Thermodynamic quantum critical behavior of the Kondo necklace model

Reyes, Daniel; Continentino, M. A.

doi:10.1103/physrevb.76.075114

Cited by 26 publications

(29 citation statements)

References 26 publications

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“…While the ground state properties of this model have been investigated rather extensively by a variety of methods [4][5][6][7][8][9][10][11][12][13][14], the thermodynamic and finite temperature critical properties, close to a magnetic instability, remain an open issue. It was observed by us, and it was our first motivation for studying the quantum critical properties of this model, as a function of the distance to the QCP jgj, at zero and low temperatures [1,15]. Now we extend this treatment introducing a finite inter-site anisotropy d in the y-spin operator component such that, 0pdp1 since the d ¼ 1 case is appropriate to describe compounds where the ordered magnetic phase has a strong Ising component.…”

Section: Introductionmentioning

confidence: 93%

“…Thereby, the transverse excitation modes coincide o k ¼ o 0 k , which corresponds to the isotropic Kondo lattice model [1].…”

Section: Introductionmentioning

confidence: 99%

“…Quantum phase transitions (QPTs) from an antiferromagnetic (AF) ordered state to a nonmagnetic Fermi liquid (FL) in heavy fermion (HF) systems have received considerable attention from both theoretical [1] and experimental points of view [2]. In contrast to classical phase transitions (CPT), driven by temperature, QPT can be driven by tuning an independent-temperature control parameter (magnetic field, external pressure, or doping).…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic quantum critical behavior of the anisotropic Kondo necklace model

Reyes¹,

Continentino²,

Wang³

2009

Journal of Magnetism and Magnetic Materials

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a b s t r a c tThe Ising-like anisotropy parameter d in the Kondo necklace model is analyzed using the bond-operator method at zero and finite temperatures for arbitrary d dimensions. A decoupling scheme on the double time Green's functions is used to find the dispersion relation for the excitations of the system. At zero temperature and in the paramagnetic side of the phase diagram, we determine the spin gap exponent nz % 0:5 in three dimensions and anisotropy between 0pdp1, a result consistent with the dynamic exponent z ¼ 1 for the Gaussian character of the bond-operator treatment. On the other hand, in the antiferromagnetic phase at low but finite temperatures, the line of Neel transitions is calculated for d51. For d42 it is only re-normalized by the anisotropy parameter and varies with the distance to the quantum critical point (QCP) jgj as, T N / jgj c where the shift exponent c ¼ 1=ðd À 1Þ. Nevertheless, in two dimensions, a long-range magnetic order occurs only at T ¼ 0 for any d51. In the paramagnetic phase, we also find a power law temperature dependence on the specific heat at the quantum critical trajectory J=t ¼ ðJ=tÞ c , T ! 0. It behaves as C V / T d for dp1 and % 1, in concordance with the scaling theory for z ¼ 1.

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Section: Introductionmentioning

confidence: 93%

“…Thereby, the transverse excitation modes coincide o k ¼ o 0 k , which corresponds to the isotropic Kondo lattice model [1].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermodynamic quantum critical behavior of the anisotropic Kondo necklace model

Reyes¹,

Continentino²,

Wang³

2009

Journal of Magnetism and Magnetic Materials

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“…B 76 (2007) 075114. [1]]. Here we extend the treatment to finite fields using a generalized bond operator representation for the localized and conduction electrons spins.…”

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confidence: 99%

Field induced magnetic quantum critical behavior in the Kondo necklace model

Reyes¹,

Continentino²

2008

Journal of Magnetism and Magnetic Materials

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“…For fixed field H or temperature T , the thermodynamic quantities can be obtained from the internal energy U . This is given by 22,23 :…”

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confidence: 99%

Bose-Einstein condensation in antiferromagnets close to the saturation field

2008

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At zero temperature and strong applied magnetic fields the ground sate of an anisotropic antiferromagnet is a saturated paramagnet with fully aligned spins. We study the quantum phase transition as the field is reduced below an upper critical Hc2 and the system enters a XY-antiferromagnetic phase. Using a bond operator representation we consider a model spin-1 Heisenberg antiferromagnetic with single-ion anisotropy in hyper-cubic lattices under strong magnetic fields. We show that the transition at Hc2 can be interpreted as a Bose-Einstein condensation (BEC) of magnons. The theoretical results are used to analyze our magnetization versus field data in the organic compound N iCl2-4SC(N H2)2 (DTN) at very low temperatures. This is the ideal BEC system to study this transition since Hc2 is sufficiently low to be reached with static magnetic fields (as opposed to pulsed fields). The scaling of the magnetization as a function of field and temperature close to Hc2 shows excellent agreement with the theoretical predictions. It allows to obtain the quantum critical exponents and confirm the BEC nature of the transition at Hc2. The organic compound N iCl 2 -4SC(N H 2 ) 2 (DTN) undergoes a field induced non-magnetic to XYantiferromagnetic transition 1,2 . This transition can be viewed as a Bose-Einstein condensation of magnons associated with the Ni spin 1 degrees of freedom. Other magnetic systems with a singlet ground state either with spin-1 Ni atoms or spin-1/2 dimers have also been shown to exhibit this transition 3,4,5 . At zero temperature it is driven by the magnetic field H that reduces the Zeeman energy of the S z = 1 state until it becomes degenerate with that of the product state of S z i = 0. At this point, H = H c1 , the antiferromagnetic (AF) interactions give rise to a long range ordered phase. Experimentally, the magnetization M at very low temperatures starts to increase above the critical magnetic field H c1 and eventually saturates above a critical magnetic field H c2 1, 2,6,7,8,9 . The transition at H c1 has been intensively investigated, both theoretically 12,13 and experimentally 1,2,6,7,8,9 , while the one at H c2 is much less studied. The DTN is the ideal BEC system to investigate the latter transition since detailed magnetization curves can be obtained close to the critical field H c2 = 12.3T. In other well known BEC systems, as BaCuSi 2 O 6 10 and T lCuCl 3 11 , the critical fields H c2 are 49T and 83T, respectively, and presently can only be reached using pulsed fields. The excellent quality of the magnetization versus field curves obtained in DTN using standard superconducting coils is essential for the scaling analysis presented here.In this paper we study the transition at H c2 . A theoretical approach is more directly developed, starting from the saturated paramagnetic (PARA) phase. We consider decreasing the external magnetic field at T = 0 to the critical value H c2 where the transverse components of the magnetization condense. A scaling approach for this transition has recently been prop...

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Thermodynamic quantum critical behavior of the Kondo necklace model

Cited by 26 publications

References 26 publications

Thermodynamic quantum critical behavior of the anisotropic Kondo necklace model

Thermodynamic quantum critical behavior of the anisotropic Kondo necklace model

Field induced magnetic quantum critical behavior in the Kondo necklace model

Bose-Einstein condensation in antiferromagnets close to the saturation field

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