24,087 research outputs found
Quantum Critical Transport Near the Mott Transition
We perform a systematic study of incoherent transport in the high temperature
crossover region of the half-filled one-band Hubbard model. We demonstrate that
the family of resistivity curves displays characteristic quantum critical
scaling of the form , with
, and . The
corresponding -function displays a "strong coupling" form
, reflecting the peculiar mirror symmetry of the
scaling curves. This behavior, which is surprisingly similar to some
experimental findings, indicates that Mott quantum criticality may be acting as
the fundamental mechanism behind the unusual transport phenomena in many
systems near the metal-insulator transition.Comment: Published version; 4+epsilon pages, 4 figure
Symmetries and classical quantization
A phenomenon of classical quantization is discussed. This is revealed in the
class of pseudoclassical gauge systems with nonlinear nilpotent constraints
containing some free parameters. Variation of parameters does not change local
(gauge) and discrete symmetries of the corresponding systems, but there are
some special discrete values of them which give rise to the maximal global
symmetries at the classical level. Exactly the same values of the parameters
are separated at the quantum level, where, in particular, they are singled out
by the requirement of conservation of the discrete symmetries. The phenomenon
is observed for the familiar pseudoclassical model of 3D P,T-invariant massive
fermion system and for a new pseudoclassical model of 3D P,T-invariant system
of topologically massive U(1) gauge fields.Comment: 10 pages, LaTe
Hidden Kondo Effect in a Correlated Electron Chain
We develop a general Bethe Ansatz formalism for diagonalizing an integrable
model of a magnetic impurity of arbitrary spin coupled ferro- or
antiferromagnetically to a chain of interacting electrons. The method is
applied to an open chain, with the exact solution revealing a ``hidden'' Kondo
effect driven by forward electron scattering off the impurity. We argue that
the so-called ``operator reflection matrices'' proposed in recent Bethe Ansatz
studies of related models emulate only forward electron-impurity scattering
which may explain the absence of complete Kondo screening for certain values of
the impurity-electron coupling in these models.Comment: 5 pages, RevTex; to appear in Phys. Rev. Let
A Quasi-Exactly Solvable N-Body Problem with the sl(N+1) Algebraic Structure
Starting from a one-particle quasi-exactly solvable system, which is
characterized by an intrinsic sl(2) algebraic structure and the
energy-reflection symmetry, we construct a daughter N-body Hamiltonian
presenting a deformation of the Calogero model. The features of this
Hamiltonian are (i) it reduces to a quadratic combination of the generators of
sl(N+1); (ii) the interaction potential contains two-body terms and interaction
with the force center at the origin; (iii) for quantized values of a certain
cohomology parameter n it is quasi-exactly solvable, the multiplicity of states
in the algebraic sector is (N+n)!/(N!n!); (iv) the energy-reflection symmetry
of the parent system is preserved.Comment: Latex, 12 page
Hidden nonlinear supersymmetries in pure parabosonic systems
The existence of intimate relation between generalized statistics and
supersymmetry is established by observation of hidden supersymmetric structure
in pure parabosonic systems. This structure is characterized generally by a
nonlinear superalgebra. The nonlinear supersymmetry of parabosonic systems may
be realized, in turn, by modifying appropriately the usual supersymmetric
quantum mechanics. The relation of nonlinear parabosonic supersymmetry to the
Calogero-like models with exchange interaction and to the spin chain models
with inverse-square interaction is pointed out.Comment: 20 pages, one reference corrected, to appear in Int. J. Mod. Phys.
Competing Valence Bond Crystals in the Kagome Quantum Dimer Model
The singlet dynamics which plays a major role in the physics of the spin-1/2
Quantum Heisenberg Antiferromagnet (QHAF) on the Kagome lattice can be
approximately described by projecting onto the nearest-neighbor valence bond
(NNVB) singlet subspace. We re-visit here the effective Quantum Dimer Model
which originates from the latter NNVB-projected Heisenberg model via a
non-perturbative Rokhsar-Kivelson-like scheme. By using Lanczos exact
diagonalisation on a 108-site cluster supplemented by a careful symmetry
analysis, it is shown that a previously-found 36-site Valence Bond Crystal
(VBC) in fact competes with a new type of 12-site "{\it resonating-columnar}"
VBC. The exceptionally large degeneracy of the GS multiplets (144 on our
108-site cluster) might reflect the proximity of the Z_2 dimer liquid.
Interestingly, these two VBC "emerge" in {\it different topological sectors}.
Implications for the interpretation of numerical results on the QHAF are
outlined.Comment: 8 pages, 5 figures, 4 tables; Figure 2 and Table II update
Gauge non-invariance as tests of emergent gauge symmetry
We motivate the concept of emergent gauge symmetry and discuss ways that this
concept can be tested. The key idea is that if a symmetry is emergent, one
should look for small violations of this symmetry because the underlying
fundamental theory does not contain the symmetry. We describe our recent work
implementing this idea in the gravity sector. We also describe the reasons why
violations of gauge symmetry may well be linked to violations of Lorentz
invariance.Comment: 5 pages, Invited talk presented at the Fifth Meeting on CPT and
Lorentz Symmetry, Bloomington, Indiana, June 28-July 2, 201
Classification of engineered topological superconductors
I perform a complete classification of 2d, quasi-1d and 1d topological
superconductors which originate from the suitable combination of inhomogeneous
Rashba spin-orbit coupling, magnetism and superconductivity. My analysis
reveals alternative types of topological superconducting platforms for which
Majorana fermions are accessible. Specifically, I observe that for quasi-1d
systems with Rashba spin-orbit coupling and time-reversal violating
superconductivity, as for instance due to a finite Josephson current flow,
Majorana fermions can emerge even in the absence of magnetism. Furthermore, for
the classification I also consider situations where additional "hidden"
symmetries emerge, with a significant impact on the topological properties of
the system. The latter, generally originate from a combination of space group
and complex conjugation operations that separately do not leave the Hamiltonian
invariant. Finally, I suggest alternative directions in topological quantum
computing for systems with additional unitary symmetries.Comment: To appear in New Journal of Physics for the Focus on Majorana
Fermions in Condensed Matter; Final version 19 pages, 6 figures: a new
section was added concerning the appearance of MFs in two coupled Rasba
semiconducting wires with proximity induced superconductivity and a finite
supercurrent flow, without the application of a magnetic field. Generally
improved discussion and references adde
- …