A compensated heat-pulse calorimeter for low temperatures

Wilhelm, H.; Lühmann, Thomas; Rus, Tania; Steglich, F.

doi:10.1063/1.1771486

Cited by 51 publications

(38 citation statements)

References 13 publications

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“…The specific heat was measured with the compensated heat-pulse technique 24 and the data were confirmed by experiments using the dual-slope method 25 on the same sample platform. The precise match between both sets of experimental data is remarkable.…”

Section: Methodsmentioning

confidence: 99%

Low-temperature thermodynamic properties near the field-induced quantum critical point in NiCl2-4SC(NH2)2

Weickert

Küchler²,

Steppke³

et al. 2012

Phys. Rev. B

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We present a comprehensive experimental and theoretical investigation of the thermodynamic properties: specific heat, magnetization, and thermal expansion in the vicinity of the field-induced quantum critical point (QCP) around the lower critical field H c1 ≈ 2 T in NiCl 2 -4SC(NH 2 ) 2 . A T 3/2 behavior in the specific heat and magnetization is observed at very low temperatures at H = H c1 , which is consistent with the universality class of Bose-Einstein condensation of magnons. The temperature dependence of the thermal expansion coefficient at H c1 shows minor deviations from the expected T 1/2 behavior. Our experimental study is complemented by analytical calculations and quantum Monte Carlo simulations, which reproduce nicely the measured quantities. We analyze the thermal and the magnetic Grüneisen parameters, which are ideal quantities to identify QCPs. Both parameters diverge at H c1 with the expected T −1 power law. By using the Ehrenfest relations at the second-order phase transition, we are able to estimate the pressure dependencies of the characteristic temperature and field scales.

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Section: Methodsmentioning

confidence: 99%

Low-temperature thermodynamic properties near the field-induced quantum critical point in NiCl2-4SC(NH2)2

Weickert

Küchler²,

Steppke³

et al. 2012

Phys. Rev. B

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“…The energy resolution, i.e., full width at half maximum (FWHM), therefore amounts to 0.057 meV. Complementary heat capacity measurements were performed by applying a quasiadiabatic heat-pulse method with additional background heating [25]. Figure 1(b) is a plot of C=T vs T in different representative magnetic fields, measured on the same large single crystal (m % 2 g) as used for neutron scattering studies.…”

mentioning

confidence: 99%

Spin Fluctuations in Normal StateCeCu2Si2on Approaching the Quantum Critical Point

Arndt

Stockert

Schmalzl³

et al. 2011

Phys. Rev. Lett.

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We report on the magnetic excitation spectrum in the normal state of the heavy-fermion superconductor CeCu92)Si(2) on approaching the quantum critical point (QCP). The magnetic response in the superconducting state is characterized by a transfer of spectral weight to energies above a spin excitation gap. In the normal state, a slowing-down of the quasielastic magnetic response is observed, which conforms to the scaling expected for a QCP of spin-density-wave type. This interpretation is substantiated by an analysis of specific heat data and the momentum dependence of the magnetic excitation spectrum. Our study represents the first direct observation of an almost critical slowing-down of the normal state magnetic response at a QCP when suppressing superconductivity. The results strongly imply that the coupling of Cooper pairs in CeCu(2)Si(2) is mediated by overdamped spin fluctuations.

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“…In this Letter we report on specific heat measurements [9] on single crystals of Cs 2 CuCl 4 at low temperatures (30 mK < T < 6 K) and high magnetic fields (B < 12 T) applied along the crystallographic a-axis. The aim of this thermodynamic study was (i) to trace the field dependence of T c (B) near B c , i.e., to extract the power law according to eq.…”

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confidence: 99%

Bose-Einstein Condensation of Magnons inCs2CuCl4

et al. 2005

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We report on results of specific heat measurements on single crystals of the frustrated quasi-2D spin-1/2 antiferromagnet Cs2CuCl4 (TN = 0.595 K) in external magnetic fields B < 12 T and for temperatures T > 30 mK. Decreasing B from high fields leads to the closure of the field-induced gap in the magnon spectrum at a critical field Bc ≃ 8.51 T and a magnetic phase transition is clearly seen below Bc. In the vicinity to Bc, the phase transition boundary is well described by the power-law Tc(B) ∝ (Bc − B)1/φ with the measured critical exponent φ ≃ 1.5. These findings are interpreted as a Bose-Einstein condensation of magnons.PACS numbers: 75.30.Kz,75.45.+j,03.75.Nt In a quantum antiferromagnet (AFM) a fully spinpolarized state can be reached at high magnetic field B exceeding a saturation field B c . In this state, spin excitations are gapped ferromagnetic magnons. With decreasing B and passing through B c , an antiferromagnetic long-range order of the transverse spin component develops. Provided the symmetry of the spin Hamiltonian is such that the rotational invariance around the applied field is preserved, the transverse spin component ordering can be regarded as a Bose-Einstein condensation (BEC) in a dilute gas of magnons. This concept was formulated theoretically many years ago [1, 2]. For most of the known AFMs, B c can be well above 100 T. An exceptionally low and easily accessible saturation field of B c ≈ 8.5 T, however, is needed in the quantum spin-1/2 AFM Cs 2 CuCl 4 . In this system the dominant exchange spin coupling J is rather weak, J = 4.34(6) K [3]. The other isotropic spin coupling constants and the anisotropic Dzyaloshinsky-Moriya (DM) interaction are smaller and were determined with high accuracy by neutron experiments [4]. Thus, the spin Hamiltonian involves the isotropic exchange H 0 , the DM anisotropic term H DM and the Zeeman energy H B and is given byCs 2 CuCl 4 falls into the class of easy-plane AFMs with U (1)-rotational invariance around the crystallographic aaxis. Thus, for B applied along the a-axis, the U (1) symmetry can be broken spontaneously due to the transverse spin component ordering at T c . This is accompanied by the appearance of a Goldstone mode with linear dispersion, which is interpreted as signature of a magnon BEC [4]. However, an unambiguous evidence for a BEC description of the field-induced phase transition would be the determination of the critical exponent φ in the field dependence of the critical temperatureTheory for a 3D Bose gas predicts a universal value φ BEC = 3/2 [5], which coincides with the result of a mean-field treatment [6].A magnon BEC in TlCuCl 3 was recently reported [6,7]. In this quantum AFM with a dimerized spinliquid ground state, the saturation field is rather high, B c,2 ≈ 60 T, and the BEC transition was studied near the first critical field, B c,1 ≃ 5.6 T. At B = B c,1 , the singlet-triplet excitation gap is expected to close and a BEC occurs for B > B c,1 [6]. However, a few experimental findings show deviations from a pure magnon BE...

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A compensated heat-pulse calorimeter for low temperatures

Cited by 51 publications

References 13 publications

Low-temperature thermodynamic properties near the field-induced quantum critical point in NiCl2-4SC(NH2)2

Low-temperature thermodynamic properties near the field-induced quantum critical point in NiCl2-4SC(NH2)2

Spin Fluctuations in Normal StateCeCu2Si2on Approaching the Quantum Critical Point

Bose-Einstein Condensation of Magnons inCs2CuCl4

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