Quantum oscillation of Hall resistance in the extreme quantum limit of an organic conductor (TMTSF)2ClO4

We report resistance and magnetic torque experiments under a high magnetic field up to 45 T in a three dimensional quantum Hall (QH) system (TMTSF)(2)ClO(4), where TMTSF = tetramethyltetraselenafulvalene. The Hall resistance shows huge oscillations accompanied with sign reversal after the final QH state, where the Landau level filling factor is unity, is removed above 26 T. The magnetic torque also oscillates with the field. The results suggest that a novel quantum state, where the character of the carriers periodically changes with the field, is stabilized in the extreme quantum limit.     

Proposal for measuring mechanically equilibrium spin currents in the rashba medium

We demonstrate that an equilibrium spin current in a 2D electron gas with Rashba spin-orbit interaction (Rashba medium) results in a mechanical torque on a substrate near an edge of the medium. If the substrate is a cantilever, the mechanical torque displaces the free end of the cantilever. The effect can be enhanced and tuned by a magnetic field. Observation of this displacement would be an effective method to prove the existence of equilibrium spin currents. The analysis of edges of the Rashba medium demonstrates the existence of localized edge states. They form a 1D continuum of states. This suggests a new type of quantum wire: spin-orbit quantum wire.     

Quantum melting of the quasi-two-dimensional vortex lattice in kappa- (ET)2Cu(NCS)(2)

We report torque magnetization measurements in regions of the mixed state phase diagram ( B approximately mu(o)H(c2) and T(c)/10(3)) of the organic superconductor kappa-(ET)2Cu(NCS)(2), where quantum fluctuations are expected to dominate thermal effects. Over most of the field range below the irreversibility line ( B(irr)), magnetothermal instabilities are observed in the form of flux jumps. The abrupt cessation of these instabilities just below B(irr) indicates a quantum melting transition from a quasi-two-dimensional vortex lattice phase to a quantum liquid phase.     

Induced currents, frozen charges and the quantum Hall effect breakdown

Puzzling results obtained from torque magnetometry in the quantum Hall effect regime are presented, and a theory is proposed for their explanation. Magnetic moment saturation, which is usually attributed to the quantum Hall effect breakdown, is shown to be related to the charge redistribution across the sample.     

All-magnonic spin-transfer torque and domain wall propagation

The spin-wave transportation through a transverse magnetic domain wall (DW) in a magnetic nanowire is studied. It is found that the spin wave passes through a DW without reflection. A magnon, the quantum of the spin wave, carries opposite spins on the two sides of the DW. As a result, there is a spin angular momentum transfer from the propagating magnons to the DW. This magnonic spin-transfer torque can efficiently drive a DW to propagate in the opposite direction to that of the spin wave.     

Interaction-driven spin precession in quantum-dot spin valves

We analyze spin-dependent transport through spin valves composed of an interacting quantum dot coupled to two ferromagnetic leads. The spin on the quantum dot and the linear conductance as a function of the relative angle theta of the leads' magnetization directions is derived to lowest order in the dot-lead coupling strength. Because of the applied bias voltage spin accumulates on the quantum dot, which for finite charging energy experiences a torque, resulting in spin precession. The latter leads to a nontrivial, interaction-dependent, theta dependence of the conductance. In particular, we find that the spin-valve effect is reduced for all theta not equal pi.     

Field-Like spin-transfer torque in a chiral helimagnet

Based on the microscopic model of sd coupling between free electrons and local moments, we present a quantum calculation of a nonadiabatic spin-transfer torque in a chiral helimagnet.     

The Casimir atomic pendulum

We want to introduce an atomic pendulum whose driving force (torque) is due to the quantum vacuum fluctuations. Applying the well-known Casimir-Polder effect to a special configuration (a combined structure of an atomic nanostring and a conducting plate), an atomic pendulum (Casimir atomic pendulum) is designed. Using practically acceptable data corresponding to the already known world of nanotechnology and based on reasonable/reliable numerical estimates, the period of oscillation for the pendulum is computed. This pendulum can be considered as both a new micro(nano)-electromechanical system and a new simple vacuum machine. Its design may be considered as a first step towards realizing the visualized vacuum (Casimir) clock!     

Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor

The precessing magnetization of a magnetic islands coupled to a quantum spin Hall edge pumps charge along the edge. Conversely, a bias voltage applied to the edge makes the magnetization precess. We point out that this device realizes an adiabatic quantum motor and discuss the efficiency of its operation based on a scattering matrix approach akin to Landauer–Büttiker theory. Scattering theory provides a microscopic derivation of the Landau–Lifshitz–Gilbert equation for the magnetization dynamics of the device, including spin-transfer torque, Gilbert damping, and Langevin torque. We find that the device can be viewed as a Thouless motor, attaining unit efficiency when the chemical potential of the edge states falls into the magnetization-induced gap. For more general parameters, we characterize the device by means of a figure of merit analogous to the ZT value in thermoelectrics.     

Reprint of : Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor

The precessing magnetization of a magnetic islands coupled to a quantum spin Hall edge pumps charge along the edge. Conversely, a bias voltage applied to the edge makes the magnetization precess. We point out that this device realizes an adiabatic quantum motor and discuss the efficiency of its operation based on a scattering matrix approach akin to Landauer–Büttiker theory. Scattering theory provides a microscopic derivation of the Landau–Lifshitz–Gilbert equation for the magnetization dynamics of the device, including spin-transfer torque, Gilbert damping, and Langevin torque. We find that the device can be viewed as a Thouless motor, attaining unit efficiency when the chemical potential of the edge states falls into the magnetization-induced gap. For more general parameters, we characterize the device by means of a figure of merit analogous to the ZT value in thermoelectrics.     

Control of atomic rotation by elliptical hollow beam carrying zero angular momentum

The interaction between linearly polarized elliptical hollow beam and a two-level atom is investigated theoretically. Although the linearly polarized elliptical hollow beam does not carry angular momentum, it can produce very high torque. The atoms initially at rest and located at off-beam-axis positions will rotate under the drive of the torque of the beam. The shorter the distance from the original location of atom to the axis is, the larger the average angular frequency of atom rotation is. The average angular frequency can reach as high as 1000 Hz. This convinces us that the elliptical hollow beam might be a useful tool in the study of quantum property of Bose–Einstein condensate or ultra cold atom media.     

Mechanism of Carbon Nanotubes Aligning along Applied Electric Field

The mechanism of single-walled carbon nanotubes （SWCNTs） aligning in the direction of external electric field is studied by quantum mechanics calculations. The rotational torque on the carbon nanotubes is proportional to the difference between the longitudinal and transverse polarizabilities and varies with the angle of SWCNTs to the external electric field. The longitudinal polarizability increases with second power of length, while the transverse polarizability increases linearly with length. A zigzag SWCNT has larger longitudinal and transverse polarizabilities than an armchair SWCNT with the same diameter and the discrepancy becomes larger for longer tubes.     

Quantum shape effects and novel thermodynamic behaviors at nanoscale

Thermodynamic properties of confined systems depend on sizes of the confinement domain due to quantum nature of particles. Here we show that shape also enters as a control parameter on thermodynamic state functions. By considering specially designed confinement domains, we demonstrate how shape effects alone modify Helmholtz free energy, entropy and internal energy of a confined system. We propose an overlapped quantum boundary layer method to analytically predict quantum shape effects without even solving Schrödinger equation or invoking any other mathematical tools. Thereby we reduce a thermodynamic problem into a simple geometric one and reveal the profound link between geometry and thermodynamics. We report also a torque due to quantum shape effects. Furthermore, we introduce isoformal, shape preserving, process which opens the possibility of a new generation of thermodynamic cycles operating at nanoscale with unique features.     

Density-of-state oscillation of quasiparticle excitation in the spin density wave phase of (TMTSF)2ClO4

Systematic measurements of the magnetocaloric effect, heat capacity, and magnetic torque under a high magnetic field up to 35 T are performed in the spin density wave (SDW) phase of a quasi-one-dimensional organic conductor (TMTSF)2ClO4. In the SDW phase above 26 T, where the quantum Hall effect is broken, rapid oscillations (ROs) in these thermodynamic quantities are observed, which provides clear evidence of the density-of-state (DOS) oscillation near the Fermi level. The resistance is semiconducting and the heat capacity divided by temperature is extrapolated to zero at 0 K in the SDW phase, showing that all the energy bands are gapped, and there is no DOS at the Fermi level. The results show that the ROs are ascribed to the DOS oscillation of the quasiparticle excitation.     

Structural Transitions in Elemental Tin at Ultra High Pressures up to 230 GPa

The quantum heat generation, interaction force, and friction torque for two rotating spherical nanoparticles with the radius R are calculated. In contrast to a static case where an upper bound in the radiative heat transfer between two particles exists, the quantum heat generation for two rotating particles diverges at distances between particles d < d ₀ = R(3/ε″(ω₀))^1/3 (where ε″(ω₀) is the imaginary part of the dielectric function for the material of a particle at the resonance frequency ω₀), when the rotation frequency coincides with poles in the excitation generation rate at Ω = 2ω₀. These poles are due to the anomalous Doppler effect and the mutual polarization of particles and exist even in the presence of dissipation in particles. The anomalous heat generation is associated with the conversion of mechanical rotation energy into heat mediated by quantum friction. Similar singularities also exist for the interaction force and friction torque. The results can be of significant importance for biomedical applications.     

Geometry of dislocated de Broglie waves

The geometrical structures implicit in the de Broglie waves associated with a relativistic charged scalar quantum mechanical particle in an external field are analyzed by employing the ray concept of the causal interpretation. It is shown how an osculating Finslerian metric tensor, a torsion tensor, and a tetrad field define respectively the strain, the dislocation density, and the Burgers vector in the natural state of the wave, which is a non-Riemannian space of distant parallelism. A quantum torque determined by the quantum potential is introduced and the example of a screw dislocated wave is discussed.     

Effect of the ac field on a single-molecule magnet bridged between conducting leads

We study quantum spin-rotation effects for a single-molecule magnet bridged between two conducting leads in the ac and dc magnetic fields. The Landau-Zener dynamics induced by the magnetic field generates mechanical torque, making the molecule to oscillate. This mechanical motion of the molecule exhibits unique features that can be detected by measuring the electronic tunneling current through the molecule.     

Manipulating the spin states in a double molecular magnets tunneling junction

We theoretically explore the spin transport through nano-structures consisting of two serially coupled single-molecular magnets (SMM) sandwiched between two nonmagnetic electrodes. We find that the magnetization of SMM can be controlled by the spin transfer torque with respect to the bias voltage direction, and the electron current can be switched on/off in different magnetic structures. Such a manipulation is performed by full electrical manner, and needs neither external magnetic field nor ferromagnetic electrodes in the tunneling junction. The proposal device scheme can be realized with the use of the present technology [6] and has potential applications in molecular spintronics or quantum information processing.     

de Haas-van Alphen oscillations in the underdoped high-temperature superconductor YBa2Cu3O6.5

The de Haas-van Alphen effect was observed in the underdoped cuprate YBa2Cu3O6.5 via a torque technique in pulsed magnetic fields up to 59 T. Above a field of approximately 30 T the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-defined, closed, and coherent, Fermi surface in the pseudogap phase of cuprates.     

The quantum potential and signalling in the Einstein-Podolsky-Rosen experiment

According to the causal interpretation of quantum mechanics, one can precisely define the state of an individual particle in a many-body system by its position, momentum, and spin. It is shown in the EPR spin experiment that the quantum torque brings about an instantaneous change in the state of one of the particles when the other undergoes a local interaction, but that such a transfer of information cannot be extracted by any experiment subject to the laws of quantum mechanics.Dedicated to David Bohm on the occasion of his 70th birthday.