Effect of pressure on the Electron Spin Resonance of a Heavy-Fermion metal
J. Sichelschmidt, H. -A. Krug von Nidda, D. V. Zakharov, I. Fazlizhanov, J. Wykhoff, T. Gruner, C. Krellner, C. Klingner, C. Geibel, A. Loidl, F. Steglich
We investigate the electron-spin resonance (ESR) phenomenon in the heavy-fermion metal YbRh2Si2 by applying hydrostatic pressure up to 3 GPa and by inducing internal pressure on the Yb site chemically in Yb(Rh1-xCox)2Si2 samples. We found that the increase in pressure, reducing the hybridization between 4f and conduction electrons, leads to a remarkable change in the temperature dependence of the g factor and broadens the ESR line. We relate the differences between the effect of internal and external pressure on the low temperature ESR parameters to the disorder induced by Co doping. The pressure effects on the Yb3+ related resonance in YbRh2Si2 again manifest its local character when compared with the resonance of diluted Gd in heavy-fermion metals.
We investigate the effect of strong electronic correlation on the massless Dirac fermion system, $α$-(BEDT-TTF)$_2$I$_3$, under pressure. In this organic salt, one can control the electronic correlation by changing pressure and access the quantum critical point between the massless Dirac fermion phase and the charge ordering phase. We theoretically study the electronic structure of this system by applying the slave-rotor theory and find that the Fermi velocity decreases without creating a mass gap upon approaching the quantum critical point from the massless Dirac fermion phase. We show that t…
Heavy Fermion superconductor CeCu$_2$Si$_2$ under high pressure: multiprobing the valence crossover
第一个重费米子超导体CeCu $_2$ Si $_2$还没有完全揭开它的神秘面纱。在高压下，超导性被认为是由价态涨落介导的，而在环境压力下，自旋涨落最有可能充当配对粘合剂。我们对高质量的CeCu $_2$ Si $_2$单晶进行了多探针（电输运、热电势、交流比热、霍尔和能斯特效应）实验，直至$7 \text{GPa}$。可靠的电阻率数据揭示了第一次的标度行为接近假定的价态转变，并允许定位在$4.5\pm0.2 \text{GPa}$和一个稍微负的温度的临界终点。在相同的压力区域，显着的功能也已被检测到的其他物理性质，作为进一步的签名的Ce价交叉和相关的临界波动。
We present a simple, but very realistic, model for a description of pressure induced valence and metal-insulator transitions in mixed valence systems. It is based on the extended Falicov-Kimball model and the supposition that the key interaction governing these transitions is the nonlocal hybridization between the localized $f$ and itinerant $d$ electrons. Taking into account, in addition, the~parametrization between the external pressure and the $d$-$f$ hybridization (the experimental fact), the model is able to describe, at least qualitatively, valence as well as metal-insulator transitions …
The dependence of the magnetic ordering temperature To of Sm metal was determined through four-point electrical resistivity measurements to pressures as high as 150 GPa. A strong increase in To with pressure is observed above 85 GPa. In this pressure range Sm ions alloyed in dilute concentration with superconducting Y exhibit giant Kondo pair breaking. Taken together, these results suggest that for pressures above 85 GPa Sm is in a highly correlated electron state, like a Kondo lattice, with an unusually high value of To. A detailed comparison is made with similar results obtained earlier on N…
Applicability of Anderson and Hubbard model for Ce metal and cerium heavy fermion compounds
研究了在金属铈和铈重费米子化合物的电子结构计算中考虑格位间$f-f$杂化的重要性。我们证明，对于重费米子系统，如铈化合物CeCu $_2$ Si $_2$ $f-f$杂化可以忽略不计，安德森模型的应用是合理的。另一方面，对于铈金属，$f-f$杂化足够强以提供与$4f$和巡回电子之间的杂化相当的杂化功能的贡献。我们认为，在Ce的情况下，只有最一般的哈伯德和安德森模型相结合的哈密顿量应使用。
Heavy-Fermion Formation at the Metal-to-Insulator Transition in Gd$_{1-x}$Sr$_x$TiO$_3$
通过电阻率、比热和电子顺磁共振（EPR）等测试手段研究了钙钛矿型过渡金属氧化物Gd $_{1-x}$ Sr $_x$ TiO $_3$。从金属区（$x \geq 0.2$）接近金属到绝缘体的转变，比热的索末菲系数$γ$变得强烈增强，并且电阻率在低温下二次增加，这两者都是强电子关联的指纹。动态磁化率的温度依赖性，从Gd $^{3+}$ -EPR线宽确定，信号的重要性，强自旋波动，观察到在重费米子化合物。
In addition to its promising potential for applications, GaV4S8 shows very interesting physical properties with temperature and magnetic field. These properties can be tuned by applying hydrostatic pressure in order to reveal and understand the physics of these materials. Not only pressure induces an insulator-to-metal transition in GaV4S8 but it also has an interesting effect on the structural and magnetic transitions. Using a combination of AC calorimetry, capacitance, and resistivity measurements under pressure, we determine the evolution of the structural and magnetic transitions with pres…
The mechanism of strange metal (SM) with unconventional charge transport near magnetic phase transitions has become an outstanding open problem in correlated electron systems. Recently, an exotic quantum critical SM phase was observed in paramagnetic frustrated heavy-fermion materials near Kondo breakdown. We establish a controlled theoretical framework to this issue via a dynamical large-N fermionic multichannel approach to the two-dimensional Kondo-Heisenberg lattice model, where KB transition separates a heavy-Fermi liquid from fermionic spin-liquid state. With Kondo fluctuations being full…
Pressure-Induced Confined Metal from the Mott Insulator Sr3Ir2O7
自旋轨道莫特绝缘体Sr 3 Ir 2 O 7提供了一个迷人的游乐场，探索绝缘体-金属过渡驱动的交织的电荷，自旋和晶格自由度。在这里，我们报告的高压电阻和共振非弹性X射线散射测量单晶Sr 3 Ir 2 O 7高达63 - 65 GPa在300 K。该材料在59.5 GPa下成为受限金属，在ab平面中显示金属性，但沿c轴显示绝缘行为。这种不寻常的现象类似于铜氧化物超导体中的奇异金属相。由于在X射线测量中没有自旋轨道或库仑相互作用崩溃的迹象，这种新型的绝缘体金属转变可能是由附近压力下的一阶结构变化驱动的。我们的发现指出了一种合成功能材料的新方法。
Strong pressure dependence of the magnetic penetration depth in single crystals of the heavy fermion superconductor CeCoIn5 studied by muon spin rotation
Recent observations of two nodeless gaps in superconducting CeCu$_2$Si$_2$ have raised intensive debates on its exact gap symmetry, while a satisfactory theoretical basis is still lacking. Here we propose a phenomenological approach to calculate the superconducting gap functions, taking into consideration both the realistic Fermi surface topology and the intra- and interband quantum critical scatterings. Our calculations yield a nodeless $s^\pm$-wave solution in the presence of strong interband pairing interaction, in good agreement with experiments. This provides a possible basis for understa…
