KANGHUN AHN - Academia.edu (original) (raw)
Papers by KANGHUN AHN
arXiv (Cornell University), Aug 13, 1996
We present a microscopic theory of skyrmion and antiskyrmion excitations in fractional quantum Ha... more We present a microscopic theory of skyrmion and antiskyrmion excitations in fractional quantum Hall systems, and calculate in an analytical fashion their excitation energies. From the calculated net spins at various fractional filling factors, we find the magnetic field dependence of the spin polarization of the skyrmion-condensated state.
We develop a theory of magneto-transport properties of two-dimensional electron gas in cylindrica... more We develop a theory of magneto-transport properties of two-dimensional electron gas in cylindrical geometry where finite bias and microwave are locally applied. By invesitgating the Landauer conductance based on Floquet theory, we obtain the conductance without perturbation analysis. We show that the dc conductance becomes negative when dc electric field is applied inside the 2DEG with sufficient microwave power. A positive sign of the current is restored by increasing dc bias. We analyze the radiation induced non-equilibrium distribution function with respect to the frequency of the applied microwave.
We propose a spin cell based on photon-assisted tunneling through a conventional semiconductor ba... more We propose a spin cell based on photon-assisted tunneling through a conventional semiconductor barrier. The Dresselhaus spin-orbit interaction is included to break the spin rotation symmetry. Due to the in-plane electric field induced asymmetric momentum distribution in one lead, continuous flows of spin currents are driven through a barrier by a AC field. The net charge current remains zero. The spin current via photon-assisted tunneling can be readily adjusted via tuning the AC frequency or the in-plane electric field. This device may function as an ideal spin cell to supply spin currents in the spintronics circuit.
We propose amplitude death phenomenon as an underlying mechanism of auditory transduction. When n... more We propose amplitude death phenomenon as an underlying mechanism of auditory transduction. When non-identical auditory hair bundles are elastically coupled, their spontaneous oscillations can be quenched to form an amplitude death state. We show, in this state, the hair cells are quiet and ready to detect oscillatory stimulus with coupling-strength dependent amplification. Numerical demonstration of the mechanism suggests that the non-uniformity of coupled hair cells can contribute to noise-robust auditory transduction.
Physical Review B, 1997
We calculate in an analyical fashion the energies and net spins of skyrmions in fractional quantu... more We calculate in an analyical fashion the energies and net spins of skyrmions in fractional quantum Hall systems, based on the suggestion that skyrmion states are spontaneously L Z and S Z symmetry-breaking states. The quasiholeskyrmion state with a charge −e/3 around ν = 1/3, where the ground state is known as a spin-polarized ferromagnetic state, is found to exist even in high magnetic fields up to about 7 T for GaAs samples.
Physical Review B, 1997
We find an analogy between the single skyrmion state in the quantum Hall system and the BCS super... more We find an analogy between the single skyrmion state in the quantum Hall system and the BCS superconducting state and address that the quantum mechanical origin of the skyrmion is electronic pairing. The skyrmion phase is found to be unstable for magnetic fields above the critical field Bc(T) at temperature T , which is well represented by the relation Bc(T)/Bc(0) ≈ [1 − (T /Tc) 3 ] 1/2 .
We investigate the transport and the dynamical properties of tunnel-coupled double charge shuttle... more We investigate the transport and the dynamical properties of tunnel-coupled double charge shuttles. The oscillation frequencies of two shuttles are mode-locked to integer multiples of the applied voltage frequency ω. We show that left/right-symmetric double shuttles may generate direct net current due to bistable motions caused by parametric instability. The symmetry-broken direct current appears near ω = Ω0/(2j − 1), (j = 1, 2,. . .), where Ω0 is the dressed resonance frequency of the relative motion of the two shuttles.
Physical Review B, 1995
We investigate the effects of electron correlations on the ground state energy and the chemical p... more We investigate the effects of electron correlations on the ground state energy and the chemical potential of a droplet confined by a parabolic potential at high magnetic fields. We demonstrate the importance of correlations in estimating the transition field at which the first edge reconstruction of the maximum density droplet occurs in the spin polarized regime.
Physical Review Letters, 2001
The nonlinear response to an external electric field is studied for classical non-interacting cha... more The nonlinear response to an external electric field is studied for classical non-interacting charged particles under the influence of a uniform magnetic field, a periodic potential, and an effective friction force. We find numerical and analytical evidence that the ratio of transversal to longitudinal resistance forms a Devil's staircase. The staircase is attributed to the dynamical phenomenon of mode-locking.
Physical Review Letters, 1999
We investigate the influence of interactions and geometry on ground states of clean chaotic quant... more We investigate the influence of interactions and geometry on ground states of clean chaotic quantum dots using the self-consistent Hartree-Fock method. We find two distinct regimes of interaction strength: While capacitive energy fluctuations δχ follow approximately a random matrix prediction for weak interactions, there is a crossover to a regime where δχ is strongly enhanced and scales roughly with interaction strength. This enhancement is related to the rearrangement of charges into ordered states near the quantum dot edge. This effect is non-universal depending on dot shape and size. It may provide additional insight into recent experiments on statistics of Coulomb blockade peak spacings.
Physical Review Letters, 2003
We investigate the energy spectra of clean incommensurate double-walled carbon nanotubes, and fin... more We investigate the energy spectra of clean incommensurate double-walled carbon nanotubes, and find that the overall spectral properties are described by the critical statistics similar to that known in the Anderson metal-insulator transition. In the energy spectra, there exist three different regimes characterized by Wigner-Dyson, Poisson, and semi-Poisson distributions. This feature implies that the electron transport in incommensurate multi-walled nanotubes can be either diffusive, ballistic, or intermediate between them, depending on the position of the Fermi energy.
Physical Review Letters, 2011
We investigate the ground and excited states of interacting electrons in a quantum point contact ... more We investigate the ground and excited states of interacting electrons in a quantum point contact using exact diagonalization method. We find that strongly localized states in the point contact appear when a new conductance channel opens due to momentum mismatch. These localized states form magnetic impurity states which are stable in a finite regime of chemical potential and excitation energy. Interestingly, these magnetic impurities have ferromagnetic coupling, which shed light on the experimentally observed puzzling coexistence of Kondo correlation and spin filtering in a quantum point contact.
Physical Review E, 2014
Hair cells conduct auditory transduction in vertebrates. In lower vertebrates such as frogs and t... more Hair cells conduct auditory transduction in vertebrates. In lower vertebrates such as frogs and turtles, due to the active mechanism in hair cells, hair bundles(stereocilia) can be spontaneously oscillating or quiescent. Recently, the amplitude death phenomenon has been proposed [K.-H. Ahn,
Physica E: Low-dimensional Systems and Nanostructures, 2008
ABSTRACT We calculate current noise and admittance of an electrically driven nano-structure in a ... more ABSTRACT We calculate current noise and admittance of an electrically driven nano-structure in a mesoscopic capacitor plate within Floquet scattering theory. We show that the interplay between quantum statistics and coherence of electrons is important in the photo-assisted non-equilibrium noise. Current noise has two different contributions; photo-assisted non-equilibrium noise and Nyquist equilibrium noise. At low frequencies ω and temperature, the photo-assisted non-equilibrium noise dominates the Nyquist equilibrium noise as their leading terms are proportional to ω2 and ω3, respectively. The Nyquist noise has peak structure as a function of the Fermi energy caused by the large delay time associated with the (photo-assisted) resonant levels. Meanwhile, the photo-assisted current noise is not simply given by the phase delay time at the Fermi level. This is because, unlike the equilibrium noise, the photo-assisted current noise is also contributed from electron states far below the Fermi level. We interpret the real admittance g′(ω) in terms of the photo-assisted phase delay time.
The European Physical Journal B, 2010
We investigate dynamical transport properties of interacting electrons moving in a vibrating nano... more We investigate dynamical transport properties of interacting electrons moving in a vibrating nanoelectromechanical wire in a magnetic field. We have built an exactly solvable model in which electric current and mechanical oscillation are treated fully quantum mechanically on an equal footing. Quantum mechanically fluctuating Aharonov-Bohm phases obtained by the electrons cause nontrivial contribution to mechanical vibration and electrical conduction of the wire. We demonstrate our theory by calculating the admittance of the wire which are influenced by the multiple interplay between the mechanical and the electrical energy scales, magnetic field strength, and the electron-electron interaction.
Applied Physics Letters, 2008
We investigate the dynamics of electrically ac-driven nanoelectromechanical shuttle arrays. The e... more We investigate the dynamics of electrically ac-driven nanoelectromechanical shuttle arrays. The electromechanical coupling enforces long-range interactions. We find multistability regimes upon changing the voltage and frequency. We show that the instability driven by parametric amplification of sinusoidal mechanical waves leads to the creation of spatially localized mechanical oscillations, discrete breathers, and subsequently to an abrupt change in the electrical transport properties. In particular, we find current rectification, which is induced by the excitation of discrete breathers. This is of potential interest and use for nanomechanical sensor application.
arXiv (Cornell University), Aug 13, 1996
We present a microscopic theory of skyrmion and antiskyrmion excitations in fractional quantum Ha... more We present a microscopic theory of skyrmion and antiskyrmion excitations in fractional quantum Hall systems, and calculate in an analytical fashion their excitation energies. From the calculated net spins at various fractional filling factors, we find the magnetic field dependence of the spin polarization of the skyrmion-condensated state.
We develop a theory of magneto-transport properties of two-dimensional electron gas in cylindrica... more We develop a theory of magneto-transport properties of two-dimensional electron gas in cylindrical geometry where finite bias and microwave are locally applied. By invesitgating the Landauer conductance based on Floquet theory, we obtain the conductance without perturbation analysis. We show that the dc conductance becomes negative when dc electric field is applied inside the 2DEG with sufficient microwave power. A positive sign of the current is restored by increasing dc bias. We analyze the radiation induced non-equilibrium distribution function with respect to the frequency of the applied microwave.
We propose a spin cell based on photon-assisted tunneling through a conventional semiconductor ba... more We propose a spin cell based on photon-assisted tunneling through a conventional semiconductor barrier. The Dresselhaus spin-orbit interaction is included to break the spin rotation symmetry. Due to the in-plane electric field induced asymmetric momentum distribution in one lead, continuous flows of spin currents are driven through a barrier by a AC field. The net charge current remains zero. The spin current via photon-assisted tunneling can be readily adjusted via tuning the AC frequency or the in-plane electric field. This device may function as an ideal spin cell to supply spin currents in the spintronics circuit.
We propose amplitude death phenomenon as an underlying mechanism of auditory transduction. When n... more We propose amplitude death phenomenon as an underlying mechanism of auditory transduction. When non-identical auditory hair bundles are elastically coupled, their spontaneous oscillations can be quenched to form an amplitude death state. We show, in this state, the hair cells are quiet and ready to detect oscillatory stimulus with coupling-strength dependent amplification. Numerical demonstration of the mechanism suggests that the non-uniformity of coupled hair cells can contribute to noise-robust auditory transduction.
Physical Review B, 1997
We calculate in an analyical fashion the energies and net spins of skyrmions in fractional quantu... more We calculate in an analyical fashion the energies and net spins of skyrmions in fractional quantum Hall systems, based on the suggestion that skyrmion states are spontaneously L Z and S Z symmetry-breaking states. The quasiholeskyrmion state with a charge −e/3 around ν = 1/3, where the ground state is known as a spin-polarized ferromagnetic state, is found to exist even in high magnetic fields up to about 7 T for GaAs samples.
Physical Review B, 1997
We find an analogy between the single skyrmion state in the quantum Hall system and the BCS super... more We find an analogy between the single skyrmion state in the quantum Hall system and the BCS superconducting state and address that the quantum mechanical origin of the skyrmion is electronic pairing. The skyrmion phase is found to be unstable for magnetic fields above the critical field Bc(T) at temperature T , which is well represented by the relation Bc(T)/Bc(0) ≈ [1 − (T /Tc) 3 ] 1/2 .
We investigate the transport and the dynamical properties of tunnel-coupled double charge shuttle... more We investigate the transport and the dynamical properties of tunnel-coupled double charge shuttles. The oscillation frequencies of two shuttles are mode-locked to integer multiples of the applied voltage frequency ω. We show that left/right-symmetric double shuttles may generate direct net current due to bistable motions caused by parametric instability. The symmetry-broken direct current appears near ω = Ω0/(2j − 1), (j = 1, 2,. . .), where Ω0 is the dressed resonance frequency of the relative motion of the two shuttles.
Physical Review B, 1995
We investigate the effects of electron correlations on the ground state energy and the chemical p... more We investigate the effects of electron correlations on the ground state energy and the chemical potential of a droplet confined by a parabolic potential at high magnetic fields. We demonstrate the importance of correlations in estimating the transition field at which the first edge reconstruction of the maximum density droplet occurs in the spin polarized regime.
Physical Review Letters, 2001
The nonlinear response to an external electric field is studied for classical non-interacting cha... more The nonlinear response to an external electric field is studied for classical non-interacting charged particles under the influence of a uniform magnetic field, a periodic potential, and an effective friction force. We find numerical and analytical evidence that the ratio of transversal to longitudinal resistance forms a Devil's staircase. The staircase is attributed to the dynamical phenomenon of mode-locking.
Physical Review Letters, 1999
We investigate the influence of interactions and geometry on ground states of clean chaotic quant... more We investigate the influence of interactions and geometry on ground states of clean chaotic quantum dots using the self-consistent Hartree-Fock method. We find two distinct regimes of interaction strength: While capacitive energy fluctuations δχ follow approximately a random matrix prediction for weak interactions, there is a crossover to a regime where δχ is strongly enhanced and scales roughly with interaction strength. This enhancement is related to the rearrangement of charges into ordered states near the quantum dot edge. This effect is non-universal depending on dot shape and size. It may provide additional insight into recent experiments on statistics of Coulomb blockade peak spacings.
Physical Review Letters, 2003
We investigate the energy spectra of clean incommensurate double-walled carbon nanotubes, and fin... more We investigate the energy spectra of clean incommensurate double-walled carbon nanotubes, and find that the overall spectral properties are described by the critical statistics similar to that known in the Anderson metal-insulator transition. In the energy spectra, there exist three different regimes characterized by Wigner-Dyson, Poisson, and semi-Poisson distributions. This feature implies that the electron transport in incommensurate multi-walled nanotubes can be either diffusive, ballistic, or intermediate between them, depending on the position of the Fermi energy.
Physical Review Letters, 2011
We investigate the ground and excited states of interacting electrons in a quantum point contact ... more We investigate the ground and excited states of interacting electrons in a quantum point contact using exact diagonalization method. We find that strongly localized states in the point contact appear when a new conductance channel opens due to momentum mismatch. These localized states form magnetic impurity states which are stable in a finite regime of chemical potential and excitation energy. Interestingly, these magnetic impurities have ferromagnetic coupling, which shed light on the experimentally observed puzzling coexistence of Kondo correlation and spin filtering in a quantum point contact.
Physical Review E, 2014
Hair cells conduct auditory transduction in vertebrates. In lower vertebrates such as frogs and t... more Hair cells conduct auditory transduction in vertebrates. In lower vertebrates such as frogs and turtles, due to the active mechanism in hair cells, hair bundles(stereocilia) can be spontaneously oscillating or quiescent. Recently, the amplitude death phenomenon has been proposed [K.-H. Ahn,
Physica E: Low-dimensional Systems and Nanostructures, 2008
ABSTRACT We calculate current noise and admittance of an electrically driven nano-structure in a ... more ABSTRACT We calculate current noise and admittance of an electrically driven nano-structure in a mesoscopic capacitor plate within Floquet scattering theory. We show that the interplay between quantum statistics and coherence of electrons is important in the photo-assisted non-equilibrium noise. Current noise has two different contributions; photo-assisted non-equilibrium noise and Nyquist equilibrium noise. At low frequencies ω and temperature, the photo-assisted non-equilibrium noise dominates the Nyquist equilibrium noise as their leading terms are proportional to ω2 and ω3, respectively. The Nyquist noise has peak structure as a function of the Fermi energy caused by the large delay time associated with the (photo-assisted) resonant levels. Meanwhile, the photo-assisted current noise is not simply given by the phase delay time at the Fermi level. This is because, unlike the equilibrium noise, the photo-assisted current noise is also contributed from electron states far below the Fermi level. We interpret the real admittance g′(ω) in terms of the photo-assisted phase delay time.
The European Physical Journal B, 2010
We investigate dynamical transport properties of interacting electrons moving in a vibrating nano... more We investigate dynamical transport properties of interacting electrons moving in a vibrating nanoelectromechanical wire in a magnetic field. We have built an exactly solvable model in which electric current and mechanical oscillation are treated fully quantum mechanically on an equal footing. Quantum mechanically fluctuating Aharonov-Bohm phases obtained by the electrons cause nontrivial contribution to mechanical vibration and electrical conduction of the wire. We demonstrate our theory by calculating the admittance of the wire which are influenced by the multiple interplay between the mechanical and the electrical energy scales, magnetic field strength, and the electron-electron interaction.
Applied Physics Letters, 2008
We investigate the dynamics of electrically ac-driven nanoelectromechanical shuttle arrays. The e... more We investigate the dynamics of electrically ac-driven nanoelectromechanical shuttle arrays. The electromechanical coupling enforces long-range interactions. We find multistability regimes upon changing the voltage and frequency. We show that the instability driven by parametric amplification of sinusoidal mechanical waves leads to the creation of spatially localized mechanical oscillations, discrete breathers, and subsequently to an abrupt change in the electrical transport properties. In particular, we find current rectification, which is induced by the excitation of discrete breathers. This is of potential interest and use for nanomechanical sensor application.