共查询到20条相似文献,搜索用时 15 毫秒
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Sharp localization transitions of chiral edge states in disordered quantum wires subject to a strong magnetic field are shown to be driven by crossovers from two-to one-dimensional localization of bulk states. As a result, the two-terminal conductance is found to exhibit discontinuous transitions at zero temperature between exactly integer plateau values and zero, reminiscent of first-order phase transitions. We discuss the corresponding phase diagram. The spin of the electrons is shown to result in a multitude of phases when the spin degeneracy is raised by the Zeeman energy. The width of conductance plateaus is found to depend sensitively on the spin flip rate 1/τs. 相似文献
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Burzurí E Luis F Barbara B Ballou R Ressouche E Montero O Campo J Maegawa S 《Physical review letters》2011,107(9):097203
We show that a crystal of mesoscopic Fe(8) single-molecule magnets is an experimental realization of the quantum Ising model in a transverse field, with dipolar interactions. Quantum annealing has enabled us to explore the quantum and classical phase transitions between the paramagnetic and ferromagnetic phases, at thermodynamical equilibrium. The phase diagram and critical exponents that we obtain agree with expectations for the mean-field universality class. 相似文献
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It is shown that in one-dimensional mesoscopic structures the electron-electron interaction leads to qualitatively new effects
in the dynamic conductivity which are best manifested in the frequency dependence of the impedance. Interelectronic repulsion
increases the resistance and narrows the resonance dips of the resistance at transit frequencies. Interelectronic attraction
gives rise to resonance peaks of the resistance against a high-conductivity background. These effects are due to the reflection
of bosonic excitations of a Luttinger liquid from the boundaries of a quantum channel with current-lead electrodes and to
resonances of these excitations over the length of the channel.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 40–44 (10 July 1997) 相似文献
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I V Golosovsky I Mirebeau G André D A Kurdyukov Y A Kumzerov S B Vakhrushev 《Physical review letters》2001,86(25):5783-5786
We present the results of a neutron diffraction study of the antiferromagnet MnO embedded in a porous glass. The type of magnetic ordering and the structural distortion are similar to those of the bulk, but the ordered magnetic moment of 3.84(4)muB/ion is strongly reduced and the Néel temperature is enhanced. The magnetic transition is second order, in contrast to the first order transition of the bulk. The size of the magnetic region is smaller than the average size of the nanoparticles. The reasons for this behavior are discussed. 相似文献
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Y. Lassailly C. Vettier F. Holtzberg A. Benoit J. Flouquet 《Solid State Communications》1984,52(8):717-719
Neutron diffraction experiments were performed on the divalent thulium compound TmTe. Magnetic structure determination leads to a type II antiferromagnet below the Néel temperature TN = .43 K. No crystal field excitations were observed. 相似文献
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D.H. Cobden A.S. Dzurak M. Field C.G. Smith A.K. Savchenko M. Pepper D.A. Ritchie J.E.F. Frost G.A.C. Jones D.G. Hasko 《Physica A》1993,200(1-4):65-79
A brief review is presented on some of the consequences of single electron transport in GaAs structures. Particular topics considered include noise and fluctuations in the ballistic regime where the quantised conductance imposes a limit on the magnitude of the random telegraphic signals and the consequences of single traps changing occupancy can be clearly observed. Results are also presented on the non-invasive detection of the Coulomb blockade and factors determining transport in the conductance minima are discussed. Thermo-electric effects in the blockade regime are discussed as these are complementary to studies of electrical transport and show that the thermopower oscillates about zero with a period corresponding to the removal of a single electron. 相似文献
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The conditions of the formation of different magnetic structures with ferromagnetic (FM) and antiferromagnetic (AFM) ordering in granular materials containing a subsystem of ferromagnetic granules are considered within the phenomenological approach. It is supposed that the magnetostatic field and the exchange interaction between conduction electrons and magnetic ions are responsible for the formation of magnetic structure. 相似文献
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The magnetic ordering in uranium monophosphide (UP) has been studied by neutron diffraction from a single crystal in a magnetic field. UP orders at TN ? 122 ± 0.1 K with the type-I antiferromagnetic structure (+-+-), the ordering taking place in a first-order transition. At T0 = 22.5 K the ordered magnetic moment jumps from 1.7 μB to 1.9 μB. With a magnetic field H = 25 kOe applied along the [11̄10] direction, it is found that UP has the collinear single- type-I structure above T0 and undergoes a first-order transition to the planar double- type-I structure, accompanied by a “moment jump” due to the change in the moment direction from <001> to <110>. 相似文献
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We reexamine the role of electron binding effects in the inelastic neutrino–atom scattering induced by the neutrino magnetic moment. The differential cross section of the process is presented as a sum of the longitudinal and transverse components, according to whether the force that the neutrino magnetic moment exerts on electrons is parallel or perpendicular to momentum transfer. The atomic electrons are treated nonrelativistically. On this basis, the recent theoretical predictions concerning the magnetic neutrino-impact ionization of atoms are critically discussed. Numerical calculations are performed for ionization of a hydrogenlike Ge+31 ion by neutrino impact. 相似文献
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I. Bâldea H. Köppel L.S. Cederbaum 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):289-299
We present a new effect that is possible for strongly correlated electrons in commensurate mesoscopic rings: the collective tunneling of electrons between classically equivalent configurations, corresponding to ordered states possessing charge and
spin density waves (CDW, SDW) and charge separation (CS). Within an extended Hubbard model at half filling studied by exact
numerical diagonalization, we demonstrate that the ground state phase diagram comprises, besides conventional critical lines
separating states characterized by different orderings (e.g. CDW, SDW, CS), critical lines separating phases with the same ordering (e.g. CDW-CDW) but with different symmetries. While the former also exist in infinite systems, the latter are specific for mesoscopic systems and directly related to a collective tunnel effect. We emphasize that, in order to construct correctly
a phase diagram for mesoscopic rings, the examination of CDW, SDW and CS correlation functions alone is not sufficient, and
one should also consider the symmetry of the wave function that cannot be broken. We present examples demonstrating that the
jumps in relevant physical properties at the conventional and new critical lines are of comparable magnitude. These transitions
could be studied experimentally e.g. by optical absorption in mesoscopic systems. Possible candidates are cyclic molecules and ring-like nanostructures of quantum
dots.
Received 27 November 2000 相似文献
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Chern GW 《Physical review letters》2010,105(22):226403
Exchange interaction tends to favor collinear or coplanar magnetic orders in rotationally invariant spin systems. Indeed, such magnetic structures are usually selected by thermal or quantum fluctuations in highly frustrated magnets. Here we show that a complex noncoplanar magnetic order with a quadrupled unit cell is stabilized by itinerant electrons on the pyrochlore lattice. Specifically, we consider a Kondo-lattice model with classical localized moments at quarter filling. The electron Fermi "surface" at this filling factor is topologically equivalent to three intersecting Fermi circles. Perfect nesting of the Fermi lines leads to magnetic ordering with multiple wave vectors and a definite handedness. The chiral order might persist without magnetic order in a chiral spin liquid at finite temperatures. 相似文献
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The magnetic ordering of frustrated arrays of nanoscale islands can be strongly influenced by the array patterns. We theoretically present three kinds of artificial geometrically frustrated systems with different brick-shaped geometries, defined as brick-shaped lattices, and investigate their magnetic dipolar ordering at the ground state using the Monte Carlo method. The simulated results show that the magnetic ordering of three brick-shaped frustrated lattices depends strongly on the strength of dipolar interactions, depending on the lattice spacing. It is found that the long-range dipolar interactions tend to suppress the long-range ordered state and induce the short-range quasi-ice state at each vertex of the lattices. In addition, the correlations for neighboring spin pairs are closely related to not only the dipolar coupling strength but also the geometry of the lattices. 相似文献
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A. Isihara 《Zeitschrift für Physik B Condensed Matter》1988,73(1):15-16
The exchange energy of a two-dimensional electron gas was evaluated exactly in the presence of a magnetic field when only the lowest Landau level is occupied fractionally. 相似文献
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B.K. Chakraverty 《Solid State Communications》1974,15(8):1271-1275
Verwey ordering of Fe2+ and Fe3+ on alternate planes along [001] direction occurring at 119° K is considered uniquely as a collective Jahn-Teller transition. The model predicts two successive second-order transitions, as a result of simultaneous coupling to both shear distortion and optical phonon mode. Expected elastic constant anomalies are calculated. The insulating state thus obtained at T = 0, does not invoke electron-electron correlation on near-neighbor sites. 相似文献