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High mechanical strength Si anode synthesis with interlayer bonded expanded graphite structure for lithium-ion batteries
Authors:
Wenhui Lai,
Jong Hak Lee,
Lu Shi,
Yuqing Liu,
Yanhui Pu,
Yong Kang Ong,
Carlos Limpo,
Ting Xiong,
Yifan Rao,
Chorng Haur Sow,
Barbaros Özyilmaz
Abstract:
Despite advancements in silicon-based anodes for high-capacity lithium-ion batteries, their widespread commercial adoption is still hindered by significant volume expansion during cycling, especially at high active mass loadings crucial for practical use. The root of these challenges lies in the mechanical instability of the material, which subsequently leads to the structural failure of the elect…
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Despite advancements in silicon-based anodes for high-capacity lithium-ion batteries, their widespread commercial adoption is still hindered by significant volume expansion during cycling, especially at high active mass loadings crucial for practical use. The root of these challenges lies in the mechanical instability of the material, which subsequently leads to the structural failure of the electrode. Here, we present a novel synthesis of a composite combining expanded graphite and silicon nanoparticles. This composite features a unique interlayer-bonded graphite structure, achieved through the application of a modified spark plasma sintering method. Notably, this innovative structure not only facilitates efficient ion and electron transport but also provides exceptional mechanical strength (Vickers hardness: up to 658 MPa, Young's modulus: 11.6 GPa). This strength effectively accommodates silicon expansion, resulting in an impressive areal capacity of 2.9 mA h cm-2 (736 mA h g-1) and a steady cycle life (93% after 100 cycles). Such outstanding performance is paired with features appropriate for large-scale industrial production of silicon batteries, such as active mass loading of at least 3.9 mg cm-2, a high-tap density electrode material of 1.68 g cm-3 (secondary clusters: 1.12 g cm-3), and a production yield of up to 1 kg per day.
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Submitted 25 June, 2025;
originally announced June 2025.
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A single atom vibration sensor
Authors:
Wenxi Lai,
Yu-Quan Ma,
Qiaoxin Li
Abstract:
Previously in vibration sensors, optical glass plates, optical fibres, carbon nanotubes, semiconductor materials, piezoelectric materials and molecules are proved to be effective transducers for sensing vibrations. In this work, for the first time, we will propose a model of vibration sensor using single atom transport in an open optical lattice. In this apparatus, information of mechanical vibrat…
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Previously in vibration sensors, optical glass plates, optical fibres, carbon nanotubes, semiconductor materials, piezoelectric materials and molecules are proved to be effective transducers for sensing vibrations. In this work, for the first time, we will propose a model of vibration sensor using single atom transport in an open optical lattice. In this apparatus, information of mechanical vibration could be transferred into shaking of optical lattice through one of a cavity mirror. Shaking lattice consequently induces Mott insulator due to quantum interference. It is found that information of vibration is encoded in the atomic current and it could be extracted by Fourier transformations. The present atomic vibration sensor has wide detection range of frequency with high precision. Our present model of sensor based on atomic system opens a new area of studying vibration sensors.
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Submitted 27 January, 2026; v1 submitted 16 May, 2024;
originally announced May 2024.
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Quantum geometric tensor and the topological characterization of the extended Su-Schrieffer-Heeger model
Authors:
Xiang-Long Zeng,
Wen-Xi Lai,
Yi-Wen Wei,
Yu-Quan Ma
Abstract:
We investigate the quantum metric and topological Euler number in a cyclically modulated Su-Schrieffer-Heeger (SSH) model with long-range hopping terms. By computing the quantum geometry tensor, we derive exactly expressions for the quantum metric and Berry curvature of the energy band electrons, and we obtain the phase diagram of the model marked by the first Chern number. Furthermore, we also ob…
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We investigate the quantum metric and topological Euler number in a cyclically modulated Su-Schrieffer-Heeger (SSH) model with long-range hopping terms. By computing the quantum geometry tensor, we derive exactly expressions for the quantum metric and Berry curvature of the energy band electrons, and we obtain the phase diagram of the model marked by the first Chern number. Furthermore, we also obtain the topological Euler number of the energy band based on the Gauss-Bonnet theorem on the topological characterization of the closed Bloch states manifold in the first Brillouin zone. However, some regions where the Berry curvature is identically zero in the first Brillouin zone results in the degeneracy of the quantum metric, which leads to ill-defined non-integer topological Euler numbers. Nevertheless, the non-integer "Euler number" provides valuable insights and provide an upper bound for absolute values of the Chern numbers.
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Submitted 11 April, 2024;
originally announced April 2024.
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A general formula for the amplitude-frequency ratio in shaking induced Mott insulator of atomtronic transistors
Authors:
Wenxi Lai,
Yu-Quan Ma,
Yi-Wen Wei
Abstract:
Mott insulator of atomic transport can be realized in shaken optical lattices by choosing particular ratio of driving amplitude and frequency, which has been studied as Floquet engineering with time-independent effective Hamiltonian approach. Here, we give a general formula of amplitude-frequency ratio for realization of the shaking induced insulator-conductor transition in a double-well open syst…
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Mott insulator of atomic transport can be realized in shaken optical lattices by choosing particular ratio of driving amplitude and frequency, which has been studied as Floquet engineering with time-independent effective Hamiltonian approach. Here, we give a general formula of amplitude-frequency ratio for realization of the shaking induced insulator-conductor transition in a double-well open system, using numerical computation with instantaneous eigenstates approach. The result is owing to the fact that the instantaneous eigenstates approach is applicable in wider parameter range compared with the time-independent effective Hamiltonian approach. Analysis from the results of quantum master equation shows that the insulator effect is originated from coherent localization of atom wave packets in optical wells.
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Submitted 12 June, 2026; v1 submitted 17 March, 2024;
originally announced March 2024.
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Atomtronic superconducting quantum interference device in synthetic dimensions
Authors:
Wenxi Lai,
Yu-Quan Ma,
Yi-Wen Wei
Abstract:
Coherence and scalability are essential properties of quantum systems required in quantum computers. This study presents a high coherent and scalable qubit system with atomtronics in synthetic dimensions. It is atomtronic counterpart of superconducting quantum interference device. Comparing with traditional superconducting quantum interference device which requires at least $2$-dimensional circuit…
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Coherence and scalability are essential properties of quantum systems required in quantum computers. This study presents a high coherent and scalable qubit system with atomtronics in synthetic dimensions. It is atomtronic counterpart of superconducting quantum interference device. Comparing with traditional superconducting quantum interference device which requires at least $2$-dimensional circuits, the synthetic dimensional superconducting quantum interference device can be realized only in $1$-dimensional circuits. The synthetic dimensional system is composed of Bose-Einstein condensate in two neighboring optical wells which is coupled to an external coherent light. Control parameter for the qubit is naturally provided by artificial magnetic flux originated from the coherent atom-light coupling. It should be a great advantage for the scalability and integration feature of quantum logic gates.
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Submitted 27 January, 2026; v1 submitted 2 March, 2023;
originally announced March 2023.
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Inhomogeneous light photovoltaic effect in neighboring quantum dots
Authors:
Wenxi Lai
Abstract:
Photovoltaic effect of double quantum dots under nonuniform light field intensity has been studied theoretically. Comparing with the traditional p-n type photovoltaic effect, the inhomogeneous light field provides asymmetric potential creating polarization of electron number distribution in the neighboring quantum dots and furthermore gives rise to net current. Current density and efficiency of su…
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Photovoltaic effect of double quantum dots under nonuniform light field intensity has been studied theoretically. Comparing with the traditional p-n type photovoltaic effect, the inhomogeneous light field provides asymmetric potential creating polarization of electron number distribution in the neighboring quantum dots and furthermore gives rise to net current. Current density and efficiency of such kind solar cells are estimated to be comparable to the traditional p-n type material based solar cells. Motion of electron is described using quantum master equation around room temperature. The inhomogeneous light photovoltaic effect has potential applications for the gain of more economical solar cells.
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Submitted 20 May, 2022; v1 submitted 7 August, 2021;
originally announced August 2021.
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Photovoltaic transistor of atoms due to spin-orbit coupling in three optical traps
Authors:
Haihu Cui,
Mingzhu Zhang,
Wenxi Lai
Abstract:
In this paper, spin-orbit coupling induced photovoltaic effect of cold atoms has been studied in a three-trap system which is an two-dimensional extension of a two-trap system reported previously. It is proposed here that atom coherent length is one of the important influence to the resistance of this photovoltaic battery. Current properties of the system for different geometrical structures of th…
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In this paper, spin-orbit coupling induced photovoltaic effect of cold atoms has been studied in a three-trap system which is an two-dimensional extension of a two-trap system reported previously. It is proposed here that atom coherent length is one of the important influence to the resistance of this photovoltaic battery. Current properties of the system for different geometrical structures of the trapping potentials are discussed. Numerical results show extension in the number of traps could cause current increase directly. Quantum master equation at finite temperature is used to treat this opened system. This work may give a theoretical basis for further development of the photovoltaic effect of neutral atoms.
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Submitted 27 July, 2021;
originally announced July 2021.
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Photovoltaic Effect of Atomtronics Induced by Artificial Gauge Field
Authors:
Wenxi Lai,
Yuquan Ma,
W. M. Liu
Abstract:
We investigate photovoltaic effect of atomtronics induced by artificial gauge field in four optical potentials. Effective magnetic flux gives rise to polarization of atom occupation probability which creates current of atomtronics. The relation between atomic current and magnetic flux behaves like the current-phase property in Josephson junction. The photovoltaic cell is well defined by the atomic…
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We investigate photovoltaic effect of atomtronics induced by artificial gauge field in four optical potentials. Effective magnetic flux gives rise to polarization of atom occupation probability which creates current of atomtronics. The relation between atomic current and magnetic flux behaves like the current-phase property in Josephson junction. The photovoltaic cell is well defined by the atomic opened system which have effective voltage and two different poles that correspond to two internal states of atomtronics. The atom flow is controllable by changing the direction of incident light and other system parameters. Detection of the atomic current intensity is available through light emission optical spectrum in experiments.
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Submitted 21 February, 2019;
originally announced February 2019.
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Conduction Bands of Atomic Tunneling Ring in Artificial Gauge Field Assisted Opened Optical Traps
Authors:
Wenxi Lai,
Yuquan Ma,
W. M. Liu
Abstract:
We show conduction bands of artificial gauge field assisted atom flow in triangle optical lattice. The conduction bands are result from periodicity boundary condition of artificial magnetic flux induced phases of atoms. The positions of conduction bands depend on geometry of the atom trajectory. We consider a cell of the triangle optical lattice which is a opened system connected to its environmen…
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We show conduction bands of artificial gauge field assisted atom flow in triangle optical lattice. The conduction bands are result from periodicity boundary condition of artificial magnetic flux induced phases of atoms. The positions of conduction bands depend on geometry of the atom trajectory. We consider a cell of the triangle optical lattice which is a opened system connected to its environment of Fermion atom clouds. The chemical potentials of the atom clouds are the same and the atom flow is absolutely created by a clock laser induced spin-orbit coupling. Our results are important for the control of atom flow in quantum circuits.
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Submitted 30 June, 2018;
originally announced July 2018.
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Two-component self-contracted droplets: long-range attraction and confinement effects
Authors:
Adrien Benusiglio,
Nate Cira,
Anna Wei Lai,
Manu Prakash
Abstract:
Marangoni self-contracted droplets are formed by a mixture of two liquids, one of larger surface tension and larger evaporation rate than the other. Due to evaporation, the droplets contract to a stable contact angle instead of spreading on a wetting substrate. This gives them unique properties, including absence of pinning force and ability to move under vapor gradients, self- and externally impo…
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Marangoni self-contracted droplets are formed by a mixture of two liquids, one of larger surface tension and larger evaporation rate than the other. Due to evaporation, the droplets contract to a stable contact angle instead of spreading on a wetting substrate. This gives them unique properties, including absence of pinning force and ability to move under vapor gradients, self- and externally imposed. We first model the dynamics of attraction in an unconfined geometry and then study the effects of confinement on the attraction range and dynamics, going from minimal confinement (vertical boundary), to medium confinement (2-D vapor diffusion) and eventually strong confinement (1-D). "Self-induced" motion is observed when single droplets are placed close to a vapor boundary toward which they are attracted, the boundary acting as an image droplet with respect to itself. When two droplets are confined between two horizontal plates, they interact at a longer distance with modified dynamics. Finally, confining the droplet in a tunnel, the range of attraction is greatly enhanced, as the droplet moves all the way up the tunnel when an external humidity gradient is imposed. "Self-induced" motion is also observed, as the droplet can move by itself towards the center of the tunnel. Confinement greatly increase the range at which droplets interact as well as their lifetime and thus greatly expands the control and design possibilities for applications offered by self-contracted droplets.
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Submitted 16 November, 2017;
originally announced November 2017.
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Optical switching of defect charge states in 4H-SiC
Authors:
D. Andrew Golter,
Chih Wei Lai
Abstract:
We demonstrate optically induced switching between bright and dark charged divacancy defects in 4H-SiC. Photoluminescence excitation and time-resolved photoluminescence measurements reveal the excitation conditions for such charge conversion. For an energy below ~1.3 eV (above ~950 nm), the PL is suppressed by more than two orders of magnitude. The PL is recovered in the presence of a higher energ…
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We demonstrate optically induced switching between bright and dark charged divacancy defects in 4H-SiC. Photoluminescence excitation and time-resolved photoluminescence measurements reveal the excitation conditions for such charge conversion. For an energy below ~1.3 eV (above ~950 nm), the PL is suppressed by more than two orders of magnitude. The PL is recovered in the presence of a higher energy repump laser with a time-averaged intensity less than 0.1% that of the excitation field. Under a repump of 2.33 eV (532 nm), the PL increases rapidly, with a time constant ~30 $μ$s. By contrast, when the repump is switched off, the PL decreases first within ~100-200 $μ$s, followed by a much slower decay of a few seconds. We attribute these effects to the conversion between two different charge states. Under an excitation at energy levels below 1.3 eV, V$_{Si}$V$_C$$^0$ are converted into a dark charge state. A repump laser with an energy above 1.3 eV can excite this charged state and recover the bright neutral state. This optically induced charge switching can lead to charge-state fluctuations but can be exploited for long-term data storage or nuclear-spin-based quantum memory.
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Submitted 6 October, 2017; v1 submitted 5 July, 2017;
originally announced July 2017.
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Layer- and Frequency-Dependent Second Harmonic Generation in Reflection from GaSe Atomic Crystals
Authors:
Yanhao Tang,
Krishna C. Mandal,
John A. McGuire,
Chih Wei Lai
Abstract:
We report optical second-harmonic generation (SHG) in reflection from GaSe crystals of 1 to more than 100 layers using a fundamental picosecond pulsed pump at 1.58 eV and a supercontinuum white light pulsed laser with energies ranging from 0.85 to 1.4 eV. The measured reflected SHG signal is maximal in samples of $\sim$20 layers, decreasing in thicker samples as a result of interference. The thick…
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We report optical second-harmonic generation (SHG) in reflection from GaSe crystals of 1 to more than 100 layers using a fundamental picosecond pulsed pump at 1.58 eV and a supercontinuum white light pulsed laser with energies ranging from 0.85 to 1.4 eV. The measured reflected SHG signal is maximal in samples of $\sim$20 layers, decreasing in thicker samples as a result of interference. The thickness- and frequency-dependence of the SHG response of samples thicker than $\sim$7 layers can be reproduced by a second-order optical susceptibility that is the same as in bulk samples. For samples $\lesssim$7 layers, the second-order optical susceptibility is reduced compared to that in thicker samples, which is attributed to the expected bandgap increase in mono- and few-layer GaSe.
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Submitted 30 June, 2016; v1 submitted 25 May, 2016;
originally announced May 2016.
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Statistical Theory of Initiation of Explosives by Impact
Authors:
Gan Ren,
Yingzhe Liu,
Weipeng Lai,
Tao Yu
Abstract:
When a given weight dropped onto an explosive charge, explosion or not is probabilistic for certain impact energy and the frequency of explosion is always increase with increasing impact energy. Based on experimental results and recently theoretical work, we propose that the hot spot formation is attributed to the activated molecules decomposition and the number of molecules initiation is proporti…
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When a given weight dropped onto an explosive charge, explosion or not is probabilistic for certain impact energy and the frequency of explosion is always increase with increasing impact energy. Based on experimental results and recently theoretical work, we propose that the hot spot formation is attributed to the activated molecules decomposition and the number of molecules initiation is proportional to the impact energy but not the dropped weight heating as the previous hot spot theory. A theoretical model based on two states model has been put forward for this phenomena. It is shown that the activated molecules to form a hot spot determine the probabilistic nature of initiation by impact. It is shown a good agreement tested with Hexogen (RDX) experimental impact data.
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Submitted 11 January, 2016;
originally announced January 2016.
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Spin splitting in 2D monochalcogenide semiconductors
Authors:
Dat T. Do,
Subhendra D. Mahanti,
Chih Wei Lai
Abstract:
We report ab initio calculations of the spin splitting of the uppermost valence band (UVB) and the lowermost conduction band (LCB) in bulk and atomically thin GaS, GaSe, GaTe, and InSe. These layered monochalcogenides appear in four major polytypes depending on the stacking order, except for the monoclinic GaTe. Bulk and few-layer $ε$- and $γ$-type, and odd-number $β$-type GaS, GaSe, and InSe crys…
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We report ab initio calculations of the spin splitting of the uppermost valence band (UVB) and the lowermost conduction band (LCB) in bulk and atomically thin GaS, GaSe, GaTe, and InSe. These layered monochalcogenides appear in four major polytypes depending on the stacking order, except for the monoclinic GaTe. Bulk and few-layer $ε$- and $γ$-type, and odd-number $β$-type GaS, GaSe, and InSe crystals are noncentrosymmetric. The spin splittings of the UVB and the LCB near the $Γ$-point in the Brillouin zone are finite, but still smaller than those in a zinc-blende semiconductor such as GaAs. On the other hand, the spin splitting is zero in centrosymmetric bulk and even-number few-layer $β$-type GaS, GaSe, and InSe, owing to the constraint of spatial inversion symmetry. By contrast, GaTe exhibits zero spin splitting because it is centrosymmetric down to a single layer. In these monochalcogenide semiconductors, the separation of the non-degenerate conduction and valence bands from adjacent bands results in the suppression of Elliot-Yafet spin relaxation mechanism. Therefore, the electron- and hole-spin relaxation times in these systems with zero or minimal spin splittings are expected to exceed those in GaAs when the D'yakonov-Perel' spin relaxation mechanism is also suppressed.
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Submitted 4 June, 2015; v1 submitted 2 April, 2015;
originally announced April 2015.
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Multiple-pulse lasing from an optically induced harmonic confinement in a highly photoexcited microcavity
Authors:
Wei Xie,
Feng-Kuo Hsu,
Yi-Shan Lee,
Sheng-Di Lin,
Chih Wei Lai
Abstract:
We report the observation of macroscopic harmonic states in an optically induced confinement in a highly photoexcited semiconductor microcavity at room temperature. The spatially photomodulated refractive index changes result in the visualization of harmonic states in a micrometer-scale optical potential at quantized energies up to 4 meV even in the weak-coupling plasma limit. We characterize the…
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We report the observation of macroscopic harmonic states in an optically induced confinement in a highly photoexcited semiconductor microcavity at room temperature. The spatially photomodulated refractive index changes result in the visualization of harmonic states in a micrometer-scale optical potential at quantized energies up to 4 meV even in the weak-coupling plasma limit. We characterize the time evolution of the harmonic states directly from the consequent pulse radiation and identify sequential multiple $\sim$10 ps pulse lasing with different emitting angles and frequencies.
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Submitted 21 July, 2015; v1 submitted 30 January, 2015;
originally announced February 2015.
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Manipulation of a single magnetic atom using polarized single electron transport in a double quantum dot
Authors:
Wenxi Lai,
Wen Yang
Abstract:
We consider theoretically a magnetic impurity spin driven by polarized electrons tunneling through a double quantum dot system. Spin blockade effect and spin conservation in the system make the magnetic impurity sufficiently interact with each transferring electron. As a results, a single collected electron carries information about spin change of the magnetic impurity. The scheme may develop all…
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We consider theoretically a magnetic impurity spin driven by polarized electrons tunneling through a double quantum dot system. Spin blockade effect and spin conservation in the system make the magnetic impurity sufficiently interact with each transferring electron. As a results, a single collected electron carries information about spin change of the magnetic impurity. The scheme may develop all electrical manipulation of magnetic atoms by means of single electrons, which is significant for the implementation of scalable logical gates in information processing systems.
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Submitted 21 September, 2015; v1 submitted 28 January, 2015;
originally announced January 2015.
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Near Unity Optical Spin Polarization in GaSe Nanoslabs
Authors:
Yanhao Tang,
Wei Xie,
Krishna C. Mandal,
John A. McGuire,
C. W. Lai
Abstract:
We report nearly complete preservation of "spin memory" between optical absorption and photoluminescence (PL) in nanometer slabs of GaSe pumped with 0.2 eV excess energy. At cryogenic temperatures, the initial degree of circular polarization ($ρ_0$) of PL approaches unity, with the major fraction of the spin polarization decaying with a time constant $>$500 ps in sub-100-nm GaSe nanoslabs. Even at…
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We report nearly complete preservation of "spin memory" between optical absorption and photoluminescence (PL) in nanometer slabs of GaSe pumped with 0.2 eV excess energy. At cryogenic temperatures, the initial degree of circular polarization ($ρ_0$) of PL approaches unity, with the major fraction of the spin polarization decaying with a time constant $>$500 ps in sub-100-nm GaSe nanoslabs. Even at room temperature, $ρ_0$ as large as 0.7 is observed, while pumping 1 eV above the band edge yields $ρ_0$ = 0.15. Angular momentum preservation for both electrons and holes is due to the separation of the non-degenerate conduction and valence bands from other bands. In contrast to valley polarization in atomically thin TMDs, here optical spin polarization is preserved in nanoslabs of 100 layers or more of GaSe.
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Submitted 21 October, 2014; v1 submitted 20 October, 2014;
originally announced October 2014.
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Spin filter of electrons through a zeeman splitting single quantum dot
Authors:
Wenxi Lai,
Mengmeng Zhang
Abstract:
Electron spin filter induced by Zeeman splitting in a few-electron quantum dot coupled to two normal electrodes is studied considering Coulomb blockade effect. Based on the Anderson model and Liouville-von Neumann equation, equation of motion of the system is derived and analytical solutions are achieved. Transport windows for perfectly polarized current, partially polarized current and non-polari…
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Electron spin filter induced by Zeeman splitting in a few-electron quantum dot coupled to two normal electrodes is studied considering Coulomb blockade effect. Based on the Anderson model and Liouville-von Neumann equation, equation of motion of the system is derived and analytical solutions are achieved. Transport windows for perfectly polarized current, partially polarized current and non-polarized current induced by the Zeeman splitting energy and Coulomb blockade potential are exploited. We will give the relations of voltage, magnetic field and temperature for high quality spin filtering.
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Submitted 22 March, 2020; v1 submitted 22 September, 2014;
originally announced September 2014.
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Dephasing of electrons in the Aharonov-Bohm interferometer with a single-molecular vibrational junction
Authors:
Wenxi Lai,
Yunhui Xing,
Zhongshui Ma
Abstract:
Phase relaxation of electrons transferring through an electromechanical transistor is studied using the Aharonov-Bohm interferometer. With the approach of quantum master equation, the phase properties of an electron are numerically analyzed based on the interference fringes. Coherence of electron is partially destroyed by its scattering on excited levels of the local nanomechanical oscillator. Tra…
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Phase relaxation of electrons transferring through an electromechanical transistor is studied using the Aharonov-Bohm interferometer. With the approach of quantum master equation, the phase properties of an electron are numerically analyzed based on the interference fringes. Coherence of electron is partially destroyed by its scattering on excited levels of the local nanomechanical oscillator. Transmission amplitudes with respect to two adjacent mechanical vibrational levels have a phase difference of $π$. The character of phase shift by $π$ depends on the oscillator frequency only and is robust for the wide range variance of the applied voltage, tunneling length and damping rate of the mechanical oscillator.
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Submitted 21 April, 2013; v1 submitted 10 November, 2012;
originally announced November 2012.
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Current-oscillator correlation and Fano factor spectrum of quantum shuttle with finite bias voltage and temperature
Authors:
Wenxi Lai,
Yunshan Cao,
Zhongshui Ma
Abstract:
A general master equation is derived to describe an electromechanical single-dot transistor in the Coulomb blockade regime. In the equation, Fermi distribution functions in the two leads are taken into account, which allows one to study the system as a function of bias voltage and temperature of the leads. Furthermore, we treat the coherent interaction mechanism between electron tunneling events a…
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A general master equation is derived to describe an electromechanical single-dot transistor in the Coulomb blockade regime. In the equation, Fermi distribution functions in the two leads are taken into account, which allows one to study the system as a function of bias voltage and temperature of the leads. Furthermore, we treat the coherent interaction mechanism between electron tunneling events and the dynamics of excited vibrational modes. Stationary solutions of the equation are numerically calculated. We show current through the oscillating island at low temperature appears step like characteristics as a function of the bias voltage and the steps depend on mean phonon number of the oscillator. At higher temperatures the current steps would disappear and this event is accompanied by the emergence of thermal noise of the charge transfer. When the system is mainly in the ground state, zero frequency Fano factor of current manifests sub-Poissonian noise and when the system is partially driven into its excited states it exhibits super-Poissonian noise. The difference in the current noise would almost be removed for the situation in which the dissipation rate of the oscillator is much larger than the bare tunneling rates of electrons.
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Submitted 10 November, 2012; v1 submitted 6 December, 2011;
originally announced December 2011.
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Nonlinear dynamics of quantum dot nuclear spins
Authors:
P. Maletinsky,
C. W. Lai,
A. Badolato,
A. Imamoglu
Abstract:
We report manifestly nonlinear dependence of quantum dot nuclear spin polarization on applied magnetic fields. Resonant absorption and emission of circularly polarized radiation pumps the resident quantum dot electron spin, which in turn leads to nuclear spin polarization due to hyperfine interaction. We observe that the resulting Overhauser field exhibits hysteresis as a function of the externa…
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We report manifestly nonlinear dependence of quantum dot nuclear spin polarization on applied magnetic fields. Resonant absorption and emission of circularly polarized radiation pumps the resident quantum dot electron spin, which in turn leads to nuclear spin polarization due to hyperfine interaction. We observe that the resulting Overhauser field exhibits hysteresis as a function of the external magnetic field. This hysteresis is a consequence of the feedback of the Overhauser field on the nuclear spin cooling rate. A semi-classical model describing the coupled nuclear and electron spin dynamics successfully explains the observed hysteresis but leaves open questions for the low field behaviour of the nuclear spin polarization.
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Submitted 12 September, 2006;
originally announced September 2006.
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Transient tunneling current of single electron transistors
Authors:
David M. -T. Kuo,
Pei-Wen Li,
W. T. Lai
Abstract:
The transient tunneling current of single electron transistors (SETs) is theoretically investigated. The time-dependent current formula given by Jauho, Wingreen and Meir [Phys. Rev. B 50, 5528 (1994)] is applied to study the temperature effect on the transient current through a single quantum dot embedded into asymmetry barrier. It is found that the tunneling rate ratio significantly influences…
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The transient tunneling current of single electron transistors (SETs) is theoretically investigated. The time-dependent current formula given by Jauho, Wingreen and Meir [Phys. Rev. B 50, 5528 (1994)] is applied to study the temperature effect on the transient current through a single quantum dot embedded into asymmetry barrier. It is found that the tunneling rate ratio significantly influences the feature of transient current. Finally, the oscillation structures on the exponential growth transient current of single hole transistors composed of germanium quantum dots is analyzed.
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Submitted 16 December, 2005;
originally announced December 2005.
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Knight Field Enabled Nuclear Spin Polarization in Single Quantum Dots
Authors:
C. W. Lai,
P. Maletinsky,
A. Badolato,
A. Imamoglu
Abstract:
We demonstrate dynamical nuclear spin polarization in the absence of an external magnetic field, by resonant circularly polarized optical excitation of a single electron or hole charged quantum dot. Optical pumping of the electron spin induces an effective inhomogeneous magnetic (Knight) field that determines the direction along which nuclear spins could polarize and enables nuclear-spin cooling…
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We demonstrate dynamical nuclear spin polarization in the absence of an external magnetic field, by resonant circularly polarized optical excitation of a single electron or hole charged quantum dot. Optical pumping of the electron spin induces an effective inhomogeneous magnetic (Knight) field that determines the direction along which nuclear spins could polarize and enables nuclear-spin cooling by suppressing depolarization induced by nuclear dipole-dipole interactions. Our observations suggest a new mechanism for spin-polarization where spin exchange with an electron reservoir plays a crucial role. These experiments constitute a first step towards quantum measurement of the Overhauser field.
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Submitted 13 December, 2005;
originally announced December 2005.