30 research outputs found
Anisotropy of transport in bulk Rashba metals
The recent experimental discovery of three-dimensional (3D) materials hosting
a strong Rashba spin-orbit coupling calls for the theoretical investigation of
their transport properties. Here we study the zero temperature dc conductivity
of a 3D Rashba metal in the presence of static diluted impurities. We show
that, at variance with the two-dimensional case, in 3D systems spin-orbit
coupling affects dc charge transport in all density regimes. We find in
particular that the effect of spin-orbit interaction strongly depends on the
direction of the current, and we show that this yields strongly anisotropic
transport characteristics. In the dominant spin-orbit coupling regime where
only the lowest band is occupied, the SO-induced conductivity anisotropy is
governed entirely by the anomalous component of the renormalized current. We
propose that measurements of the conductivity anisotropy in bulk Rashba metals
may give a direct experimental assessment of the spin-orbit strength.Comment: 7 pages, 3 figure
Unconventional dc transport in Rashba electron gases
We discuss the transport properties of a disordered two-dimensional electron
gas with strong Rashba spin-orbit coupling. We show that in the high-density
regime where the Fermi energy overcomes the energy associated with spin-orbit
coupling, dc transport is accurately described by a standard Drude's law, due
to a non-trivial compensation between the suppression of back-scattering and
the relativistic correction to the quasi-particle velocity. On the contrary,
when the system enters the opposite dominant spin-orbit regime, Drude's
paradigm breaks down and the dc conductivity becomes strongly sensitive to the
spin-orbit coupling strength, providing a suitable tool to test the
entanglement between spin and charge degrees of freedom in theseComment: 6 pages, 4 figures+Supplemental Material. To appear in Phys. Rev.
Let
Rashba-metal to Mott-insulator transition
The recent discovery of materials featuring strong Rashba spin-orbit coupling
(RSOC) and strong electronic correlation raises questions about the interplay
of Mott and Rashba physics. In this work, we employ cluster perturbation theory
to investigate the spectral properties of the two-dimensional Hubbard model in
the presence of a significant or large RSOC. We show that RSOC strongly favors
metallic phases and competes with Mott localization, leading to an
unconventional scenario for the Mott transition which is no longer controlled
by the ratio between the Hubbard and an effective bandwidth. The results
show a strong sensitivity to the value of the RSOC.Comment: 11 pages, 9 figure
Floquet theory of Cooper pair pumping
In this work we derive a general formula for the charge pumped in a
superconducting nanocircuit. Our expression generalizes previous results in
several ways, it is applicable both in the adiabatic and in the non-adiabatic
regimes and it takes into account also the effect of an external environment.
More specifically, by applying Floquet theory to Cooper pair pumping, we show
that under a cyclic evolution the total charge transferred through the circuit
is proportional to the derivative of the associated Floquet quasi-energy with
respect to the superconducting phase difference. In the presence of an external
environment the expression for the transferred charge acquires a transparent
form in the Floquet representation. It is given by the weighted sum of the
charge transferred in each Floquet state, the weights being the diagonal
components of the stationary density matrix of the system expressed in the
Floquet basis. In order to test the power of this formulation we apply it to
the study of pumping in a Cooper pair sluice. We reproduce the known results in
the adiabatic regime and we show new data in the non-adiabatic case.Comment: 9 page
Non-abelian superconducting pumps
Cooper pair pumping is a coherent process. We derive a general expression for
the adiabatic pumped charge in superconducting nanocircuits in the presence of
level degeneracy and relate it to non-Abelian holonomies of Wilczek and Zee. We
discuss an experimental system where the non-Abelian structure of the adiabatic
evolution manifests in the pumped charge.Comment: 5 pages, 3 figure
Pauli metallic ground state in Hubbard clusters with Rashba spin-orbit coupling
We study the "phase diagram" of a Hubbard plaquette with Rashba spin-orbit coupling. We show that the peculiar way in which Rashba coupling breaks the spin-rotational symmetry of the Hubbard model allows a mixing of singlet and triplet components in the ground-state that slows down and it changes the nature of the Mott transition and of the Mott insulating phases
Resonant all-electric spin pumping with spin-orbit coupling
All-electric devices for the generation and filtering of spin currents are of
crucial importance for spintronics experiments and applications. Here we
consider a quantum dot between two metallic leads in the presence of spin-orbit
coupling, and we analyze in the frame of a scattering matrix approach the
conditions for generating spin currents in an adiabatically driven two-terminal
device. We then focus on a dot with two resonant orbitals and show by specific
examples that both spin filtering and pure spin current generation can be
achieved. Finally, we discuss the effect of the Coulomb interaction.Comment: 4 pages, corrected typo in list of author
Phase diffusion and locking in single-qubit lasers
Motivated by recent experiments, which demonstrated lasing and cooling of the
electromagnetic field in an electrical resonator coupled to a superconducting
qubit, we study the phase coherence and diffusion of the system in the lasing
state. We also discuss phase locking and synchronization induced by an
additional {\sl ac} driving of the resonator. We extend earlier work to account
for the strong qubit-resonator coupling and to include the effects of
low-frequency qubit's noise. We show that the strong coupling may lead to a
double peak structure of the spectrum, while the shape and width are determined
to the low-frequency noise.Comment: Revised version with a new section about the validity of the model
when applied to describe experiment
Non-abelian Thouless pumping in a photonic lattice
Non-abelian gauge fields emerge naturally in the description of adiabatically
evolving quantum systems having degenerate levels. Here we show that they also
play a role in Thouless pumping in the presence of degenerate bands. To this
end we consider a photonic Lieb lattice having two degenerate non-dispersive
modes and we show that, when the lattice parameters are slowly modulated, the
propagation of the photons bear the fingerprints of the underlying non-abelian
gauge structure. The non-dispersive character of the bands enables a high
degree of control on photon propagation. Our work paves the way to the
generation and detection of non-abelian gauge fields in photonic and optical
lattices.Comment: 11 pages, 6 figure