magnetic-field metal-insulator transition in a strongly interacting two-dimensional electron system in ultra-clean SiGe/Si/SiGe quantum wells. We find that the temperature $$T_{\text {max}}$$ T max , at which the resistivity exhibits a maximum, is close to the renormalized Fermi temperature. However, rather than increasing along with the Fermi temperature, the value $$T_{\text {max}}$$ T max decreases appreciably for spinless electrons in spin-polarizing (parallel) magnetic fields. The observed behaviour of $$T_{\text {max}}$$ T max cannot be described by existing theories. The results indicate the spin-related origin of the effect.
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Critical behavior of the specific heat in Ti-Si amorphous alloys at the metal-insulator transition
In this paper, we report the measurements of specific heat of an amorphous Ti9.5Si90.5 alloy located very close to the critical point of the metal-insulator transition. In the presence of a magnetic field, the specific heat is dominated by the Schottky anomaly caused by magnetic moments associated with the dangling bonds in the matrix of amorphous Si. Subtraction of this contribution exposes the behavior of the electronic specific heat coefficient γ . The coefficient is temperature independent above 2 K and is, in order of magnitude, close to the value expected in the absence of electron-electron interactions. In the temperature range 0.4–1.5 K, the coefficient γ shows an anomalous downturn, which can be approximated by the dependence γ (T ) = γ0 ln(T/T0 ), with T0 ≈ 0.2 K. In a companion paper, we found that the Hall coefficient in Ti-Si alloys is affected by the electron-electron interaction up to much higher temperature of 150 K and also varies critically across the metal-insulator transition. We compare our results with theoretical predictions for three models, which can potentially explain the anomalous behavior of the specific heat: generalized nonlinear σ model, Coulomb glass, and many-body localization.
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- Award ID(s):
- 1904221
- PAR ID:
- 10530471
- Publisher / Repository:
- Americal Physical Society
- Date Published:
- Journal Name:
- Physical review B Condensed matter and materials physics
- Volume:
- 106
- ISSN:
- 1550-235X
- Page Range / eLocation ID:
- 18204
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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