39 research outputs found
Metal-Insulator Transition in Disordered Two-Dimensional Electron Systems
We present a theory of the metal-insulator transition in a disordered
two-dimensional electron gas. A quantum critical point, separating the metallic
phase which is stabilized by electronic interactions, from the insulating phase
where disorder prevails over the electronic interactions, has been identified.
The existence of the quantum critical point leads to a divergence in the
density of states of the underlying collective modes at the transition, causing
the thermodynamic properties to behave critically as the transition is
approached. We show that the interplay of electron-electron interactions and
disorder can explain the observed transport properties and the anomalous
enhancement of the spin susceptibility near the metal-insulator transition
Temperature-induced spontaneous time-reversal symmetry breaking on the honeycomb lattice
Phase transitions involving spontaneous time-reversal symmetry breaking are
studied on the honeycomb lattice at finite hole-doping with
next-nearest-neighbor repulsion. We derive an exact expression for the
mean-field equation of state in closed form, valid at temperatures much less
than the Fermi energy. Contrary to standard expectations, we find that
thermally induced intraband particle-hole excitations can create and stabilize
a uniform metallic phase with broken time-reversal symmetry as the temperature
is "raised" in a region where the groundstate is a trivial metal
Quantum theory of structured monochromatic light
Applications that envisage utilizing the orbital angular momentum (OAM) at
the single photon level assume that the OAM degrees of freedom that the photons
inherit from the classical wave solutions are orthogonal. To test this critical
assumption, we quantize the beam-like solutions of the vector Helmholtz
equation from first principles to delineate its elementary quantum mechanical
degrees of freedom. We show that although the beam-photon operators do not in
general satisfy the canonical commutation relations, implying that the photon
states they create are not orthogonal, the states are nevertheless bona fide
eigenstates of the number and Hamiltonian operators. The explicit
representation for the photon operators presented in this work forms a natural
basis to study light-matter interactions and quantum information processing at
the single photon level
Renormalization group study of intervalley scattering and valley splitting in a two-valley system
Renormalization group equations are derived for the case when both valley
splitting and intervalley scattering are present in a two-valley system. A
third scaling parameter is shown to be relevant when the two bands are split
but otherwise distinct. The existence of this parameter changes the
quantitative behavior at finite temperatures, but the qualitative conclusions
of the two-parameter theory are shown to be unaffected for realistic choice of
parameters
Magnetoconductivity in the presence of Bychkov-Rashba spin-orbit interaction
A closed-form analytic formula for the magnetoconductivity in the diffusive
regime is derived in the presence of Bychkov-Rashba spin-orbit interaction in
two dimensions. It is shown that at low fields B << B_{so}, where B_{so} is the
characteristic field associated with spin precession, D'yakonov-Perel'
mechanism leads to spin relaxation, while for B >> B_{so} spin relaxation is
suppressed and the resulting spin precession contributes a Berry phase-like
spin phase to the magnetoconductivity. The relative simplicity of the formula
greatly facilitates data fitting, allowing for the strength of the spin-orbit
coupling to be easily extracted
Test of scaling theory in two dimensions in the presence of valley splitting and intervalley scattering in Si-MOSFETs
We show that once the effects of valley splitting and intervalley scattering
are incorporated, renormalization group theory consistently describes the
metallic phase in silicon metal-oxide-semiconductor field-effect transistors
down to the lowest accessible temperatures