7,767 research outputs found
Modified Josephson Relation
For type II superconductors, Josephson has shown that vortices moving with
velocity v_L create an effective electric field E'=-v_L x B. By definition the
effective electric field is gradient of the electrochemical potential, what is
the quantity corresponding to voltage observed with the use of Ohmic contacts.
It relates to the true electric field E via the local chemical potential mu as
E'=E - grad(mu)/e. We argue that at low temperatures the true electric field in
the bulk can be approximated by a modified Josephson relation E=(v_s-v_L) x B,
where v_S is the condensate velocity.Comment: 3 page
Spin density in frustrated magnets under mechanical stress: Mn-based antiperovskites
In this paper we present results of our calculations of the non-collinear
spin density distribution in the systems with frustrated triangular magnetic
structure (Mn-based antiperovskite compounds, Mn_{3}AN (A=Ga, Zn)) in the
ground state and under external mechanical strain. We show that the spin
density in the (111)-plane of the unit cell forms a "domain" structure around
each atomic site but it has a more complex structure than the uniform
distribution of the rigid spin model, i.e. Mn atoms in the (111)-plane form
non-uniform "spin clouds", with the shape and size of these "domains" being
function of strain. We show that both magnitude and direction of the spin
density change under compressive and tensile strains, and the orientation of
"spin domains" correlates with the reversal of the strain, i.e. switching
compressive to tensile strain (and vice versa) results in "reversal" of the
domains. We present analysis for the intra-atomic spin-exchange interaction and
the way it affects the spin density distribution. In particular, we show that
the spin density inside the atomic sphere in the system under mechanical stress
depends on the degree of localization of electronic states
Impact of Quantum Phase Transitions on Excited Level Dynamics
The influence of quantum phase transitions on the evolution of excited levels
in the critical parameter region is discussed. The analysis is performed for 1D
and 2D systems with first- and second-order ground-state transitions. Examples
include the cusp and nuclear collective Hamiltonians.Comment: 6 pages, 4 figure
Coulomb analogy for nonhermitian degeneracies near quantum phase transitions
Degeneracies near the real axis in a complex-extended parameter space of a
hermitian Hamiltonian are studied. We present a method to measure distributions
of such degeneracies on the Riemann sheet of a selected level and apply it in
classification of quantum phase transitions. The degeneracies are shown to
behave similarly as complex zeros of a partition function.Comment: 4 page
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