Towards a model of a dynamical Jahn-Teller coupling at very low temperatures inTb2Ti2O7

Abstract

We present an interpretation of zero-field energy integrated ("diffuse") neutron scattering and of high-field magnetization data at very low temperature in the frustrated pyrochlore system Tb 2 Ti 2 O 7. This material has antiferromagnetic exchange interactions, and it is expected to have an Ising character at low temperature. Contrary to expectations, it shows no magnetic ordering down to 0.05 K, being thus labeled a "spin liquid." However, the ground state in Tb 2 Ti 2 O 7 is not a mere fluctuating moment paramagnet but, as demonstrated by very recent experiments, a state where the electronic degrees of freedom are hybridized with the phononic variables in an unconventional way. We show here that, by approximating this complex and still unraveled electron-phonon interaction by a dynamic Jahn-Teller coupling, one can account rather well for the diffuse neutron scattering and the low-temperature isothermal magnetization.

Mesoscopic correlations inTb2Ti2O7spin liquid

“…The magnetoelastic coupling also induces original properties in the pyrochlore family, such as giant magnetostriction 20,21 and very low thermal conductivity 22 . All these features suggest that the Tb 2 Ti 2 O 7 ground state is determined by an interaction between quadrupolar moments, for which a dynamical Jahn-Teller distortion could be the first (mean-field) approximation 17,23,24 .In Tb 2 Ti 2 O 7 an exotic transition has been observed around 0.4 K, as shown initially by anomalies of the specific heat 25 . Below this temperature, spin fluctuations coexist with static spin correlations and spin glass-like irreversibilities 26,27 .…”

“…The magnetoelastic coupling also induces original properties in the pyrochlore family, such as giant magnetostriction 20,21 and very low thermal conductivity 22 . All these features suggest that the Tb 2 Ti 2 O 7 ground state is determined by an interaction between quadrupolar moments, for which a dynamical Jahn-Teller distortion could be the first (mean-field) approximation 17,23,24 .…”

Incipient Ferromagnetism inTb2Ge2O7: Application of Chemical Pressure to the Enigmatic Spin-L

“…Another theoretical construct that attempts to account for the lack of static order in Tb 2 Ti 2 O 7 is a quantum spin ice state [11][12][13][14][15]. A third proposed scenario is that the non-Kramers doublet ground state of Tb 2 Ti 2 O 7 is split into two non-magnetic singlets through a symmetry reducing structural distortion [16][17][18].Other studies sought to uncover the origin of the spin liquid state in Tb 2 Ti 2 O 7 by focusing on mechanisms of its destruction, such as: external pressure [19], magnetic fields [18,20,21], and a combination of the two [22]. Partial antiferromagnetic order is induced in Tb 2 Ti 2 O 7 with external hydrostatic pressures of 8.6 GPa, resulting in a 1% compression of the lattice [19].…”

“…Another theoretical construct that attempts to account for the lack of static order in Tb 2 Ti 2 O 7 is a quantum spin ice state [11][12][13][14][15]. A third proposed scenario is that the non-Kramers doublet ground state of Tb 2 Ti 2 O 7 is split into two non-magnetic singlets through a symmetry reducing structural distortion [16][17][18].…”

Spin dynamics in highly frustrated pyrochlore magnets

“…A model based on the most simple on-site quadrupolar term has been proposed, phenomenologically connected with a possible tetragonal distortion precursor to a T 0 Jahn-Teller transition [53,61,[70][71][72][75][76][77]. Despite being rather successful in explaining a number of experimental results [61,[71][72][73][74], this model is however incomplete as it predicts a CEF singlet state on each site, a feature which is not compatible with the existence of elastic correlations.…”