Band-structure and anomalous contributions to the Hall effect of YbRh2Si2

Friedemann, Sven; Oeschler, N.; Krellner, C.; Geibel, C.; Wirth, S.; Steglich, F.; Paschen, S.; MaQuilon, S.; Fisk, Z.

doi:10.1016/j.physb.2007.10.118

Cited by 12 publications

(10 citation statements)

References 10 publications

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“…Remarkably, in both thermopower and Hall effect isotherms the values in the magnetically ordered ground state of YbRh 2 Si 2 (with localized 4 f states in the presence of a small Fermi surface) approach the corresponding values of the non-magnetic reference compound LuRh 2 Si 2 . 25,26) In the latter, no 4 f states contribute to the (small) Fermi surface either.…”

Section: Sa002-2mentioning

confidence: 98%

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: Sa002-2mentioning

confidence: 98%

Break Up of Heavy Fermions at an Antiferromagnetic Instability

et al. 2011

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“…Consequently, these measurements indicate a reconstruction of the Fermi surface at the QCP. However, this Hall effect study was discussed controversially particularly in view of sample dependences in the low temperature Hall coefficient [12]: The Hall coefficient is extremely sensitive to small changes in the relative scattering rates of the two dominating bands which almost compensate each other [13]. These changes in the scattering rates seem to originate from tiny variations in the chemical composition as they only affect samples from different batches.…”

Section: Introductionmentioning

confidence: 99%

Discontinuous Hall coefficient at the quantum critical point in YbRh₂Si₂

Friedemann

Oeschler

Wirth

et al. 2011

J. Phys.: Condens. Matter

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Abstract. YbRh 2 Si 2 is a model system for quantum criticality. Particularly, Hall effect measurements helped identify the unconventional nature of its quantum critical point. Here, we present a high-resolution study of the Hall effect and magnetoresistivity on samples of different quality. We find a robust crossover on top of a sample dependent linear background contribution. Our detailed analysis provides a complete characterization of the crossover in terms of its position, width, and height. Importantly, we find in the extrapolation to zero temperature a discontinuity of the Hall coefficient occurring at the quantum critical point for all samples. Particularly, the height of the jump in the Hall coefficient remains finite in the limit of zero temperature. Hence, our data solidify the conclusion of a collapsing Fermi surface. Finally, we contrast our results to the smooth Halleffect evolution seen in Chromium, the prototype system for a spin-density-wave quantum critical point.

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“…Moreover, the Hall crossover has alternatively been interpreted in terms of a background contribution in the non-magnetic heavy-fermion phase through either minute valence variations [15] or Zeeman splitting of the bands [16,17], leaving the nature of the quantum critical single-electron excitations uncertain. In addition, the observation of sample dependences in the lowtemperature Hall coefficient raises the important question of how these affect the Hall crossover [18]. To resolve these fundamental issues, we carry out comprehensive, in-depth Halleffect measurements over a wide range of the control parameter, the magnetic field, down to very low temperatures.…”

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Fermi-surface collapse and dynamical scaling near a quantum-critical point

Friedemann

Oeschler

Wirth

et al. 2010

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

149

136

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Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh 2 Si 2 , a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E∕T , scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic manybody excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finitetemperature behavior in a broad range of strongly correlated quantum systems.YbRh2Si2 | Kondo effect | magnetotransport | antiferromagnetism | local quantum criticality Q uantum criticality epitomizes the richness of quantum effects in macroscopic settings (1). The traditional description is based on the framework of Ginzburg and Landau (2), which focuses on the notion of an order parameter, a classical variable. The order parameter delineates the symmetry breaking of the macroscopic phases, while its fluctuations at ever-increasing length and time scales characterize the approach toward a second-order quantum phase transition. For metallic antiferromagnets, this theory appears in the form of a spin-density-wave quantum-critical point (QCP) (3, 4). Here, the macroscopic fluctuations of the order parameter are described by a Gaussian theory at the fixed point, with a vanishing effective coupling among the collective modes in the zero-temperature (T ¼ 0), zero-energy (E ¼ 0) and infinite-length limit. Consequently (5), the collective fluctuations will violate E∕T scaling.By contrast, an unconventional class of quantum criticality, emerging from studies in recent years (1), incorporates not only the slow fluctuations of the order parameter, but also some inherent quantum modes. For heavy-fermion metals, the additional quantum modes are associated with a critical breakdown of the Kondo screening effect and the concomitant single-electron Kondo resonance excitations (6-8). These additional critical modes can lead to a critical field theory that is interacting, instead of Gaussian, and the collective fluc...

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Band-structure and anomalous contributions to the Hall effect of YbRh2Si2

Cited by 12 publications

References 10 publications

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Discontinuous Hall coefficient at the quantum critical point in YbRh₂Si₂

Fermi-surface collapse and dynamical scaling near a quantum-critical point

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Band-structure and anomalous contributions to the Hall effect of YbRh2Si2

Cited by 12 publications

References 10 publications

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Break Up of Heavy Fermions at an Antiferromagnetic Instability

Discontinuous Hall coefficient at the quantum critical point in YbRh2Si2

Fermi-surface collapse and dynamical scaling near a quantum-critical point

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Product

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Discontinuous Hall coefficient at the quantum critical point in YbRh₂Si₂