Solitons in the one-dimensional antiferromagnet TMMC

It is shown that magnetic solitons are expected to occur when a magnetic field is applied to a planar antiferromagnetic chain. Neutron inelastic scattering measurements have been performed at low energy on the one dimensional antiferromagnetic compound TMMC. A new fluctuation is observed, around q = π and ω = 0 which is well interpreted in terms of magnetic solitons.     

Energy gaps in the spin-wave dispersion of the linear antiferromagnet TMMC

By means of neutron scattering, we have measured magnetic excitations in the linear-chain antiferromagnet TMMC at T =1.8 K. An energy gap is observed at q=0 associated with zz-spin correlations, thus giving direct evidence for the importance of the dipolar xy anisotropy for the spin dynamics at low temperatures. A finite magnetic field applied perpendicular to the chains creates a second q=0 gap. There are substantial discrepancies between field dependence of the spin-wave dispersion and the predictions of linear spin-wave theory.     

Anomalous shift of EPR field in the one-dimensional magnet TMMC

An anomalous angular variation of the paramagnetic resonance field is observed in the one-dimensional magnet TMMC at room temperature. The extremely large shift at 9.45 GHz cannot be explained by the static dipolar field and strongly suggests the dynamic effect.     

The specific heat of CeAl2 between 0.02 and 1 K

We report specific heat measurements on a CeAl₂ single crystal between 0.02 and 1 K. Above 0.08 K, we found C₀ = γT + βT³ with γ = (130±0.5) mJ/K²mole and β = (142±1) mJ/K⁴mole in good agreement with previous results above 0.3 K. Below 0.08 K, an excess specific heat C_N = αT^?2 with α = (6.4±1) mJK/mole was detected and interpreted in terms of hyperfine splitting of the Al²⁷ nuclear states. Our results suggest that in CeAl₂ (complex) antiferromagnetism coexists with the Kondo effect at least down to 20 mK.     

Nuclear relaxation at high temperature in the one-dimensional paramagnet TMMC

The dependence of the proton spin-lattice relaxation on the magnitude and on the orientation of the magnetic field has been studied in (CH₃)₄NMnCl₃ at room temperature. The results are interpreted in terms of a one-dimensional spin diffusion process, limited by cut off effects, which are shown to be field dependent.     

Tomonaga-Luttinger liquid in a quasi-one-dimensional S = 1 antiferromagnet observed by specific heat measurements

Specific-heat experiments on single crystals of the S = 1 quasi-one-dimensional bond-alternating antiferromagnet Ni(C9H24N4)(NO2)ClO2 (NTENP) have been performed in magnetic fields applied both parallel and perpendicular to the spin chains. We have found for the parallel field configuration that the magnetic specific heat (C(mag)) is proportional to temperature (T) above a critical field H(c), at which the energy gap vanishes, in a temperature region above that of the long-range ordered state. The ratio C(mag)/T increases as the magnetic field approaches H(c) from above. The data are in good quantitative agreement with the prediction of the c= 1 conformal field theory in conjunction with the velocity of the excitations calculated by a numerical diagonalization, providing conclusive evidence for a Tomonaga-Luttinger liquid.     

Magnetic properties of the S = 1/2 one-dimensional antiferromagnet MgVO

The magnetic susceptibility and the electron spin resonance in the X-band of the transition metal oxide compound MgVO₃ are reported. We show that this compound, made of weakly coupled infinite chains of VO₅ pyramids, behaves as a S =1/2 one-dimensional Heisenberg antiferromagnet. From the ESR and magnetic experiments we deduce the Néel temperature K, the in-chain coupling constant K and the g-factor values g x = g z =1.972(2), g y =1.946(1) for V⁴⁺ ions in MgVO₃. Received 14 July 1999     

Low temperature specific heat of the one-dimensional Heisenberg antiferromagnet α-bis-(N-Methylsalicylaldiminato) — Copper (II) [α-CuNSal]

Measurement of the specific heat of α-bis-(N-Methyl-Salicylaldiminato) - copper (II) (α-CuNSal) over the temperature range 0.07–3.5 K in applied magnetic fields of 0, 10, and 18 kOe is foundto be consistent with that of a one-dimensional spin-$\text{1}\text{2}$ Heisenberg antiferromagnet. Below 0.2 K, deviations from theory are interpreted as probably associated with the onset of three dimensional magnetic ordering.     

The electronic specific heat of a one-dimensional crystal with a sinusoidal potential

Summary The electronic specific heat of a one-dimensional crystal with a sinusoidal potential is examined in the second quantized formulation. Two electrons per lattice site are assumed to be under the influence of the potential; electron-electron interactions via Coulomb repulsion are ignored. The Green’s function equation-of-motion technique is utilized to obtain an exact expression for the specific heat forK, the allowed linear momenta, restricted to two Brillouin ones. The specific heat shows metal, semiconductor-to-metal, or insulator-to-metal behavior as a function of temperature, dependent upon the well depth of the sinusoidal potential.

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Riassunto Sie esamina il calore specifico elettronico di un cristallo unidimensionale con un potenziale sinusoidale nella seconda formulazione quantizzata. Si assume che due elettroni per loco del reticolo cristallino siano sotto l’influenza del potenziale; si ignorano le interazioni elettrone-elettrone mediante repulsione di Coulomb. Si utilizza la tecnica dell’equazione di moto della funzione di Green per ottenere un’espressione esatta per il calore specifico perK, gli impulsi lineari permessi, ristretta a due zone di Brillouin. Il calore specifico mostra un comportamento tipo metallo, da semiconduttore a metallo, o da isolante a metallo in funzione della temperatura, in dipendenza dalla profondità del pozzo del potenziale sinusoidale.

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Резюме Используя метод вторичного квантования, исследуется электронная удельная теплоемкость одномерного кристалла с синусоидальным потенциалом. Предполагается, что в узле решетки имеются два электрона: электрон-электронными взаимодействиями пренебрегают. Используется уравнение функции Грина для получения точного выражения для удельной теплоемкости дляK, принимая во внимание импульсы, ограниченные двумя зонами Бриллюэна. Удельная теплоемкость обнатуживает различные свойства в зависимости от температуры и глубины ямы синусоидального потенциала.

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To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Quantum-statistical mechanics of non-linear excitations in the one-dimensional antiferromagnet

We study the quantum-statistical mechanics, at low temperatures, of a one-dimensional antiferromagnetic Heisenberg model with two anisotropies. In the weak-coupling limit, the temperature dependences of the soliton energy, and the soliton density are determined. At temperaturesT<m ₁ c (wherem ₁ c is the energy of the lowest energy magnon) the soliton density agrees with the classical statistical-mechanics results if the soliton energy in the classical theory is replaced by the renormalized one of the present theory.     

Crystal field analysis of the one-dimensional antiferromagnet CsCoCl3

In the past quadrupole splitting data for⁵⁷Fe doped CsCoCl₃ has been fitted to a model with crystal fields and spin-orbit coupling for T>T _N1. However there is poor agreement with data below T _N1. In this paper the results of attempting to refit the data over all temperatures, and the effects of the orbit lattice interaction are reported.     

A simple model for the enhancement of the low temperature heat capacity of vitreous silica above 1 K

It is suggested that a simple modification to the Debye model can be made by using a “suitably averaged” sound velocity for vitreous systems, which results in an enhancement of the Debye heat capacity, as seen in experiments.     

Residual entropy of the one-dimensional Ising antiferromagnet with general spin

We have calculated the ground-state degeneracy and the concominant residual entropy of the one-dimensional Ising antiferromagnet in a critical magnetic field. We demonstrate that the results obtained can be related to the ground-state properties of the q-state Potts antiferromagnet in the corresponding external field.     

The specific heat of Sm metal between 0.45 and 6 K

The heat capacity of an isotopically enriched (98.3%) ₆₂¹⁵²Sm metal specimen has been measured. Because the nuclear contribution to C_p is absent in an even-even isotope, the electronic specific heat, C_E = 13.5 T mJ/mole·K², could be determined with higher accuracy (± 2%) than before.     

Effect of the magnetic field on the 3d ordering and on the spin correlations of the linear antiferromagnet TMMC

The effect of an external magnetic field in the range 6–47 kOe on the low temperature proton spin-lattice relaxation rate in TMMC has been investigated. A peak in T₁^?1 at the 3d ordering temperature has been detected. Values of T_N for fields up to 47 kOe have been determined.     

Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb₄As₃ have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT ² with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K² is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m ₀ and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.     

Thermal transport in the one-dimensional spin-1/2 anisotropic antiferromagnet in a staggered magnetic field

We study the thermal transport in the one-dimensional spin-1/2 Heisenberg antiferromagnet in a staggered magnetic field. The thermal conductivity was calculated using bosonization and the Kubo linear response formalism in order to determine the thermal Drude weight D_th(T).