9,478 research outputs found
Roles of Critical Valence Fluctuations in Ce- and Yb-Based Heavy Fermion Metals
The roles of critical valence fluctuations of Ce and Yb are discussed as a
key origin of several anomalies observed in Ce- and Yb-based heavy fermion
systems. Recent development of the theory has revealed that a magnetic field is
an efficient control parameter to induce the critical end point of the
first-order valence transition. Metamagnetism and non-Fermi liquid behavior
caused by this mechanism are discussed by comparing favorably with CeIrIn5,
YbAgCu4, and YbIr2Zn20. The interplay of the magnetic order and valence
fluctuations offers a key concept for understanding Ce- and Yb-based systems.
It is shown that suppression of the magnetic order by enhanced valence
fluctuations gives rise to the coincidence of the magnetic-transition point and
valence-crossover point at absolute zero as a function of pressure or magnetic
field. The interplay is shown to resolve the outstanding puzzle in CeRhIn5 in a
unified way. The broader applicability of this newly clarified mechanism is
discussed by surveying promising materials such as YbAuCu4, beta-YbAlB4, and
YbRh2Si2.Comment: 17 pages, 8 figures, invited paper in special issue on strongly
correlated electron system
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
Antiferromagnetic order in CeCoIn5 oriented by spin-orbital coupling
An incommensurate spin density wave ( phase) confined inside the
superconducting state at high basal plane magnetic field is an unique property
of the heavy fermion metal CeCoIn. The neutron scattering experiments and
the theoretical studies point out that this state come out from the soft mode
condensation of magnetic resonance excitations. We show that the fixation of
direction of antiferromagnetic modulations by a magnetic field reported by
Gerber et al., Nat. Phys. {\bf 10}, 126 (2014) is explained by spin-orbit
coupling. This result, obtained on the basis of quite general phenomenological
arguments, is supported by the microscopic derivation of the
susceptibility dependence on the mutual orientation of the basal plane magnetic
field and the direction of modulation of spin polarization in a multi-band
metal.Comment: 7 pages plus 2 pages with 2 figure
Moduli space volume of vortex and localization
Volume of moduli space of BPS vortices on a compact genus h Riemann surface
Sigma_h is evaluated by means of topological field theory and localization
technique. Vortex in Abelian gauge theory with a single charged scalar field
(ANO vortex) is studied first and is found that the volume of the moduli space
agrees with the previous results obtained more directly by integrating over the
moduli space metric. Next we extend the evaluation to non-Abelian gauge groups
and multi-flavors of scalar fields in the fundamental representation. We find
that the result of localization can be consistently understood in terms of
moduli matrix formalism wherever possible. More details are found in our paper
in Prog.Theor.Phys.126 (2011) 637.Comment: 10 pages, talk at the international conference "quantum theory and
symmetries 7" in prague, august 7-13, 201
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