209 research outputs found
Intrinsic temperature dependences of transport coefficients within the hot-spot model for normal state YBCO
The temperature dependences of the galvanomagnetic and thermoelectric
transport coefficients within a generic hot-spot model are reconsidered.
Despite the recent success in explaining ac Hall effect data in
YBa_{2}Cu_{3}O_{7}, a general feature of this model is a departure from the
approximately universal temperature dependences observed for normal state
transport in the optimally doped cuprates. In this paper, we discuss such
systematic deviations and illustrate some of their effects through a concrete
numerical example using the calculated band structure for YBa_{2}Cu_{3}O_{7}.Comment: 4 pages, LaTex, 2 EPS figure
Nematic Bond Theory of Heisenberg Helimagnets
We study classical two-dimensional frustrated Heisenberg models with
generically incommensurate groundstates. A new theory for the spin-nematic
"order by disorder" transition is developed based on the self-consistent
determination of the effective exchange coupling bonds. In our approach,
fluctuations of the constraint field imposing conservation of the local
magnetic moment drive nematicity at low temperatures. The critical temperature
is found to be highly sensitive to the peak helimagnetic wavevector, and
vanishes continuously when approaching rotation symmetric Lifshitz points.
Transitions between symmetry distinct nematic orders may occur by tuning the
exchange parameters, leading to lines of bicritical points.Comment: 4 pages, 4 figure
Nonequilibrium Transport through a Kondo Dot: Decoherence Effects
We investigate the effects of voltage induced spin-relaxation in a quantum
dot in the Kondo regime. Using nonequilibrium perturbation theory, we determine
the joint effect of self-energy and vertex corrections to the conduction
electron T-matrix in the limit of transport voltage much larger than
temperature. The logarithmic divergences, developing near the different
chemical potentials of the leads, are found to be cut off by spin-relaxation
rates, implying that the nonequilibrium Kondo-problem remains at weak coupling
as long as voltage is much larger than the Kondo temperature.Comment: 16 pages, 4 figure
Transconductance of a double quantum dot system in the Kondo regime
We consider a lateral double-dot system in the Coulomb blockade regime with a
single spin-1/2 on each dot, mutually coupled by an anti-ferromagnetic exchange
interaction. Each of the two dots is contacted by two leads. We demonstrate
that the voltage across one of the dots will have a profound influence on the
current passing through the other dot. Using Poor Man's scaling, we find that
the Kondo-effect can lead to a strong enhancement of this {\it
transconductance}.Comment: updated to published versio
Exchange cotunneling through quantum dots with spin-orbit coupling
We investigate the effects of spin-orbit interaction (SOI) on the exchange
cotunneling through a spinful Coulomb blockaded quantum dot. In the case of
zero magnetic field, Kondo effect is shown to take place via a Kramers doublet
and the SOI will merely affect the Kondo temperature. In contrast, we find that
the breaking of time-reversal symmetry in a finite field has a marked influence
on the effective Anderson, and Kondo models for a single level. The nonlinear
conductance can now be asymmetric in bias voltage and may depend strongly on
direction of the magnetic field. A measurement of the angle dependence of
finite-field cotunneling spectroscopy thus provides valuable information about
orbital, and spin degrees of freedom and their mutual coupling.Comment: 5 pages, 2 figure
Coulomb interacting Dirac fermions in disordered graphene
We study interacting Dirac quasiparticles in disordered graphene and find
that an interplay between the unscreened Coulomb interactions and
pseudo-relativistic quasiparticle kinematics can be best revealed in the
ballistic regime, whereas in the diffusive limit the behavior is qualitatively
(albeit, not quantitatively) similar to that of the ordinary 2DEG with
parabolic dispersion. We calculate the quasiparticle width and density of
states that can be probed by photoemission, tunneling, and magnetization
measurements.Comment: Latex, 4 page
The antiferromagnetic phase of the Floquet-driven Hubbard model
A saddle point plus fluctuations analysis of the periodically driven
half-filled two-dimensional Hubbard model is performed. For drive frequencies
below the equilibrium gap, we find discontinuous transitions to time-dependent
solutions. A highly excited, generically non-thermal distribution of magnons
occurs even for drive frequencies far above the gap. Above a critical drive
amplitude, the low-energy magnon distribution diverges as the frequency tends
to zero and antiferromagnetism is destroyed, revealing the generic importance
of collective mode excitations arising from a non-equilibrium drive
Nodal Quasiparticle Lifetimes in Cuprate Superconductors
A new generation of angular-resolved photoemission spectroscopy (ARPES)
measurements on the cuprate superconductors offer the promise of enhanced
momentum and energy resolution. In particular, the energy and temperature
dependence of the on-shell nodal (k_x=k_y) quasiparticle scattering rate can be
studied. In the superconducting state, low temperature transport measurements
suggest that one can describe nodal quasiparticles within the framework of a
BCS d-wave model by including forward elastic scattering and spin-fluctuation
inelastic scattering. Here, using this model, we calculate the temperature and
frequency dependence of the on-shell nodal quasiparticle scattering rate in the
superconducting state which determines the momentum width of the ARPES momentum
distribution curves. For a zero-energy quasiparticle at the nodal momentum k_N,
both the elastic and inelastic scattering rate show a sudden decrease as the
temperature drops below Tc, reflecting the onset of the gap amplitude. At low
temperatures the scattering rate decreases as T^3 and approaches a zero
temperature value determined by the elastic impurity scattering. For T>T_c, we
find a quasilinear dependence on T. At low reduced temperatures, the elastic
scattering rate for the nodal quasiparticles exhibits a quasilinear increase at
low energy which arises from elastic scattering processes. The inelastic
spin-fluctuation scattering leads to a low energy omega^3 dependence which, for
omega>~Delta_0, crosses over to a quasilinear behavior.Comment: 8 pages, 7 figures, minor revision
Self-energy of a nodal fermion in a d-wave superconductor
We re-consider the self-energy of a nodal (Dirac) fermion in a 2D d-wave
superconductor. A conventional belief is that Im \Sigma (\omega, T) \sim max
(\omega^3, T^3). We show that \Sigma (\omega, k, T) for k along the nodal
direction is actually a complex function of \omega, T, and the deviation from
the mass shell. In particular, the second-order self-energy diverges at a
finite T when either \omega or k-k_F vanish. We show that the full summation of
infinite diagrammatic series recovers a finite result for \Sigma, but the full
ARPES spectral function is non-monotonic and has a kink whose location compared
to the mass shell differs qualitatively for spin-and charge-mediated
interactions.Comment: 4pp 3 eps figure
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