1,655 research outputs found
Effects of Crystalline Electronic Field and Onsite Interorbital Interaction in Yb-based Quasicrystal and Approximant Crystal
To get an insight into a new type of quantum critical phenomena recently
discovered in the quasicrystal YbAlAu and approximant
crystal (AC) YbAlAu under pressure, we discuss the
property of the crystalline electronic field (CEF) at Yb in the AC and show
that uneven CEF levels at each Yb site can appear because of the Al/Au mixed
sites. Then we construct the minimal model for the electronic state on the AC
by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at
Yb. Numerical calculation for the ground state shows that the lattice constant
dependence of the Yb valence well explains the recent measurement done by
systematic substitution of elements of Al and Au in the quasicrystal and AC,
where the quasicrystal YbAlAu is just located at the point
from where the Yb-valence starts to change drastically. Our calculation
convincingly demonstrates that this is indeed the evidence that this material
is just located at the quantum critical point of the Yb-valence transition.Comment: 12 pages, 8 figures, Invited Paper in the 26th International
Conference on High Pressure Science & Technology (AIRAPT 26
Wide Quantum Critical Region of Valence Fluctuations: Origin of Robust Quantum Criticality in Quasicrystal Yb15Al34Au51 under Pressure
The mechanism of the emergence of robust quantum criticality in the
heavy-electron quasicrystal Yb15Al34Au51 is analyzed theoretically. By
constructing a minimal model for the quasicrystal and its crystalline
approximant, which contain concentric shell structures with Yb and Al-Au
clusters, we show that a set of quantum critical points of the first-order
valence transition of Yb appears as spots in the ground-state phase diagram.
Their critical regions overlap each other, giving rise to a wide quantum
critical region. This well explains the robust criticality observed in
Yb15Al34Au51 under pressure, and predicts the emergence of the common
criticality in the crystalline approximant under pressure. The wider critical
region in the quasicrystal than that in the crystalline approximant in the T-P
phase diagram and the field-induced valence-crossover "region" in the T-H phase
diagram are predicted to appear.Comment: 6 pages, 3 figures, conference proceedings based on the talk at
SCES2014 constituted of partly published results in section 2 (J. Phys. Soc.
Jpn. 83 (2013) 061006) and new results in section 3 as the self-contained
for
Charge Transfer Effect under Odd-Parity Crystalline Electric Field: Divergence of Magnetic Toroidal Fluctuation in -YbAlB
A novel property of the quantum critical heavy fermion superconductor
-YbAlB is revealed theoretically. By analyzing the crystalline
electronic field (CEF) on the basis of the hybridization picture, odd parity
CEF is shown to exist because of sevenfold configuration of B atoms around Yb,
which breaks the local inversion symmetry. This allows onsite admixture of 4f
and 5d wavefunctions with a pure imaginary coefficient, giving rise to the
magnetic toroidal (MT) degree of freedom. By constructing a realistic minimal
model for -YbAlB, we show that onsite 4f-5d Coulomb repulsion drives
charge transfer between the 4f and 5d states at Yb, which makes the MT
fluctuation as well as the electric dipole fluctuation diverge simultaneously
with the critical Yb-valence fluctuation at the quantum critical point of the
valence transition.Comment: 5 pages, 3 figure
Sharp Valence Change as Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure
The drastic changes of Fermi surfaces as well as transport anomalies near
P=Pc~2.35 GPa in CeRhIn5 are explained theoretically from the viewpoint of
sharp valence change of Ce. It is pointed out that the key mechanism is the
interplay of magnetic order and Ce-valence fluctuations. It is shown 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 naturally explains the de
Haas-van Alphen measurement and also the transport anomalies of T-linear
resistivity emerging simultaneously with the residual resistivity peak at P=Pc
in CeRhIn5.Comment: 4 pages, 2 figures, to appear in Journal of Physics: Conference
Serie
Competition between crystalline electric field singlet and itinerant states of f electrons
A new kind of phase transition is proposed for lattice fermion systems with
simplified f^2 configurations at each site. The free energy of the model is
computed in the mean-field approximation for both the itinerant state with the
Kondo screening, and a localized state with the crystalline electric field
(CEF) singlet at each site. The presence of a first-order phase transition is
demonstrated in which the itinerant state changes into the localized state
toward lower temperatures. In the half-filled case, the insulating state at
high temperatures changes into a metallic state, in marked contrast with the
Mott transition in the Hubbard model. For comparison, corresponding states are
discussed for the two-impurity Kondo system with f^1 configuration at each
site.Comment: 10 pages LaTeX , 2 eps figures Accepted for publication in Z.Phys.
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