Browsing by Author "West, K.W."

Now showing 1 - 8 of 8
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    Depinning transition of bubble phases in a high Landau level
    (American Physical Society, 2015) Wang, Xuebin; Fu, Hailong; Du, Lingjie; Liu, Xiaoxue; Wang, Pengjie; Pfeiffer, L.N.; West, K.W.; Du, Rui-Rui; Lin, Xi
    In the higher Landau levels (N>0) a reentrant integer quantum Hall effect (RIQHE) state, which resides at fractional filling factors but exhibits integer Hall plateaus, has been previously observed and studied extensively. The nonlinear dynamics of the RIQHE were measured by microwave resonance, with the results consistent with an electronic bubble phase pinned by impurities. We have carried out depinning experiments on the N=2 bubble phases by using Corbino geometry, where depinning threshold values have been systematically measured as a function of magnetic fields and temperatures. Domain sizes and pinning potential of the bubble phases have been estimated from the nonlinear transport data.
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    Enhancement of the v=5/2 Fractional Quantum Hall State in a Small In-Plane Magnetic Field
    (American Physical Society, 2012) Liu, Guangtong; Zhang, Chi; Tsui, D.C.; Knez, Ivan; Levine, Aaron; Du, R.R.; Pfeiffer, L.N.; West, K.W.
    Using a 50-nm-width ultraclean GaAs=AlGaAs quantum well, we have studied the Landau level filling factor v=5/2 fractional quantum Hall effect in a perpendicular magnetic field B 1:7 Tand determined its dependence on tilted magnetic fields. Contrary to all previous results, the 5=2 resistance minimum and the Hall plateau are found to strengthen continuously under an increasing tilt angle 0< <25 (corresponding to an in-plane magnetic field 060 , and the composite fermion series [2 þ p=ð2p 1Þ, p ¼ 1; 2] can be identified. Based on our results, we discuss the relevance of a Skyrmion spin texture at v= 5/2 associated with small Zeeman energy in wide quantum wells, as proposed by Wo´js et al
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    Millimeter wave transmission spectroscopy of gated two-dimensional hole systems
    (American Institute of Physics, 2012) Stone, K.; Du, R.R.; Manfra, M.J.; Pfeiffer, L.N.; West, K.W.
    We developed a differential transmission to study cyclotron resonance of GaAs/AlxGa1 xAs two-dimensional hole samples. The technique utilizes a modulated AuPd gate isolated by a Si3N4 dielectric from the sample, which is irradiated opposite the gate by millimeter waves ranging from 2 to 40GHz. This technique effectively removes the background signal and yields a hole effective mass of 0:41me with a cyclotron scattering time of 20 ps, consistent with the previous results using different techniques.
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    Scaling properties of the plateau transitions in the two-dimensional hole gas system
    (American Physical Society, 2016) Wang, Xuebin; Liu, Haiwen; Zhu, Junbo; Shan, Pujia; Wang, Pengjie; Fu, Hailong; Du, Lingjie; Pfeiffer, L.N.; West, K.W.; Xie, X.C.; Du, Rui-Rui; Lin, Xi
    The behavior of phase coherence is studied in two-dimensional hole gas through the integer quantum Hall plateau-to-plateau transition. From the plateau transition as a function of temperature, scaling properties of multiple transitions are analyzed. Our results are in good agreement with the assumption of the zero-point fluctuations of the coherent holes, and support the intrinsic saturation of the coherence time at low temperature limit. The critical exponent p can also be determined under the scheme of the zero-point fluctuations. The similarity and difference in experimental observations between quantum Griffiths singularity and plateau transition is discussed. The spin-orbit coupling effect's influence on the plateau transition is explored by comparing the results from different transitions.
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    Shifted Landau ladders and low field magneto-oscillations in high-mobility GaAs 2D hole systems
    (AIP Publishing, 2017) Zhang, Po; Wang, Jianli; Zhang, Chi; Du, Rui-Rui; Pfeiffer, L.N.; West, K.W.
    We present well-developed low-field magneto-resistance oscillations originating from zero-field spin splitting (ZFSS) of heavy holes in high mobility GaAs/AlGaAs quantum wells. This low field oscillation is 1/B-periodic and emerges before the onset of Shubnikov–de Haas oscillations. The effect can be explained by resonant scattering between two Landau ladders shifted by the ZFSS gap, which in turn can be measured by comparing with the hole cyclotron energy. A front gate is fabricated to tune the ZFSS and hence the oscillation period.
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    Simultaneous measurements of microwave photoresistance and cyclotron reflection in the multiphoton regime
    (American Physical Society, 2018) Zhang, Jie; Du, Rui-Rui; Pfeiffer, L.N.; West, K.W.
    We simultaneously measure photoresistance with electrical transport and coupled plasmon-cyclotron resonance using microwave reflection spectroscopy in high-mobility GaAs/AlGaAs quantum wells under a perpendicular magnetic field. Multiphoton transitions are revealed as sharp peaks in the resistance and the cyclotron reflection on samples with various carrier densities. Our main finding is that plasmon coupling is relevant in the cyclotron reflection spectrum but has not been observed in the electrical conductivity signal. We discuss possible mechanisms relevant to reflection or dc conductivity signal to explain this discrepancy. We further confirm a trend that more multiphoton features can be observed using higher carrier density samples.
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    Thermopower and Nernst measurements in a half-filled lowest Landau level
    (American Physical Society, 2018) Liu, Xiaoxue; Li, Tingxin; Zhang, Po; Pfeiffer, L.N.; West, K.W.; Zhang, Chi; Du, Rui-Rui
    Motivated by the recent proposal by Potter et al. [Phys. Rev. X 6, 031026 (2016)] concerning possible thermoelectric signatures of Dirac composite fermions, we perform a systematic experimental study of thermoelectric transport of an ultrahigh-mobility GaAs/AlxGa1−xAs two-dimensional electron system at filling factor v=1/2. We demonstrate that the thermopower Sxx and Nernst Sxy are symmetric and antisymmetric with respect to B=0 T, respectively. The measured properties of thermopower Sxx at v=1/2 are consistent with previous experimental results. The Nernst signals Sxy of v=1/2, which have not been reported previously, are nonzero and show a power-law relation with temperature in the phonon-drag dominant region. In the electron-diffusion dominant region, the Nernst signals Sxy of v=1/2 are found to be significantly smaller than the linear temperature dependent values predicted by Potter et al., and decreasing with temperature faster than linear dependence.
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    Transport of a sliding Wigner crystal in the four flux composite fermion regime
    (American Physical Society, 2015) Zhang, Chi; Du, Rui-Rui; Manfra, M.J.; Pfeiffer, L.N.; West, K.W.
    In two-dimensional (2D) electron systems, Wigner crystals (WC) and fractional quantum Hall effect (FQHE) liquids are competing ground states under low temperatures (T) and high magnetic fields (B). Here we report differential conductivity results demonstrating the reentrant insulating phase around ν=1/5 in a 2D hole system in AlGaAs/GaAs quantum wells and unexpected features in the solid-liquid phase transition between WC and FQHE liquids in ultrahigh magnetic fields up to 45 T. Remarkably, the electric field (E) plays an equivalent role as the temperature does in our phase diagram. From the E−T “duality” analysis, a characteristic length of 450 nm is derived, which can be understood as the phase-coherent domain size of WC. Moreover, evidence shows that with weak disorder the insulating phase and composite fermion liquid could be coexisting around ν= 1/5, pointing to the possibility that the insulating phase is the four flux quantum Wigner crystal, as proposed by theories.