8,411 research outputs found
Zeros of the Partition Function for Higher--Spin 2D Ising Models
We present calculations of the complex-temperature zeros of the partition
functions for 2D Ising models on the square lattice with spin , 3/2, and
2. These give insight into complex-temperature phase diagrams of these models
in the thermodynamic limit. Support is adduced for a conjecture that all
divergences of the magnetisation occur at endpoints of arcs of zeros protruding
into the FM phase. We conjecture that there are such arcs for , where denotes the integral part of .Comment: 8 pages, latex, 3 uuencoded figure
Dynamical conductance in the two-channel Kondo regime of a double dot system
We study finite-frequency transport properties of the double-dot system
recently constructed to observe the two-channel Kondo effect [R. M. Potok et
al., Nature 446, 167 (2007)]. We derive an analytical expression for the
frequency-dependent linear conductance of this device in the Kondo regime. We
show how the features characteristic of the 2-channel Kondo quantum critical
point emerge in this quantity, which we compute using the results of conformal
field theory as well as numerical renormalization group methods. We determine
the universal cross-over functions describing non-Fermi liquid vs. Fermi liquid
cross-overs and also investigate the effects of a finite magnetic field.Comment: 11 pages in PRB forma
Coulomb charging energy for arbitrary tunneling strength
The Coulomb energy of a small metallic island coupled to an electrode by a
tunnel junction is investigated. We employ Monte Carlo simulations to determine
the effective charging energy for arbitrary tunneling strength. For small
tunneling conductance, the data agree with analytical results based on a
perturbative treatment of electron tunneling, while for very strong tunneling
recent semiclassical results for large conductance are approached. The data
allow for an identification of the range of validity of various analytical
predictions.Comment: 4 pages REVTeX, incl 3 figures, to appear in Europhys.Let
Low temperature series expansions for the square lattice Ising model with spin S > 1
We derive low-temperature series (in the variable )
for the spontaneous magnetisation, susceptibility and specific heat of the
spin- Ising model on the square lattice for , 2, , and
3. We determine the location of the physical critical point and non-physical
singularities. The number of non-physical singularities closer to the origin
than the physical critical point grows quite rapidly with . The critical
exponents at the singularities which are closest to the origin and for which we
have reasonably accurate estimates are independent of . Due to the many
non-physical singularities, the estimates for the physical critical point and
exponents are poor for higher values of , though consistent with
universality.Comment: 14 pages, LaTeX with IOP style files (ioplppt.sty), epic.sty and
eepic.sty. To appear in J. Phys.
Coulomb Blockade with Dispersive Interfaces
What quantity controls the Coulomb blockade oscillations if the dot--lead
conductance is essentially frequency--dependent ? We argue that it is the ac
dissipative conductance at the frequency given by the effective charging
energy. The latter may be very different from the bare charging energy due to
the interface--induced capacitance (or inductance). These observations are
supported by a number of examples, considered from the weak and strong coupling
(perturbation theory vs. instanton calculus) perspectives.Comment: 4 page
Transport through a quantum dot with SU(4) Kondo entanglement
We investigate a mesoscopic setup composed of a small electron droplet (dot)
coupled to a larger quantum dot (grain) also subject to Coulomb blockade as
well as two macroscopic leads used as source and drain. An exotic Kondo ground
state other than the standard SU(2) Fermi liquid unambiguously emerges: an
SU(4) Kondo correlated liquid. The transport properties through the small dot
are analyzed for this regime, through boundary conformal field theory, and
allow a clear distinction with other regimes such as a two-channel spin state
or a two-channel orbital state.Comment: 13 pages, 3 figure
Internal Time Peculiarities as a Cause of Bifurcations Arising in Classical Trajectory Problem and Quantum Chaos Creation in Three-Body System
A new formulation of the theory of quantum mechanical multichannel scattering
for three-body collinear systems is proposed. It is shown, that in this simple
case the principle of quantum determinism in the general case breaks down and
we have a micro-irreversible quantum mechanics. The first principle
calculations of the quantum chaos (wave chaos) were pursued on the example of
an elementary chemical reaction Li+(FH)->(LiFH)*->(LiF)+H.Comment: 7 pages, 3 figures, accepted for publication in Int. J. of
Bifurcation & Chao
- …