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標題: Using the coplanar waveguide to detect the high-frequency magnetotransport properties of two-dimensional system
作者: 萬德昌
關鍵字: 共平面波導
coplanar waveguide
high-frequency magnetotransport properties
integer quantum Hall effect
phase lock loop
localization length
scaling theory
出版社: 物理學系
摘要: We study the high-frequency magnetotransport properties of two-dimensional system at a temperature of 0.3K in high magnetic fields (0~10T) by using coplanar waveguide (CPW) and our homemade RF plused phase lock loop (PLL) detecting system. A meandering CPW is patterned on the surface of the 2DES and 2DHS samples, which are enbedded in MBE grown GaAs/AlGaAs and Si/SiGe heterojunction, respectively. Both the real part and imaginary part of the longitudinal conductivity will affect the propagation constant of CPW, and can be detected by our PLL system. From the high-frequency measurement data of the 2DES sample (GaAs/AlGaAs), we observed: (1) the Shubnikov-de Hass (SdH) oscillations at low fields and the integer quantum Hall effect (IQHE) at high fields; (2) a special power law dependence between the localization length x near the center of the IQHE plateau and the magnetic field difference away from the plateau center, x | B - Bi |b , with an exponent b very close to the critical exponent ; (3) a scaling behavior between and in the frequency range between 1.5GHz and 2.5GHz and for <0.1 e2/h. We can also observe the SdH oscillations in the high-frequency data for 2DES sample (Si/SiGe).
本篇論文主要是利用共平面波導(coplanar waveguide, CPW)與RF脈衝訊號量測技術探討二維系統位於低溫(約0.3K)與高磁(0~10T)環境下的高頻磁傳輸特性。我們將meandering CPW的圖案製作於GaAs/AlGaAs與Si/SiGe異質接面(heterojunction)所形成的二維電子系統(2DES)及二維電洞系統(2DHS)樣品的表面上,並將此CPW樣品元件連接於量測系統內可調變RF脈衝訊號的type-Ⅱ鎖相迴路(phase lock loop, PLL)中。二維系統之縱向電導率(longitudinal conductivity, )(包括實部與虛部)的變化情形將會影響著可藉由PLL量測得到的CPW傳播常數(propagation constant)。 由GaAs/AlGaAs異質結構之2DES樣品的高頻磁傳輸特性,我們觀察到:(1)低磁場下的Shubnikov-de Haas振盪與較高磁場中的整數量子霍爾效應(IQHE);(2)位於IQHE plateau中心位置附近的侷域長度( )與對應其中心位置的磁場變化量有著特殊的相對應關係 x | B - Bi |b,且其指數b的數值非常接近臨界指數項數值(critical exponent) ;(3)介於頻率為1.5GHz 至 2.5GHz且 <0.1 e2/h的區域範圍內,位於IQHE plateau中心位置之間的 與 對應關係中,有著不受頻率影響的scaling行為。 在Si/SiGe異質結構的2DHS樣品中,我們也觀察到Shubnikov-de Haas振盪的行為表現。
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