7,443 research outputs found
Weak and strong coupling limits of the two-dimensional Fr\"ohlich polaron with spin-orbit Rashba interaction
The continuous progress in fabricating low-dimensional systems with large
spin-orbit couplings has reached a point in which nowadays materials may
display spin-orbit splitting energies ranging from a few to hundreds of meV.
This situation calls for a better understanding of the interplay between the
spin-orbit coupling and other interactions ubiquitously present in solids, in
particular when the spin-orbit splitting is comparable in magnitude with
characteristic energy scales such as the Fermi energy and the phonon frequency.
In this article, the two-dimensional Fr\"ohlich electron-phonon problem is
reformulated by introducing the coupling to a spin-orbit Rashba potential,
allowing for a description of the spin-orbit effects on the electron-phonon
interaction. The ground state of the resulting Fr\"ohlich-Rashba polaron is
studied in the weak and strong coupling limits of the electron-phonon
interaction for arbitrary values of the spin-orbit splitting. The weak coupling
case is studied within the Rayleigh-Schr\"odinger perturbation theory, while
the strong-coupling electron-phonon regime is investigated by means of
variational polaron wave functions in the adiabatic limit. It is found that,
for both weak and strong coupling polarons, the ground state energy is
systematically lowered by the spin-orbit interaction, indicating that the
polaronic character is strengthened by the Rashba coupling. It is also shown
that, consistently with the lowering of the ground state, the polaron effective
mass is enhanced compared to the zero spin-orbit limit. Finally, it is argued
that the crossover between weakly and strongly coupled polarons can be shifted
by the spin-orbit interaction.Comment: 11 pages, 5 figure
Polar type density of states in non-unitary odd-parity superconducting states of gap with point nodes
It is shown that the density of states (DOS) proportional to the excitation
energy, the so-called polar like DOS, can arise in the odd-parity states with
the superconducting gap vanishing at points even if the spin-orbit interaction
for Cooper pairing is strong enough. Such gap stuructures are realized in the
non-unitary states, F_{1u}(1,i,0), F_{1u}(1,varepsilon,varepsilon^{2}), and
F_{2u}(1,i,0), classified by Volovik and Gorkov, Sov. Phys.-JETP Vol.61 (1985)
843. This is due to the fact that the gap vanishes in quadratic manner around
the point on the Fermi surface. It is also shown that the region of quadratic
energy dependence of DOS, in the state F_{2u}(1,varepsilon,varepsilon^{2}), is
restricted in very small energy region making it difficult to distinguish from
the polar-like DOS.Comment: 5 pages, 3 figures, submitted to J. Phys.: Condens. Matter Lette
Huge Enhancement of Impurity Scattering due to Critical Valence Fluctuations in a Ce-Based Heavy Electron System
On the basis of the Ward-Pitaevskii identity, the residual resistivity
is shown to exhibit huge enhancement around the quantum critical
point of valence transition in Ce-based heavy electron systems. This explains a
sharp peak of observed in CeCuGe under the pressure at
16GPa where the superconducting trasition temperature also exhibit the
sharp peak.Comment: 5 pages, 1 figur
A theory of new type of heavy-electron superconductivity in PrOs_4Sb_12: quadrupolar-fluctuation mediated odd-parity pairings
It is shown that unconventional nature of superconducting state of
PrOs_4Sb_12, a Pr-based heavy electron compound with the filled-Skutterudite
structure, can be explained in a unified way by taking into account the
structure of the crystalline-electric-field (CEF) level, the shape of the Fermi
surface determined by the band structure calculation, and a picture of the
quasiparticles in f-configuration with magnetically singlet CEF ground
state. Possible types of pairing are narrowed down by consulting recent
experimental results. In particular, the chiral "p"-wave states such as
p_x+ip_y is favoured under the magnetic field due to the orbital Zeeman effect,
while the "p"-wave states with two-fold symmetery such as p_x can be stabilized
by a feedback effect without the magnetic field. It is also discussed that the
double superconducting transition without the magnetic field is possible due to
the spin-orbit coupling of the "triplet" Cooper pairs in the chiral state.Comment: 12 pages, 2 figures, submitted to J. Phys.: Condens. Matter Lette
Theory of Quasi-Universal Ratio of Seebeck Coefficient to Specific Heat in Zero-Temperature Limit in Correlated Metals
It is shown that the quasi-universal ratio of
the Seebeck coefficient to the specific heat in the limit of T=0 observed in a
series of strongly correlated metals can be understood on the basis of the
Fermi liquid theory description. In deriving this result, it is crucial that a
relevant scattering arises from impurities, but not from the mutual scattering
of quasiparticles. The systematics of the sign of is shown to reflect the
sign of the logarithmic derivative of the density of states and the inverse
mass tensor of the quasiparticles, explaining the systematics of experiments.
In particular, the positive sign of for Ce-based and -based heavy
fermions, and the negative sign for Yb-based and -based heavy fermions,
are explained. The case of non-Fermi liquid near the quantum critical point
(QCP) is briefly mentioned, showing that the ratio decreases considerably
toward antiferromagnetic QCP while it remains essentially unchanged for the
ferromagnetic QCP or QCP due to a local criticality.Comment: 12 pages, 1 figur
Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure
The mechanism of drastic change of Fermi surfaces as well as transport
anomalies near P=Pc=2.35 GPa in CeRhIn5 is explained theoretically. The key
mechanism is pointed out to be the interplay of magnetic order and Ce-valence
fluctuations. We show that the antiferromagnetic state with "small" Fermi
surfaces changes to the paramagnetic state with "large" Fermi surfaces with
huge enhancement of effective mass of electrons with keeping finite c-f
hybridization. This explains the drastic change of the de Haas-van Alphen
signals. Furthermore, it is also consistent with the emergence of T-linear
resistivity simultaneous with the residual resistivity peak at P=Pc in CeRhIn5.Comment: 5 pages, 3 figures, submitted to Journal of Physical Society of Japa
Low-energy models for correlated materials: bandwidth renormalization from Coulombic screening
We provide a prescription for constructing Hamiltonians representing the low
energy physics of correlated electron materials with dynamically screened
Coulomb interactions. The key feature is a renormalization of the hopping and
hybridization parameters by the processes that lead to the dynamical screening.
The renormalization is shown to be non-negligible for various classes of
correlated electron materials. The bandwidth reduction effect is necessary for
connecting models to materials behavior and for making quantitative predictions
for low-energy properties of solids.Comment: 4 pages, 2 figure
Singular Effects of Impurities near the Ferromagnetic Quantum-Critical Point
Systematic theoretical results for the effects of a dilute concentration of
magnetic impurities on the thermodynamic and transport properties in the region
around the quantum critical point of a ferromagnetic transition are obtained.
In the quasi-classical regime, the dynamical spin fluctuations enhance the
Kondo temperature. This energy scale decreases rapidly in the quantum
fluctuation regime, where the properties are those of a line of critical points
of the multichannel Kondo problem with the number of channels increasing as the
critical point is approached, except at unattainably low temperatures where a
single channel wins out.Comment: 4 pages, 2 figure
Abandoned agricultural lands in Central and Eastern Europe: biomass production as a sustainable future land management option, and its socio-economic and environmental implications
Following the collapse of the ‘Eastern Bloc’ in 1989, a large area of agricultural land was abandoned in Central and Eastern Europe. This was not only due to the biophysical marginality of the lands but also as a result of comprehensive political, institutional and socio-economic changes during the post-socialist transitions. Since the mid-2000’s the re-cultivation for food crops has already started on some of these lands in Central and Eastern Europe, which indicates potential sustainability challenges. In this context, one of the possible sustainable land management options for abandoned agricultural land is the introduction of a low intensive crop production system such as perennial biomass crops. In a large number of global studies, the use of abandoned agricultural land for biomass production had been suggested to prevent further land use change (LUC) effects due to the expansion of energy crop production worldwide (1)(2). Perennial biomass crops, in particular, are also expected to remedy a number of natural resource management problems such as soil acidification, soil erosion and water quality degradation and to enhance biodiversity in the arable landscape (3). In addition, the production of biomass crops on abandoned agricultural land has potential to create new opportunities for the economically marginal rural regions in Central and Eastern Europe, which are facing serious agricultural decline and the resulting socio-economic challenges. In our research we focused on four countries in Central and Eastern Europe – Ukraine, Romania, Poland and Latvia - to analyse the drivers for land abandonment and the environmental implications, and derived possible land management options for abandoned agricultural land from a literature review. We then suggested the potential land management scenarios of biomass production on these lands using a case study in north-eastern Poland considering the potential trade-offs between socio-economic and environmental effects of the biomass production scenarios
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