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arXiv 0906.2097cond-mat.str-el
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YbRh_2Si_2中场致量子临界点的磁化研究

Magnetization study on the field-induced quantum critical point in YbRh_2Si_2

Y. Tokiwa, C. Geibel, F. Steglich, P. Gegenwart

摘要:

我们用低温磁化强度$M(T)$和磁格林奈森比$Γ_{\rm mag}$测量研究了YbRh $_2$ Si $_2$的场致量子临界点,并将结果与以前的热膨胀$β(T)$和临界格林奈森比$Γ^{cr}(T)$,YbRh $_2$(Si $_{0.95}$ Ge $_{0.05}$)$_2$的数据进行了比较.在后一种情况下,轻微的负化学压力已被用来调整系统向其零场QCP。磁化导数$-dM/dT$远比热膨胀更奇异,反映了恒定熵下场的强烈温度依赖压力导数,$(dH/dP)_S=V_mβ/(dM/dT)$($V_m$:摩尔体积),其在$T\to 0$的$(0.15\pm 0.04)$ T/GPa处饱和。先前在霍尔和热力学测量中观察到的线$T^\star(H)$将较强$(ε>1$)和较弱$(ε<1$)发散$Γ_{\rm mag}(T)\propto T^{-ε}$的$T$-$H$相空间中的区域分开。

英文摘要:

We study the field-induced quantum critical point (QCP) in YbRh$_2$Si$_2$ by low-temperature magnetization, $M(T)$, and magnetic Grüneisen ratio, $Γ_{\rm mag}$, measurements and compare the results with previous thermal expansion, $β(T)$, and critical Grüneisen ratio, $Γ^{cr}(T)$, data on YbRh$_2$(Si$_{0.95}$Ge$_{0.05}$)$_2$. In the latter case, a slightly negative chemical pressure has been used to tune the system towards its zero-field QCP. The magnetization derivative $-dM/dT$ is far more singular than thermal expansion, reflecting a strongly temperature dependent pressure derivative of the field at constant entropy, $(dH/dP)_S=V_mβ/(dM/dT)$ ($V_m$: molar volume), which saturates at $(0.15\pm 0.04)$ T/GPa for $T\to 0$. The line $T^\star(H)$, previously observed in Hall- and thermodynamic measurements, separates regimes in $T$-$H$ phase space of stronger $(ε>1$) and weaker $(ε<1$) divergent $Γ_{\rm mag}(T)\propto T^{-ε}$.

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