Thermodynamics of the coupled spin-dimer system close to a quantum phase transition

Abstract

We present thermal expansion α, magnetostriction and specific heat C measurements of TlCuCl3, which shows a quantum phase transition from a spin-gap phase to a Néel-ordered ground state as a function of magnetic field around HC0 ≃ 4.8 T. Using Ehrenfest's relation, we find huge pressure dependencies of the spin gap for uniaxial as well as for hydrostatic pressure. For T → 0 and H ≃ HC0 we observe a diverging Grüneisen parameter Γ(T ) = α/C, in qualitative agreement with theoretical predictions. However, the predicted individual temperature dependencies α(T ) and C(T ) are not reproduced by our experimental data.

Ferroelectric order versus metallicity in Sr1−xCaxTiO3−δ ( x<

“…2) up to at least n = 0.72 × 10 19 cm −3 , i.e., the transition remains present in metallic samples which finally become superconducting at lower temperature 30 . On further increasing n, however, the α/T anomalies do not vanish and, in particular, our data do not give any indication for a sign change of the α/T anomalies as a function of n. Thus, the general behavior of α and the corresponding Grüneisen ratio Γ = α/c p is different from other materials showing quantum phase transitions as a function of magnetic field, pressure, or n as external control parameter [39][40][41][42][43][44][45][46][47] . On the one hand, this could mean the absence of a quantum phase transition, if the ferroelectriclike order changes just continuously disappears towards larger n. On the other hand, however, it is also clear from Figs.…”

“…However, characteristic features of the ferroelectric order in Sr 1−x Ca x TiO 3 are still observed upon weak charge-carrier doping suggesting a ferroelectriclike transition that vanishes via a quantum phase transition as indicated by minima in the resitivity data ρ(T, n) 30 . The aim of the present study was to further clarify this issue via thermal-expansion measurements, which are a sensitive thermodynamic probe to detect and characterize pressure-dependent quantum phase transitions 36,37,[39][40][41][42][43][44][45][46][47] . The existence of a welldefined ferroelectriclike transition in the metallic samples is clearly confirmed by the pronounced α/T anomalies (see Fig.…”

Spin-12XXZChain SystemCs2CoCl4in a Tra

“…The sign change of seen in Fig. 3(b) is related to the accumulation of entropy near the critical field and is, in fact, characteristic for quantum criticality [19,22,23].…”

Critical elasticity at zero and finite temperature

“…Moreover, Γ also changes sign close to a quantum critical point, and the sign changes reveal the locations of entropy acummulation [3]. Measurements of Γ [4,5,6,7] and its magnetic counterpart, the magnetocaloric effect [8,9,10,11,12,13], have proven useful in the investigation of various quantum critical systems, see Refs. [14,15,16] for reviews.…”