Strong Field Quenching of the Quasiparticle Effective Mass in Heavy Fermion Compound YbCo2Zn20

概要

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We found a metamagnetic like anomaly at $H_{\text{m}}\simeq 5$ kOe in a heavy fermion compound YbCo2Zn20 below the characteristic temperature $T_{\chi_{\text{max}}}=0.32$ K where the ac-susceptibility shows a broad peak, suggesting that an electronic state with a very low Kondo temperature is realized. Interestingly, the metamagnetic like behavior was observed as two peaks at 4.0 and 7.5 kOe at 95 mK in the magnetic field dependence of the electronic specific heat $C/T$. The extremely large values of the electronic specific heat coefficient $\gamma\simeq 8000$ mJ/(K2$\cdot$mol) and $A=160$ μ$\Omega$$\cdot$cm/K2 in the electrical resistivity $\rho=\rho_{0}+AT^{2}$ at $H=0$ kOe are most likely due to the very low Kondo temperature. The $\sqrt{A}$ value was, however, found to be strongly reduced from $\sqrt{A}=12.6$ (μ$\Omega$$\cdot$cm/K2)1/2 at 0 kOe to 0.145 (μ$\Omega$$\cdot$cm/K2)1/2 at 150 kOe. Therefore, we considered that the corresponding cyclotron effective mass $m_{\text{c}}^{*}$, which was determined from the temperature dependence of the de Haas–van Alphen (dHvA) amplitude, is also reduced with increasing magnetic field and is in fact not large, ranging from 2 to $9m_{0}$ at 117 kOe. From the field dependence of $\sqrt{A}$ and $m_{\text{c}}^{*}$, we estimated the cyclotron effective mass at 0 kOe to be $100--500m_{0}$, revealing the largest cyclotron mass as far as we know.
2010-08-15