Zeeman effect in dynamic Jahn-Teller impurities (original) (raw)
Dynamic and Static Jahn-Teller Effect in Impurities: Determination of the Tunneling Splitting
Vibronic Interactions and the Jahn-Teller Effect, 2011
In this paper we review the concepts of dynamic and static Jahn-Teller (JT) effects and study their influence in the electron paramagnetic resonance (EPR) spectra of transition metal impurities in wide gap insulators. We show that the key quantities involved in this problem are the tunneling splitting, usually denoted 3Γ, and the splitting, δ, between ∼3z 2 − r 2 and ∼x 2 − y 2 energy levels due to the random strain field which is present in every real crystal. It is pointed out that in the E ⊗ e JT problem the kinetic energy of nuclei involved in the ground state plays a key role for understanding the actual value of 3Γ and thus the existence of dynamic JT effect. The results of ab initio calculations on a variety of JT systems show that 3Γ values span a much larger range than previously suggested. In particular, we find that 3Γ = 235 cm −1 for MgO:Cu 2+ while 3Γ = 10 −4 cm −1 for KCl:Ag 2+. We also show that the dynamic JT effect can only appear for such large values of 3Γ as those found in MgO:Cu 2+ since usual strain fields lead to δ values of the order of 10 cm −1 that would otherwise localize the system in only one of the JT wells. The present results explain satisfactorily why the JT effect for Cu 2+ and Ag 2+ impurities in MgO is dynamic while static for Ag 2+-doped CaO and alkali chlorides. The origin of such a difference is discussed in detail.
Symmetry, 2021
In a mostly review paper, we show that the important problem of symmetry, broken symmetry, and spontaneous broken symmetry of polyatomic systems is directly related to the Jahn–Teller (JT) and pseudo-Jahn–Teller (PJT) effects, including the hidden-JT and hidden-PJT effects, and these JT effects (JTEs) are the only source of spontaneous symmetry breaking in matter. They are directly related to the violation of the adiabatic approximation by the vibronic and other nonadiabatic couplings (jointly termed nonadiabaticity) in the interaction between the electrons and nuclei, which becomes significant in the presence of two or more degenerate or pseudodegenerate electronic states. In a generalization of this understanding of symmetry, we suggest an improved (quantum) definition of stereo-chemical polyatomic space configuration, in which, starting with their high-symmetry configuration, we separate all atomic systems into three distinguishable groups: (1) weak nonadiabaticity, stable high-s...
Geometric phase effect at N -fold electronic degeneracies in Jahn-Teller systems
International Journal of Quantum Chemistry, 2004
The geometric phase effect at arbitrary integral N-fold electronic degeneracies is investigated in Jahn-Teller systems. It is shown to be a property inherent to inversion of the adiabatic electronic wave vectors in the N-dimensional electronic wave-vector space. The relationship between the geometric phase and mixing angles has also been established.
Journal of Molecular Structure, 2007
In this (partly review) paper several important situations are analyzed in which molecular systems are distorted, but there are no apparent degeneracies or close in energy states to justify their origin as due to the Jahn-Teller effect (JTE) or pseudo JTE (PJTE). It is shown that in all these cases above the JTE are ''hidden'' in the excited states of the undistorted configuration even when the energy gap to these states is very large, and the involvement of these states in the vibronic coupling explains the JT origin of the distortions. This confirms the general validity of the JTE as the only source of instabilities and distortions of high-symmetry configurations of polyatomic systems. For the example of the ozone molecule, which has no degenerate ground state, neither in the distorted (obtuse-triangular), nor in the undistorted (regular triangular) configurations, and there are no low-lying excited states, the distortion is shown to emerge from the JTE in the excited E state situated at 8.3eVabovethegroundstate.TheJTstabilizationenergyismorethan8.3 eV above the ground state. The JT stabilization energy is more than 8.3eVabovethegroundstate.TheJTstabilizationenergyismorethan9 eV which makes the distorted configuration the lowest in energy.
Theory of the Jahn-Teller-Kondo effect
Physical review. B, Condensed matter, 1988
There is a Kondo effect associated with ions such as Cu + which have an orbital doublet in a cubic field. The ground state is a Jahn-Teller-Kondo singlet which can have a characteristic energy 10 cm '. This large energy might stabilize the pseudocubic site recently observed in YBa2Cu307. Mehran eral. ' have observed electron spin resonance (ESR) signals, associated with Cu +, from single-crystal, single-phase, samples of YBazCu307 which exhibit a pseudocubic site symmetry and are unique in the ESR literature. The signal does not come from an impurity phase. These are high-quality single crystals, but unannealed, and exhibit no appreciable diamagnetic response above-60 K; however"other than in this final treatment, the samples are identical to similar crystals with a narrow-90-K transition, but which do not exhibit an ESR signal. The absence of a signal from the annealed samples suggests that the Cu moments are somehow "compensated" in this final stage of preparation. Within experimental error, below 100 K, the magnetic ground state of the Cuz+ observed via ESR refiects cubic symmetry. Above this temperature the ground state remains close to, but not exactly, cubic while at all temperatures the partially resolved hyperfine structure exhibits an-20% anisotropy. These latter two facts indicate that the local site symmetry of the Cu is far from cubic. Somewhat similar signals for dielectrics are associated with the dynamic Jahn-Teller "vibronic" singlet. z However, there are no Cu sites in the high-T', materials which have (even close to) the cubic coordination which is essential for a classical Jahn-Teller effect.
A New Method to Describe the Multimode Jahn–Teller Effect Using Density Functional Theory
Springer Series in Chemical Physics, 2009
A new method for the analysis of the adiabatic potential energy surfaces of Jahn-Teller (JT) active molecules is presented. It is based on the analogy between the JT distortion and reaction coordinates. Within the harmonic approximation the JT distortion can be analysed as the linear combination of all totally symmetric normal modes in the low symmetry minimum energy conformation. Contribution of the normal modes to the distortion, their energy contribution to the JT stabilisation energy, the forces at high symmetry cusp and detailed distortion path can be estimated quantitatively. This approach gives direct insight into the coupling of electronic structure and nuclear displacements. Further more, it is reviewed how multideterminental DFT can be applied for the calculation of the JT parameters. As examples the results for VCl 4 , cyclopentadienyl radical and cobaltocene are given.
Phase Separation in Jahn-Teller Systems with Localized and Itinerant Electrons
Physical Review Letters, 2005
The phase diagram for doped manganites and related compounds is analyzed in terms of the Kondolattice model taking into account an interplay between electrons localized due to lattice distortions and those in the band states. It is shown that the number of itinerant charge carriers can be significantly lower than that implied by the doping level. The competition between the homogeneous (ferromagnetic or antiferromagnetic) and phase-separated states is discussed and a strong tendency to the phase separation was revealed for a wide doping range.
Relativistic Jahn–Teller and pseudo-Jahn–Teller couplings in systems
Chemical Physics, 2012
The Hamiltonian for linear and quadratic Jahn-Teller (JT) and pseudo-JT (PJT) coupling as well as zerothorder and linear spin-orbit (SO) coupling in the 2 E þ 2 B 2 electronic multiplet in D 2d systems is derived. The SO coupling is described by the microscopic Breit-Pauli operator. It is shown that the 2 E state exhibits a 2 E Â e JT effect which is of relativistic origin, that is, it arises from the SO operator. The relativistic PJT coupling of the 2 E and 2 B 2 states involves the normal modes of b 1 ; b 2 and e symmetry. The 2 E Â ðb 1 þ b 2 þ eÞ JT Hamiltonian is analytically transformed to a SO-adapted electronic basis in which the zeroth-order SO operator is diagonal. In the special case of 2 E À 2 B degeneracy, the ð 2 E þ 2 B 2 Þ Â ðb 1 þ b 2 þ eÞ JT + PJT Hamiltonian also is transformed to a SO-adapted basis.
Effect of local electron-electron correlation in hydrogen-like impurities in Ge
Physical Review B, 2013
We have studied the electronic and local magnetic structure of the hydrogen interstitial impurity at the tetrahedral site in diamond-structure Ge, using an empirical tight binding + dynamical mean-field-theory approach because within the local-density approximation (LDA) Ge has no gap. We first establish that within LDA the 1s spectral density bifurcates due to entanglement with the four neighboring sp 3 antibonding orbitals, providing an unanticipated richness of behavior in determining under what conditions a local moment hyperdeep donor or Anderson impurity will result, or on the other hand, a gap state might appear. Using a supercell approach, we show that the spectrum, the occupation, and the local moment of the impurity state displays a strong dependence on the strength of the local on-site Coulomb interaction U , the H-Ge hopping amplitude, the depth of the bare 1s energy level H , and we address to some extent the impurity concentration dependence. In the isolated impurity, strong interaction regime a local moment emerges over most of the parameter ranges, indicating magnetic activity, and spectral density structure very near (or in) the gap suggests possible electrical activity in this regime.