Pressure-induced magnetically ordered Kondo lattice state in

Alami-Yadri, K.; Wilhelm, H.; Jaccard, D.

doi:10.1007/s100510050520

Cited by 38 publications

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“…In contrast to the Ce-based HF systems, T max of YbIr 2 Si 2 monotonically decreases with increasing pressure (dT max /dp = −11.3 K/GPa), becoming saturated at p c ≃ 8 GPa above which a magnetic transition appears. Similar features of T max (p) were observed also in YbCu 2 Si 2 [15], but not in YbRh 2 Si 2 [7,9] and YbNi 2 Ge 2 [16]. In the latter two compounds, the resistivity maximum at T max is split into two maxima under pressure, corresponding to the contributions from the Kondo effect and the crystalline-electric-field (CEF) as frequently observed in the Ce-based HF compounds.…”

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“…How these two (magnetic and valence) transitions are interacting with each other remains an interesting question which can not, however, be answered based on the available results. For example, in YbCu 2 Si 2 the magnetic transition appears around 8 GPa, but ρ 0 and A peak at 10 GPa, where the KW relation starts to deviate [15]. On the other hand, in YbIr 2 Si 2 the valence transition appears prior to the magnetic transition.…”

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Quantum phase transition in the heavy-fermion compoundYbIr2Si2

et al. 2006

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We investigate the pressure-temperature phase diagram of YbIr2Si2 by measuring the electrical resistivity ρ(T ). In contrast to the widely investigated YbRh2Si2, YbIr2Si2 is a paramagnetic metal below pc ≃ 8 GPa. Interestingly, a first-order, presumably ferromagnetic, transition develops at pc. Similar magnetic properties were also observed in YbRh2Si2 and YbCu2Si2 at sufficiently high pressures, suggesting a uniform picture for these Yb compounds. The ground state of YbIr2Si2 under pressure can be described by Landau Fermi-liquid (LFL) theory, in agreement with the nearly ferromagnetic Fermi-liquid (NFFL) model. Moreover, evidence of a weak valence transition, characterized by a jump of the Kadowaki-Woods (KW) ratio as well as an enhancement of the residual resistivity ρ0 and of the quasiparticle-quasiparticle scattering cross section, is observed around 6 GPa. The study of quantum critical phenomena has attracted considerable attention because of the fascinating physical properties caused by quantum fluctuations. In the Ce-based heavy fermion (HF) systems, unconventional superconductivity, most likely paired via antiferromagnetic (AFM) spin fluctuations, has been widely observed around a spin-density-wave (SDW) type quantum critical point (QCP) [1]. On the other hand, YbRh 2 Si 2 has been established as a model system to study quantum physics at a "local" QCP [2], around which no superconductivity has yet been observed at T > 10 mK. Recent efforts have been largely concentrated on weakly first-order quantum phase transitions (QPT), e.g., the ferromagnetic (FM) transition in MnSi [3,4], the metamagnetic transition in Sr 3 Ru 2 O 7 [5], and the valence transition inThe HF compound YbRh 2 Si 2 undergoes an AFM transition at T N = 70 mK [7]. A small magnetic field or a slight expansion of the unit cell by substituting Si with Ge can eventually suppress the AFM order at a QCP [2,8], at which the conventional LFL theory breaks down (see the inset of Fig. 1). As tuning away from the QCP, LFL behavior immediately recovers at the lowest temperature. On the other hand, the weak AFM transition in YbRh 2 Si 2 is stabilized by applying pressure [7,9,10]. In particular, the magnetic phase undergoes a first-order transition from a small-moment state (AFM-type) to a large-moment state around 10 GPa [9]. Furthermore, it was argued that in YbRh 2 Si 2 FM quantum critical fluctuations dominate over a wide range in the phase diagram except for the close vicinity of the AFM QCP [11,12]. In order to better understand the nature of the "local" QCP, YbIr 2 Si 2 , a sister compound of YbRh 2 Si 2 , was recently synthesized by Hossain et al. [13]. YbIr 2 Si 2 (I-type) is a moderate HF compound with a paramagnetic ground state at zero pressure and, therefore, was expected to cross a magnetic QCP by applying a small pressure of . A large-moment order, presumably FM-type, develops at a critical pressure pc. The ground-state properties in both the high-p phase and the paramagnetic state can be described by LFL theory. Uniquely, in YbRh2Si2...

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Quantum phase transition in the heavy-fermion compoundYbIr2Si2

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“…In metals with strongly interacting electrons and magnetic order the contributions to ρ 0 are not well understood. So far, a noticeable ρ 0 (p)-dependence has been found in several HF systems either in the magnetic phase (CeCu 5 Au [19] and YbCu 2 Si 2 [10]), close to p c (CeAl 3 [47]) or in the paramagnetic phase (CeCu 2 Ge 2 and CeCu 2 Si 2 [17]). Following the suggestion by Miyake and Maebashi [48] quantum critical fluctuations should give rise to an enhanced impurity potential.…”

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Calorimetric and transport investigations ofCePd2+xGe2−x
Wilhelm
¹
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Jaccard²
2002
Phys. Rev. B
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The influence of pressure on the magnetically ordered CePd2.02Ge1.98 has been investigated by a combined measurement of electrical resistivity, ρ(T ), and ac-calorimetry, C(T ), for temperatures in the range 0.3 K < T < 10 K and pressures, p, up to 22 GPa. Simultaneously CePd2Ge2 has been examined by ρ(T ) down to 40 mK. In CePd2.02Ge1.98 and CePd2Ge2 the magnetic order is suppressed at a critical pressure pc = 11.0 GPa and pc = 13.8 GPa, respectively. In the case of CePd2.02Ge1.98 not only the temperature coefficient of ρ(T ), A, indicates the loss of magnetic order but also the ac-signal 1/Vac ∝ C/T recorded at low temperature. The residual resistivity is extremely pressure sensitive and passes through a maximum and then a minimum in the vicinity of pc. The (T, p) phase diagram and the A(p)-dependence of both compounds can be qualitatively understood in terms of a pressure-tuned competition between magnetic order and the Kondo effect according to the Doniach picture. The temperature-volume (T, V ) phase diagram of CePd2Ge2 combined with that of CePd2Si2 shows that in stoichiometric compounds mainly the change of interatomic distances influences the exchange interaction. It will be argued that in contrast to this the much lower pc-value of CePd2.02Ge1.98 is caused by an enhanced hybridization between 4f and conduction electrons.

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“…Two competing energy scales, the Ruderman-Kittel-Kasuya-Yosida (RKKY) T RKKY ∝ (J N(E F )) 2 and the Kondo energy T K ∝ e −1/J N (E F ) (where J is the spin coupling constant and N(E F ) is the density of states at the Fermi level), give rise to either Kondo, HF, or HF superconducting behavior when T K ≫ T RKKY , or magnetic when T RKKY ≫ T K . [12][13][14][15][16] A crossover from Kondo lattice or HF to an intermediate valence state has been observed in a number of Kondo lattice or HF compounds, such as doped CeCu 2 Si 2 , 17 CePtSi, 18 or under pressure in YbCu 4 Ag, 19 CeCu 6 , 20 and CeBe 13 . 21 In this study, a continuous solid solution (Lu 1−x Yb x ) 3 Rh 4 Ge 13 displays a continuous evolution from superconductivity in a disordered metal close to x = 0 (Ref.…”

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