Discontinuous Hall coefficient at the quantum critical point in YbRh<sub>2</sub>Si<sub>2</sub>

Friedemann, Sven; Oeschler, N.; Wirth, S.; Krellner, C.; Geibel, C.; Steglich, F.; Paschen, S.; Kirchner, Stefan; Si, Qimiao

doi:10.1088/0953-8984/23/9/094216

Cited by 15 publications

(34 citation statements)

References 31 publications

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“…20) In fact, the considered single crystals which span the hole range of sample dependences 21) show that the crossover persists in its extrapolation to zero temperature. 22) The change from a positive to a negative value of R H observed in this nearly compensated metal at T = 20 mK was shown to be consistent with results from (renormalized) band structure calculations. 21) As the temperature is lowered, the crossover shifts to lower fields as illustrated in the phase diagram in the inset of Fig.…”

Section: Sa002-2supporting

confidence: 81%

“…On the one hand, the vanishing width of the Hall crossover at zero temperature implies a discontinuity of the Hall coefficient and, hence, a discontinuous evolution of the Fermi surface at the QCP. 22) Such a Fermi surface reconstruction is incompatible with the smooth crossover predicted for an SDW QCP. Rather, the Fermi surface reconstruction points towards a disintegration of the quasiparticles due to the breakdown of the Kondo effect.…”

Section: Sa002-2mentioning

confidence: 91%

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Break Up of Heavy Fermions at an Antiferromagnetic Instability

et al. 2011

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We present results of high-resolution, low-temperature measurements of the Hall coefficient, thermopower, and specific heat on stoichiometric YbRh 2 Si 2 . They support earlier conclusions of an electronic (Kondo-breakdown) quantum critical point concurring with a field induced antiferromagnetic one. We also discuss the detachment of the two instabilities under chemical pressure. Volume compression/expansion (via substituting Rh by Co/Ir) results in a stabilization/weakening of magnetic order. Moderate Ir substitution leads to a non-Fermi-liquid phase, in which the magnetic moments are neither ordered nor screened by the Kondo effect. The so-derived zero-temperature global phase diagram promises future studies to explore the nature of the Kondo breakdown quantum critical point without any interfering magnetism.KEYWORDS: quantum criticality, heavy fermion, YbRh 2 Si 2 , Kondo breakdown Different types of quantum critical pointsQuantum phase transitions in matter arise due to competing interactions, which result in competing ground-state properties. When a quantum phase transition is continuous it marks a quantum critical point (QCP). In the last decade, antiferromagnetic (AF) heavy-fermion metals turned out to be model systems to study quantum criticality. In these systems, QCPs are caused by the competition between the local Kondo and the non-local Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction. Studies on the interplay between these two phenomena have revealed different types of QCPs.1) In the itinerant, spin-density-wave (SDW) scenario the heavy fermions keep their integrity at the QCP. In such a case the QCP can be treated as a continuous classical phase transition in an effective dimension d + z, where d is the spatial dimensionality and z, the dynamic exponent defined via ξ t ∼ ξ z r , describes the number of additional spatial dimensions that the time dimension corresponds to. ξ r and ξ t denote the correlation length and correlation time which both diverge at a QCP.2-4) Several heavy-fermion compounds, e. g., CeCu 2 Si 2 , 5) CeNi 2 Ge 2 6) and Ce 1−x La x Ru 2 Si 2 7) were found to exhibit this type of itinerant AF QCP.However, in a few heavy-fermion metals the AF instability appears to be accompanied by a breakdown of the Kondo effect, [8][9][10] 15)The two FL phases adjacent to the QCP appear to posses different Fermi surfaces as inferred from a variety of electronic transport measurements closely related to the Fermi surface properties. Most important evidence stems from Hall effect measurements in the so called crossed-field geometry. Here, two perpendicular magnets are used to disentangle the two tasks of the magnetic field: One field, B 1 , generates the Hall response, and a second field, B 2 , tunes the ground state of the sample. The power of the crossed-field setup lies in the ability to extract the initial-slope Hall coefficient as a linear response to B 1 despite measuring at a finite tuning field B 2 .Isotherms of the field dependent Hall coefficient R H (B 2 ) depicted in Fig. 1(a) show...

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Section: Sa002-2supporting

confidence: 81%

Section: Sa002-2mentioning

confidence: 91%

Break Up of Heavy Fermions at an Antiferromagnetic Instability

et al. 2011

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“…In Fig. 2, we compare our results with the data for sample #1 of Friedemann et al 24 Here, assuming an analytic dependence of the impurity scattering rate on the magnetic field, we approximated the magnetic field dependence of the background resistivity by ρ(0, H)) = c 1 + c 2 H 2 , assuming an analytic dependence of the impurity scattering rate on the magnetic field. The characteristic energy u = h 2 / F , where F ≈ 10K and h is obtained from Eq.…”

Section: -5mentioning

confidence: 85%

Spin-flip scattering of critical quasiparticles and the phase diagram ofYbRh2Si2

Wölfle

Abrahams

2015

Phys. Rev. B

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Several observed transport and thermodynamic properties of the heavy-fermion compound YbRh2Si2 in the quantum critical regime are unusual and suggest that the fermionic quasiparticles are critical, characterized by a scale-dependent diverging effective mass. A theory based on the concept of critical quasiparticles scattering off antiferromagnetic spin fluctuations in a strongcoupling regime has been shown to successfully explain the unusual existing data and to predict a number of so far unobserved properties. In this paper, we point out a new feature of a magnetic field-tuned quantum critical point of a heavy-fermion metal: anomalies in the transport and thermodynamic properties caused by the freezing out of spin-flip scattering of critical quasiparticles and the scattering off collective spin excitations. We show that a step-like behavior as a function of magnetic field of e.g. the Hall coefficient and magnetoresistivity results, which accounts quantitatively for the observed behavior of these quantities. That behavior has been described as a crossover line T * (H) in the T − H phase diagram of YbRh2Si2. Whereas some authors have interpreted this observation as signaling the breakdown of Kondo screening and an associated abrupt change of the Fermi surface, our results suggest that the T * line may be quantitatively understood within the picture of robust critical quasiparticles.

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“…1). In addition to these phase boundaries and crossover lines, Hall effect and other measurements in YRS (9)(10)(11) show anomalies at a temperature T Ã ðHÞ in the critical region. The origin of the T Ã ðHÞ line is not clear at present.…”

mentioning

confidence: 75%

Critical quasiparticle theory applied to heavy fermion metals near an antiferromagnetic quantum phase transition

Abrahams

Wölfle²

2012

Proc. Natl. Acad. Sci. U.S.A.

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We use the recently developed critical quasiparticle theory to derive the scaling behavior associated with a quantum critical point in a correlated metal. This is applied to the magnetic-field induced quantum critical point observed in YbRh 2 Si 2 , for which we also derive the critical behavior of the specific heat, resistivity, thermopower, magnetization and susceptibility, the Grüneisen coefficient, and the thermal expansion coefficient. The theory accounts very well for the available experimental results.dynamical scaling | non-Fermi-liquid properties | spin excitation spectrum | non-Gaussian fluctuations R ecent advances in low-temperature experimental techniques have stimulated much interest in quantum critical phenomena, which comprise phase transitions at zero temperature ("quantum critical point") and associated effects due to quantum fluctuations at very low temperatures. Ref. 1 gives an introductory review of the subject.These developments have generated a variety of difficult theoretical questions; among them is the issue of how to treat the regime of strongly interacting quantum fluctuations. In a recent paper (2), we developed an extension of the quasiparticle concept of Fermi liquid theory to the non-Fermi-liquid regime near a quantum critical point (QCP). In essence, the theory goes beyond the Gaussian regime of critical fluctuations by introducing interactions among the quantum fluctuations into the correlation function of the fluctuations. Central to the analysis is the concept of critical quasiparticles, which is based on the recognition that the single-particle spectral function can display a quasiparticle peak at nonzero excitation energy or temperature. This is expressed as a nonzero quasiparticle weight ZðωÞ for jωj not too small, although, as in a non-Fermi liquid, at the Fermi surface Zðω ¼ 0Þ ¼ 0.We realized the critical quasiparticle theory for the case of an antiferromagnetic quantum critical point and applied it to several quantities, principally resistivity and specific heat, for successful comparison to experimental results on the heavy-fermion metal YbRh 2 Si 2 (YRS), thereby showing that the theory, which describes a physically transparent scenario, is capable of accounting for experimental results on a quantum critical metal.The implementation of the theory for an antiferromagnetic (AFM) quantum critical point for a heavy-fermion compound is based on the recognition that below a "lattice Kondo temperature" T KL , hybridization between conduction (s, p, d) electrons and local magnetic moments (f orbitals) produces a heavyelectron liquid with an associated mass enhancement due to the originally localized character of the f electrons. However, the f electrons are also responsible for the antiferromagnetism in a region of the phase diagram of the material. Near the AFM critical point, critical spin fluctuations are enhanced and interact with the heavy quasiparticles. This produces further mass enhancement and occurs in two stages. Above a certain temperature T x but below T KL , the...

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Discontinuous Hall coefficient at the quantum critical point in YbRh₂Si₂

Cited by 15 publications

References 31 publications

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Spin-flip scattering of critical quasiparticles and the phase diagram ofYbRh2Si2

Critical quasiparticle theory applied to heavy fermion metals near an antiferromagnetic quantum phase transition

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Discontinuous Hall coefficient at the quantum critical point in YbRh2Si2

Cited by 15 publications

References 31 publications

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Spin-flip scattering of critical quasiparticles and the phase diagram ofYbRh2Si2

Critical quasiparticle theory applied to heavy fermion metals near an antiferromagnetic quantum phase transition

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Discontinuous Hall coefficient at the quantum critical point in YbRh₂Si₂