arXiv subjects

W. Pan

Publications and source records attributed to W. Pan.

57 records · Page 4Linked to original sources

arXiv1999

Exact Quantization of Even-Denominator Fractional Quantum Hall State at $ν$=5/2 Landau Level Filling Factor

We report ultra-low temperature experiments on the obscure fractional quantum Hall effect (FQHE) at Landau level filling factor $ν$=5/2 in a very high mobility specimen of $μ=1.7 \times 10^7$ cm$^2$/Vs. We achieve an electron temperature as low as $\sim$ 4~mK, where we observe vanishing $R_{xx}$ and, for the first time, a quantized Hall resistance, $R_{xy}=h/(5/2e^2)$ to within 2 ppm. $R_{xy}$ at the neighboring odd-denominator states $ν$=7/3 and 8/3 is also quantized. The temperature dependences of the $R_{xx}$-minima at these fractional fillings yield activation energy gaps $Δ_{5/2}$=0.11K, $Δ_{7/3}$=0.10K, and $Δ_{8/3}$=0.055K.

cond-mat.mes-hall↗

arXiv1999

Strongly Anisotropic Electronic Transport at Landau Level Filling Factor $ν= 9/2$ and $ν= 5/2$ Under Tilted Magnetic Field

We have investigated the influence of an increasing in-plane magnetic field on the states at half-filling of Landau levels ($ν$ = 11/2, 9/2, 7/2, and 5/2) of a two-dimensional electron system. In the electrically anisotropic phase at $ν$ = 9/2 and 11/2 an in-plane magnetic field of $\sim$ 1-2 T overcomes its initial pinning to the crystal lattice and {\it reorient} this phase. In the initially isotropic phases at $ν$ = 5/2 and 7/2 an in-plane magnetic field {\it induces} a strong electrical anisotropy. In all cases, for high in-plane fields, the high resistance axis is parallel to the direction of the in-plane field.

cond-mat.mes-hall↗

arXiv1999

Mass enhancement of two-dimensional electrons in thin-oxide Si-MOSFET's

We wish to report in this paper a study of the effective mass (m^*) in thin-oxide Si-metal-oxide-semiconductor field-effect-transistors, using the temperature dependence of the Shubnikov-de Haas (SdH) effect and following the methodology developed by J.L. Smith and P.J. Stiles, Phys. Rev. Lett. {\bf 29}, 102 (1972). We find that in the thin oxide limit, when the oxide thickness $d_{ox}$ is smaller than the average two-dimensional electron-electron separation r, m^* is still enhanced and the enhancement can be described by $m^*/m_B = 0.815 + 0.23(r/d_{ox})$, where $m_B = 0.195 m_e$ is the bulk electron mass, $m_e$ the free electron mass. At $n_s = 6 \times 10^{11}/cm^2$, for example, $m^* \simeq 0.25 m_e$, an enhancement doubles that previously reported by Smith and Stiles. Our result shows that the interaction between electrons in the semiconductor and the neutralizing positive charges on the metallic gate electrode is important for mass enhancement. We also studied the magnetic-field orientation dependence of the SdH effect and deduced a value of $3.0 \pm 0.5$ for the effective $g$ factor in our thin oxide samples.

cond-mat.mes-hall↗