Showing 1–35 of 35 results for author: Tu, T

Reply to: Low-frequency quantum oscillations in LaRhIn$_5$: Dirac point or nodal line?

Authors: Chunyu Guo, A. Alexandradinata, Carsten Putzke, Amelia Estry, Teng Tu, Nitesh Kumar, Feng-Ren Fan, Shengnan Zhang, Quansheng Wu, Oleg V. Yazyev, Kent R. Shirer, Maja D. Bachmann, Hailin Peng, Eric D. Bauer, Filip Ronning, Yan Sun, Chandra Shekhar, Claudia Felser, Philip J. W. Moll

Abstract: We thank G.P. Mikitik and Yu.V. Sharlai for contributing this note and the cordial exchange about it. First and foremost, we note that the aim of our paper is to report a methodology to diagnose topological (semi)metals using magnetic quantum oscillations. Thus far, such diagnosis has been based on the phase offset of quantum oscillations, which is extracted from a "Landau fan plot". A thorough an… ▽ More We thank G.P. Mikitik and Yu.V. Sharlai for contributing this note and the cordial exchange about it. First and foremost, we note that the aim of our paper is to report a methodology to diagnose topological (semi)metals using magnetic quantum oscillations. Thus far, such diagnosis has been based on the phase offset of quantum oscillations, which is extracted from a "Landau fan plot". A thorough analysis of the Onsager-Lifshitz-Roth quantization rules has shown that the famous $π$-phase shift can equally well arise from orbital- or spin magnetic moments in topologically trivial systems with strong spin-orbit coupling or small effective masses. Therefore, the "Landau fan plot" does not by itself constitute a proof of a topologically nontrivial Fermi surface. In the paper at hand, we report an improved analysis method that exploits the strong energy-dependence of the effective mass in linearly dispersing bands. This leads to a characteristic temperature dependence of the oscillation frequency which is a strong indicator of nontrivial topology, even for multi-band metals with complex Fermi surfaces. Three materials, Cd$_3$As$_2$, Bi$_2$O$_2$Se and LaRhIn$_5$ served as test cases for this method. Linear band dispersions were detected for Cd$_3$As$_2$, as well as the $F$ $\approx$ 7 T pocket in LaRhIn$_5$. △ Less

Submitted 12 March, 2023; originally announced March 2023.

Comments: Response to Matter arising for Nature Communications 12, 6213 (2021)

Evolution of the Fe-3$d$ impurity band state as the origin of high Curie temperature in p-type ferromagnetic semiconductor (Ga,Fe)Sb

Authors: Takahito Takeda, Shoya Sakamoto, Kohsei Araki, Yuita Fujisawa, Le Duc Anh, Nguyen Thanh Tu, Yukiharu Takeda, Shin-ichi Fujimori, Atsushi Fujimori, Masaaki Tanaka, Masaki Kobayashi

Abstract: (Ga$_{1-x}$,Fe$_x$)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature ($T_{\rm C}$) is above 300 K when the Fe concentration $x$ is equal to or higher than ~0.20. However, the origin of the high $T_{\rm C}$ in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-p… ▽ More (Ga$_{1-x}$,Fe$_x$)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature ($T_{\rm C}$) is above 300 K when the Fe concentration $x$ is equal to or higher than ~0.20. However, the origin of the high $T_{\rm C}$ in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-principles calculations to investigate the $x$ dependence of the Fe 3$d$ states in (Ga$_{1-x}$,Fe$_x$)Sb ($x$ = 0.05, 0.15, and 0.25) thin films. The observed Fe 2$p$-3$d$ RPES spectra reveal that the Fe-3$d$ impurity band (IB) crossing the Fermi level becomes broader with increasing $x$, which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3$d$ partial density of states and the first-principles calculations suggests that the Fe-3$d$ IB originates from the minority-spin ($\downarrow$) $e$ states. The results indicate that enhancement of the interaction between $e_\downarrow$ electrons with increasing $x$ is the origin of the high $T_{\rm C}$ in (Ga,Fe)Sb. △ Less

Submitted 18 August, 2020; originally announced August 2020.

Journal ref: Phys. Rev. B 102, 245203 (2020)

Hybridization between the ligand $p$ band and Fe-3$d$ orbitals in the p-type ferromagnetic semiconductor (Ga,Fe)Sb

Authors: Takahito Takeda, Masahiro Suzuki, Le Duc Anh, Nguyen Thanh Tu, Thorsten Schmitt, Satoshi Yoshida, Masato Sakano, Kyoko Ishizaka, Yukiharu Takeda, Shin-ichi Fijimori, Munetoshi Seki, Hitoshi Tabata, Atsushi Fujimori, Vladimir N. Strocov, Masaaki Tanaka, Masaki Kobayashi

Abstract: (Ga,Fe)Sb is a promising ferromagnetic semiconductor for practical spintronic device applications because its Curie temperature ($T_{\rm C}$) is above room temperature. However, the origin of ferromagnetism with high $T_{\rm C}$ remains to be elucidated. Here, we use soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to investigate the valence-band (VB) structure of (Ga$_{0.95}$,Fe… ▽ More (Ga,Fe)Sb is a promising ferromagnetic semiconductor for practical spintronic device applications because its Curie temperature ($T_{\rm C}$) is above room temperature. However, the origin of ferromagnetism with high $T_{\rm C}$ remains to be elucidated. Here, we use soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to investigate the valence-band (VB) structure of (Ga$_{0.95}$,Fe$_{0.05}$)Sb including the Fe-3$d$ impurity band (IB), to unveil the mechanism of ferromagnetism in (Ga,Fe)Sb. We find that the VB dispersion in (Ga$_{0.95}$,Fe$_{0.05}$)Sb observed by SX-ARPES is similar to that of GaSb, indicating that the doped Fe atoms hardly affect the band dispersion. The Fe-3$d$ resonant ARPES spectra demonstrate that the Fe-3$d$ IB crosses the Fermi level ($E_{\rm F}$) and hybridizes with the VB of GaSb. These observations indicate that the VB structure of (Ga$_{0.95}$,Fe$_{0.05}$)Sb is consistent with that of the IB model which is based on double-exchange interaction between the localized 3$d$ electrons of the magnetic impurities. The results indicate that the ferromagnetism in (Ga,Fe)Sb is formed by the hybridization of the Fe-3$d$ IB with the ligand $p$ band of GaSb. △ Less

Submitted 9 January, 2020; originally announced January 2020.

Comments: 24 pages, 6 figures

Journal ref: Phys. Rev. B 101, 155142 (2020)

Temperature dependence of quantum oscillations from non-parabolic dispersions

Authors: Chunyu Guo, A. Alexandradinata, Carsten Putzke, Amelia Estry, Teng Tu, Nitesh Kumar, Feng-Ren Fan, Shengnan Zhang, Quansheng Wu, Oleg V. Yazyev, Kent R. Shirer, Maja D. Bachmann, Hailin Peng, Eric D. Bauer, Filip Ronning, Yan Sun, Chandra Shekhar, Claudia Felser, Philip J. W. Moll

Abstract: The phase offset of quantum oscillations is commonly used to experimentally diagnose topologically non-trivial Fermi surfaces. This methodology, however, is inconclusive for spin-orbit-coupled metals where $π$-phase-shifts can also arise from non-topological origins. Here, we show that the linear dispersion in topological metals leads to a $T^2$-temperature correction to the oscillation frequency… ▽ More The phase offset of quantum oscillations is commonly used to experimentally diagnose topologically non-trivial Fermi surfaces. This methodology, however, is inconclusive for spin-orbit-coupled metals where $π$-phase-shifts can also arise from non-topological origins. Here, we show that the linear dispersion in topological metals leads to a $T^2$-temperature correction to the oscillation frequency that is absent for parabolic dispersions. We confirm this effect experimentally in the Dirac semi-metal Cd$_3$As$_2$ and the multiband Dirac metal LaRhIn$_5$. Both materials match a tuning-parameter-free theoretical prediction, emphasizing their unified origin. For topologically trivial Bi$_2$O$_2$Se, no frequency shift associated to linear bands is observed as expected. However, the $π$-phase shift in Bi$_2$O$_2$Se would lead to a false positive in a Landau-fan plot analysis. Our frequency-focused methodology does not require any input from ab-initio calculations, and hence is promising for identifying correlated topological materials. △ Less

Submitted 27 March, 2022; v1 submitted 16 October, 2019; originally announced October 2019.

Journal ref: Nat. Commun. 12, 6213 (2021)

In-plane to perpendicular magnetic anisotropy switching in heavily-Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb with high Curie temperature

Authors: Shobhit Goel, Le Duc Anh, Nguyen Thanh Tu, Shinobu Ohya, Masaaki Tanaka

Abstract: We report switching of magnetic anisotropy (MA) from in-plane to perpendicular with increasing the thickness d of a (001)-oriented ferromagnetic-semiconductor (FMS) (Ga0.7,Fe0.3)Sb layer with a high Curie temperature (Tc > 320 K), using ferromagnetic resonance at room temperature. We show that the total MA energy (E) along the [001] direction changes its sign from positive (in-plane) to negative (… ▽ More We report switching of magnetic anisotropy (MA) from in-plane to perpendicular with increasing the thickness d of a (001)-oriented ferromagnetic-semiconductor (FMS) (Ga0.7,Fe0.3)Sb layer with a high Curie temperature (Tc > 320 K), using ferromagnetic resonance at room temperature. We show that the total MA energy (E) along the [001] direction changes its sign from positive (in-plane) to negative (perpendicular) with increasing d above an effective critical value \mathrm{d}_\mathrm{C}^\mathrm{*}\ ~ 42 nm. We reveal that (Ga,Fe)Sb has two-fold symmetry in the film plane. Meanwhile, in the plane perpendicular to the film including the in-plane [110] axis, the two-fold symmetry with the easy magnetization axis along [110] changes to four-fold symmetry with easy magnetization axis along <001> with increasing d. This peculiar behavior is different from that of (Ga,Mn)As, in which only the in-plane MA depends on the film thickness and has four-fold symmetry due to its dominant cubic anisotropy along the <100> axes. This work provides an important guide for controlling the easy magnetization axis of high-Tc FMS (Ga,Fe)Sb for room-temperature device applications. △ Less

Submitted 2 July, 2019; originally announced July 2019.

Journal ref: Phys. Rev. Materials 3, 084417 (2019)

Heavily Fe-doped n-type ferromagnetic semiconductor (In,Fe)Sb with high Curie temperature and large magnetic anisotropy

Authors: Nguyen Thanh Tu, Pham Nam Hai, Le Duc Anh, Masaaki Tanaka

Abstract: We present high-temperature ferromagnetism and large magnetic anisotropy in heavily Fe-doped n-type ferromagnetic semiconductor (In1-x,Fex)Sb (x = 20 - 35%) thin films grown by low-temperature molecular beam epitaxy. The (In1-x,Fex)Sb thin films with x = 20 - 35% maintain the zinc-blende crystal and band structure with single-phase ferromagnetism. The Curie temperature (TC) of (In1-x,Fex)Sb reache… ▽ More We present high-temperature ferromagnetism and large magnetic anisotropy in heavily Fe-doped n-type ferromagnetic semiconductor (In1-x,Fex)Sb (x = 20 - 35%) thin films grown by low-temperature molecular beam epitaxy. The (In1-x,Fex)Sb thin films with x = 20 - 35% maintain the zinc-blende crystal and band structure with single-phase ferromagnetism. The Curie temperature (TC) of (In1-x,Fex)Sb reaches 390 K at x = 35%, which is significantly higher than room temperature and the highest value so far reported in III-V based ferromagnetic semiconductors. Moreover, large coercive force (HC = 160 Oe) and large remanent magnetization (Mr/MS = 71%) have been observed for a (In1-x,Fex)Sb thin film with x = 35%. Our results indicate that the n-type ferromagnetic semiconductor (In1-x,Fex)Sb is very promising for spintronics devices operating at room temperature. △ Less

Submitted 6 January, 2019; originally announced January 2019.

Comments: arXiv admin note: text overlap with arXiv:1706.00735

Electronic structure of the novel high-$T_{\rm C}$ ferromagnetic semiconductor (Ga,Fe)Sb: x-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

Authors: Shoya Sakamoto, Nguyen Thanh Tu, Yukiharu Takeda, Shin-ichi Fujimori, Pham Nam Hai, Le Duc Anh, Yuki K. Wakabayashi, Goro Shibata, Masafumi Horio, Keisuke Ikeda, Yuji Saitoh, Hiroshi Yamagami, Masaaki Tanaka, Atsushi Fujimori

Abstract: The electronic structure and the magnetism of the novel ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature $T_{\rm C}$ can exceed room temperature, were investigated by means of x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetis… ▽ More The electronic structure and the magnetism of the novel ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature $T_{\rm C}$ can exceed room temperature, were investigated by means of x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable amount of 3$d^{6}$ contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and non-dispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3$d$ electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3$d$ states have finite contribution to the DOS at the Fermi energy. These states presumably consisting of majority-spin $p$-$d$ hybridized states or minority-spin $e$ states would be responsible for the ferromagnetic order in this material. △ Less

Submitted 18 November, 2018; originally announced November 2018.

Journal ref: Phys. Rev. B 100, 035204 (2019)

Raman Spectra and Strain Effects in Bismuth Oxychalcogenides

Authors: Ting Cheng, Congwei Tan, Shuqing Zhang, Teng Tu, Hailin Peng, Zhirong Liu

Abstract: A new type of two-dimensional layered semiconductor with weak electrostatic but not van der Waals interlayer interactions, Bi2O2Se, has been recently synthesized, which shown excellent air stability and ultrahigh carrier mobility. Herein, we combined theoretical and experimental approaches to study the Raman spectra of Bi2O2Se and related bismuth oxychalcogenides (Bi2O2Te and Bi2O2S). The experime… ▽ More A new type of two-dimensional layered semiconductor with weak electrostatic but not van der Waals interlayer interactions, Bi2O2Se, has been recently synthesized, which shown excellent air stability and ultrahigh carrier mobility. Herein, we combined theoretical and experimental approaches to study the Raman spectra of Bi2O2Se and related bismuth oxychalcogenides (Bi2O2Te and Bi2O2S). The experimental peaks were fully consistent with the calculated results, and were successfully assigned. Bi2O2S was predicted to have more Raman-active modes due to its lower symmetry. The shift of the predicted frequencies of Raman active modes was also found to get softened as the interlayer interaction decreases from bulk to monolayer Bi2O2Se and Bi2O2Te. To reveal the strain effects on the Raman shifts, a universal theoretical equation was established based on the symmetry of Bi2O2Se and Bi2O2Te. It was predicted that the doubly degenerate modes split under in-plane uniaxial/shear strains. Under a rotated uniaxial strain, the changes of Raman shifts are anisotropic for degenerate modes although Bi2O2Se and Bi2O2Te were usually regarded as isotropic systems similar to graphene. This implies a novel method to identify the crystallographic orientation from Raman spectra under strain. These results have important consequences for the incorporation of 2D Bismuth oxychalcogenides into nanoelectronic devices. △ Less

Submitted 22 May, 2018; originally announced May 2018.

Comments: 40 Pages, 18 figures

A new class of ferromagnetic semiconductors with high Curie temperatures

Authors: Nguyen Thanh Tu, Pham Nam Hai, Le Duc Anh, Masaaki Tanaka

Abstract: Ferromagnetic semiconductors (FMSs), which have the properties and functionalities of both semiconductors and ferromagnets, provide fascinating opportunities for basic research in condensed matter physics and device applications. Over the past two decades, however, intensive studies on various FMS materials, inspired by the influential mean-field Zener (MFZ) model have failed to realise reliable F… ▽ More Ferromagnetic semiconductors (FMSs), which have the properties and functionalities of both semiconductors and ferromagnets, provide fascinating opportunities for basic research in condensed matter physics and device applications. Over the past two decades, however, intensive studies on various FMS materials, inspired by the influential mean-field Zener (MFZ) model have failed to realise reliable FMSs that have a high Curie temperature (Tc > 300 K), good compatibility with semiconductor electronics, and characteristics superior to those of their non-magnetic host semiconductors. Here, we demonstrate a new n type Fe-doped narrow-gap III-V FMS, (In,Fe)Sb, in which ferromagnetic order is induced by electron carriers, and its Tc is unexpectedly high, reaching ~335 K at a modest Fe concentration of 16%. Furthermore, we show that by utilizing the large anomalous Hall effect of (In,Fe)Sb at room temperature, it is possible to obtain a Hall sensor with a very high sensitivity that surpasses that of the best commercially available InSb Hall sensor devices. Our results reveal a new design rule of FMSs that is not expected from the conventional MFZ model. (This work was presented at the JSAP Spring meeting, presentation No. E15a-501-2: https://confit.atlas.jp/guide/event/jsap2017s/subject/15a-501-2/advanced) △ Less

Submitted 2 June, 2017; originally announced June 2017.

Fabrication and characterization of an undoped GaAs/AlGaAs quantum dot device

Authors: Hai-Ou Li, Gang Cao, Ming Xiao, Jie You, Da Wei, Tao Tu, Guang-Can Guo, Hong-Wen Jiang, Guo-Ping Guo

Abstract: We demonstrate the development of a double quantum dot with an integrated charge sensor fabricated in undoped GaAs/AlGaAs heterostructures using a double top-gated design. Based on the evaluation of the integrated charge sensor, the double quantum dot can be tuned to a few-electron region. Additionally, the inter-dot coupling of the double quantum dot can be tuned to a large extent according to th… ▽ More We demonstrate the development of a double quantum dot with an integrated charge sensor fabricated in undoped GaAs/AlGaAs heterostructures using a double top-gated design. Based on the evaluation of the integrated charge sensor, the double quantum dot can be tuned to a few-electron region. Additionally, the inter-dot coupling of the double quantum dot can be tuned to a large extent according to the voltage on the middle gate. The quantum dot is shown to be tunable from a single dot to a well-isolated double dot. To assess the stability of such design, the potential fluctuation induced by 1/f noise was measured. Based on the findings herein, the quantum dot design developed in the undoped GaAs/AlGaAs semiconductor shows potential for the future exploitation of nano-devices. △ Less

Submitted 27 June, 2014; originally announced June 2014.

Journal ref: Journal of Applied Physics 116, 174504 (2014)

Suspending Effect on Low-Frequency Charge Noise in Graphene Quantum Dot

Authors: Xiang-Xiang Song, Hai-Ou Li, Jie You, Tian-Yi Han, Gang Cao, Tao Tu, Ming Xiao, Guang-Can Guo, Hong-Wen Jiang, Guo-Ping Guo

Abstract: Charge noise is critical in the performance of gate-controlled quantum dots (QDs). Here we show the 1/f noise for a microscopic graphene QD is substantially larger than that for a macroscopic graphene field-effect transistor (FET), increasing linearly with temperature. To understand its origin, we suspended the graphene QD above the substrate. In contrast to large area graphene FETs, we find that… ▽ More Charge noise is critical in the performance of gate-controlled quantum dots (QDs). Here we show the 1/f noise for a microscopic graphene QD is substantially larger than that for a macroscopic graphene field-effect transistor (FET), increasing linearly with temperature. To understand its origin, we suspended the graphene QD above the substrate. In contrast to large area graphene FETs, we find that a suspended graphene QD has an almost-identical noise level as an unsuspended one. Tracking noise levels around the Coulomb blockade peak as a function of gate voltage yields potential fluctuations of order 1 "μeV", almost one order larger than in GaAs/GaAlAs QDs. Edge states rather than substrate-induced disorders, appear to dominate the 1/f noise, thus affecting the coherency of graphene nano-devices. △ Less

Submitted 13 October, 2015; v1 submitted 16 June, 2014; originally announced June 2014.

Comments: 14pages,5figure

Journal ref: Scientific Reports 5, 8142 (2015)

Observation of Kondo Effect in a Quadruple Quantum Dots

Authors: Runan Shang, Hai-Ou Li, Gang Cao, Guodong Yu, Ming Xiao, Tao Tu, Guang-Can Guo, Hongwen Jiang, A. M. Chang, Guo-Ping Guo

Abstract: We investigate the Kondo effect in a quadruple quantum dot device of coupled-double quantum dots (DQDs), which simultaneously contains intra-DQDs and inter-DQDs coupling. A variety of novel behaviors are observed. The differential conductance dI/dV is measured in the upper DQDs as a function of source drain bias. It is found to exhibit multiple peaks, including a zero-bias peak, where the number o… ▽ More We investigate the Kondo effect in a quadruple quantum dot device of coupled-double quantum dots (DQDs), which simultaneously contains intra-DQDs and inter-DQDs coupling. A variety of novel behaviors are observed. The differential conductance dI/dV is measured in the upper DQDs as a function of source drain bias. It is found to exhibit multiple peaks, including a zero-bias peak, where the number of peaks exceeds five. Alternatively, tuning the lower DQDs yielded regions of four peaks. In addition, a Kondo-effect switcher is demonstrated, using the lower DQDs as the controller. △ Less

Submitted 9 December, 2013; originally announced December 2013.

Comments: 14 pages including 5 figures

Charge Number Dependence of the Dephasing Rates of a Graphene Double Quantum Dot in a Circuit QED Architecture

Authors: Guang-Wei Deng, Da Wei, J. R. Johansson, Miao-Lei Zhang, Shu-Xiao Li, Hai-Ou Li, Gang Cao, Ming Xiao, Tao Tu, Guang-Can Guo, Hong-Wen Jiang, Franco Nori, Guo-Ping Guo

Abstract: We use an on-chip superconducting resonator as a sensitive meter to probe the properties of graphene double quantum dots at microwave frequencies. Specifically, we investigate the charge dephasing rates in a circuit quantum electrodynamics architecture. The dephasing rates strongly depend on the number of charges in the dots, and the variation has a period of four charges, over an extended range o… ▽ More We use an on-chip superconducting resonator as a sensitive meter to probe the properties of graphene double quantum dots at microwave frequencies. Specifically, we investigate the charge dephasing rates in a circuit quantum electrodynamics architecture. The dephasing rates strongly depend on the number of charges in the dots, and the variation has a period of four charges, over an extended range of charge numbers. Although the exact mechanism of this fourfold periodicity in dephasing rates is an open problem, our observations hint at the fourfold degeneracy expected in graphene from its spin and valley degrees of freedom. △ Less

Submitted 21 February, 2016; v1 submitted 23 October, 2013; originally announced October 2013.

Journal ref: Phys. Rev. Lett. 115, 126804 (2015)

Symmetric reflection line resonator for semiconductor circuit quantum electrodynamics

Authors: Miao-Lei Zhang, Guang-Wei Deng, Shu-Xiao Li, Hai-Ou Li, Gang Cao, Tao Tu, Ming Xiao, Guang-Can Guo, Hong-Wen Jiang, Irfan Siddiqi, Guo-Ping Guo

Abstract: We have designed and fabricated a half-wavelength reflection line resonator (RLR) that consists of a pair of two coupled microstrip lines on a GaAs/AlGaAs heterostructure. By changing the top gate voltage on a square of two dimensional electron gas under the resonator, a large range of the quality factors can be obtained. Energy loss in the two-dimensional electron gas can be minimized, thus reali… ▽ More We have designed and fabricated a half-wavelength reflection line resonator (RLR) that consists of a pair of two coupled microstrip lines on a GaAs/AlGaAs heterostructure. By changing the top gate voltage on a square of two dimensional electron gas under the resonator, a large range of the quality factors can be obtained. Energy loss in the two-dimensional electron gas can be minimized, thus realizing a versatile resonator suitable for integration with semiconductor quantum circuits. △ Less

Submitted 31 August, 2013; originally announced September 2013.

Comments: 9 pages, 3 figures

Journal ref: Appl. Phys. Lett. 104, 083511(2014)

Photon-assisted-tunneling in a coupled double quantum dot out of thermal equilibrium

Authors: Runan Shang, Haiou Li, Gang Cao, Ming Xiao, Tao Tu, Guang-Can Guo, Hong-Wen Jiang, Guo-Ping Guo

Abstract: We perform photon-assisted-tunneling (PAT) experiments on a GaAs double quantum dot device under high microwave excitation power. Photon-assisted absorption of up to 14 photons is observed, when electron temperature (>1K) are far above the lattice temperature. Signatures of Landau-Zener-Stückelberg (LZS) interference are found even in this non-equilibrium PAT spectrum. In addition, the charge stat… ▽ More We perform photon-assisted-tunneling (PAT) experiments on a GaAs double quantum dot device under high microwave excitation power. Photon-assisted absorption of up to 14 photons is observed, when electron temperature (>1K) are far above the lattice temperature. Signatures of Landau-Zener-Stückelberg (LZS) interference are found even in this non-equilibrium PAT spectrum. In addition, the charge state relaxation time T_1~8ns measured in this out of thermal equilibrium double quantum dot is in agreement with other previous reports. △ Less

Submitted 16 August, 2013; originally announced August 2013.

Comments: 12pages, 4figures

Journal ref: Appl. Phys. Lett. 103, 162109 (2013)

Tuning inter-dot tunnel coupling of an etched graphene double quantum dot by adjacent metal gates

Authors: Da Wei, Hai-Ou Li, Gang Cao, Gang Luo, Zhi-Xiong Zheng, Tao Tu, Ming Xiao, Guang-Can Guo, Hong-Wen Jiang, Guo-Ping Guo

Abstract: Graphene double quantum open the possibility to use charge or spin degrees of freedom for storing and manipulating quantum information in this new electronic material. However, impurities and edge disorders in etched graphene nano-structures hinder the ability to control the inter-dot tunnel coupling, tc,the most important property of the artificial molecule. Here we report measurements of tc in a… ▽ More Graphene double quantum open the possibility to use charge or spin degrees of freedom for storing and manipulating quantum information in this new electronic material. However, impurities and edge disorders in etched graphene nano-structures hinder the ability to control the inter-dot tunnel coupling, tc,the most important property of the artificial molecule. Here we report measurements of tc in an all-metal-gates-tuned graphene DQD. We find that tc can be controlled continuously about a factor of four by employing a single gate. Furthermore, tc, can be changed monotonically about another factor of four as electrons are gate-pumped into the dot one by one. The results suggest that the strength of tunnel coupling in etched DQDs can be varied in a rather broad range and in a controllable manner, which improves the outlook to use graphene as a base material for qubit applications. △ Less

Submitted 24 July, 2013; v1 submitted 22 July, 2013; originally announced July 2013.

Comments: 18pages,10 figures

Journal ref: Scientific Reports 3, 3175 (2013)

Quantum simulation of Kibble-Zurek mechanism with a semiconductor electron charge qubit

Authors: Cheng Zhou, Li Wang, Tao Tu, Hai-Ou Li, Guang-Can Guo, Hong-Wen Jiang, Guo-Ping Guo

Abstract: The Kibble-Zurek mechanism provides a description of the topological structure occurring in the symmetry breaking phase transitions, which may manifest as the cosmological strings in the early universe or vortex lines in the superfulid. A particularly intriguing analogy between Kibble-Zurek mechanism and a text book quantum phenomenon, Landau-Zener transition has been discovered, but is difficult… ▽ More The Kibble-Zurek mechanism provides a description of the topological structure occurring in the symmetry breaking phase transitions, which may manifest as the cosmological strings in the early universe or vortex lines in the superfulid. A particularly intriguing analogy between Kibble-Zurek mechanism and a text book quantum phenomenon, Landau-Zener transition has been discovered, but is difficult to observe up to now. In recent years, there has been broad interest in quantum simulations using different well-controlled physical setups, in which full tunability allows access to unexplored parameter regimes. Here we demonstrate a proof-of-principle quantum simulation of Kibble-Zurek mechanism using a single electron charge qubit in double quantum dot, set to behave as Landau-Zener dynamics. We measure the qubit states as a function of driven pulse velocity and successfully reproduce Kibble-Zurek like dependence of topological defect density on the quench rate. The high-level controllability of semiconductor two-level system make it a platform to test the key elements of topological defect formation process and shed a new insight on the aspect of non-equilibrium phase transitions. △ Less

Submitted 23 January, 2013; originally announced January 2013.

Comments: 14 pages, 4 figures

Journal ref: Phys. Rev. A 89, 022337 (2014)

Electron Number Dependence of Spin Triplet-Singlet Relaxation Time

Authors: Gang Cao, Ming Xiao, HaiOu Li, Tao Tu, GuoPing Guo

Abstract: In a GaAs single quantum dot, the relaxation time T_{1} between spin triplet and singlet states has been measured for the last few even number of electrons. The singlet-triplet energy separation E_{ST} is tuned as a control parameter for the comparison of T_{1} between different electron numbers. T_{1} shows a steady decrease from 2-electrons, 4-electrons, to 6-electrons, and we found this implies… ▽ More In a GaAs single quantum dot, the relaxation time T_{1} between spin triplet and singlet states has been measured for the last few even number of electrons. The singlet-triplet energy separation E_{ST} is tuned as a control parameter for the comparison of T_{1} between different electron numbers. T_{1} shows a steady decrease from 2-electrons, 4-electrons, to 6-electrons, and we found this implies an enhancement of the spin-orbital coupling strength in a multi-electron quantum dot. △ Less

Submitted 6 May, 2012; originally announced May 2012.

Electron Spin Excited States Spectroscopy in a Quantum Dot Probed by QPC Back-action

Authors: HaiOu Li, Ming Xiao, Gang Cao, Cheng Zhou, RuNan Shang, Tao Tu, GuangCan Guo, HongWen Jiang, GuoPing Guo

Abstract: The quantum point contact (QPC) back-action has been found to cause non-thermal-equilibrium excitations to the electron spin states in a quantum dot (QD). Here we use back-action as an excitation source to probe the spin excited states spectroscopy for both the odd and even electron numbers under a varying parallel magnetic field. For a single electron, we observed the Zeeman splitting. For two el… ▽ More The quantum point contact (QPC) back-action has been found to cause non-thermal-equilibrium excitations to the electron spin states in a quantum dot (QD). Here we use back-action as an excitation source to probe the spin excited states spectroscopy for both the odd and even electron numbers under a varying parallel magnetic field. For a single electron, we observed the Zeeman splitting. For two electrons, we observed the splitting of the spin triplet states $|T^{+}>$ and $|T^{0}>$ and found that back-action drives the singlet state $|S>$ overwhelmingly to $|T^{+}>$ other than $|T^{0}>$. All these information were revealed through the real-time charge counting statistics. △ Less

Submitted 11 December, 2011; originally announced December 2011.

Back-action Driven Electron Spin Singlet-Triplet Excitation in a GaAs Quantum Dot

Authors: Gang Cao, Ming Xiao, HaiOu Li, Cheng Zhou, RuNan Shang, Tao Tu, GuangCan Guo, GuoPing Guo, HongWen Jiang

Abstract: In a single quantum dot (QD), the electrons were driven out of thermal equilibrium by the back-action from a nearby quantum point contact (QPC). We found the driving to energy excited states can be probed with the random telegraph signal (RTS) statistics, when the excited states relax slowly compared with RTS tunneling rate. We studied the last few electrons, and found back-action driven spin sing… ▽ More In a single quantum dot (QD), the electrons were driven out of thermal equilibrium by the back-action from a nearby quantum point contact (QPC). We found the driving to energy excited states can be probed with the random telegraph signal (RTS) statistics, when the excited states relax slowly compared with RTS tunneling rate. We studied the last few electrons, and found back-action driven spin singlet-triplet (S-T) excitation for and only for all the even number of electrons. We developed a phenomenological model to quantitatively characterize the spin S-T excitation rate, which enabled us to evaluate the influence of back-action on spin S-T based qubit operations. △ Less

Submitted 16 November, 2011; v1 submitted 26 September, 2011; originally announced September 2011.

Comments: 4 pages, 4 figures

Back-action Induced Non-equilibrium Effect in Electron Charge Counting Statistics

Authors: HaiOu Li, Ming Xiao, Gang Cao, Cheng Zhou, RuNan Shang, Tao Tu, GuangCan Guo, GuoPing Guo, HongWen Jiang

Abstract: We report our study of the real-time charge counting statistics measured by a quantum point contact (QPC) coupled to a single quantum dot (QD) under different back-action strength. By tuning the QD-QPC coupling or QPC bias, we controlled the QPC back-action which drives the QD electrons out of thermal equilibrium. The random telegraph signal (RTS) statistics showed strong and tunable non-thermal-e… ▽ More We report our study of the real-time charge counting statistics measured by a quantum point contact (QPC) coupled to a single quantum dot (QD) under different back-action strength. By tuning the QD-QPC coupling or QPC bias, we controlled the QPC back-action which drives the QD electrons out of thermal equilibrium. The random telegraph signal (RTS) statistics showed strong and tunable non-thermal-equilibrium saturation effect, which can be quantitatively characterized as a back-action induced tunneling out rate. We found that the QD-QPC coupling and QPC bias voltage played different roles on the back-action strength and cut-off energy. △ Less

Submitted 16 November, 2011; v1 submitted 22 August, 2011; originally announced August 2011.

Comments: 4 pages, 4 figures, 1 table

Molecule States in a Gate Tunable Graphene Double Quantum Dot

Authors: L. J. Wang, H. O. Li, Z. Su, T. Tu, G. Cao, C. Zhou, X. J. Hao, G. C. Guo, G. P. Guo

Abstract: We have measured a graphene double quantum dot device with multiple electrostatic gates that are used to enhance control to investigate it. At low temperatures the transport measurements reveal honeycomb charge stability diagrams which can be tuned from weak to strong interdot tunnel coupling regimes. We precisely extract a large interdot tunnel coupling strength for this system allowing for the o… ▽ More We have measured a graphene double quantum dot device with multiple electrostatic gates that are used to enhance control to investigate it. At low temperatures the transport measurements reveal honeycomb charge stability diagrams which can be tuned from weak to strong interdot tunnel coupling regimes. We precisely extract a large interdot tunnel coupling strength for this system allowing for the observation of tunnel-coupled molecular states extending over the whole double dot. This clean, highly controllable system serves as an essential building block for quantum devices in a nuclear-spin-free world. △ Less

Submitted 24 November, 2010; originally announced November 2010.

Comments: 10 pages, 14 figures

Journal ref: APPLIED PHYSICS LETTERS 100, 022106 (2012)

Tomography of the two-electron spin qubits in semiconductors

Authors: Zhan Su, Tao Tu, Gang Cao, Guang-Can Guo, Guo-Ping Guo

Abstract: We propose an approach to reconstruct two-electron spin qubit states in semiconductor quantum dots by employing tomographic techniques. This procedure exploits the combination of fast gate operations on electron spins trapped in dots and dynamical nuclear polarization of the underlying Ga and As nuclei. The presented method can be an important tool in solid state quantum computation for complete c… ▽ More We propose an approach to reconstruct two-electron spin qubit states in semiconductor quantum dots by employing tomographic techniques. This procedure exploits the combination of fast gate operations on electron spins trapped in dots and dynamical nuclear polarization of the underlying Ga and As nuclei. The presented method can be an important tool in solid state quantum computation for complete characterization of qubit states and theirs correlations. △ Less

Submitted 18 November, 2010; v1 submitted 9 November, 2010; originally announced November 2010.

Comments: This paper has been withdrawn by the authors. 8 pages, 5 figures

A Graphene Quantum Dot with a Single Electron Transistor as Integrated Charge Sensor

Authors: Ling-Jun Wang, Gang Cao, Tao Tu, Hai-Ou Li, Cheng Zhou, Xiao-Jie Hao, Zhan Su, Guang-Can Guo, Guo-Ping Guo, Hong-Wen Jiang

Abstract: We have developed an etching process to fabricate a quantum dot and a nearby single electron transistor as a charge detector in a single layer graphene. The high charge sensitivity of the detector is used to probe Coulomb diamonds as well as excited spectrum in the dot, even in the regime where the current through the quantum dot is too small to be measured by conventional transport means. The gra… ▽ More We have developed an etching process to fabricate a quantum dot and a nearby single electron transistor as a charge detector in a single layer graphene. The high charge sensitivity of the detector is used to probe Coulomb diamonds as well as excited spectrum in the dot, even in the regime where the current through the quantum dot is too small to be measured by conventional transport means. The graphene based quantum dot and integrated charge sensor serve as an essential building block to form a solid-state qubit in a nuclear-spin-free quantum world. △ Less

Submitted 28 August, 2010; originally announced August 2010.

Comments: 11 pages, 4 figures

Journal ref: Applied. Phys. Letters 97, 262113 (2010)

Strong and Tunable Spin-Orbit Coupling of One-Dimensional Holes in Ge/Si Core/Shell Nanowires

Authors: Xiao-Jie Hao, Tao Tu, Gang Cao, Cheng Zhou, Hai-Ou Li, Guang-Can Guo, Wayne Y. Fung, Zhongqing Ji, Guo-Ping Guo, Wei Lu

Abstract: We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell nanowires. Negative magneto-conductance was observed, which is a signature of one-dimensional weak antilocalization of holes in the presence of strong spin-orbit coupling. The temperature and back gate dependences of phase coherence length, spin-orbit relaxation time, and background conductance were stud… ▽ More We investigate the low-temperature magneto-transport properties of individual Ge/Si core/shell nanowires. Negative magneto-conductance was observed, which is a signature of one-dimensional weak antilocalization of holes in the presence of strong spin-orbit coupling. The temperature and back gate dependences of phase coherence length, spin-orbit relaxation time, and background conductance were studied. Specifically, we show the spin-orbit coupling strength can be modulated by more than five folds with an external electric field. These results suggest the Ge/Si nanowire system possesses strong and tunable spin-orbit interactions and may serve as a candidate for spintronics applications. △ Less

Submitted 11 August, 2010; originally announced August 2010.

Comments: 14 pages with Supporting Information

Journal ref: Nano Letters 10(8), 2956 (2010)

Andreev reflection enhanced single hole tunneling in Ge/Si core/shell nanowire quantum dot

Authors: Xiao-Jie Hao, Guo-Ping Guo, Hai-Ou Li, Cheng Zhou, Gang Cao, Guang-Can Guo, Wayne Y. Fung, Zhongqing Ji, Wei Lu, Tao Tu

Abstract: We experimentally study the electrical transport properties of Ge/Si core/shell nanowire device with two superconducting leads in the Coulomb blockade regime. Anomalous zero field magnetoconductance peaks are observed for the first time at the gate voltages where Coulomb blockade oscillation peaks present. Many evidences indicate this feature is due to Andreev reflection enhanced phase coherent si… ▽ More We experimentally study the electrical transport properties of Ge/Si core/shell nanowire device with two superconducting leads in the Coulomb blockade regime. Anomalous zero field magnetoconductance peaks are observed for the first time at the gate voltages where Coulomb blockade oscillation peaks present. Many evidences indicate this feature is due to Andreev reflection enhanced phase coherent single hole tunneling through the quantum dot, which can be suppressed by an external magnetic field without destroying the superconducting states in the electrodes. △ Less

Submitted 27 May, 2010; originally announced May 2010.

Comments: 10 pages, 5 figures

Coulomb blockade in graphene quantum dots

Authors: Qiong Ma, Tao Tu, Zhi-Rong Lin, Guang-Can Guo, Guo-Ping Guo

Abstract: We study the conductance spectrum of graphene quantum dots, both single and multiple cases. The single electron tunneling phenomenon is investigated and the periodicity, amplitude and line shape of the Coulomb blockade oscillations at low temperatures are obtained. Further, we discuss the transport behavior when multiple dots are assembled in array and find a phase transition of conductance spec… ▽ More We study the conductance spectrum of graphene quantum dots, both single and multiple cases. The single electron tunneling phenomenon is investigated and the periodicity, amplitude and line shape of the Coulomb blockade oscillations at low temperatures are obtained. Further, we discuss the transport behavior when multiple dots are assembled in array and find a phase transition of conductance spectra from individual Coulomb blockade to collective Coulomb blockade. △ Less

Submitted 15 November, 2009; originally announced November 2009.

Comments: 7 pages, 6 figures

Substrate Modulated Graphene Quantum Dot

Authors: Qiong Ma, Zhi-Rong Lin, Tao Tu, Guang-Can Guo, Guo-Ping Guo

Abstract: We propose a new method to use gapped graphene as barrier to confine electrons in gapless graphene and form a good quantum dot, which can be realized on an oxygen-terminated $SiO_{2}$ substrate partly H-passivated. In particular, we use ferromagnetic insulators deposited on top of barrier which give rise to a spin related energy spectrum and transport properties. Compared to the complexity of et… ▽ More We propose a new method to use gapped graphene as barrier to confine electrons in gapless graphene and form a good quantum dot, which can be realized on an oxygen-terminated $SiO_{2}$ substrate partly H-passivated. In particular, we use ferromagnetic insulators deposited on top of barrier which give rise to a spin related energy spectrum and transport properties. Compared to the complexity of etched quantum dots in graphene, the setup suggested here is a promising candidate for practical applications. △ Less

Submitted 25 October, 2009; originally announced October 2009.

Probing Quantum Hall Pseudospin Ferromagnet by Resistively Detected NMR

Authors: G. P. Guo, Y. J. Zhao, T. Tu, X. J. Hao, G. C. Guo, H. W. Jiang

Abstract: Resistively Detected Nuclear Magnetic Resonance (RD-NMR) has been used to investigate a two-subband electron system in a regime where quantum Hall pseudo-spin ferromagnetic (QHPF) states are prominently developed. It reveals that the easy-axis QHPF state around the total filling factor $ν=4 $ can be detected by the RD-NMR measurement. Approaching one of the Landau level (LL) crossing points, the… ▽ More Resistively Detected Nuclear Magnetic Resonance (RD-NMR) has been used to investigate a two-subband electron system in a regime where quantum Hall pseudo-spin ferromagnetic (QHPF) states are prominently developed. It reveals that the easy-axis QHPF state around the total filling factor $ν=4 $ can be detected by the RD-NMR measurement. Approaching one of the Landau level (LL) crossing points, the RD-NMR signal strength and the nuclear spin relaxation rate $1/T_{1}$ enhance significantly, a signature of low energy spin excitations. However, the RD-NMR signal at another identical LL crossing point is surprisingly missing which presents a puzzle. △ Less

Submitted 6 April, 2009; originally announced April 2009.

Journal ref: Phys. Rev. B 81, 041306 (2010)

Quantum computation with graphene nanoribbon

Authors: Guo-Ping Guo, Zhi-Rong Lin, Xiao-Peng Li, Tao Tu, Guang-Can Guo

Abstract: We propose a scalable scheme to implement quantum computation in graphene nanoribbon. It is shown that electron or hole can be naturally localized in each zigzag region for a graphene nanoribbon with a sequence of Z-shaped structure without exploiting any confined gate. An one-dimensional graphene quantum dots chain is formed in such graphene nanoribbon, where electron or hole spin can be encode… ▽ More We propose a scalable scheme to implement quantum computation in graphene nanoribbon. It is shown that electron or hole can be naturally localized in each zigzag region for a graphene nanoribbon with a sequence of Z-shaped structure without exploiting any confined gate. An one-dimensional graphene quantum dots chain is formed in such graphene nanoribbon, where electron or hole spin can be encoded as qubits. The coupling interaction between neighboring graphene quantum dots is found to be always-on Heisenberg type. Applying the bang-bang control strategy and decoherence free subspaces encoding method, universal quantum computation is argued to be realizable with the present techniques. △ Less

Submitted 12 August, 2008; originally announced August 2008.

Comments: 10 pages, 4 figures

Journal ref: New J. Phys. 11 123005 (2009)

Numerical Studies of Quantum Hall Ferromagnetism in Two-Subband Systems

Authors: Xiao-Jie Hao, Tao Tu, Yong-Jie Zhao, Guang-Can Guo, H. W. Jiang, Guo-Ping Guo

Abstract: We carry out a numerical study of the quantum Hall ferromagnetism in a two-subband system using a set of experimental parameters in a recently experiment [X. C. Zhang, I. Martin, and H. W. Jiang, Phys. Rev. B \textbf{74}, 073301 (2006)]. Employing the self-consistence local density approximation for growth direction wave function and the Hartree-Fock theory for the pseudospin anisotropy energy,… ▽ More We carry out a numerical study of the quantum Hall ferromagnetism in a two-subband system using a set of experimental parameters in a recently experiment [X. C. Zhang, I. Martin, and H. W. Jiang, Phys. Rev. B \textbf{74}, 073301 (2006)]. Employing the self-consistence local density approximation for growth direction wave function and the Hartree-Fock theory for the pseudospin anisotropy energy, we are able to account for the easy-axis and easy-plane quantum Hall ferromagnetism observed at total filling factor $ν= 3$ and $ν= 4$, respectively. Our study provides some insight of how the anisotropy energy, which highly depends upon the distribution of growth direction wave functions, determines the symmetry of the quantum Hall ferromagnets. △ Less

Submitted 2 July, 2008; originally announced July 2008.

Comments: 8 pages, 4 figures

Journal ref: J. Phys.: Condens. Matter 21 455802 (2009)

Experimental Studies of Scaling Behavior of a Quantum Hall System with a Tunable Landau Level Mixing

Authors: Y. J. Zhao, T. Tu, X. J. Hao, G. C. Guo, H. W. Jiang, G. P. Guo

Abstract: Temperature dependence of the longitudinal and Hall resistance is studied in the regime of localization-delocalization transition. We carry out measurements of a scaling exponent $κ$ in the Landau level mixing region at several filling factors. The localization exponent $γ$ is extracted using an approach based on the variable range hopping theory. The values of $γ$ and $κ$ are found to be univer… ▽ More Temperature dependence of the longitudinal and Hall resistance is studied in the regime of localization-delocalization transition. We carry out measurements of a scaling exponent $κ$ in the Landau level mixing region at several filling factors. The localization exponent $γ$ is extracted using an approach based on the variable range hopping theory. The values of $γ$ and $κ$ are found to be universal, independent of filling factor in our sample. We can conclude that although Landau level mixing can change the degeneracy of a quantum Hall state, the value of the scaling exponent remains the same for a given sample that contains a fixed disorder profile. △ Less

Submitted 2 July, 2008; originally announced July 2008.

Comments: 11 pages, 4 figures

Journal ref: Phys. Rev. B 78, 233301 (2008)

Observation of an in-plane magnetic-field-driven phase transition in a quantum Hall system with SU(4) symmetry

Authors: G. P. Guo, Y. J. Zhao, T. Tu, X. J. Hao, X. C. Zhang, G. C. Guo, H. W. Jiang

Abstract: In condensed matter physics, the study of electronic states with SU(N) symmetry has attracted considerable and growing attention in recent years, as systems with such a symmetry can often have a spontaneous symmetry-breaking effect giving rise to a novel ground state. For example, pseudospin quantum Hall ferromagnet of broken SU(2) symmetry has been realized by bringing two Landau levels close t… ▽ More In condensed matter physics, the study of electronic states with SU(N) symmetry has attracted considerable and growing attention in recent years, as systems with such a symmetry can often have a spontaneous symmetry-breaking effect giving rise to a novel ground state. For example, pseudospin quantum Hall ferromagnet of broken SU(2) symmetry has been realized by bringing two Landau levels close to degeneracy in a bilayer quantum Hall system. In the past several years, the exploration of collective states in other multi-component quantum Hall systems has emerged. Here we show the conventional pseudospin quantum Hall ferromagnetic states with broken SU(2) symmetry collapsed rapidly into an unexpected state with broken SU(4) symmetry, by in-plane magnetic field in a two-subband GaAs/AlGaAs two-dimensional electron system at filling factor around $ν=4$. Within a narrow tilting range angle of 0.5 degrees, the activation energy increases as much as 12 K. While the origin of this puzzling observation remains to be exploited, we discuss the possibility of a long-sought pairing state of electrons with a four-fold degeneracy. △ Less

Submitted 11 September, 2007; v1 submitted 10 September, 2007; originally announced September 2007.

Comments: 13 pages, 4 figures

Report number: CAS-KITPC/ITP-008

Journal ref: Phys. Rev. B 78, 233305 (2008)

Scaling Behavior and Variable Hopping Conductivity in the Quantum Hall Plateau Transition

Authors: Tao Tu, Yong-Jie Zhao, Guo-Ping Guo, Xiao-Jie Hao, Guang-Can Guo

Abstract: We have measured the temperature dependence of the longitudinal resistivity $% ρ_{xx}$ of a two-dimensional electron system in the regime of the quantum Hall plateau transition. We extracted the quantitative form of scaling function for $ρ_{xx}$ and compared it with the results of ordinary scaling theory and variable range hopping based theory. We find that the two alternative theoretically prop… ▽ More We have measured the temperature dependence of the longitudinal resistivity $% ρ_{xx}$ of a two-dimensional electron system in the regime of the quantum Hall plateau transition. We extracted the quantitative form of scaling function for $ρ_{xx}$ and compared it with the results of ordinary scaling theory and variable range hopping based theory. We find that the two alternative theoretically proposed scaling functions are valid in different regions. △ Less

Submitted 27 March, 2007; originally announced March 2007.

Comments: 4 pages, 4 figures

Renormalization Group Theory for a Perturbed KdV Equation

Authors: Tao Tu, Hua Sheng

Abstract: We show that renormalization group(RG) theory can be used to give an analytic description of the evolution of a perturbed KdV equation. The equations describing the deformation of its shape as the effect of perturbation are RG equations. The RG approach may be simpler than inverse scattering theory(IST) and another approaches, because it dose not rely on any knowledge of IST and it is very conci… ▽ More We show that renormalization group(RG) theory can be used to give an analytic description of the evolution of a perturbed KdV equation. The equations describing the deformation of its shape as the effect of perturbation are RG equations. The RG approach may be simpler than inverse scattering theory(IST) and another approaches, because it dose not rely on any knowledge of IST and it is very concise and easy to understand. To the best of our knowledge, this is the first time that RG has been used in this way for the perturbed soliton dynamics. △ Less

Submitted 5 June, 2001; originally announced June 2001.

Comments: 4 pages, no figure, revtex