1,015 research outputs found
Spin fractionalization of an even number of electrons in a Quantum dot
An experiment is proposed of non perturbative tunneling in a Quantum dot
connected to leads in a pillar configuration, which would shed light on the
physics of the mesoscopic Kondo problem. We propose for the first time that
what is coupled to the leads in the case of even number of electrons on the dot
is not just the electrons on the QD, with their own spins, but the very total
spin of the dot macroscopic state itself, that displays features of the Kondo
physics, that leads to fractionalization of the spin in the dot, that is to a
"spinon box".Comment: 4 pages revtex file, 1 figur
Hamiltonian theory of the strongly-coupled limit of the Kondo problem in the overscreened case
By properly generalizing Nozie`res' Fermi liquid theory, we construct an
Hamiltonian approach to the scattering of conduction electrons off a spin-1/2
impurity in the ovescreneed Kondo regime, as T -> 0. We derive the S-matrix at
the interacting fixed point, and the corresponding phase shifts, together with
leading energy corrections to the unitary limit. We apply our results to obtain
the low-temperature dependence of the 2-channel Kondo conductance, and we
relate it to possible transport experiments in a Quantum DotComment: 22 pages, 1 figur
Compact lattice U(1) and Seiberg-Witten duality: a quantitative comparison
It was conjectured some time ago that an effective description of the
Coulomb-confinement transition in compact U(1) lattice gauge field theory could
be described by scalar QED obtained by soft breaking of the N=2 Seiberg-Witten
model down to N=0 in the strong coupling region where monopoles are light. In
two previous works this idea was presented at a qualitative level. In this work
we analyze in detail the conjecture and obtain encouraging quantitative
agreement with the numerical determination of the monopole mass and the dual
photon mass in the vicinity of the Coulomb to confining phase transition.Comment: 14 pag, 5 figure
Superconductive proximity in a Topological Insulator slab and excitations bound to an axial vortex
We consider the proximity effect in a Topological Insulator sandwiched
between two conventional superconductors, by comparing s-wave spin singlet
superconducting pairing correlations and odd-parity triplet pairing
correlations with zero spin component orthogonal to the slab ("polar " phase).
A superconducting gap opens in the Dirac dispersion of the surface states
existing at the interfaces. An axial vortex is included, piercing the slab
along the normal to the interfaces with the superconductors. It is known that,
when proximity is s-wave, quasiparticles in the gap are Majorana Bound States,
localized at opposite interfaces. We report the full expression for the quantum
field associated to the midgap neutral fermions, as derived in the two-orbital
band model for the TI. When proximity involves odd-parity pairing, midgap modes
are charged Surface Andreev Bound States, and they originate from interfacial
circular states of definite chirality, centered at the vortex singularity and
decaying in the TI film with oscillations. When the chemical potential is moved
away from midgap, extended states along the vortex axis are also allowed. Their
orbital structure depends on the symmetry of the bulk band from where the
quasiparticle level splits off.Comment: 13 pages no figures, accepted for publication in Phys. Rev.
Entanglement entropy of two disjoint blocks in critical Ising models
We study the scaling of the Renyi and entanglement entropy of two disjoint
blocks of critical Ising models, as function of their sizes and separations. We
present analytic results based on conformal field theory that are
quantitatively checked in numerical simulations of both the quantum spin chain
and the classical two dimensional Ising model. Theoretical results match the
ones obtained from numerical simulations only after taking properly into
account the corrections induced by the finite length of the blocks to their
leading scaling behavior.Comment: 4 pages, 5 figures. Revised version accepted for publication in PR
Junction of three off-critical quantum Ising chains and two-channel Kondo effect in a superconductor
We show that a junction of three off-critical quantum Ising chains can be
regarded as a quantum spin chain realization of the two-channel spin-1/2
overscreened Kondo effect with two superconducting leads. We prove that, as
long as the Kondo temperature is larger than the superconducting gap, the
equivalent Kondo model flows towards the 2 channel Kondo fixed point. We argue
that our system provides the first controlled realization of 2 channel Kondo
effect with superconducting leads. This, besides its the theoretical interest,
is of importance for potential applications to a number of context, including
the analysis of the quantum entanglement properties of a Kondo system.Comment: 14 pages, 4 .eps figure
Adiabatic Control of the Electron Phase in a Quantum Dot
A Berry phase can be added to the wavefunction of an isolated quantum dot by
adiabatically modulating a nonuniform electric field along a time-cycle. The
dot is tuned close to a three-level degeneracy, which provides a wide range of
possibilities of control. We propose to detect the accumulated phase by
capacitively coupling the dot to a double-path inteferometer. The effective
Hamiltonian for the phase-sensitive coupling is discussed in detail.Comment: 14 pages, 2 .eps figure
Tensor Networks for Lattice Gauge Theories with continuous groups
We discuss how to formulate lattice gauge theories in the Tensor Network
language. In this way we obtain both a consistent truncation scheme of the
Kogut-Susskind lattice gauge theories and a Tensor Network variational ansatz
for gauge invariant states that can be used in actual numerical computation.
Our construction is also applied to the simplest realization of the quantum
link models/gauge magnets and provides a clear way to understand their
microscopic relation with Kogut-Susskind lattice gauge theories. We also
introduce a new set of gauge invariant operators that modify continuously
Rokshar-Kivelson wave functions and can be used to extend the phase diagram of
known models. As an example we characterize the transition between the
deconfined phase of the lattice gauge theory and the Rokshar-Kivelson
point of the U(1) gauge magnet in 2D in terms of entanglement entropy. The
topological entropy serves as an order parameter for the transition but not the
Schmidt gap.Comment: 27 pages, 25 figures, 2nd version the same as the published versio
- …