Spin dynamics of YbRh<sub>2</sub>Si<sub>2</sub>observed by electron spin resonance

Sichelschmidt, J.; Wykhoff, J.; Nidda, H.-A. Krugg von; Ferstl, J.; Geibel, C.; Steglich, F.

doi:10.1088/0953-8984/19/11/116204

Cited by 25 publications

(38 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…8) NMR 10) and ESR 11) signals are also consistent. These non-Fermi-liquid properties are all contradicting the standard theory [2][3][4][5] for the AF QCP and are under extensive debates.…”

mentioning

confidence: 58%

YbRh₂Si₂: Quantum Tricritical Behavior in Itinerant Electron Systems

2008

View full text Add to dashboard Cite

We propose that the proximity of the first-order transition manifested by the quantum tricritical point (QTCP) explains non-Fermi-liquid properties of YbRh 2 Si 2 . Here, at the QTCP, a continuous phase transition changes into first order at zero temperature. The non-Fermi-liquid behaviors of YbRh 2 Si 2 are veiled in several prominent mysteries; diverging ferromagnetic susceptibility at the antiferromagnetic transition and enhancement of magnetization as well as specific heat. These puzzles are solved by an unconventional criticality derived from our spin fluctuation theory for the QTCP; especially, diverging ferromagnetic susceptibility is quantitatively reproduced.KEYWORDS: quantum critical phenomena, quantum tricritical point, YbRh 2 Si 2 , non-Fermi-liquid behavior, selfconsistent renormalization theory DOI: 10.1143/JPSJ.77.093712Critical temperatures of the symmetry-breaking phase transitions can be lowered to zero at the quantum critical point (QCP) by tuning quantum fluctuations such as by magnetic fields, as shown in Fig. 1(a). Quantum critical phenomena in metals have attracted much interest from both theoretical and experimental points of view, not only in their own right but also because of the unconventional superconductivity as well as the non-Fermi-liquid behavior observed near the QCP. 1,2)The conventional spin fluctuation theory of the QCP by Moriya, Hertz, and Millis 2-5) has succeeded in explaining a number of non-Fermi-liquid properties. However, this picture has been challenged by the results of many recent experiments, 1,2,6) where the criticalities of thermodynamic and transport properties do not follow it.A typical heavy-fermion compound YbRh 2 Si 2 1) belongs to such an unconventional category. At the magnetic field H ¼ 0, it exhibits an antiferromagnetic (AF) transition at the Néel temperature T N ¼ 0:07 K. An AF QCP emerges at the critical magnetic field H c $ 0:06 T along the ab plane. 7,8) Near H c , the Sommerfeld coefficient of specific heat is logarithmically increased with lowering temperature T above 0.3 K and even faster below it 9) in contrast to the conventional theory predicting convergence to a constant. Transport and optical data roughly show the resistivity linearly scaled with T and frequency. signals are also consistent. These non-Fermi-liquid properties are all contradicting the standard theory 2-5) for the AF QCP and are under extensive debates. 6)A hint to the origin of the anomalous properties comes from the fact that the first-order transition is observed for YbRh 2 Si 2 under pressure.12) Actually, the proximity to the first-order transition is common in many compounds with unconventional non-Fermi-liquid properties. Our idea is that the proximity to the first-order transition, namely, tricriticality solves the puzzle because the tricriticality necessarily induces a ferromagnetic tendency even at a clear AF transition.At T 6 ¼ 0, the tricritical point (TCP) where phase transitions change from continuous to first order, as shown in Fig. 1(b), has been studied in de...

show abstract

mentioning

confidence: 58%

YbRh₂Si₂: Quantum Tricritical Behavior in Itinerant Electron Systems

2008

View full text Add to dashboard Cite

show abstract

“…NMR 24 and electron spin resonance (ESR) 40 signals also indicate the enhancement of the FM susceptibility near the AFM QCP. In accordance with the diverging enhancement of the FM susceptibility, the magnetization curve has convex magnetic-field dependence.…”

mentioning

confidence: 99%

Spin Fluctuation Theory for Quantum Tricritical Point Arising in Proximity to First-Order Phase Transitions: Applications to Heavy-Fermion Systems, YbRh₂Si₂, CeRu₂Si₂, and β-YbAlB₄

2009

View full text Add to dashboard Cite

We propose a phenomenological spin fluctuation theory for antiferromagnetic quantum tricritical point (QTCP), where the first-order phase transition changes into the continuous one at zero temperature. Under magnetic fields, ferromagnetic quantum critical fluctuations develop around the antiferromagnetic QTCP in addition to antiferromagnetic ones, which is in sharp contrast with the conventional antiferromagnetic quantum critical point. For itinerant electron systems, we show that the temperature dependence of critical magnetic fluctuations around the QTCP are given as χQ ∝ T −3/2 (χ0 ∝ T −3/4 ) at the antiferromagnetic ordering (ferromagnetic) wave number q = Q (q = 0). The convex temperature dependence of χ −1 0 is the characteristic feature of the QTCP, which is never seen in the conventional spin fluctuation theory. We propose that the general theory of quantum tricriticality that has nothing to do with the specific Kondo physics itself, solves puzzles of quantum criticalities widely observed in heavy-fermion systems such as YbRh2Si2, CeRu2Si2, and β-YbAlB4. For YbRh2Si2, our theory successfully reproduces quantitative behaviors of the experimental ferromagnetic susceptibility and the magnetization curve by choosing the phenomenological parameters properly. The quantum tricriticality is also consistent with singularities of other physical properties such as specific heat, nuclear magnetic relaxation time 1/T1T , and Hall coefficient. For CeRu2Si2 and β-YbAlB4, we point out that the quantum tricriticality is a possible origin of the anomalous diverging enhancement of the uniform susceptibility observed in these materials.

show abstract

“…HF-ESR was carried out in a reflection geometry with a Millimeterwave Vector Network Analyzer (AB Millimetre) at ν = 93 − 360 GHz in a field range 0 -14 T. We used a very sensitive induction mode scheme that detects the change of the microwave's polarization at the resonance [10]. The strong anisotropy of the ESR response corresponds to the strong magnetic anisotropy of YbRh 2 Si 2 [2,11] and is nicely reflected in the HF-ESR data: For B c-axis no ESR response has been found, whereas a well defined resonance line with a g-factor ∼ 3.5 has been observed for B ⊥ c (Fig. 1, right).…”

mentioning

confidence: 99%

Evolution of the Kondo State ofYbRh2Si2Probed by High-Field ESR

et al. 2009

View full text Add to dashboard Cite

An electron spin resonance (ESR) study of the heavy fermion compound YbRh2Si2 for fields up to ∼ 8 T reveals a strongly anisotropic signal below the single ion Kondo temperature TK ∼ 25 K. A remarkable similarity between the T -dependence of the ESR parameters and that of the specific heat and the 29 Si nuclear magnetic resonance data gives evidence that the ESR response is given by heavy fermions which are formed below TK and that ESR properties are determined by their field dependent mass and lifetime. The signal anisotropy, otherwise typical for Yb 3+ ions, suggests that, owing to a strong hybridization with conduction electrons at T < TK, the magnetic anisotropy of the 4f states is absorbed in the ESR of heavy quasiparticles. Tuning the Kondo effect on the 4f states with magnetic fields ∼ 2 − 8 T and temperature 2 − 25 K yields a gradual change of the ESR g-factor and linewidth which reflects the evolution of the Kondo state in this Kondo lattice system. PACS numbers: 71.27.+a, 75.20.Hr, Strong electron-electron (EE) interactions in metals yield a fascinating variety of novel and often interrelated quantum phenomena, such as quantum phase transitions, breakdown of the Landau Fermi-liquid (LFL) state, unconventional superconductivity, etc. (for an overview see, e.g., [1]). In intermetallic compounds where 4f (5f ) magnetic ions (e.g. Yb, Ce, U etc.) build up a regular Kondo lattice, strong EE correlations are established by the coupling of local f -magnetic moments with the conduction electrons (CE). As a consequence, a large effective mass enhancement of the quasiparticles (QP) hallmarks the properties of paramagnetic heavy fermion metals. A competing interaction, the so-called RKKY-interaction between the local f -states via the sea of CE, favors a magnetically ordered ground state.An important realization of a system where the delicate balance between Kondo and RKKY interactions can be investigated is the intermetallic compound YbRh 2 Si 2 where antiferromagnetic order, quantum criticality, heavy fermion-and non-LFL (NFL) behavior can be tuned by a magnetic field B and temperature T [2,3,4,5,6] (Fig. 1). In the parameter domain where these remarkable electronic crossovers take place a strong hybridization of 4f electrons with CE significantly broadens the otherwise atomically sharp f -states. That is why the observation of a narrow electron spin resonance (ESR) signal in the Kondo state of YbRh 2 Si 2 was very surprising [7]. While the reported pronounced anisotropy of the signal is indeed in accordance with an ESR of localized Yb 3+ 4f moments, a non-local picture is suggested by the observation of this signal down to the lowest accessible temperatures of 0.69 K [8] where the single ion Kondo effect is expected to screen the magnetic moments. On the other hand the conduction electron ESR seems also unlikely because in this compound comprising heavy metal elements the spin-orbit (SO) coupling drastically shortens the electron spin lifetime [9].To unravel a controversial nature of this resonance response w...

show abstract

Spin dynamics of YbRh₂Si₂observed by electron spin resonance

Cited by 25 publications

References 15 publications

YbRh₂Si₂: Quantum Tricritical Behavior in Itinerant Electron Systems

YbRh₂Si₂: Quantum Tricritical Behavior in Itinerant Electron Systems

Spin Fluctuation Theory for Quantum Tricritical Point Arising in Proximity to First-Order Phase Transitions: Applications to Heavy-Fermion Systems, YbRh₂Si₂, CeRu₂Si₂, and β-YbAlB₄

Evolution of the Kondo State ofYbRh2Si2Probed by High-Field ESR

Contact Info

Product

Resources

About

Spin dynamics of YbRh2Si2observed by electron spin resonance

Cited by 25 publications

References 15 publications

YbRh2Si2: Quantum Tricritical Behavior in Itinerant Electron Systems

YbRh2Si2: Quantum Tricritical Behavior in Itinerant Electron Systems

Spin Fluctuation Theory for Quantum Tricritical Point Arising in Proximity to First-Order Phase Transitions: Applications to Heavy-Fermion Systems, YbRh2Si2, CeRu2Si2, and β-YbAlB4

Evolution of the Kondo State ofYbRh2Si2Probed by High-Field ESR

Contact Info

Product

Resources

About

Spin dynamics of YbRh₂Si₂observed by electron spin resonance

YbRh₂Si₂: Quantum Tricritical Behavior in Itinerant Electron Systems

YbRh₂Si₂: Quantum Tricritical Behavior in Itinerant Electron Systems

Spin Fluctuation Theory for Quantum Tricritical Point Arising in Proximity to First-Order Phase Transitions: Applications to Heavy-Fermion Systems, YbRh₂Si₂, CeRu₂Si₂, and β-YbAlB₄